A Meta-Analysis of Coordinate Systems and Bibliography of Their Use on Pluto from Charonâ€™S Discovery to the Present

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Icarus 246 (2015) 93–145

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Icarus

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A meta-analysis of coordinate systems and bibliography of their use on Pluto from Charon’s discovery to the present day ⇑ Amanda Zangari

Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO 80302, United States Department of Earth, Atmospheric and Planetary Science, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, United States article info abstract

Article history: This paper aims to alleviate the confusion between many different ways of defining latitude and Received 21 January 2014 longitude on Pluto, as well as to help prevent future Pluto papers from drawing false conclusion due Revised 15 October 2014 to problems with coordinates. In its 2009 meeting report, the International Astronomical Union Working Accepted 21 October 2014 Group on Cartographic Coordinates and Rotational Elements redefined Pluto coordinates to follow a Available online 4 November 2014 right-handed system (Archinal, B.A., et al. [2011a]. Celest. Mech. Dynam. Astron. 109, 101–135; Archinal, B.A., et al. [2011b]. Celest. Mech. Dynam. Astron. 110, 401–403). However, before this system was Keywords: redefined, both the previous system (defining the north pole to be north of the invariable plane), and Pluto the ‘‘new’’ system (the right-hand rule system) were commonly used. A summary of major papers on Charon Pluto, surface Pluto and the system each paper used is given. Several inconsistencies have been found in the literature. The vast majority of papers and most maps use the right-hand rule, which is now the IAU system and the system recommended here for future papers. Ó 2014 The Author. Published by Elsevier Inc. This is an open access article under the CC BY-NC-SA license (http://creativecommons.org/licenses/by-nc-sa/3.0/).

1. Introduction and Motivation 1996). Thus, New Horizons will image Pluto’s surface as it will be in 2015, a single snapshot. All data taken before, since or after will The New Horizons spacecraft will provide the first close-up look be compared to the New Horizons data set. of Pluto on 2015-07-14. The LORRI instrument will map the surface A proper comparison requires the knowledge of both the loca- at scales as fine as 70 meters during closest approach (Young et al., tion of the New Horizons observations and the position of Pluto 2008b), bringing to Earth images of a planetary surface described as seen from the ground at the time the measurements were made. as the ‘‘second most contrastive extraterrestrial surface in the Solar In theory, the definitions of longitude and latitude on Pluto, as for System’’ (Tholen and Buie, 1997a). Before the approach of the New all major planets, minor planets and dwarf planets are made by the Horizons spacecraft, clever solutions have been used to make some IAU Working Group on Cartographic Coordinates and Rotational sense of this barely resolvable planet, including exploiting the Elements, which meets every three years. In practice, the ‘‘official’’ mutual events (Young et al., 2001a), matrix inversion of decades’ way to define coordinates has often been ignored, and when worth of light curves (Drish et al., 1995) and eking out variations updated, ignored again in favor of the previous system. Thus in the surface brightness across the handful of pixels that comprise throughout the literature, each pole of Pluto has been identified the most detailed view of Pluto as seen from the Hubble Space as north and three major methods have been used to identify Telescope (Buie et al., 2010b). Observations at different times and rotational phase or less primitively, longitude. Such variance in different sub-Earth locations have shown that Pluto’s surface coordinate system choice is not necessarily problematic when varies not only spatially, but temporally (Drish et al., 1995). As the coordinate system is clearly defined, but coordinate confusion Pluto journeys from a perihelion of 29.6 AU to 48.9 AU and its high can easily be created. Somewhat problematically, a paper can obliquity creates a century of winter for each hemisphere, Pluto’s define its coordinate system in the text, but present the latitudes atmosphere undergoes periods of expansion and decline, and frost and longitudes in an opposite manner. Other papers present new is deposited on the surface with the seasons (Hansen and Paige, observations of Pluto, but when comparing results to previous work, fail to accommodate for the difference in coordinates systems. Such mistakes can result in faulty conclusions. ⇑ Address: Southwest Research Institute, 1050 Walnut St, Suite 300, Boulder, CO This paper aims to alleviate coordinate confusion surrounding 80302, United States. E-mail address: [email protected] discourse on Pluto by doing the following: http://dx.doi.org/10.1016/j.icarus.2014.10.040 0019-1035/Ó 2014 The Author. Published by Elsevier Inc. This is an open access article under the CC BY-NC-SA license (http://creativecommons.org/licenses/by-nc-sa/3.0/). 94 A. Zangari / Icarus 246 (2015) 93–145

1. Chronicle the history of the use of cartographic coordinates to the east. East is defined not to be the direction in which the Sun describe locations on Pluto, and detail the IAU recommenda- rises, but the direction to the right of an observer facing north. tions throughout time. Indeed, if a planet has retrograde rotation, then the planetographic 2. Provide clear definitions of all coordinate systems used to and planetocentric longitudes are the same.1 The 1979 report describe locations on Pluto and explain methods for recognition defines a pole, longitude zero and rotation rate for Pluto: Pluto’s pole of coordinate systems. is given as a0 = 305°, d0 =5 . The ephemeris position of Pluto’s prime 3. Index papers, books and major technologies that use each coor- meridian is given as W = 360.0–56.367 d. Despite the fact that dinate system or none at all. Charon had been discovered, the prime meridian was arbitrarily 4. Identify ambiguities and errors in the literature and correct chosen to coincide with the epoch of B1950.0. The negative value them where possible. of W_ indicates retrograde rotation – the source of almost all the 5. Identify trends in coordinate use. coordinate woes. Charon’s (called S/1978 P1) pole is noted to point 6. Warn the reader of Pluto literature to be wary of potential in the same direction as Pluto’s pole with no rotation period given problems. (Davies et al., 1980). 7. Suggest data presentation methods and clear language that will The IAU Working group has met every three years since the first avoid future errors. meeting in 1979. Table 1 gives a list of each meeting, the Pluto pole 8. Advocate for a unified coordinate system to be used in future position, rotation rates, Pluto radius, and a citation for the meeting work, including data collected by the New Horizons spacecraft report. Minor revisions were made to Pluto’s pole position from based on what is most appropriate given the current body of 1980 until 2006; the coordinates were adjusted to the J2000.0 literature on Pluto, here the right-hand rule. epoch and the pole position has been updated a small handful of times. In 1991, the pole position was updated to use the sub- 2. History of coordinates on Pluto Charon meridian as the prime meridian (Davies et al., 1992). Before the prime meridian redefinition, no published paper ever counted Up until the first determination of Pluto’s rotational period by back to the epoch of 1950 to determine Pluto’s prime meridian. Walker and Hardie (1955), very little was known about Pluto. Rather, papers that noted a longitude on Pluto had always chosen Much of the research in the 25 years since Tombaugh’s 1930 the sub-Charon meridian. In fact, all the recommendations by the discovery had been related to astrometry. ‘‘Finally, someone had IAU working group were almost completely ignored. obtained a concrete observational result about the planet’’, notes Instead of longitude, different times of Pluto’s day were Marcialis (1997b) of the discovery. Walker and Hardie (1955) matched up using rotational phase. Rotational phase spans from found Pluto’s brightness varied by 0.1 magnitude over 6.39 d. This 0 to 1 and indicates the modulo fraction of an rotation an object first light curve was plotted as a function of rotational phase, which has undergone since a certain epoch, usually given in Julian date. extended from 0 to 1. The zero point was arbitrarily chosen such The choice of epoch of Walker and Hardie (1955) was for ‘‘conve- that V = 14.90 (in the period where Pluto’s light was rapidly nience’’, later papers chose one of two very similar zero points. decreasing), marked the zero epoch. Minimum light was at a phase The two most common places to define the zero point of Pluto’s of roughly 0.2. The authors speculate that such a ‘‘large’’ light curve rotational phase are light-curve minimum, and greatest northern amplitude must be due to an equator-on position of Pluto. In real- elongation of Charon (see Fig. 1). By a coincidence that Richard P. ity, it would be three more decades until Pluto would be viewed Binzel states that astronomers have largely ‘‘gotten over’’, these equator-on from Earth. The amplitude of Pluto’s light curve, which two points are different by just a few hours (Binzel, personal com- is produced by albedo variations and not shape, was at its most munication, 2012). dramatic when seen equator-on during the mutual events from Rotational phase can be problematic for several reasons. Firstly, 1985 to 1990. However, the first determination of Pluto’s pole as Pluto’s rotational period was still being refined in the 1980s, was made by Andersson and Fix (1973), with the currently- each paper defined its own epoch and rotation rate. However, there accepted pole position just outside the range of errors given by were some attempts at standardization. At the time of the first the authors (see Marcialis (1997b) for a comparison of the two). detection of a mutual event (Binzel et al., 1985b) Binzel defines a Just one year after Charon’s discovery (Christy and Harrington, rotational phase such that Charon transits Pluto at 0.25 (an 1978), the first meeting of the IAU Working Group on Cartographic ‘‘inferior’’ event) and Pluto occults Charon at 0.75 (a ‘‘superior’’ Coordinates and Rotational Elements of the Planets and Satellites event). The chosen epoch was JD 2444240.661 (approximately was held in 1979. The group was commissioned at the previous 3:51:50 UT on January 2, 1980) and occurs at the ‘‘greatest north- meeting in 1976 due to ‘‘confusion regarding the rotational ele- ern elongation’’ of Charon. Here, Charon is at the point farthest ments of some of the planets’’. The hope was that the group’s edicts north in terms of declination on the sky with respect to Pluto. As this would avoid problems when future missions mapped the satellites paper heralded the arrival of the mutual events season, other of Jupiter and Saturn, and ‘‘avoid a proliferation of inconsistent papers choose to calculate their rotational phase from this same cartographic and rotational systems’’. epoch. Table 2 lists the epoch type, the Julian date epoch choice, To do so, the committee formally reaffirmed the following rules rotational period and citation of the papers that use rotational from the 1970 meeting: phase. However, data between two papers that use rotational phase cannot be compared unless the epochs and periods are the 1. The rotational pole of a planet or satellite which lies on the same! To further complicate things, some papers, such as Binzel north side of the invariable plane shall be called north, and et al. (1985b), included a light time correction with their epoch northern latitudes shall be designated as positive. definitions (and note the Julian date is Plutocentric), but most 2. The planetographic longitude of the central meridian, as did not. observed from a direction fixed with respect to an inertial coordinate system, shall increase with time. The range of longitudes shall extend from 0 to 360. (Trans. IAU 14B, p. 128, 1971). 1 Strictly speaking, for retrograde planets, planetographic longitudes and planetocentric longitudes are not completely identical. Planetographic coordinates are defined with respect to a reference surface, while planetocentric coordinates are The 1979 meeting report defines two types of longitudes: calculated using vectors that pass through the system origin. Pluto’s reference surface planetographic, which increases in the direction opposite rotation, is a perfect sphere (Davies et al., 1980). Table 1 shows the evolution of the and thus increases in time and planetocentric, which increases to recommended radius of Pluto’s reference sphere. A. Zangari / Icarus 246 (2015) 93–145 95

Table 1 Pluto pole and reference radius recommendations by the IAU through time.

Meeting year Pole a0(°) Pole d0(°) W W_ R (km) Source

1979 305 5 360a 56.367 1500 Davies et al. (1980) 1982 311 4.00 360a 56.364000 1500 Davies et al. (1983) 1985 311.63 4.18 252.66b 56.3640000 1500 Davies et al. (1986) 1988 311.63 4.18 252.66b 56.3640000 1162 ± 20 Davies et al. (1989) 1991 313.02 9.09 236.77c 56.3623195 1151 ± 6 Davies et al. (1992) 1994 313.02 9.09 236.77 56.3623195 1195 ± 5 Davies et al. (1996) 1997d –––– – 2000 313.02 9.09 236.77 56.3623195 1195 ± 5 Seidelmann et al. (2002) 2003e –––– –Seidelmann et al. (2005) 2006 312.993 6.163 237.305 56.3625225 1195 ± 5 Seidelmann et al. (2007) 2009f 132.993 6.163 237.305g 56.3625225 1195 ± 5 Archinal et al. (2011a) 2009 erratumf – – 302.695 56.3625225 1195 ± 5 Archinal et al. (2011b)

a Zero was defined with respect to the epoch of B1950.0: JED 2433282.5, north pole of invariable plane 272.40 a, +66.99 d. b Zero was defined with respect to the epoch of J2000.0: JD 2451545.0, north pole of invariable plane 273.85 a, +66.99 d. c Zero was defined with respect to the sub-Charon point, and this has been the zero point thereafter. d No report exists from the 1997 meeting in Kyoto (Seidelmann et al., 2005). e While a report does exist for this meeting, it states that no values of planetary rotation, poles or reference radii were redefined. Thus, they were not reprinted in the report. f Uses the right-hand rule pole. g This value is incorrect, causing the publication of the erratum.

and upside down, its planetocentric coordinates do not match the planetographic coordinates. No formal printed announcement was made to suggest that astronomers use the opposite coordinate system – not even in the ‘‘Ninth Planet News’’, a newsletter written to coordinate the mutual event observations (Buie and Tedesco, 1987). However, with only two very early exceptions (van Hemelrijck, 1982; Apt et al., 1983), all other papers written before the year 2000 defined the north pole of Pluto according to the right-hand rule anyway. Pos- sibly the earliest usage of the right-hand rule was in Robert Mar- cialis’s 1983 master’s thesis (Marcialis, 1983), which concerned the creation of a two-spot model for Pluto’s surface. Tholen and Tedesco (1994) call the definition ‘‘natural’’. Perhaps it is the presence of Charon that makes it so difficult to think of Pluto as rotating backwards, in favor of an object that is tipped upside down. For some reason, after the year 2000, the first papers began to crop up that followed IAU conventions. By that point, the Pluto community had been ignoring the IAU’s dictum for an over a dec- Fig. 1. Rotational phase system as defined by Charon’s orbital revolution. In the ade with its choice of pole. What had changed? The most likely 1980s, the epoch of rotational phase was readjusted to have a zero point at the explanation for the change is that the sub-Earth/observer/solar greatest northern elongation of Charon. Coincidently, the greatest northern elongation lines up very nearly to light-curve minimum, another phase definition. coordinates can be easily found using internet ephemeris generators, such as the JPL Horizons tool. These tools must return the ‘‘official’’ coordinates. From then on, some papers continued to Secondly, Pakull and Reinsch (1986) note that authors often do use the right-hand rule while others followed the IAU conventions. not distinguish between sidereal and synodic periods or fail to However, at the very end of the 2006 IAU meeting, Pluto was mention which type of period is being referred to. In the end, reclassified as a dwarf planet. As a new class of object, there were Buie and Tholen (1989) advocate a switch from rotational phase no rules about which coordinate system should be used. Should to sub-Earth longitude as a way to decouple parallax. Finding the dwarf planets follow the previously-outlined rules for major planet sub-Earth longitude is more than simply calculating the number and their satellites, or should they be treated as minor planets, of rotations (and fraction of a rotation) since a certain epoch– it their satellites and comets and use the right-hand rule? also takes into account the position of the observer. Eventually, The coordinate system for minor planets, their satellites and more and more papers used sub-Earth longitude instead of comets had been specifically defined to follow the right-hand rule rotational phase, and by the mid-1990s, use of rotational phase in 2003 (Seidelmann et al., 2005). Noting that pole precession was all but extinct in the literature. could cause the named north and south poles of comets to swap When it came to defining the north and south poles of Pluto in location if a system based on the invariable plane was used, the the literature, astronomers defied the IAU again. Instead of WGCCRE sought to move away from potentially-confusing Earth- designating the pole that was north of the ecliptic as the north based terminology. Instead of using the terms north and south, pole, the opposite pole – which aligned with Pluto’s angular the term ‘‘positive’’ was bought into being, and the positive pole momentum vector according to the right-hand rule, was desig- was chosen by the right-hand rule, eliminating the concept of nated the north pole. This new choice of pole also tipped the hand retrograde rotation. Longitude was also to increase by the with longitude as well. To create a map that did not have to be right-hand rule, eliminating the left-handed ‘‘longitude always flipped to wrap around a globe, east, or planetocentric coordinates increases in time’’ paradigm. These new minor planet rules must be used. For retrograde planets, the planetocentric and plane- matched the de facto coordinate system Pluto, save for the use of tographic coordinates are the same. However, if Pluto is prograde, cardinal points to describe poles and features. 96 A. Zangari / Icarus 246 (2015) 93–145

Table 2 Evolution of rotational phase: period and epochs.

Paper Physical zeroa Epoch (JD)a Period (d)a Citationa

Walker and Hardie (1955) phase at which Vo = 14.90 2434800.26 6.390 Hardie (1965) 6.3867 Andersson and Fix (1973) min. light 6.3867 Neff et al. (1974) min. light 2434476.38 6.3874 Lane et al. (1976) 6.3874 Neff et al. (1974) Renschen (1977) 6.3867 Andersson and Fix (1973) Neff et al. (1974)b Harrington and Christy (1980b) n. and s. elong. January 1980 to August 1981 6.3867 Tedesco and Tholen (1980) min. light = n. elong. Harrington and Christy (1980b) Bonneau and Foy (1980) s. elong. 2444409.991c 6.3867 Harrington and Christy (1980b) Breger and Cochran (1982) min. light = n. elong. 2444611.167 6.3867 Lyutyi and Tarashchuk (1982) min. light 2441334.91 6.3867 Neff et al. (1974)d Marcialis (1983) 2444240.59 6.3867 Hardie (1965)e Binzel and Mulholland (1983) first min. light 1980 2444240.59 6.3867 Tedesco and Tholen (1980) Mulholland and Binzel (1984) 6.3867 Binzel and Mulholland (1983) Lyutyi and Tarashchuk (1984) min. light 2434469.354 6.386628 Binzel and Mulholland (1984) 2444240.59 6.3874 Tholen and Tedesco (1984) 6.38755 Binzel et al. (1985a) min. light 2444240.661 6.38726 ‘‘Tholen’s Formula’’ Binzel et al. (1985b)f min. light, near n. elong. 2444240.661 6.38726 Bosh et al. (1986)f 2444240.59 6.3874 Binzel and Mulholland (1984) Pakull and Reinsch (1986) 6.38718 Buie and Fink (1987)f 2444240.661 6.38726 Reinsch and Pakull (1987) 6.38718 Marcialis (1988) 2444240.661 6.3867 Binzel et al. (1985b), Hardie (1965) Stern et al. (1988b) 6.387 Christy and Harrington (1980) Banks and Budding (1990) 2444240.59g 6.387 Tedesco and Tholen (1980) Marcialis (1990b) 6.387245 Burwitz et al. (1991) 6.38718 Bosh et al. (1992) Binzel et al. (1985b) Tholen and Tedesco (1994)f first corr. min. light 1980 2444240.66101 6.38726 Young (1994)f 6.387246 Binzel et al. (1985b) Binzel et al. (1985b), Tholen and Buie (1990)h Drish et al. (1995) 6.3872 Tholen and Buie (1997a) 6.38726 Foust et al. (1997) first n. elongation of 1980 Buie et al. (1997a) Young et al. (1999) 0.46111 at 2446600.5 2444240.66101 Tholen and Tedesco (1994) Miles (2010) 2454958.151 6.3868

a An absence of an entry indicates omission from the paper. b Captions credit both papers. c The epoch printed in this Table (JD 2444409.991) has been corrected from the paper’s printed epoch (JD 244409.991) to ﬁx a typographical error. d Neff et al. (1974) tests the period of Hardie (1965) with a unique zero point and proposes an improved rotation period. Lyutyi and Tarashchuk (1982) cite the test period, not the improved one. e Paper uses period of Hardie (1965). The epoch (JD 2444240.59) is cited as being from an ‘‘in press’’ paper by Tholen and Tedesco set to be published in Icarus in 1983. This paper likely later became Tholen and Tedesco (1994) published a decade later. As seen in the table above, the epoch was corrected slightly. f These periods include a light time correction. For details, see the paper’s entry in Appendix A. g The epoch printed in this Table (JD 2444240.59) has been corrected from the paper’s printed epoch (JD 24444240.59) to ﬁx a typographical error. h Paper uses period of Tholen and Buie (1990) but epoch of Binzel et al. (1985b).

In its next report (2009 meeting), the IAU WGCCRE declared had already been implemented (Stern, personal communication, that dwarf plants should follow the right-hand rule, noting: 2012). The new pole and longitude were not updated in JPL Horizons until August of 2013, and 2013 marked the first year that the US Naval Taking all of this into account, our recommendation is that lon- Observatory’s Astronomical Almanac reflected the new pole (however, gitudes on dwarf planets, minor planets, their satellites, and the longitude remained unchanged). comets should be measured positively from 0 to 360 using a While scientists do not necessarily agree on which coordinate right-hand system from a designated prime meridian. The ori- system to use, there is no disagreement on the physical realities gin is the center of mass, to the extent known. of the Pluto system: the pole that points in the direction of Pluto’s Latitude is measured positive and negative from the equator; angular momentum vector points toward the southern side of the latitudes toward the positive pole are designated as positive invariable plane. Since the late 1980s, this pole has been lit by the (Archinal et al., 2011a). Sun and will be continuously lit until 2113 (Stern and Mitton, These changes flipped both latitude and longitude: the north 2005). The right-handed spin pole is currently visible from Earth. pole of Pluto became the negative pole and the south pole became Scientists also agree that Pluto makes one rotation on its axis the positive pole. This decision also meant that Pluto’s longitude approximately every 6.38 d. Charon revolves around Pluto in that would not be described using planetographic longitudes. same time frame, in a doubly-tidally locked configuration. The The new decision was not well-publicized among scientists. Many dimmest point of the Pluto light curve occurs at approximately papers continued to follow the old rules, stating that they were using the time at which Charon is at its greatest northern elongation. the ‘‘IAU convention’’, unaware that it had changed. While New Hori- Charon’s location in its orbit and Pluto’s sub-observer longitude zons scientists had welcomed the endorsement of a better coordinate are known and can be found in ephemerides. Fig. 2 shows the system, they were fearful that changes in software packages might orientation of Pluto on the sky as seen from Earth during the P8 create bugs in vital spacecraft code, in which the previous system occultation on 1988-06-09, and on 2015-07-14, the day of New A. Zangari / Icarus 246 (2015) 93–145 97

most visually distinct due to its epoch near minimum light. Its gradual rise, then steep decline should also be committed to memory: the increasing longitude light curve follows the same pattern, albeit with its minimum at 270. The decreasing longitude light curve is a mirror image of this pattern. Fig. 3 shows a mock up of Pluto’s light curve using each system. Table 3 provides a guide to converting between systems. Note that the rotational phase conversion is a bit contrived. It assumes that 0 is at the greatest northern elongation and Charon’s orbit is Fig. 2. Sub-Earth view of Pluto on 1988-06-09 (left) and 2015-07-14 (right) circular. Rotational phase also requires a zero point and does not oriented north up, east left as seen on the sky. Arrows mark the rotational direction take into account movement of the Earth. However, the formula of Pluto. Since the mutual events in the late 1980s, the same pole of Pluto has been given will allow a user to estimate where a measurement might visible, and will be for another century. Pluto rotates counter-clockwise around the currently visible pole, and the rotational angular momentum vector currently fall on a different light curve. The only true way to convert points toward Earth. Thus, any current measurements that have a positive or measurements to sub-Earth longitude is to use an ephemeris that northern sub-Earth latitude use the spin north system. gives the sub-Earth longitude at the appropriate time.

Horizons’ closest approach to Pluto. The known position of Pluto 3. A survey of Pluto coordinates from Charon’s discovery to the can be used to determine which coordinate system is being used present day by asking two simple questions: What follows is a survey of Pluto coordinate use throughout the 1. What is the pole that has been visible since the late 1980s published literature. The survey was conducted through the use of called? the SAO/NASA Astrophysics Data System. On the ADS search page, 2. Does sub-Earth longitude increase with time? Pluto was entered into the title field, and approximately 2000 records were returned. Of these records, only entries that returned For papers that assume that the north pole aligns with the spin full text (noted by an ‘‘E’’ or ‘‘F’’ link) are reviewed below. Thus, vector, the southern hemisphere was visible from Pluto’s discovery recent conference abstracts were not included, but scanned up through the mutual events, after which the northern hemi- abstracts up through the early 90s were included, as were the sphere became visible. In this system, Charon covered the northern full-page abstracts from conferences such as EPSC. Records were hemisphere during the early inferior mutual events and the south- excluded if the article’s subject was not astronomy– for example, ern hemisphere in the later events. Throughout the rest of this the magnetohydrodynamic code ‘‘PLUTO’’ or geology papers paper, I will refer to this convention as spin north.2 For papers that assume that the north pole lies on the northern side of the invariable plane, the northern hemisphere was visible from Pluto’s discovery up through the mutual events, after which the southern hemisphere became visible. In this system, Charon covered the southern hemisphere during the early inferior mutual events and the northern hemisphere in the later events. Throughout the rest of this paper, I will refer to this convention as ecliptic north.3 Converting between the two latitudes is a mere matter of flip- ping the sign. In general, papers that use the spin north system, also use east longitude, and the sub-Earth point decreases as seen from Earth. To make the longitude definition independent from its north pole, it shall be referred to as decreasing longitude throughout the paper. This independence of definition is crucial for two reasons. Firstly, some papers use sub-Earth longitude without mentioning a pole or latitude at all. Secondly, in the ecliptic north system, east longitude matches planetographic longitude and thus increases in time. Thus it will be referred to as increasing longitude. Convert- ing between the two is a matter of calculating 360k. Thus for a table of consecutive Pluto measurements, one simply examines the table and notes whether the sub-Earth longitude goes up or down. In the absence of a pair of measurements, an ephemeris must be consulted. However, longitudes of 0 (sub- Charon) and 180 (anti-Charon) without further context will be degenerate as to which system they belong. Because the plotted light curve of Pluto has such a distinct shape, knowledge of the light curve allows one to identify the system used on sight. The rotational phase light curves are the Fig. 3. Comparison of Pluto’s light curve plotted using each of the three major longitude systems, based on data from Buie et al. (2010a). Top: rotational 2 As noted earlier, the WGCCRE version of the spin north convention, adopted for phase. Middle: increasing longitude, associated with the pre-2009 WGCCRE Pluto in the 2009 report, eliminates the designations north and south in favor of recommendations. Bottom: decreasing longitude, currently endorsed by the positive and negative poles, cutting ties with Earth. WGCCRE. Note that increasing longitude and rotational phase share the same 3 The ecliptic and invariable plane are inclined to each other by about 2. In all shape, just shifted, while decreasing longitude is a mirror image of increasing cases, the poles of the major planets and Pluto fall on the same side of the ecliptic as longitude. Thus, for the latter curve, the sub-observer longitude decreases with time the invariable plane. (hence ‘‘decreasing longitude’’) and time goes from right to left. 98 A. Zangari / Icarus 246 (2015) 93–145

Table 3 Converting coordinates between systems to match angular momentum north/decreasing longitude system.

No longitude/phase Decreasing longitude Increasing longitude Rotational Phase

No pole – No change 360-Longitude 360–360 (phase-0.25) Angular momentum north No change No change 360-Longitude 360–360 (phase-0.25) Ecliptic north -Latitude -Latitude -Latitude -Latitude 360-Longitude 360–360 (phase-0.25)

discussing Plutonic rocks were omitted. Papers which compared 4. Converting rotational phase to sub-Earth longitude without any various TNOs to Pluto (hence its inclusion in the title) are part of correction for the differing prime meridian between the two the survey, and are listed here under the heading ‘‘not about systems. Pluto’’. Also included were book reviews, introductory articles 5. Presenting data using the ‘‘ecliptic north’’, ‘‘increasing’’ system, written by a third party that accompany other articles in Science but failing to correct the coordinates before over-plotting the and Nature, PhD theses, if accessible, magazine articles, articles in data on a map that uses the ‘‘spin north’’, ‘‘decreasing system’’. foreign languages and books about Pluto. In general, books were 6. Noting in the text that the ‘‘spin north’’ system was used, but treated as single entities. However, the articles in the Pluto and presenting ‘‘ecliptic north’’ sub-Earth latitudes in a table. Charon Arizona Space Series book (Stern and Tholen, 1997) were 7. Compiling data from different projects in a review paper and treated individually. not declaring that different coordinates are being used in each The text, figures and tables of each paper were scanned visually scenario. for mention of longitude, latitude or rotational phase on Pluto. If 8. Declaring the coordinate system used by citing another article, optical character recognition was available, the paper was also which actually uses a different system than the one presented. searched for those terms. The coordinate system was determined 9. False coordinates. using methods described in the previous section. A few sentences are written to describe each paper, and if mention of coordinates The listing of the papers can be found in the Appendices. All was made, it was also tracked. If necessary, ephemerides were papers are ordered by year within their current subsection. consulted to verify the accuracy of the presented coordinates. As Appendix A contains papers which use some sort of coordinate shown in Table 1, several significant adjustments have been made system. Appendix A.1 contains papers that use rotational phase, to the pole position across the years. Thus, if a measurement of while Appendix A.2 contains papers that use rotational phase longitude, latitude or phase disagreed by a few degrees or a few and spin pole north. Appendix A.3 contains papers that use spin hundredths of a rotation, that does not mean there is a problem pole north and decreasing longitude, while Appendix A.4 contains with the coordinates in the paper. If the points listed in a paper’s papers that use ecliptic north and increasing longitude. Appendix description were noted as being ‘‘consistent with ephemerides’’, A.5 contains papers that use spin north without longitude while the sub-Earth points were recalculated for that paper to confirm Appendix A.6 uses ecliptic north without longitude. Appendix A.7 accuracy. Thus the latitudes and longitudes given were found to uses decreasing longitude only while Appendix A.8 uses increasing be accurate given the small amount of error consistent with the longitude only. Appendix A.9 uses ecliptic north and decreasing changes in Pluto’s pole position. However, recalculating sub-Earth longitude. Finally, papers that made one of the above errors can longitudes for every point in every paper published is simply not be found in Appendix A.10. A summary of the papers in Appendix feasible. In some cases, ephemerides needed to be consulted to A.10 can be found in Table 4. If a paper uses two coordinate sys- determine the system used for latitude measurements in the late tems to actively present work, the paper will be listed in multiple 1980s. While the sub-solar point moves smoothly across Pluto’s sections. Papers that present Pluto maps are called out specifically. surface, the sub-Earth point rises and falls with Earth’s motion The vast majority of papers about Pluto do not contain any (see Buie et al. (1997b)). coordinate system reference. However, their inclusion serves two Confirming the accuracy of occultation immersion and emer- purposes: firstly, these papers can be marked as checked by this sion longitudes and latitudes on Pluto’s surface is consequently study. Secondly, inclusion of all papers in the survey groups more involved. The calculation requires knowledge of the occulta- together Pluto research from the past in topic-organized histories tion path closest approach parameter, Pluto’s motion and a chosen for those looking for papers on a particular topic. For example, half-light radius along the path of the occultation. Zangari (2013) one topic, ‘‘moons beyond Charon’’, highlights attempted searches independently recalculated many occultation longitudes and that did not detect Styx, Nix, Kerberos and Hydra. latitudes using the spin north, decreasing system. If necessary, Appendices B and C contain papers that do not use any Pluto these calculations were consulted to confirm the coordinate coordinates. Topics where papers may have included coordinates, system but were not re-checked for this work. such as those that describe observations, can be found in Appendix Many papers had some sort of error with the coordinate system B. Topics for this section include UV spectra (Appendix B.1), visible used. For listing purposes here, a paper is assumed to be okay if it spectra (Appendix B.2), IR spectra (Appendix B.3), far-IR spectra uses a coordinate system not (at the time) designated by the IAU. and beyond (Appendix B.4), Charon (Appendix B.5), mutual events This convention here is not intended to approve or disapprove of (Appendix B.6), photometry/images (Appendix B.7), occultation such usage. Rather, there is an error if the coordinate system used reports (Appendix B.8), composition/formation (Appendix B.9), is ill-defined, or inconsistent. atmosphere/weather (Appendix B.10), New Horizons (Appendix Types of errors made include: B.11), and impacts/magnetic fields/solar wind (Appendix B.12). Papers that were less likely to mention coordinates have been 1. Omitted or additional digits in the listing of the Julian date of an placed in Appendix C. Topics for this section include article epoch. introductions/secondary sources/memoirs/letters (Appendix C.1), 2. Conflating inferior (Charon in front of Pluto) and superior (Pluto occultation prediction papers (Appendix C.2), space missions to in front of Charon) mutual events. Pluto besides New Horizons (Appendix C.3), planethood (Appendix 3. Rotational phase that was not zeroed at the greatest northern C.4), book reviews (Appendix C.5), astrometry (Appendix C.6), elongation, light curve minimum or another specific zero point. dynamics (Appendix C.7), ice in the lab (Appendix C.8), moons A. Zangari / Icarus 246 (2015) 93–145 99

Table 4 Summary of Errors from Appendix A.10.

Paper Error System after fix How to adjust coordinates Bonneau and Foy (1980) The nearest elongation point is Rotational phase (greatest southern JD 244409.991 should be JD missing a digit elongation) 2444409.991 Barker et al. (1989) Phase has zero at sub-Charon Rotational phase Add 0.25 to all phases, except last longitude, not greatest northern phase. For last point, make 0.7 be elongation 0.84a Stern et al. (1989a) Incorrect phases in paper Table 1 Rotational phase See Table A.8 and Schindhelm et al. (2015) for replacement coordinates Banks and Budding (1990) Digit added to rotational phase epoch Spin north/rotational phase JD 24444240.59 should be JD 2444240.59 Banks and Budding (1990) Phase is given in degrees Spin north/rotational phase Divide each phase by 360° to convert into 0 to 1 format Barker et al. (1991) Rotational phases given do not match Rotational phase See Table A.9 calculated phases Stern et al. (1991a) Incorrect phases in paper Table 1 Rotational phase See Table A.10 and Schindhelm et al. (2015) for replacement coordinates. Adjust figures (esp. Fig. 4) Stern et al. (1991a) Incorrect longitudes in paper Table 1 Decreasing longitude See Table A.11 and Schindhelm et al. (2015) for replacement coordinates. Adjust figures (esp. Fig. 4) Stern (1992) Pluto north pole is given as B1950 Spin north Define Pluto pole at B1950 a ¼ 312; d ¼9 epoch. One a ¼ 132; d ¼9 coordinate is consistent with spin pole north (d) and the other is consistent with ecliptic north pole (a) Stern (1992) Paper notes ‘‘superior events occur at Spin north Replace 0° with 180° 0.75 rotational phase, corresponding to Plutocentric longitudes centered around 0 degrees’’ Stern et al. (1995) Fig. 1 erroneously labels globe with Spin north Rotate globe images 180° ‘‘Pluto North at Top’’ Foust et al. (1997) The 1994 Astronomical Almanac uses Spin north/rotational phase Ignore Astronomical Almanac citation the ecliptic north system, but north is given as the angular momentum vector Foust et al. (1997) Buie et al. (1997a) do not use the first Spin north/rotational phase Replace Buie et al. (1997a) citation minimum light of 1980 as zero point with Tedesco and Tholen (1980) Sykes (1999) Paper Table II presents data from Decreasing longitude See Table A.12 Stern et al. (1993), Jewitt (1994) and Altenhoff et al. (1988). Some calculated sub-Earth longitudes for these papers are incorrect Grundy and Buie (2001) The paper notes that the mutual Spin north/decreasing longitude Mutual event maps are based on event maps were based on superior inferior events events Brown (2002) In paper Fig. 6, data from Drish et al. Rotational phase (Fig. 6 only), spin In Fig. 6, change abscissa caption (1995), a compilation of Pluto albedo north/decreasing (rest of paper) ‘‘sub-Earth latitude’’ to ‘‘rotational versus time curves are depicted as a phase’’. Divide by 360°. Data are now function of sub-Earth latitude from 0° in rotational phase to 360° Grundy and Buie (2002) One of the longitudes differs from Spin north/decreasing See Table A.13 calculations by about 10° Elliot et al. (2003a) Increasing longitude is described as Ecliptic north/increasing longitude Ignore ‘‘east’’ descriptor ‘‘east longitude’’ Cook et al. (2007) Charon longitudes listed are Ecliptic north/decreasing See Table A.14 for more accurate ambiguous. One is false (due to mis- times and corrected date for reported date) measurement Olkin et al. (2007) Paper Table 1 lists points as Spin north/decreasing longitude Fig. 13: for points ‘‘I, K, S, I’’ clustered increasing/ecliptic north. In paper (Fig. 13 only), ecliptic north/ on right side of the map, adjust 360- Fig. 13, when plotted atop Stern et al. increasing (rest of paper) long. Leave point S to the left at (1997a) maps, points are flipped to longitude 45 alone match spin pole north, but do not accommodate that longitude is decreasing on this plot. Data from Sasaki et al. (2005b) is plotted correctly at 45° Schmude (2008) Describes coordinate system ecliptic Spin north/decreasing longitude Reverse sign of all latitudes and north/increasing but presents spin north/south descriptions in the text north, decreasing longitude maps and rename description from Stern et al. (1997a) Schmude (2008) States that the brightest light curve Decreasing longitude Note dimmest point matches to 100 points were at sub-Earth longitude of and the brightest point matches to 100 and the dimmest points were at 220 a sub-Earth longitude of 230 DeMeo et al. (2010) Plots points atop Stern et al. (1997a) Spin north/decreasing longitude Flip points in paper Fig. 1 in latitude

(continued on next page) 100 A. Zangari / Icarus 246 (2015) 93–145

Table 4 (continued)

Paper Error System after ﬁx How to adjust coordinates maps. Sub-Earth latitude not adjusted (paper Fig. 1 only), ecliptic north/ increasing longitude (rest of paper) Merlin et al. (2010) Claim they are following the Ecliptic north/decreasing Do not compare directly with Olkin conventions of Olkin et al. (2007). et al. (2007) Actually ecliptic north/decreasing Stern et al. (2012) Claim they are following spin north/ Spin north/decreasing Flip latitude signs in text decreasing convention. Text lists ecliptic north latitudes Stern et al. (2012) Pluto and Charon are listed as having Spin north/decreasing Change Charon sub-Earth longitudes same sub-Earth longitudes from 95 and 273 to 275 and 93 Zalucha and Gulbis (2012) P8 latitudes should be reversed Ecliptic north/increasing Flip latitudes for P8 results

a See error in Stern et al. (1991a).

Table 5 Approximate number of papers in each system (excluding the 21 papers with errors).

No longitude/phase Decreasing longitude Increasing longitude Rotational Phase No pole – 10 2 33 Spin north 42 38 0 16 Ecliptic north 9 1 13 0

beyond Charon (Appendix C.9) and articles that are not about Table 6 Pluto (Appendix C.10). The topic division is not perfect: for example, General rules for coordinate choices. some papers about the mutual events could also to be considered to Ecliptic north Spin north (n. pole be about Charon, as could papers that present spectroscopic (s. pole visible) visible) measurements. Rather, the ‘‘Charon’’ section contains information Sub-Earth longitude + JPL Horizons Astron. Almanac 2013–? about its discovery and articles specifically concerning size ?–August 2013 and mass. (Specific papers can be found by searching the GeoViz bibliography.) IAU 1979–2006 Astron. Almanac Tools have been divided into a separate Section (Appendix D), as ?2012 a single tool may change its system over time or allow for the use Sub-Earth longitude Stern/Buie’s HST maps of different systems at any time. Tools discussed are The Astronom- Pluto mutual event ical Almanac, GeoViz, ISIS, JMars, JPL Horizons, and SPICE. observations Stern and Tholen (1997) IAU 2009–? 4. Discussion – General trends JPL Horizons August 2013–? What general trends can be extrapolated from the Pluto coordi- Phase at greatest northern Old light curves elongation nate data? Table 5 aggregates the number of papers in each cate- Some mutual events gory, omitting the number of papers that use no system. If a Stern and Tholen (1997) paper used two systems (cross-listed), it was counted for both.4 If a paper was listed in the errors/ambiguity section (see Appendix A.10), it was not included in the total count. There were 21 papers gained ground. Decreasing longitude remained in favor until with errors. Tools were not included in the count. In general, if a increasing longitude came into prominence after the year 2000, paper used the ecliptic north system, increasing longitude was used. most likely due to the rise of ephemeris generators such as JPL If a paper used the spin north system, either decreasing longitude or Horizons. Fig. 4 also shows the latitude convention versus year. rotational phase was used. The paper that used decreasing longitude Like longitude, the ecliptic north convention system did not come with the ecliptic north system – Buratti et al. (2003) –isa into use until after 2000, likely for the same reasons, though two cross-listed paper that presented new data using the increasing very early papers used the system. longitude convention, but also included one figure in the decreasing Why do so many errors and inconsistencies occur throughout format, clearly acknowledging the difference between the two the literature? One of the most common causes of error is the systems. coexistence of multiple systems, a ripe environment for human Table 6 gives an overview of the some important entities error: the ecliptic north/increasing system and spin/decreasing featuring each system. An index of papers can be found in system are connected by sign flips. Without physical grounding, Appendix A. the two can seem interchangeable. While the text of many of the Fig. 4 shows the longitude system used versus year. The rota- indexed papers show that the Pluto scientific community is aware tional phase system is exclusively used before the mutual events that there is a difference between the two systems, they have not pinned down Pluto’s pole, after which decreasing longitude slowly necessarily been vigilant about clearly describing or documenting the system used. Without strict documentation, it will not occur 4 The decision to cross list a paper was made if the data were actively presented in to new Plutophiles to ask themselves whether the coordinate sys- both systems. For example, Roush et al. (1996) note that rotational phase 0.75 tem described could be different from what was used elsewhere. corresponds to 180 longitude, but data are presented using rotational phase, so this Even with meticulous documentation some errors will still slip paper is not cross-listed. On the other hand, Buratti et al. (2003) use increasing longitude for most figures, but one figure uses decreasing longitude (clearly denoted through, as some coordinate errors have been caused by factors in the text), so this paper is cross-listed. other than the confusion with the two systems. For example, most A. Zangari / Icarus 246 (2015) 93–145 101

individual sub-Earth longitudes. The best coordinate system veriﬁca- tion is based on recalculation of the sub-solar and sub-observer points, a vital step due to the changing pole location, though readers should be aware that differences of a few degrees between ephemeris and published values can be expected. In the case of papers that merge data sets, readers should verify that measurements have been correctly transcribed from the cited document to the new work. Additionally, readers should be wary of east longitude, and note the term can be used to describe different longitudes depending on the pole choice. While generally used to refer to the right-hand rule system, it was not incorrect to refer to planetographic longitude as east longitude, so long as the north pole was north of the ecliptic. Again, a reader should make a second conﬁrmation of the system, either by calculating the coordinates in question or by matching the light curve shape with the appropriate system using Fig. 3.

5.2. Advice for writers

The stark reality of the situation is that many individual scientists are immune to IAU recommendations and will choose which- ever conventions please them most or will continue to do what they have done in the past. Though not necessarily ‘‘wrong’’ by itself, choosing a contrary convention makes it much more difficult for others to build on an author’s work, and could be considered by some to be an example of poor communication. Future authors who combine data or incorrectly correct others’ data when merg- ing data sets can create serious consequences, including false results and loss of mission. Writers hoping to promote a non–official convention should be aware that certain journals, institutions, and repositories will require their scientists to follow the IAU recommendations. Non-standard use should be well-justified. Fig. 4. Top: Trends of longitude choice through time. Cross-listed papers have been No matter what system is chosen, writers should be aware of counted for each system. Bottom: Trends of latitude choice through time. Cross- the following: listed papers that use spin north (e.g. rotational phase, spin north and decreasing longitude, spin north) were not counted twice. Both plots show that the ecliptic north, increasing system was not regularly used until after the year 2000. The large A coordinate system should not be solely described by a citation number of papers written in 1997 were due to the articles in Stern and Tholen to another research paper or access date to a tool. System (1997), while the large number of 2008 papers were from the publication of the descriptions should be fully self-contained without requiring a New Horizons articles in Space Science Reviews (Russell, 2008). reader to look up outside information that may or may not be an accurate description of the system used. Instead, ties to of the false coordinate instances occurred with papers that physical characteristics of the system, such as angular momen- published a small number of observations. Speculating upon this, tum, sunlight, location of Charon, spin direction, and changes in the coordinates were probably calculated by hand, increasing the the sub-Earth point should be used to describe coordinates. If likelihood of typographical errors. In the case of Cook et al. there is a need to cite a paper to explain a system, the official (2007), the error was not with the given coordinates, but rather a IAU reports are preferred over general Pluto research papers. typo in the date. Larger lists of coordinates tended to be more As the IAU conventions have officially changed so recently, robust – they were most likely calculated by a machine that read it is still confusing to propose to refer to the new angular in a list of observation times and created a table of longitude and momentum convention as the IAU convention. It is also latitude values without human intervention. confusing to mistakenly refer to the ecliptic north convention as the IAU way, because it no longer is! If invoking the IAU to 5. Conclusions state that the visible pole is north/positive, authors should also cite the most recent decision by the IAU (currently Archinal 5.1. Warnings for readers et al., 2011a). As the next mutual events will not occur until 2109, it is not While every attempt has been made to ensure the accuracy and unreasonable to refer to Pluto as having a currently visible pole completeness of the categorization of the above articles, it is possible as seen from Earth. From there, the authors can identify it as that not every characterization of every paper is completely accu- positive, north or south in accordance with their preferences. rate. Instead, readers should use the information herein as a jumping Looking to our great-grandchildren, who will be faced with off point to approach coordinates used in papers about Pluto. our out-of-date papers as well as current historians trying to No assumptions should be made that coordinate information is eke out more information from pre-mutual event papers, the accurate in a paper, or that a paper has properly reported term discovery pole should be sufficient to identify the other coordinates from another work. Instead, one should verify the pole one. The drama of a new mutual event season of Pluto should choice and longitude information for every instance in the paper, hopefully provoke enough notoriety that researchers before as previous papers have shown that a work may not be wholly and after will not be confused about which pole is which. consistent throughout. One should do a ‘‘sanity-check’’ and see For longitude, paper-writers should specify whether the sub- which pole is in sunlight or if any information has been given about Earth/solar longitude increases or decreases in time. Use of the location of Charon. When feasible, it is worthwhile to verify the word ‘‘east’’ should be avoided, as definition of east depends 102 A. Zangari / Icarus 246 (2015) 93–145

on the choice of pole. At this point, it is well-understood that well as with New Horizons funds from Southwest Research Insti- the zero point of the longitude system is reckoned from the tute. I would also like to thank Marc Buie for the detailed read sub-Charon prime meridian, though this extra detail is not nec- through, as well as Susan Benecchi and Brent Archinal for their essarily extraneous. In the future, Pluto’s longitude will be helpful suggestions and careful review of such a monstrous paper. defined by a surface feature discovered by New Horizons. Finally, I would like to thank Alan Stern for being a good sport. If one wishes to follow the new IAU conventions to the letter, Writing a paper of this magnitude would simply not have been the use of cardinal directions should be avoided entirely to possible without the help of technology, specifically, LaTeX, the avoid tying the system to Earth. Removing these terms stops Internet and ADS. The sentence ‘‘This research has made use of the confusion of a ‘‘north’’ pole that points in a direction that NASA’s Astrophysics Data System’’. does not even begin to cover is opposite the Earth’s. Instead, the right-hand rule pole can how helpful and crucial the ADS has been for creating this paper. be the ‘‘positive’’ pole and the ‘‘spinward’’ replacing ‘‘east’’. Vital as well was the journal access at MIT, and the in-person Papers that separately image Pluto and Charon and provide resources at the Harvard-Smithsonian Center For Astrophysics longitudes should also be explicit about the fact that Pluto (which has a copy of the ‘‘Ninth Planet News’’). Also appreciated and Charon have sub-Earth longitudes that are offset from each were those who have helped to make their scientific results avail- other by 180. able to the public at no charge. When combining data from others’ work, data should be transformed into a unified coordinate system. Papers should make explicit whether a coordinate change or no change at all Appendix A. Pluto articles with references to cartographic was required. Even if no system transformation is required, all coordinates longitude and latitude points should be recalculated to account for any pole changes. DeMeo et al. (2010) provide an excellent A.1. Rotational phase only example of a table that notes when Pluto longitudes from several different papers and data sets had to be altered to match Walker and Hardie (1955) present blue and yellow light mea- the increasing system. surements from 1954 and 1955, converted to the V magnitude To allow future researchers to combine observations, mid-times system as well as 1953 V measurements by Kuiper. This is one of observations, accurate to the nearest hour or better, should of the earliest light curves of Pluto and establishes the be included. ‘‘elements of light variation’’ of Pluto as ‘‘JD 2434800.26 ± When making new maps of Pluto’s surface, the invisible portion 0.06 + 6.390E ± .003E’’. The zero point of the rotational period of Pluto’s surface should be clearly marked as being in shadow is established as the phase where Vo = 14.90. Light curve instead of being interpolated from old information. A large minimum occurs where the phase is approximately 0.2. black bar both indicates shadow and provides a visual cue to Hardie (1965) report new observations of Pluto from 1964 and the reader about what system is being used. report a larger amplitude than in 1955 and an improved synodic rotational period of 6 days, 9 h 16 min and 54 s ± 26 s (6.3867 d). 5.3. Recommendations for choosing a coordinate system Possible zero point photometry errors from the previous 1950s data are mentioned. This is an abstract. Given the history of rampant non-compliance with official coor- Lacis and Fix (1972) use Fourier fits to light curves from data dinate system rules, it may be a bit arrogant to believe one can described by Hardie (1965) (this is the abstract, the data are compel planetary scientists to use a single coordinate system for published in Sky & Telescope (1965), 29, 140). The light curves Pluto in the future. The confusion seen in the literature and the are used to estimate the surface distribution of Pluto features. potential for mistakes make a strong case to recommend one any- While light and dark areas can be identified, there is not enough way. Indeed the purpose of the IAU WGCCRE is to avoid such errors information to determine limb darkening. A rotational period in the first place by sticking to a uniform coordinate system. and epoch are not given. The right-handed system with spin north and decreasing longi- Andersson and Fix (1973) present U, B and V observations of tude is the most appropriate to use for many reasons. Firstly, it Pluto from 1971-3 and are the first to suggest an obliquity for matches all currently published maps of Pluto, avoiding the risk Pluto. The new observations are plotted by rotational phase of errors with over-plotted points. Secondly, the number of papers against data from Walker and Hardie (1955) and Hardie that use the right-hand rule vastly outnumber the ecliptic north (1965). A rotational period of 6.3867 d is given without epoch, system. Thirdly, the IAU endorsement, which did matter to some, and is oriented to minimum light. This paper suggests that there now points toward the right-hand rule. Finally, JPL Horizons and may have been an error with the zero point calibration for the SPICE have finally adopted the right-hand rule system, so no mod- 1955 data. A range of right ascensions and declinations are ifications need to be made when using these online resources to shown in the paper’s Fig. 2 for just one of the potential poles, make calculations. The combination of these four factors make and the authors acknowledge that there is not sufficient infor- the right-handed system a better choice than any other system. mation to determine which pole this is in the ‘‘IAU sense’’ (what At this point in time, there is no compelling reason to continue that means is not specified). use of the ecliptic north, increasing system, or the use of rotational Note that Marcialis (1997b) re-plots this paper’s Fig. 2 as its phase or any longitude system that is not based from the sub- Fig. 9, showing not one, but both potential pole ranges and Charon point. the currently known positions for each pole in the spin north system. It reveals that the pole that is north of the invariable Acknowledgments plane, labelled by Marcialis as ‘‘south’’, was just outside of the range printed. I would like to thank Richard Binzel and Michael J. Person for Neff et al. (1974) present 1973 V photometry of Pluto to test supporting me in this project, giving advice, allowing me to focus two rotational periods found by Hardie (1965): the correct for several months of simply reading literature on Pluto, and let- 6.3867 ± 0.0003 d period (epoch JD 2441041.62) and the spuri- ting me to add an unplanned chapter to my thesis. This work ous 1.1819 ± 0.0002 day period (epoch JD 2441041.62). A least was carried out in part under New Horizons Grant NASW-02008 squares fit of 6.3874 ± 0.00018 d with epoch JD 2434476.38 is and NASA Planetary Astronomy Grant (NNX10AB27G) to MIT as presented as a better fit to the data. A. Zangari / Icarus 246 (2015) 93–145 103

Lane et al. (1976) present V and 0.86 lm measurements of Pluto and Christy and Harrington (1978)). It is suggested that light in 1974–1975 as well as BVRI measurements by Hardie. Rota- curve variations over the years and the ‘‘dimming’’ of Pluto tional phases are given for each measurement, and the paper could be explained by brighter poles than equatorial regions. notes that a period of 6.3874 d after Neff et al. (1974) was used. Binzel and Mulholland (1984) report 1983 B photometry of Renschen (1977) attempts to create the first albedo map from Pluto centered around rotational phases where mutual events light curve observations for Pluto without knowing the location were likely to be seen, though no eclipses were detected. The of Pluto’s pole. Taking the statement from Andersson and Fix observations are used to create a solar phase curve and redefine (1973) that Pluto’s inclination is greater than 50°, sub-Earth Pluto’s rotation period from 6.3867 d used in Binzel and latitude changes are calculated for the 1955, 1965 and 1972 Mulholland (1983) to 6.3874 d in agreement with Neff et al.’s observations. The paper notes that identification of the north (1974) least squares fit, but not the Harrington and Christy and south poles is currently impossible, so latitudes are simply (1981) period of 6.3871 d. It is implied that the Binzel and represented as positive. The latitude (u) becomes more positive Mulholland (1983) epoch of JD 2444240.59 is unchanged. The from the 1950s to the 1970s in all cases, however, the text notes new rotational period definition causes the mutual events to that ‘‘the observed increase of the amplitude implies the line of occur at rotational phase 0.26 and 0.76. sight is directed more equatorially than in 1954/1955’’, and that Lyutyi and Tarashchuk (1984) add U, B, V photometry from co-latitude, starting with one pole at 0 and increasing to 180 is 1982 and 1983 to their study of the change in Pluto’s light curve in use. An albedo map of features from cos u = 0.9 (25)to since the 1950s and note a decline in Pluto’s brightness. They cos u = 0.7 (45) is made. The x-axis is plotted in degrees. Based predict a red equatorial region and note a shift in the light curve on the locations of dark and light features, rotational phase is minima. Their observations do not include the rotational phase simply translated into degrees. Earlier in the paper, one light 0.33, the location of the previous eclipse claims. The authors do curve is plotted that compares data from Walker and Hardie fit a new period of 6.36628 ± 0.000058 d and zero point of JD (1955), Hardie (1965) and Andersson and Fix (1973), while 2434469.354 ± 0.065. The authors note that the zero point of another shows a curve after Neff et al. (1974). Both have rota- minima combines with the elongation of Charon, and agree tional periods of 6.3867 d. Based on the Pluto maps it is clear the supposed 1981 measurement of a mutual event at rota- that longitude, k, is derived from translating rotational phase tional phase 0.96 could not be an eclipse. into degrees. Mulholland and Binzel (1984) plot predictions for the shape, Tedesco and Tholen (1980) report photometric observations timing and duration of the mutual events. The authors use these of Pluto’s light-curve from 1980. A figure of a B light-curve predictions to show that the spurious points detected by Lyutyi of Pluto is plotted with zero at minimum light and and Tarashchuk (1982) do not constitute a mutual event. Their rotational phase increases in time. Rotational changes in argument relies on the prediction that the mutual events should the spectrum are not found at 0.55, 0.70 and 0.86 lm. The occur at a phase of 0.28 and 0.78, while the points of Lyutyi and authors note that minimum light and northern elongation Tarashchuk (1982) were at rotational phase 0.33 and 0.97, of Pluto’s satellite are the same, under the zero points which would require a large eccentricity of Charon that was described by Harrington and Christy (1980b). This is a unsupported by any observations. The authors claim the conference abstract. rotational phase definition of Lyutyi and Tarashchuk (1982),is Whyte (1980) compiles Pluto research up through 1979. The 0.042 off from this paper’s, which cites Binzel and rotational phase light curve and pole position charts from Mulholland (1983), but prints neither zero point. The authors Andersson and Fix (1973) are reproduced in Chapter 6. No note they use 6.3867 d as Pluto’s rotation period as per epoch is given for the rotational phase curve. It is also repeated Harrington and Christy (1981), Neff et al. (1974), and Bonneau that there was no way to determine which pole was north or and Foy (1980). The Pluto rotational phase had not yet been south at that time. This is a book. defined to have mutual events occur at 0.25 and 0.75. Breger and Cochran (1982) measure the polarization of Pluto Binzel and Mulholland (1985) report that the expected Pluto– based on solar phase angle. The authors suggest that the Charon mutual events have not yet occurred at phases 0.25 or measured constant polarization over both solar and rotational 0.75 as of the 1984 opposition. The authors emphasize the phase indicates a thin atmosphere for Pluto. They set JD importance of more light curve observations to distinguish a 2444611.167 ± 6.3867 d as the zero point for minimum mutual event from the flat curve at 0.25 and steep curve at light/time of northern elongation (here given to be approxi- 0.75. Data are not described in any specific terms, though the mately the same time). Rotational phases for observations are authors confirm previous years’ solar phase curve measure- consistent with observational times. ments, and promise to share results from the 1985 observa- Lyutyi and Tarashchuk (1982) present U, B and V photome- tions. This is a conference abstract. try of Pluto and Charon that covers a full light curve in Binzel et al. (1985a) report times and greatest magnitude depths of February–April 1981. The authors discuss changes in light the first successful mutual event observations. These rotational curve amplitude and object brightness from historical phases are calculated based on a minimum rotational brightness measurements. The authors cite the minimum light of Neff at ‘‘JD 2444240.661 +/6.38726E’’ using ‘‘Tholen’s Formula’’. Tran- et al. (1974) as JD 2441334.91 + 6.3867 d (this period is sits of the satellite across Pluto are defined to occur at phase = 0.25, not the improved rotational period, but the ‘‘long’’ period while occultations of the satellite occur at 0.75. the authors seek to test). The paper claims to have detected Binzel et al. (1985b) present the light curves of the first mutual a mutual event, but was refuted by Mulholland and Binzel event observations, and events are designated to take place at (1984). phase of 0.25 and 0.75. The article includes a definition for Binzel and Mulholland (1983) present 18 nights of opposition B phase (E) where filter photometry of the Pluto–Charon system in preparation for JD 0:0058D 2444240:661 the upcoming mutual events and included phase and Julian E ¼ : 6:38726 dates for each measurement. They note that a zero phase epoch is at JD 2444240.59 (first minimum light of 1980 as determined Here D is the Earth–Pluto distance in astronomical units, a light by Tedesco and Tholen (1980) with a rotational period of time correction term. The epoch Julian date is noted as being 6.3837 d as determined by Hardie (1965), Neff et al. (1974), Plutocentric. 104 A. Zangari / Icarus 246 (2015) 93–145

Bosh et al. (1986) include Pluto rotational phase when provid- and 0.15), while the abstract states Owen et al. (1993b) have ing SNR estimates for various potential Pluto occultation stars data that are within the 0.1 to 0.3 rotational phase (the paper from 1985 to 1990. Rotational phase was defined with zero gives these rotational phases to be 0.096 and 0.255, see the point JD 2444240.59 and period 6.3874 d from Binzel and following entry). The paper proposes time-resolved observa- Mulholland (1984) with a light time correction of tions and notes that data collected by de Bergh et al. (1993) ‘‘approximately four hours’’. Occultation candidate ‘‘P9’’, not are on the opposite hemisphere as the two previously men- observed, may have been during a mutual event. tioned papers. It is not immediately apparent where this data Pakull and Reinsch (1986) summarize the mutual events for a set was published. This is a conference abstract. general scientific audience, and present ESO observations in Owen et al. (1993b) present a 1.4–2.4 lm spectrum of Pluto both B and V of the Pluto light curve (with phase = 0 as taken on the UT dates 1992-05-27 and 1992-05-28 and com- minimum amplitude) and the mutual events. The authors note pare it to Triton. The footnotes give ‘‘Charon phases’’ of 0.096 that the period of 6.3867 ± 0.0003 d had not been refined much and 0.255 respectively. No epoch or zero point is given for rota- in recent literature. They also assert that many authors do not tional phase, but it is noted that the zero point of rotational distinguish between the synodic and sidereal period. The phase is at greatest northern elongation and 0.25 is eastern. authors provide 6.38718 ± 0.00009 d as the sidereal rotational The two phases are consistent with ephemerides. period for Pluto (an identical orbital period with a slightly larger Young and Binzel (1994a) determine new radii of Pluto and error is also given). Charon from the mutual event data by looking at inferior and Reinsch and Pakull (1987) report on density measurements superior events separately. Pluto’s light-curve from Binzel and based on mutual event data from 1986. The article notes that Mulholland (1984) is plotted with respect to phase and fit with mutual events occur at phases 0.25 and 0.75 (citing a ninth order polynomial. It is noted that phase is historically Mulholland and Binzel (1984)), where the zero phase is defined zero at light curve minimum, but inferior (Charon in front) as the photometric minimum of the light curve. Photometry events have a phase of 0.25. No mention of north or south is from 1982, 1983 and 1985 are also included, and a light curve made. from 1985 is plotted using rotational phase. Four mutual event Roush et al. (1995) determine Charon’s geometric albedo observation attempts are given in the paper’s Table 1, along between 1.4 and 2.5 lm. Rotational phase is defined by north- with rotational phases. These phases are consistent with ephe- ern and southern elongation at phases of 0.0 and 0.5, and merides. The synodic period of 6.387 from Hardie (1965) is mutual events at 0.25 and 0.75. This work is expanded on by quoted earlier in the paper, but a sidereal orbital period of Roush et al. (1996). This is a conference abstract. 6.38718 ± 0.00013 d and a sidereal rotational period of Roush et al. (1996) use spectra of Buie et al. (1987) from 1.4 to 6.38718 ± 0.00009 d are later deduced. These periods are 2.5 lm to determine geometric albedos of Charon and Pluto. noted to be consistent with Tholen’s (1985b) period of Rotational phase is defined by northern and southern elonga- 6.38723 ± 0.00027 d. tion at phases of 0.0 and 0.5, and mutual events at 0.25 and Stern et al. (1988b) make predictions about how Pluto’s albedo 0.75. Data from Bosh et al. (1992), Fink and Disanti (1988) and light curve will change as volatiles freeze out and subli- and Marcialis et al. (1992) with their published phases (0.06, mate. Several Pluto rotational light curves from 1954 to 1982 0.43, 0.75 and 0.75) are repeated and the authors note that are super-imposed and plotted using rotational phase, with a the Buie and Shriver (1994) study had a sub-Earth east phase of 0 corresponding to minimum light curve amplitude. longitude of 180, corresponding with a phase of 0.75. Not Young et al. (1991) calculate the K magnitude difference cross-listed. between Pluto and Charon at rotational phases 0.42, 0.96, and Cruikshank et al. (1997) describe Pluto’s surface based on 0.06 using appulse data from the IRTF. No dates are listed to spectroscopy (0.3–2.5 lm, divided by wavelength region), analo- confirm the rotational phase. However, these data are published gous structures on other planets, and temperature measure- with dates by Bosh et al. (1992), and the rotational phases and ments. The paper mentions particular sub-Earth longitudes and dates match. This is a conference abstract. describes the general brightness of the light-curve. A footnote Bosh et al. (1992) present relative H, J, and K-band photometry later in the chapter (page 91) defines the rotational phase as zero for Pluto and Charon (presented at a conference as Young et al. at northern elongation and 90 sub-Earth longitude (consistent (1991)). These measurements are combined with data in other with the decreasing system). Later sections that speculate on sur- filters and phases (using the convention of Binzel et al. face features provide an overview of features on other Solar Sys- (1985b)) from Reitsema et al. (1983), Albrecht et al. (1991), tem moons. This article is part of the Arizona Space Science Series and Jones et al. (1988)) as well as superior event photometry book, Pluto and Charon. Cross-listed in Appendix A.7. from Marcialis et al. (1987), Buie et al. (1987) and Binzel Tholen and Buie (1997a) describe bulk properties of Pluto and (1988a). The authors calculate phase where appropriate. Charon. Pluto’s light-curve is plotted in terms of sub-Earth east Marcialis et al. (1992) present Pluto and Charon albedos from longitude with an additional axis for rotational phase. While not three separate observations of the 1987-03-03 occultation of specified explicitly, the longitude is consistent with decreasing Charon by Pluto: in B and V (previously published as Marcialis longitude. A rotation period of 6.38726 ± 0.00007 d is given (1990b)) as spectra from 0.4 to 1.0 lm (previously published for Pluto and an orbital period of 6.387223 ± 0.000017 d is given as Fink and Disanti (1988)) and at 1.5, 1.7, 2.0 and 2.35 lm (pre- for Charon. This article is part of the Arizona Space Science Ser- viously published as Marcialis et al. (1987)). The observations ies book, Pluto and Charon. Cross-listed in Appendix A.7. are identified as occurring at approximately phase 0.75, short- Miles (2010) presents a V light-curve of Pluto based on data hand for a superior mutual event. taken in 2009 with Faulkes and Sierra Stars. Phase 0 is listed Marcialis (1993a) notes that Owen et al. (1993b) and Marcialis as JD 2454958.151 with a 6.3868 d rotation period. and Lebofsky (1991) draw contradictory conclusions about

whether CH4 and N2 must be mixed, and note that the observa- A.2. Spin pole is north and rotational phase tions made by the two papers overlap in rotational phase. The data from Marcialis and Lebofsky (1991) are noted to cover a Marcialis (1983) creates a two-spot model to explain Pluto’s third of the light curve near minimum light (the referenced light curve. The thesis compiles light curves from Walker and paper gives six discrete phases: 0.78, 0.85, 0.94, 0.00, 0.08, Hardie (1955), an unpublished 1964 light curve of Hardie, A. Zangari / Icarus 246 (2015) 93–145 105

Hardie (1965), Kiladze (1967), Andersson and Fix (1973), Neff – Issue 8 (September 1989) notes that the upcoming observing et al. (1974), Lane et al. (1976), Walker (1980), Tholen and season will have sub-Earth latitudes ‘‘closest to last contact’’. Tedesco (1994),5 and Binzel and Mulholland (1983), and lists Buie and Fink (1987) present four spectrophotometric observa- corrected B magnitudes and the ‘‘PJD’’ for each measurement in tions of Pluto from 5600 Å to 10,500 Å at phases of 0.19, 0.35, the Appendix. Comparative light-curves based on these points, 0.48 and 0.95 (data were taken from 1983-04-18 to 1983-04- as well as light curve predictions for the mid-to-late 1980s are 23). Phase is given relative to JD 2444240.661 with a rotation plotted in the figures. All are based on the rotational phase sys- period of 6.38726 d and light time correction of 0.167 d. It is tem. The 6.3867 d rotational period of Hardie (1965) is used with noted in the text that light curve minimum occurs at a phase an epoch of JD 2444240.59.6 The thesis recalculates the light- of 0.98. The results are compared to the spot models of curve period and epoch, and finds no significant changes need Marcialis (1983). The paper notes that the coordinates (23S, to be made to the epoch but a revised period of 6.3866 d is found. 0W, and 23S, 134W) of the spots use a system where the spin These light curves, save for the data from Kiladze (1967) and pole is north, and longitude is zero at 0 phase (minimum light). Walker (1980) are used to create a two-spot model for Pluto. The longitude of the spots is described as both increasing and The thesis notes that ‘‘we have been viewing primarily the south- ‘‘west’’. Not cross-listed: this reflects a simple units change to ern hemisphere of Pluto since its discovery in 1930’’. The two degrees. spots are also located in the southern hemisphere, with their Marcialis (1988) creates a two spot model by combining histor- sizes and separation given in degrees. This is a master’s thesis. ical and modern light light curves from Walker and Hardie The Ninth Planet News (Buie and Tedesco, 1987) was a special (1955), Hardie (1965), Kiladze (1967), Andersson and Fix nine-issue newsletter sent out to coordinate observations of (1973), Neff et al. (1974), Lane et al. (1976), Tedesco and the Pluto–Charon mutual events from January 1987 to February Tholen (1980), Tholen (1983), and Binzel and Mulholland 1990. The newsletter provided a central place for observers to (1983). In the text, the north pole is defined explicitly as follow- share data. It summarized workshops and listed upcoming ing the angular momentum vector, opposite of Davies et al. events, past observations, publications about mutual events (1980), the author states this definition avoids ambiguity. This and provided observing advice. It also advocated that the read- definition is consistently applied throughout the paper to refer ers experiment with something called ‘‘e-mail’’ to report obser- to the formerly-visible hemisphere as southern. The previously- vations. While the newsletter follows a spin north, rotational unseen northern hemisphere is described as having the larger phase system for Pluto coordinates, it is rarely mentioned, and polar cap. at no point do the authors discuss their choice of measurements The geometry of the spots are given in terms of spot radii (in or suggest that others follow them (though mutual event papers degrees), the latitude of the spot centers and their separation did so). The newsletter does contain discussion of time stan- in degrees longitude. At one point, the article describes the large dardization, the authors devote two articles worth of space to spot was ‘‘initially assumed to lie at 0 longitude’’. Pictures of recommending UT. the model results suggest this spot may have been at Each newsletter issues provides lists of upcoming and previous phase = 0.0 instead. Throughout the paper, Pluto’s light curve events. The events are identified by UT and designated ‘‘supe- is defined in phase, with an epoch of JD 2444240.661 and rior’’ (Pluto occults Charon) or ‘‘inferior’’ (Charon transits Pluto). rotation period of 6.3867 d. – Issue 2 (March 1987) describes Charon as blocking only the Marcialis (1990b) reports on a variety of topics related to the portion of Pluto northward of about 30 north latitude. mutual events – Charon’s surface, CH4 escape, composition Additionally, the issue states the following: and albedo correlations, wavelength-albedo dependence, topographic relaxation, Pluto astrometry, and an analysis of the Starting in February, the southernmost latitude covered by technological advances in astronomy that enabled Charon’s dis- Charon during an inferior event will begin to increase – Charon covery. Rotational phase is given for 1–2.65 lm spectrophotom- will be heading back to toward the brighter north polar region. etry measurements of Pluto. No epoch is given for the This quote is consistent with two things: the latitude Charon measurements – throughout the work, the rotational period of blocked during transit was not monotonically increasing or decreas- Pluto is referred to as 6.4 d, though a later mention of Charon’s ing, and based on schematics in articles such as Binzel and Hubbard orbital period is given as 6.387245 d. The maps from Marcialis (1997), Charon’s overall coverage went from north to south in the (1988) are reproduced in a similar orientation to their original spin north system. publication, which designates the spin pole as north. While a – Issue 5 (March 1988) mentions phases, referring to a phase north pole is not explicitly mentioned with maps, speculation

of 0.25 and 0.75, when mutual events occur in the phase is made that CH4 bands should strengthen as ‘‘the northern system. polar cap swings into view’’. This is a PhD dissertation. – Issue 6 (September 1988) provides geometric sketches of Burwitz et al. (1991) summarize mutual event results. A picture events in 1989, though no orientation was provided. of the event track over the years identiﬁes Charon transiting the northern hemisphere of Pluto ﬁrst and then the southern hemisphere, consistent with spin north. A rotational light curve is

5 The paper for Tholen and Tedesco’s 1980 and 1981 light curves is listed as being also plotted, and Pluto–Charon’s sidereal orbit period is given ‘‘in press’’ in Icarus for 1983. This survey found no paper matching that description. as 6.387244 ± 0.000007 d. The period of the rotational light Marcialis (1988), the summary paper of this work, simply cites Tholen (1983). A paper curve is given as 6.38718 d. published a decade later (Tholen and Tedesco, 1994) has the appropriate author list Marcialis and Lebofsky (1991) present the 1–2.65 lm spectro- and content, contain light curves from 1980–1983 with data taken on many of the photometry measurements of Pluto that made up a chapter of same dates that are listed in the thesis. However, the paper and the thesis each contain measurements taken on dates that do not appear in the other work. Marcialis (1990b). The observations are described as spanning Additionally, the magnitudes listed in the thesis have been corrected to a common a third of a rotation centered around minimum light, and the solar phase, Pluto–Sun and Pluto–Earth distance, while the paper does not appear to rotational phase is given for each observation (0.78, 0.85, 0.94, make these corrections. Sorting out any discrepancies between these two works is 0.08, 0.15) without epoch or precise period beyond 6.4 d. The beyond the scope of this paper. north pole is described as swinging into view, indicating spin 6 This epoch is attributed to the ‘‘in press’’ paper by Tholen and Tedesco described in the previous footnote. The eventually-published paper used a different epoch, north. The light curve is also compared with the spot model though this particular rotational epoch was used in previous work. of Marcialis (1988). 106 A. Zangari / Icarus 246 (2015) 93–145

Maps Reinsch et al. (1994) present a map of the sub-Charon is given and it is noted that Marcialis (1988) is credited with hemisphere of Pluto based on observations of Pluto’s rotational compiling the light curve data that are replotted in the paper, light curve and the mutual events. Visible light curves in the B, for which sources are given in the paper’s Table 1. No epoch is V, and R are presented following the rotational phase conven- reprinted. North is defined by the right-hand rule, consistent tion with a period of 6.38718 d, but no epoch is given. An orbital with the southern sub-Earth longitudes given for the 1954– period of 6.387244 d is also given in a table of orbital parame- 1986 pre-mutual event data sets. Several different maps are ters. Data were taken using the UBVRI set in addition to Gunn produced based on the combination of the historical light and Walraen filter sets. The maps follow the angular curves. Some create north or south polar caps, while others do momentum convention for north and south, and the not. However, the large residuals on the map (that include both sub-Charon hemisphere is divided into grid points. The maps 1954 and the 1980s) suggest that the bright south polar cap suggest a dark north polar cap, a bright southern polar cap, created is not realistic. These maps also provide evidence for and a moderately bright mid-latitude area in the north that surface changes. Light curve predictions are provided for darkens in the southern mid-latitudes. The dark northern hemi- 2000, 2010 and 2020. The maps are also projected onto globes,7 sphere contradicts models such as Marcialis (1988). and the rotational phase convention is used. The sub-Charon Tholen and Tedesco (1994) present a decade-old data set of meridian is at 1/4 of a rotation and phase increases positively high-precision B Pluto–Charon system light-curves observed in time. However, because this system is left-handed, the maps from 1980–1983 in preparation for the Pluto–Charon mutual are presented in a right-handed manner such that the sub-Earth events in the latter half of the decade. The Pluto light-curves point moves to the left in time, and the sub-Charon meridian are plotted where 0.0 is the light-curve minimum. A Fourier Ser- comprises the edge of map. Thus the boundaries and orientation ies is fit for the light curve data and a light time corrected zero of these maps are identical to maps that use the right-hand rule epoch of JD 2444240.66101 is given with a synodic rotation per- and decreasing longitude convention, such as Stern et al. (1997a). iod of 6.38726 ± 0.00007 d. There is an extensive discussion on Maps Grundy (1995) compares observed 0.5–2.5 lm spectra of

zero points and differing period values. The authors also retract Pluto with laboratory measurement of N2 and CH4 in order to the sidereal period of 6.38755 ± of 0.00007 d presented in create a composition map of Pluto’s surface. The sub-Earth Tholen and Tedesco (1984) due to ‘‘failure to account for the longitude and latitudes are given along with observation dates retrograde loop’’, and promise to recalculate a new sidereal for the list of spectra taken for this study, and are in spin north, period in a future paper. The authors also suggest that the decreasing longitude format. A composition map is presented rotation period calculated by Lyutyi and Tarashchuk (1984) and the observation sub-Earth points are plotted atop maps may have such an extreme difference due to the inclusion of from Buie et al. (1992). Cross-listed in Appendix A.3. data from 1953 and a possible sub-Earth latitude dependence Grundy and Fink (1996) aggregate 15 years worth of 0.5–1.0 lm on light curve minimum. As for latitude, the paper ‘‘adopt[s] spectroscopy of Pluto and Charon to show the rotation-depen-

the natural definition of north as lying in the direction of the dence of CH4 band depths and create a composition map of angular momentum vector’’ and the north pole is noted as Pluto. Sub-solar longitudes and latitudes are given along with swinging into view. The paper finds that Pluto does not dim sig- Julian date for each observation, and the sub-solar points are nificantly during the years the light curve was observed for this plotted atop an albedo map from Buie et al. (1992). For rota- paper, suggesting that northern hemisphere has only a slightly tion-based plots, the x-axis presents both east longitude and darker albedo than the southern hemisphere. These predictions phase. No epoch is given for phase, but rather the minimum are consistent with albedo maps by Buie et al. (1992) and Young and maximum light curve brightnesses are marked. Light curve and Binzel (1993) and later light curve observations by Buie and minimum coincides with a rotational phase of 0.0/1.0, though Tholen (1989). not 90 longitude in the right-handed system, but rather 100. Young (1994) characterizes the bulk properties of Pluto and No comment on the difference between light curve minimum Charon. As part of a discussion on mapping results, bright frost and greatest northern elongation/the circularity of Charon’s is mentioned at the south pole as defined by the right-hand orbit is given. Cross-listed in Appendix A.3. rule. B, V, R and I observations of Pluto and Charon from 1992 Binzel and Hubbard (1997) summarize the mutual event are presented, and the offset of Pluto and Charon from their observations and stellar occultation research. The article defines centers of light is given with respect to the north pole. The north rotational phases of 0.25 and 0.75 as the location of inferior and pole would be visible at the time under the right-hand rule. superior events. The north pole is defined by the right-hand rule Orbit residuals are plotted as a function of rotational phase. in the text. Note in this system Charon covers northern latitudes Light-corrected rotational phase p (and longitude u) at time first, then southern latitudes. A detailed event progression map (JD) is defined by is in the chapter’s Fig. 5. This article is part of the Arizona Space Science Series book, Pluto and Charon. u uo JD ðD=cÞJD ¼ p p ¼ 0 ; Marcialis (1997b) summarizes Pluto research carried out in the 360 0 P first fifty years since Pluto’s discovery. In the chapter, Fig. 2 where u0 and p0 are the longitude and rotational phase respec- shows a version of Baade’s 1934 light-curve attempts recast in tively at a time JD0. The speed of light is c, rotational period is rotational phase. Epoch and rotation rate are not given, though P and D is the distance from Pluto to the observer. the predicted amplitude estimates are given from the spot mod- It is noted that 1992-03-01 9:53:27 UT has an equivalent phase els of Marcialis (1983, 1988). Later refinements to the rotation to that at JD 2446600.5 (an orbital epoch used by many papers), period are discussed. Pluto’s pole and Andersson and Fix however this epoch has a phase of 0.46111, as calculated with (1973)’s original polar regions are plotted in the chapter’s the orbital epoch of Binzel et al. (1985b) and orbital period of Fig. 9. The pole identified as north is the spin pole, based on Tholen and Buie (1990), 6.387246 ± 0.000011 d. This is a PhD its right ascension and declination. This article is part of the Thesis. Arizona Space Science Series book, Pluto and Charon. Maps Drish et al. (1995) combine visible rotational light curves complied by Marcialis (1988) and the data from Buie and 7 The term ‘‘globe’’ is a shorthand used throughout this paper to refer to an Tholen (1989) to create surface albedo maps using matrix orthographic projection map. This projection is designed to give the appearance of lightcurve inversion. A synodic period of rotation of 6.3872 d one looking at a globe from an infinite distance or an object in space. A. Zangari / Icarus 246 (2015) 93–145 107

Young et al. (1999) present maps of Pluto created from observa- Maps Buie et al. (1992) present single scattering albedo maps tions of the mutual events. Event pictures clearly mark Pluto’s from the mutual events and historical light curves. The maps orientation on the sky, identify Pluto’s rotation, mark the spin use a spin pole and ‘‘east longitude scale to maintain a right- pole as north, and show the latitude of Charon for each event. handed coordinate system’’. To account for the potential case Two equations for Pluto’s rotation are used. The first invokes of an eccentric Charon, the zero point of longitude is the sub- rotational phase after Tholen and Tedesco (1994), which Charon meridian at Charon’s periapse. Sub-Earth and sub-solar uses Pluto phase (increasing in time) with zero point at JD longitudes are listed with mutual event observation dates. The 2444240.66101. The second uses sub-Earth longitude, and the south pole is said to be brighter than the north pole. paper notes that east longitude increases in the opposite sense Millis et al. (1993b) provide a detailed analysis of all the P8 of rotational phase. Cross-listed in Appendix A.3. occultation data, including speculation on global differences in Stern and Mitton (2005) provide a complete overview of Pluto atmosphere measurement. The chosen coordinate system is research from discovery to just before New Horizons, summariz- not explicitly defined. The text gives the sub-Earth longitude ing research in a manner accessible to the non-specialist, high- at the time of the occultation as 308 (the observation was lighting many of the people involved along the way. Mention of made at 1988-06-09 10:40 UTC). The paper’s Fig. 3 shows a pic- coordinates has been found in the following instances: ture of Pluto on the sky with occultation immersion and emer- – Fig. 2.2 gives a reproduction of the plot of historical sion sites marked while its Figs. 8 and 9 plot the temperature rotational phase light curves from Stern et al. (1988b). The versus latitude. Matching the longitude with ephemerides, rotational phase system is used. and the figures with each other indicates a spin north and – Fig. 3.11 reprints the two-model of Marcialis (1988), which decreasing system. uses spin north. Maps Stern (1993b) summarizes important developments in – Fig. 3.15 models the 1988-02-06 Charon transit across the Pluto science since 1976 and states the goals and concepts for sky. The pole that is marked north is consistent with the spin sending spacecraft to Pluto, including the Pluto Fast Flyby. north system. There is a mention of asymmetric caps and contour maps of – Fig. 3.16 compares the mutual event maps of Buie et al. Pluto features from Buie et al. (1992) and Young and Binzel (1992) and Young and Binzel (1993). The text notes that (1993), however, no identification of orientation is made. The the two models differ: both agree on a bright southern pole, paper’s figure, however, is a reproduction of Fig. 8 from Young but Young and Binzel (1993) predict a small bright northern and Binzel (1993), which uses the spin north orientation. cap, and Buie et al. (1992) predict a larger, darker cap. These Young and Binzel (1993) make comparative maps of Pluto’s predictions are consistent with spin north. sub-Charon hemisphere using data from the mutual events. – Fig. 7.3 plots Pluto’s sub-solar longitude throughout time as North is defined in the direction of the spin angular momentum well as the fraction of surface lit by the Sun. Sub-solar longi- vector and the zero is the sub-Charon longitude. The authors tudes are depicted as southern before the mutual events, and note that as the mutual events progressed, Charon first transit- northern after, consistent with spin north. ed Pluto’s northern hemisphere, and secondly its southern – Figs. 9.1 and 9.2 show Hubble images of Pluto and the albedo hemisphere, and a diagram is provided. In the erratum, Young globe models derived from these observations. Sub-Earth and Binzel (1994b) present cleaned-up versions of the surface coordinates are given for each observation – while no obser- maps in the paper’s Fig. 4 which did not get reproduced well vation times are presented for the images, the image num- in the initial paper. bers correspond to observations from Stern et al. (1997a), Young (1993) presents maps of Pluto and Charon from the and the latitudes and longitudes given are consistent with mutual events. North is defined by the right-hand rule (identi- that paper and spin north, decreasing ephemerides. The fied in figures throughout the paper, many of which also repro- globes are consistent with the Stern et al. (1997a) maps as duced elsewhere in the literature). Points are also given as east well. and west of zero longitude at the sub-Charon hemisphere, Stern and Mitton (1998) is an earlier edition of the same work and instead of an east longitude ranging from 0 to 360. The use appears to be similar. of west makes sense in this context since the prime meridian This entry is also cross-listed in Appendix A.3. is central when the mapping the sub-Charon hemisphere. The thesis’s Fig. 21 compares the sub-Charon hemisphere globe A.3. Spin pole is north, and decreasing sub-Earth longitude with with one from Buie et al. (1992), and several features are sub-Charon zero annotated. Identification of a feature B (in the upper left) as ‘‘northwest’’ confirms that east longitude must increase in the Buie and Tholen (1986) present the location of spots on Pluto, direction of rotation, consistent with the paradigm that east improving on the models of Marcialis (1984). There is a larger longitude decreases in time. Additionally, it is noted that during north polar cap and spots at (16,99) and (8, 217). The a mutual event, features to the extreme east disappear while longitude is described at being 90 at minimum light, which features to the west come into view due to rotation during implies a zero point near the sub-Charon longitude and a the course of an event, though neither extreme side will be decreasing system. The spin pole north designation must be blocked by Charon. assumed, as southern latitudes for the spot centers and a larger Buie and Shriver (1994) present differential IR photometry of northern cap are properties of the Marcialis (1988) model. This Pluto and Charon in the J, H and K filters as well as special filters is a conference abstract. at 1.5 and 1.75 lm in order to determine the rotational Buie and Tholen (1989) present and test two spot models based uniformity of water ice on Charon. The authors state that the on historical light curves of Pluto against mutual event observa- coordinate system used to present sub-Earth longitude and tions. Longitude is used instead of phase to define 0 of east lon- sub-Earth latitude was defined in Buie et al. (1992). The sub- gitude to be at the sub-Charon point in order to decouple Earth points listed in the table confirm that it is spin north parallax. North is aligned with the angular momentum vector, and decreasing in time. as indicated by the southern sub-Earth longitudes of historical Maps Grundy (1995) compares observed 0.5–2.5 lm spectra of

light curves. The model required polar caps on both the Pluto with laboratory measurements of N2 and CH4 in order to northern and southern poles. create composition map of Pluto’s surface. The sub-Earth 108 A. Zangari / Icarus 246 (2015) 93–145

longitude and latitudes are given along with observation dates limb’’ is to the left. The sub-Earth points are labeled. The maps for the list of spectra taken for this study, and are in spin north, produced are compared directly to maps by Buie et al. (1992) decreasing longitude format. A composition map is presented and the photometry is plotted against a light curve model using and the observation sub-Earth points are plotted atop maps decreasing longitude. from Buie et al. (1992). Cross-listed in Appendix A.2. Yelle and Elliot (1997) describe results from the KAO Pluto Carlowicz (1996) announces Pluto surface maps by Stern et al. occultation. The globe in the chapter’s Fig. 1 shows Pluto’s ori- (1997a). The maps have a spin north, decreasing longitude orientation on the sky as seen from Earth at the time of each entation. Reproduction is poor. observing site. No pole is marked, however, later graphs rep- Maps Grundy and Fink (1996) aggregate 15 years worth of rinted from Millis et al. (1993b), must be plotted under the spin 0.5–1.0 lm spectroscopy of Pluto and Charon to show the rota- north system based on the given longitudes, the locations of the

tion-dependence of CH4 band depths and create a composition observing sites and the dots on the Pluto globe. This article is map of Pluto. Sub-solar longitudes and latitudes are given along part of the Arizona Space Science Series book, Pluto and Charon. with Julian date for each observation, and the sub-solar points Hollis (1999a) summarizes the current state of knowledge are plotted atop an albedo map from Buie et al. (1992). For rota- about Pluto and the Kuiper Belt and reports efforts to observe tion-based plots, the x-axis presents both east longitude and Pluto by the British amateur community. The paper prints a phase. No epoch is given for phase, but rather the minimum poor reproduction of the Pluto/Charon albedo map, also shown and maximum light curve brightnesses are marked. Light curve in Stern et al. (1997a), and mentions the discovery of a bright minimum coincides with a rotational phase of 0.0/1.0, though southern polar cap and a dark equatorial region from the not 90 longitude in the right-handed system, but rather 100. mutual events. It also reports the efforts to demote Pluto from No comment on the difference between light curve minimum being a major planet and promotes the proposed Pluto–Kuiper and greatest northern elongation/the circularity of Charon’s Express mission. orbit is given. Cross-listed in Appendix A.2. Young et al. (1999) present maps of Pluto created from observa- Buie et al. (1997a) present separate light curves of Pluto and tions of the mutual events. Event pictures clearly mark Pluto’s Charon taken from HST in the F439W and F555W filters from orientation on the sky, identify Pluto’s rotation, mark spin pole 1992–1993. Light curves are plotted against ‘‘east’’ longitude. as north, and show the latitude of Charon for each event. Two The longitudes given in the table and northern sub-Earth lati- equations for Pluto’s rotation are used. The first invokes rota- tudes are consistent with a right-handed system based on the tional phase after Tholen and Tedesco (1994) which uses Pluto times of observation. phase (increasing in time) with zero point at JD 2444240.66101. Buie et al. (1997b) provide an overview of specific surface fea- The second uses sub-Earth longitude, and the paper notes that tures of Pluto. The chapter’s Fig. 1 plot of sub-Earth latitude ‘‘east’’ longitude increases in the opposite sense of rotational with time shows a spin north paradigm is in use. The article phase. Cross-listed in Appendix A.2. notes that sub-solar latitude moves from south to north, but Buie and Grundy (2000) present 1.4–2.5 lm HST spectra of sub-Earth latitude moves in a sinusoidal pattern. The chapter’s Pluto and Charon from 1998 with a focus on water in Charon’s Fig. 2 plots tracks covered by Charon during the mutual events. spectrum. Based on the sub-Earth longitude and latitude listed, The planet has been rotated so the north (spin) pole is up, and the spin north, decreasing longitude convention is used. Sub- Charon covers northern latitudes first, again consistent with Earth longitudes are listed for both Pluto and Charon (180 off- spin north. The maps are plotted spin north up and with set from Pluto’s longitude). Charon’s band depth and V light decreasing longitude starting at 0. There is a section comparing curve are plotted as a function of east longitude. maps and a section describing the quality of mapping data at Lellouch et al. (2000a) present Infrared Space Observatory far-IR different sub-Earth areas between maps. This article is part of measurements of Pluto at 60, 100, 150, and 200 lm. Tempera- the Arizona Space Science Series book, Pluto and Charon. ture globes of Pluto for different thermal inertias are drawn. Spencer et al. (1997) discuss how seasonal changes affect vola- The paper notes that it uses the same coordinate system as tile transport and individual surface features. The paper defines Buie et al. (1997a), and processed to describe it as a ‘‘right- ‘‘‘north’ as the direction of the spin angular momentum vector’’, handed’’ system with the z axis in the direction of the angular and notes the southern pole was sunlit before perihelion. The momentum, and the zero point of longitude at the equator. southern pole is identified as having the brighter cap. Maps The zero point of longitude is noted to be at the sub-Charon are reproduced, and centered longitude-wise on the sub-Charon point, and longitude is noted to be called ‘‘east’’ and decreasing zero. Longitude is decreasing. Fig. 7 (in the chapter) shows a in time. Sub-Earth latitude is noted to be increasing northward. map of temperatures by time since ‘‘midnight’’ to illustrate The listed longitudes for each measurement, as well as other how a patch at perihelion equator might heat and cool over sub-Earth latitudes are consistent with this system. The far-IR one rotation. Table 1 (in the chapter) lists thermal observations flux is plotted against a thermal light curve, which is inverted of the system in spin north, decreasing longitude format. This from the visible curve. article is part of the Arizona Space Science Series book, Pluto Lellouch et al. (2000b) present 1.2-mm bolometric observations and Charon. with IRAM, a 30-m telescope. While no coordinate system is Maps Stern et al. (1997a) present high-resolution maps of Pluto defined, the sub-Earth longitudes are consistent with ephemer- based on HST observations from 1994. The paper notes that the ides for decreasing longitude, and the positive sub-Earth lati- angular momentum north pole is used. The paper’s Table 1 tudes are consistent with a spin north system. Measurements summarizes the 20 images that make up this map and list lon- from this work along with data from Altenhoff et al. (1988) gitudes and latitudes, all of which are consistent with ephemer- (with sub-Earth longitudes calculated by Spencer et al. ides for the spin north, decreasing longitude system. The paper’s (1997)) are plotted against east longitude. Fig. 1 presents the locations of Pluto and Charon in the north up, Maps Young et al. (2001a) present two color maps of Pluto’s east left for each observing epoch; the orbital positions are con- sub-Charon hemisphere based on mutual event data. The paper sistent with the decreasing longitudes given in the lower right notes that sub-Earth latitude is traveling northward and Charon corner of each image. The paper’s Figs. 2 and 3 label and name travelled west to east and north to south over the course of the surface features on the best image of each epoch, oriented so events. It points out that when Charon transited the north pole that Pluto’s right hand rule pole is facing up and the ‘‘morning of Pluto, the north pole was in darkness and when Pluto A. Zangari / Icarus 246 (2015) 93–145 109

transited the south pole, the south pole was in darkness. As the periapse, and zero longitude on Charon is at the sub-Pluto point. map is restricted to the sub-Charon hemisphere, the map makes The orientation of the maps is consistent with this system and use of both east and west longitude. East longitude is consistent descriptions in the text note that the south pole has slipped with decreasing longitude. A prominent bright spot is located at out view with an increasing northern view. Many maps and 17N and 45E, while the southern polar cap extends up to 40S globes of Pluto and Charon are rendered in this paper. The paper before giving way to the dark band around the equator. also notes that the north pole is the larger and brighter pole, and Grundy et al. (2002) present 2.8–4.1 lm spectra of Pluto and that the north pole has been becoming brighter of late. Triton taken with SpeX on the IRTF in July 2000. The sub-Earth NA (2010b) summarizes recent astronomy and space mission longitudes and latitudes given are consistent with ephemerides news and includes globes of Pluto from Buie et al. (2010b) at for the spin north, decreasing longitude convention, though no 90, 180 and 270. No description of coordinates were provided coordinate system is explicitly defined. for the maps. However, the maps match the orientation of the Rudy et al. (2003) present NIR 0.8–2.5 lm spectra of Pluto taken original publication – spin north and decreasing longitude. on 2002-07-18.25. The sub-Earth coordinates are explicitly The article notes that since 1994, the northern hemisphere given by the right-hand rule and the authors provide a labelled has brightened while the southern hemisphere has darkened. picture of right-hand rule longitude and latitude at the current These changes are credited to sublimation of ices on the sunlit view of Pluto. The authors compare their work to Douté et al. side and refreezing on the winter pole. (1999), and note that it shares the spin system along with Maps Toigo et al. (2010) calculate thermal tides on Pluto to Grundy and Buie (2002) and Stern et al. (1997a). They also note reproduce the density fluctuations seen with stellar occultation that Dumas et al. (2001) uses increasing/ecliptic north after measurements of the atmosphere. The paper states that it uses Davies et al. (1996). the convention where local north is indicated by the angular Stern and Mitton (2005) provide a complete overview of Pluto momentum convention rather than the IAU’s ecliptic-based research from discovery to just before New Horizons, summariz- convention. Longitude increases eastward. A new frost map ing research in manner accessible to the non-specialist, high- based on the Stern et al. (1997a) maps is presented. The paper lighting many of the people involved along the way. This considers alternate frost map starting points based on maps entry is also cross-listed in Appendix A.2, and a complete from Lellouch et al. (2000b) and Grundy and Buie (2001). Grav- description can be found there. ity wave amplitude is plotted for specific latitudes and longi- Schaefer et al. (2008) present B and V photometry digitized tudes and times of day. from photographic plates of Pluto taken in the 1930s. They Lellouch et al. (2011b) describe VLT observations of Pluto and use a ‘‘right-handed coordinate system as described in Buie Triton in the NIR. The Pluto measurements made with CRIRES et al. (1992)’’. Pluto’s rotational period is given to be at 1.6 lm were originally described by Lellouch et al. (2009). 6.387223 ± 0.000017 d from Tholen and Buie (1997a).A A coordinate system is not explicitly defined, but one figure sub-Earth longitude and latitude is given for each plate in presents a map from the 2002-3 HST observations first accordance with that system. These data were taken during a published in Buie et al. (2010b). period where Pluto’s sub-Earth latitude was identical to what Lellouch et al. (2011c) present Spitzer MIPS photometry of Pluto it was when Walker and Hardie (1955) made the first light at 24, 70 and 160 lm and IRS spectra from 20–37 lm. The curve and period determination for Pluto in the 1950s and allow authors cite Buie et al. (1997a) and Lellouch et al. (2000b) and the determination that Pluto’s albedo darkened about 5% over note they use the same convention, where the northern hemi- the intervening period. Sub-Earth latitude is plotted as a sphere is currently in summer and the sub-observer longitude function of time, and the longitude of the sub-Earth points of decreases in time. Flux is plotted as a function of sub-Earth each measurement are plotted in time. The south pole was at longitude and the visible light-curve is plotted for comparison. its most extreme state in the late 1940s. Maps from Grundy and Fink (1996), Lellouch et al. (2000b) and Lellouch et al. (2009) present spectra and occultation tempera- Grundy and Buie (2001) are reproduced in the spin north, ture models for Pluto based on VLT/CRIRES measurements at decreasing longitude manner.

the 2v3 band of CH4 at 1.6 lm. The paper states it uses the con- Buie et al. (2012a) use HST observations to refine Charon’s orbit vention of Buie et al. (1997a) where ‘‘the north pole is currently and prove that Charon’s orbit is circular. It is noted that Pluto’s facing the Sun’’. The sub-Earth longitudes are listed as ‘‘east’’, rotational pole coincides with Charon’s orbital axis, implying and are consistent with the decreasing system. The paper is spin north. As part of the center of light/center of body testing, introduced by NA (2009).8 maps from Buie et al. (2010b) (spin north, decreasing longitude) Buie et al. (2010a) present individual HST observations of Pluto are used, along with modified fake versions that have bright/ and Charon in ‘‘B’’ (F435W) and ‘‘V’’ (F555W) filters. The paper dim north or south poles as well as modulated/non equatorial states that it uses the right-handed system presented in Stern regions. Residuals are plotted against sub-Earth longitude. The et al. (1997a) and Buie et al. (1997a) where north follows the decreasing system is confirmed with a note that minimum light angular momentum vector with longitude increasing to the of Pluto’s rotational light curve occurs at 90 and the maximum east. Zero longitude on Pluto is at the sub-Charon point at at 210. periapse, and zero longitude on Charon is at the sub-Pluto point. Tegler et al. (2012) present three new 0.8–2.4 lm IRTF SpeX Sub-Earth points given for various measurement epochs are spectra, and a previously published spectrum from Tegler consistent with this system. et al. (2010). Sub-Earth longitudes and latitudes are included Maps Buie et al. (2010b) present two-color maps of Pluto. The for each observation. It is noted that the coordinates are based paper states that it uses the right-handed system presented in on the ‘‘right-hand rule’’, which is consistent with ephemerides Stern et al. (1997a) and Buie et al. (1997a) where north follows for the observation times. the angular momentum vector with longitude increasing to the Young (2012) provides expressions for volatile transport. The east. Zero longitude on Pluto is at the sub-Charon point at paper states it follows the right-hand rule, decreasing longitude convention. A map that also follows the spin north, decreasing longitude conventions is reproduced from Grundy and Fink 8 This press release is one of several releases, newsletters and magazine articles (1996). The paper notes that occultation observations of that do not contain a byline. These articles are shelved under NA (no author given). Young et al. (2010) found the pressure at longitudes 297–12 110 A. Zangari / Icarus 246 (2015) 93–145

were lower than those found at longitude 82–187 using the ‘‘longitude’’. Technically, increasing longitude is also east Grundy and Fink (1996) (decreasing, spin north) coordinate longitude in the ecliptic north system. This paper is not listed conventions. However, there is insufficient information to con- as having an error because the text is always explicit about firm the accuracy of the coordinates. which system is being used in different parts of the paper, Grundy et al. (2013) present spectra of Pluto from 0.8 lmto and the differing systems do not appear to be mixed up. 2.4 lm taken at the IRTF over 65 nights from 2001 to 2012. Cross-listed in Appendix A.9. The paper notes that north pole was defined by the right-hand Guo and Farquhar (2005) describe the plans for the New Hori- rule, the Sun rises in the east and the prime meridian is at the zons encounter with Pluto. The sub-solar position 10 days sub-Charon point. The paper notes that it calculates Pluto’s lon- before approach (2015-07-04) is given as 49.4,33 (consis- gitudes and latitudes using the orbit of Charon from Buie et al. tent with ephemerides for the ecliptic north, increasing system) (2012a) and an assumption that Pluto is tidally locked to it. A and the visible hemisphere is referred to as the southern hemi- sub-Earth point is given for each measurement, with a positive sphere. Similar to Guo and Farquhar (2008). sub-Earth latitude and decreasing longitude. A light-curve and Guo and Farquhar (2006) discuss New Horizons and present the sub-Earth points for each measurement are properly super- alternatives if the original launch window had failed (this paper imposed over the spin north decreasing longitude orientated is pre-launch). The sub-solar position ten days before closest surface maps of Pluto from Buie et al. (2010b). The 180 merid- approach (2015-07-04) is given as 49.4,33 and the visible ian is also properly marked as the anti-Charon side, as well as hemisphere is referred to as the southern hemisphere. An the leading apex and trailing apex at roughly 305 and 55, updated version of this paper was published as Guo and respectively.9 The paper mentions that southern summer ended Farquhar (2008). in the 1980s and the northern pole is rotating into view. Schmude (2006) gives advice for observing Pluto, Uranus and Zangari (2013) presents several projects related to spatial varia- Neptune in 2004. The sub-Earth latitude of Pluto at opposition tion of surface and atmospheric variation on Pluto’s surface, as is listed as 33S, indicating the ecliptic north convention. well as testing of an occultation instrument. One chapter is a pre- Elliot et al. (2007) report results for the P384.2 stellar occulta- vious version of this work on Pluto coordinates; all work in this tion and compare them to previous occultation observations. document supersedes what is printed therein. While all coordi- The geocentric sub-Earth point is reported using the ‘‘IAU’’ con- nate systems are described and explained in the coordinates vention (then ecliptic north), and Pluto’s position as seen from chapter, all later chapters use the spin north decreasing longitude Earth is correctly plotted on the sky. The currently visible pole convention exclusively. Parts that use Pluto coordinates include is identified as south, consistent with the ecliptic north conven- the display of maps from Buie et al. (2010a) and Grundy and tion. The longitude and latitudes of immersion and emersion at Buie (2001), sub-Earth points for Magellan observations as well the half-light radius is given for each station. The Siding Spring as longitudes and latitudes for occultation sites on Pluto. points are consistent with the ecliptic north/increasing convention and match the AAT points (same observatory) as calculated A.4. North pole is north of the invariable plane (‘‘ecliptic north’’) and by Zangari (2013). The other longitudes and latitudes are con- increasing longitude with sub-Charon zero sistent with the ecliptic north/increasing convention based on the accuracy of the Siding Spring calculation and their positions Dumas et al. (2001) present 1.1–2.4 lm HST spectra of Pluto on the Pluto globe. and Charon, but focus on Charon. The paper notes that coordi- Verbiscer et al. (2007) present 0.8–2.5 lm resolved Pluto and nates were calculated according to the planetocentric conven- Charon spectra taken with CorMASS on a Magellan telescope tions of Davies et al. (1996). The paper correctly describes the in ‘‘May 2005’’. A negative sub-Earth latitude is given (ecliptic southern polar region as increasing in visibility. The sub-Earth north), and a sub-Earth longitude of 123 is mentioned without points are given for each of the observations, which are consis- regard to a reference system. Communication with the author tent with ephemerides for the ecliptic north, increasing system. gave an exact observation window of 7:36–7:58 UT on 2005- It is noted that one observation is near Pluto’s light curve max- 05-02 and thus the longitude given is consistent with increasing imum (99.6) and the other is near its minimum (273.2). Char- longitude for that time. on’s sub-Earth longitude is correctly given as 180 off from the Guo and Farquhar (2008) discuss the flyby design of the New Pluto sub-Earth longitudes and the leading and trailing hemi- Horizons mission. In the paper’s Fig. 10, the approach position spheres are properly identified. is given on a cartoon map as 49.4, 30.7 oriented so Pluto’s Buratti et al. (2003) present B, V, R and 0.89 lm photometry of shadowed north pole is vertical. The sub-solar position is con- Pluto from 1990–1993, 1999 and 2000. The ecliptic north/ sistent with ecliptic north and increasing ephemerides for increasing longitude convention used for the majority of the 10 days before closest approach. The pole in shadow is identi- paper is in accordance with the IAU, and it is noted that the fied as north. This paper also provides context for the timing rotational pole is at 90 south. This convention is used for tables of the flyby: a Charon occultation occurs twice per orbit and listing sub-Earth longitudes and latitudes for observations and ‘‘Pluto first’’ was preferred. light curve plots in the paper’s Figs. 1, 3, 4, and 5. The paper’s Protopapa et al. (2008b) present resolved IR NACO spectra of Fig. 7 shows a light curve model compared with data from pre- Pluto and Charon from 1 to 5 lm. Sub-observer longitudes vious observations, as well as a model based on the HST maps of and latitudes given are consistent with ephemerides for the Stern et al. (1997a). Because the HST maps use ‘‘east longitude’’, ecliptic north, increasing longitude convention. These spectra the data in the paper’s Fig. 7 were plotted in that format as well. are compared with Keck data from Olkin et al. (2007) taken To contrast with the east longitude of the decreasing system, on 2001-08-12. A sub-Earth longitude of 198 is given for this increasing longitude is referred to as ‘‘west longitude’’ or simply Keck spectrum (and is reported in the original paper), which is also consistent with ephemerides for the increasing longitude, ecliptic north convention. A slope change between 2.9 9 Due to the fact that the system barycenter is above Pluto’s surface, Pluto has a and 3.1 lm that could be based on either latitude changes or leading and a trailing apex. Ordinarily, these points would be found at 270 and 90. resurfacing was found. However, the barycenter is relatively close to Pluto, so the apexes are pulled towards to the sub-Charon longitude. Their exact location is dependent on the still-uncertain Zalucha and Gulbis (2011) discuss a new Pluto Global Pluto radius (Grundy, personal communication, 2014). Circulation Model. The immersion and emersion latitudes of A. Zangari / Icarus 246 (2015) 93–145 111

the 2006-06-12 occultation by Pluto as seen from Siding Springs of Charon and its shadow for inferior and superior events. The are given as 33 and 53. Based on independent calculations paper also explains that the overall annual motion of Charon from Zangari (2013), these latitudes are consistent with the during inferior events is north to south. However, due to the ecliptic north model. It is also noted that westward winds are Earth’s motion, Charon goes from southern to northern latitudes prograde with Pluto’s rotation, consistent with increasing from before opposition to after opposition. Because the paper’s longitude. This is a conference abstract. Fig. 1 mimics north up and east left on the sky, Pluto’s tilt puts Zalucha (2012) present global circulation models for Pluto, the spin pole on the right side, so the paper refers to north as Mars, Triton and GJ 1214b. It is noted that easterly zonal winds right and south as left in the text. The north polar region is around the pole are prograde, indicating increasing longitude. noted to be brighter than the equatorial regions, with the south- The GCM results are also plotted as a function of latitude, which ern brightness as yet unknown. is unspecified. However, comparison with other works by this Binzel (1988a) presents color differences between Pluto and author indicate that the ecliptic north convention was used. Charon based on mutual event data from the 1987-04-04 Mousis et al. (2013a) model clathrates on Pluto’s surface and occultation of Charon behind Pluto and the 1987-05-22 transit make predictions for observations by the Alice instrument of Charon in front of Pluto. Differences between depths of aboard New Horizons. Airglow observations on approach are mutual events are attributed to Charon first transiting northern simulated, and a sub-spacecraft longitude and latitude and latitudes, then the equator, consistent with the spin north sub-solar longitude and latitude are given for when the definition. No phases are given for the measurements, but it is

Pluto-New Horizons distance is 99 Rp. No time is given, but clear that they refer to phases of 0.75 and 0.25, since these New Horizons is at that range from Pluto at roughly 9:32 UT are mutual even observations. on 2015-07-14, and the longitudes and latitudes given are Binzel (1988b) discusses preliminary albedo results for the consistent for those calculated by GeoViz at that time for the mutual events. The Charon transits are described as covering increasing, ecliptic north system. northern latitudes in 1985 and 1986, then equatorial and Zalucha and Michaels (2013) present a 3D global circulation southern latitudes in 1987 and 1988. The paper notes that the model for Pluto. The paper notes that the north pole of the Pluto northern polar region is both brighter and bluer than equatorial is on the same side of the north pole of the ecliptic and regions, and that the south polar region will not be probed until longitude increases eastward. The south pole is noted to be 1989 and 1990. This is a conference abstract. the summer pole in the 2000s, consistent with this system. Horne et al. (1988) discuss the first steps in making maximum entropy maps of Pluto based the mutual event data and A.5. Spin pole is north but longitude not mentioned rotational light curves. Given that the sub-Earth point is presented as being in Pluto’s southern hemisphere when the Dobrovolskis and Harris (1983) present the history of Pluto’s data were taken, this paper uses the spin north convention. This obliquity. The angle of obliquity is defined to be the angle is a conference abstract. between the orbit normal and the rotational pole. Both are Tholen and Buie (1989) provide an update on the mutual defined in the ‘‘right-hand sense’’. It is later noted that Pluto event analysis, noting that the 1989 transits covered the has always been ‘‘somewhat retrograde’’. south polar region, consistent with the spin north system. Marcialis (1984) describes a two spot model for Pluto’s surface. The abstract reports that the south was found to have an The spots are in the southern hemisphere, suggesting a spin equally bright cap. The abstract provides a list of parameters north designation, because in that system, the south pole had for the Pluto system and sets the epoch to be JDE 2446600.5 been visible during this time. All papers that describe this spot with a period of 6.387245 ± 0.00012 d. This is a conference model use a spin north system and give southern latitudes for abstract.

the centers of the two spots. This is a conference abstract. Binzel (1990a) discusses the impact of Pluto’s seasons on CH4 Cochran and Sawyer (1986) present 0.74–1.02 lm spectra of transport. The south pole, the brightest region on the Pluto, is Pluto at different times in its rotation phase (date ranges, but identified as being formerly visible and the north pole is identi- no phases, are given). The article cites two spots located at fied as emerging after perihelion, indicating spin north. This is a southern latitudes from Marcialis (1983), consistent with a spin conference abstract. north designation. This is a conference abstract. Binzel (1990b) discusses why Pluto’s south polar cap poses a Dunbar and Tedesco (1986) describe the mathematics of a ‘‘first puzzle and suggests that there could be a reservoir of volatiles. order’’ model for a Pluto and Charon mutual event (this model The southern cap is identified as being transited by Charon in includes shadows, while zeroth order models do not). Sub-Earth the later mutual events from 1989–1990, indicating spin north. latitude (w) is mentioned as a part of the model but is not This is a conference abstract. explicitly defined as spin north. However, the latitudes given Marcialis (1990a) reports 0.96–2.65 lm observations of Pluto for specific events suggest a spin north designation. that look for a spectral variation with rotational phase. It notes Tholen et al. (1987a) present several mutual event observations that minimum light of the rotational light curve corresponds

from the early half of the season (through 1986) that show with the deepest CH4 bands. A rotational phase for the event variations in transit/occultation depth between superior and is not given, however it is mentioned that the sub-Earth point inferior events. Data are plotted with respect to universal time. is traveling northward, indicating a spin north system. A description of the different polar regions notes that north Young and Binzel (1990) present a sub-Charon albedo map of follows the angular momentum convention. Pluto (not shown in the abstract). The abstract reports on Plu- Tholen et al. (1987c) provide mutual event circumstances for to’s unusually bright southern pole in contrast to the northern the year 1988. Events are referred to as either inferior or hemisphere. The paper notes that the south pole had been superior. No mention of rotational phase or longitude on Pluto oriented toward the Sun during the approach to perihelion, is made, though an epoch of JD 2446600.5 with an orbital indicating a spin north convention. This is a conference abstract. period of 6.387217 d is given. The paper does mention the east Tancredi and Fernandez (1991) try to account for the angular longitudes at which Earth observers will be able to see the momentum of the Pluto system. The unnumbered equation event. The text notes that north is defined to lie in the direction immediately before Eq. (9) has a term defined with respect to of the angular-momentum vector. A figure shows the position a ‘‘north rotation pole’’. 112 A. Zangari / Icarus 246 (2015) 93–145

Binzel (1992) summarizes his work on the Pluto mutual events Hansen and Paige (1996) create ice models for Pluto’s polar caps as part of a write-up of the Urey Prize lecture. The spin pole has to determine at what point in Pluto’s orbit the north and south been identified as north with the reproduction of the mutual polar caps should appear and disappear. Various papers which event schematic from Young and Binzel (1993). The bright find changing bright and dim caps are cited. The paper defines south pole is revisited. north using the ‘‘right-hand rule’’ as opposed to the old IAU Buratti et al. (1992) presents V mutual event results from convention. A map of Pluto’s orbit around the Sun mentions Palomar. The paper also notes that both Pluto and Triton have which pole is lit, and is also consistent with spin north.

unexpectedly bright south polar regions, which is odd, because Duxbury et al. (1997) discuss the implications of N2 condensa- both south poles are ‘‘in insolation [but] show the least evi- tion in the laboratory for Pluto and Charon. While longitude fig- dence of sublimation’’. The coordinate system is not explicitly ures into a global vapor pressure equilibrium equation, only defined, but a brighter south polar cap indicates spin north. This latitude on Pluto is explicitly specified. The paper notes that is a conference abstract. the sub-solar latitude of Pluto was 16N in 1994, and examines NA (1992) publishes a picture of Pluto and Charon by a German the bright southern cap and dark northern regions. artist. The bright south pole and dimmer north pole are drawn Terrile et al. (1997) describe the early stages of planning for and identified as part of the picture, indicating a spin-based different types of spacecraft visits to Pluto. Arrival before the orientation. ‘‘deep southern hemisphere winter’’ (spin north is in sunlight) Young and Binzel (1992) present models for sublimation driven is one concern. This article is part of the Arizona Space Science winds that could explain Pluto’s bright south polar cap and the Series book, Pluto and Charon. lack of a north polar cap. North is explicitly defined by the Tholen and Buie (1997b) present HST data from 1992–1993 to right-hand rule. This is a conference abstract. determine the orbit of Charon. The paper describes the southern Young et al. (1992) hope to explain Pluto’s bright southern cap. pole has having the brightest regions on Pluto, but also some of The north pole is explicitly defined as being in the direction of the darkest, while the northern regions are less contrastive. The the angular momentum vector. This is a conference abstract. paper also discusses differences between the orbital and Maps Young and Buie (1993) present IR maps of Pluto from the rotational periods found by various papers, and notes that mutual events based on data at 1.53, 1.75, 2.00, and 2.35 lmto minimum light can be affected by a stripe that is oriented at

search for CH4 frost. The system used is not defined, but the an angle relative to Pluto’s equator. An orbital period of ‘‘bright south pole’’ (the only bright region that may have CH4 6.387223 ± 0.000017 d with an epoch of JD 2449000.5 is frost) implies a right-handed coordinate system. This is a presented for Charon. The sub-Earth latitude is described as conference abstract. migrating from northward, consistent with the spin north Albrecht et al. (1994) present HST F342W and F550M images of system. Pluto taken in 1994 after the first HST servicing mission and Trafton et al. (1997) describe atmospheric escape processes. compare the results with the mutual event map from Buie While most discussion occurs without reference to a north or et al. (1992). The paper notes that the north pole is chosen using south pole, the southern polar cap of Binzel (1990a) is men- the ‘‘right-hand law’’, opposite the IAU. No sub-Earth longitude tioned in the orbital precession section, indicating a spin north or rotational phase is defined. A Pluto globe model of the aspect system. This article is part of the Arizona Space Science Series of the HST observations is shown, with the globe rotated to book, Pluto and Charon. match Pluto’s orientation on the sky in the original HST image. Grundy et al. (1999) report on NIR spectra from HST taken with Another figure notes that north is in the 8 o’clock position. Rota- NICMOS (the wavelength range is not listed the abstract). tion of the globe so that north is at 12 o’clock puts the visible Pluto’s sub-Earth latitude is described as increasing northward pole in its correct sky position at that time. At the time of the consistent with spin north. This is a conference abstract and a HST observations, Pluto’s sub-Earth longitude was approxi- companion to Buie et al. (1999) (see Appendix A.7). mately 246 in the decreasing system [as calculated by this Stansberry and Yelle (1999) calculate the relative amounts of N2 paper]. The globe pictured is consistent with the globe from in the a and b phases as a function of latitude on Pluto. The Buie et al. (1992), note that the map is centered on 0 longitude, paper does not explicitly state which pole is north, but the so the sub-Earth point is at 114. Similar to Albrecht (1995). paper’s Fig. 4, which depicts Pluto in the year 2030, shows war- Albrecht (1995) presents HST F342W and F550M images of Pluto mer temperatures at northern latitudes, and the paper’s Fig. 5 taken in 1994 after the first HST servicing mission and compare shows a warmer northern hemisphere after perihelion. This is the results with the mutual event map from Buie et al. (1992). consistent with a sunlit north pole and spin north convention. The paper notes that the north pole is chosen using the Grundy and Stansberry (2000) model the seasonal evolution of

‘‘right-hand law’’, opposite the IAU. No sub-Earth longitude or N2 on Pluto and Triton. Pluto’s then-current sub-Earth latitude rotational phase is defined. A Pluto globe model of the aspect is given as 24 in a plot of Pluto’s diurnal energy balance in of the HST observations is shown, with the globe rotated to 1999, consistent with the spin north orientation. No formal match Pluto’s orientation on the sky in the original HST image. definition of a pole is given in the paper. Another figure notes that north is in the 8 o’clock position. Rota- Rubincam (2000) presents a dynamical analysis of precession of tion of the globe so that north is at 12 o’clock puts the visible solar torques that could cause Charon’s orbital plane and Pluto’s pole in its correct sky position at that time. At the time of the equator to come out of alignment. The axial tilt is presented at HST observations, Pluto’s sub-Earth longitude was approximately 116, which implies consideration of the spin pole as north. 246 in the decreasing system [as calculated by this paper]. The However, no mention is made of proper latitude or longitude. globe pictured is consistent with the globe from Buie et al. Colatitude, as measured from the poles is mentioned. Naturally, (1992), note that the map is centered on 0 longitude, so the being a dynamical paper, the unit vectors of Charon’s orbital sub-Earth point is at 114. Similar to Albrecht et al. (1994). plane (b^) and Pluto’s spin axis (^s) point in the same direction Buratti et al. (1995) publish several mutual event observations as the rotational angular momentum vector. from Palomar Observatory, both in table and graphical form. Rubincam (2003) discusses polar wander on Pluto and Triton. The data are presented as UT-date and magnitude difference from While retrograde Triton’s pole is defined by Neptune’s rotation a baseline light-curve. The spin vector is identified as north as part axis, Pluto’s pole is not defined at all, though in the Triton of a general summary of the data in the conclusions section. section it is noted that a positive spin pole should pierce the A. Zangari / Icarus 246 (2015) 93–145 113

northern hemisphere under ‘‘normal’’ circumstances. The paper from ephemerides to be December 1987 and September 1989 does say that both Triton and Pluto have bright polar caps in the respectively), and thus, the south pole (the spin north pole) south. It cites Spencer et al. (1997), which defines the spin pole was sunlit during perihelion. It is noted that because the north as north and discusses a south polar cap. pole is in sunlight for a longer amount of time due to slow Sage (2003) discusses the changes in occultation results from motion at aphelion, the total amount of light received at each 1988 to 2002 in the context of Hansen and Paige (1996), noting pole over the course of a Plutonian year is similar. When the north pole’s gasses would sublime more rapidly as the north insolation is plotted against planetocentric solar longitude in pole comes into illumination. Sage notes that Elliot and Sicardy the paper’s Figs. 1, 2 and 3, it refers to the amount Pluto use the ecliptic north convention, and provides a detailed expla- has travelled in its orbit around the Sun, not features on the nation of the pole controversy. The subject of the definition of surface. Pluto as a planet is also broached. Not cross-listed. Apt et al. (1983) present spectra of Pluto from 0.45 to 0.95 lm. Rubincam (2009) discusses the paradox of a bright south polar A picture of Pluto’s orientation and sub-Earth latitude is cap and refer to it as visible during the approach to perihelion, provided in the paper’s Fig. 2. The caption gives a northern indicating that it was visible before the mutual events, making sub-Earth latitude and notes the pole identification was this a spin north convention. This is a conference abstract. ‘‘recommended by the IAU’’. Greaves et al. (2011) present evidence of CO in Pluto’s atmo- Sicardy et al. (2003) present results from two stellar sphere from 1.3 mm wavelength observations of CO. A descrip- occultations by Pluto observed in August 2002. The south pole tion in the introduction (citing Buie et al. (2010a),b) identifies is described as being constantly in sunlight. the northern pole as brightening as it came into sunlight after Sicardy et al. (2005) discuss the changes in Pluto’s atmosphere perihelion, and an unexpected darkening of the southern pole, between the 1988 and 2002 stellar occultations by Pluto. The consistent with spin north. currently-visible pole is identified as the south pole. Vangvichith et al. (2011) report on a Pluto GCM that models Person et al. (2008) present data from the 2007 March 18 conditions in 1989, 2002 and 2015. For the 1989 model, the occultation by Pluto (P445.3). The visible spin pole is defined

authors note ‘‘N2 ice sublimates in the north and condensates as the southern pole in accordance with ‘‘IAU convention’’ and in the southern hemisphere as it is the winter hemisphere in negative Pluto sub-Earth latitudes are given. 1989’’. Ephemerides show that Pluto turned from the ecliptic Tyler et al. (2008) describe REX, a radio instrument aboard New north pole being visible to the spin north pole visible in 1988. Horizons which is poised to examine Pluto’s atmosphere. Pluto’s The authors include a dark equatorial region, a small northern sub-solar point is described as moving into the southern hemi- polar cap and a large southern polar cap as a starting point for sphere, and the north polar cap will grow as the southern cap is their map based upon Lellouch et al. (2000a), which uses a spin depleted. Work from Hansen and Paige (1996) and Spencer pole north, decreasing longitude system (and mentions a cur- et al. (1997), which use the spin north convention, is cited rently large southern cap). This is a conference abstract. and appropriate switches seem to have been made. Kerr (2013) summarizes the July 2013 meeting ‘‘The Pluto Sys- Young et al. (2008a) present data from the observations of the tem on the Eve of Exploration by New Horizons", by interviewing 2006-06-12 occultation by Pluto and refer to sub-Earth latitude several scientists about their predictions. The article notes Plu- in accordance with ‘‘IAU convention’’. Based on the identifica- to’s northern hemisphere has been gradually turning toward tion of Pluto having a southern sub-Earth latitude in September the Sun, consistent with the spin north paradigm. 1989 and a figure showing the spin pole as south, the ecliptic Olkin et al. (2013) present occultation results from the 2013-05- north system is used. No mention of longitude is made in the 04 occultation by Pluto that are consistent with the ‘‘permanent paper. northern volatile’’ paradigm which states that Pluto’s Young et al. (2008b) provide a broad overview of the science to atmosphere does not collapse. The paper uses a rotational be performed by New Horizons. The authors note that the IAU definition for the north pole and notes that the north pole is north pole (pre-revision) is the rotational south pole and the currently sunlit. All descriptions of north and south, and figures ‘‘current winter pole’’, are all equivalent statements. Current are consistent with this paradigm. Available on the ArXiv. sub-solar latitudes are given as negative, also consistent with Person et al. (2013) report observations of a stellar occultation the ecliptic north convention. The paper also presents a figure by Pluto on 2011-06-23 from the Stratospheric Observatory from Young et al. (2001a) which is properly flipped from its For Infrared Astronomy. While no coordinate system is defined, original publication orientation to match the ecliptic north the introductory material notes that Pluto’s southern pole has convention. Longitude is not defined in the review paper, receded from view, citing Hansen and Paige (1996). A receding though observations to be made 30 apart in longitude are southern pole is consistent with the spin north system. mentioned. Young (2013) uses 3D volatile transport code to predict the fate Sicardy et al. (2011a) use a 2008 occultation of both Charon and of Pluto’s atmosphere. Three scenarios are mapped out, includ- Pluto to constrain the orbital position of Charon. The right ing one called ‘‘permanent northern volatiles’’. The author notes ascension and declination of the north pole of Pluto is listed, that the rotational north pole convention is being used, and that and is consistent with the ecliptic north convention. In a figure the north pole is currently facing the Sun, consistent with spin showing the occultation path, the currently visible pole is north. labelled as south. Zalucha et al. (2011a) re-analyze Pluto occultation light curves A.6. North pole is north of the invariable plane (‘‘ecliptic north’’) but using a radiative-conductive model. The ‘‘IAU convention’’ (here longitude not mentioned referring to ecliptic north) is used. The conclusions note that immersion is in the southern hemisphere and emersion occurs van Hemelrijck (1982) calculates the insolation at Pluto in the northern hemisphere. Occultation light curves from throughout a Plutonian year. The author chooses ecliptic north 1988, 2002 and 2006 are mentioned in the paper, and this based on the IAU and Davies et al. (1980). In terms of daily statement is consistent with that convention for all light curves. instantaneous insolation, the south pole (the pole that is cur- (No longitudes and latitudes are actually listed for immersion rently visible today) will receive more light than the north pole, and emersion, but independent calculation from Zangari due to the fact that equinox occurs before perihelion (calculated (2013) are in agreement with this statement.) 114 A. Zangari / Icarus 246 (2015) 93–145

A.7. Decreasing longitude with sub-Charon zero only would have a Pluto sub-Earth longitude of 180 and a Charon sub-Earth longitude of 0. Charon spectra are also compared Trafton and Stern (1996) present UV spectra taken with the with low-resolution spectra from Roush et al. (1996), but no Faint Object Camera on HST. An ‘‘east’’ longitude is given for longitudes are given. each measurement, and these measurements are consistent Krasnopolsky (2001) presents 0.2–0.25 lm HST UV spectra of with ephemerides for decreasing longitude. The UV rotational Pluto and Charon. The paper defines the difference between light curve and UV slope are plotted as a function of east the rotational phase system and the decreasing longitude longitude. system, noting that at 0 phase, longitude is 90. Sub-Earth lon- Cruikshank et al. (1997) describes Pluto’s surface based on gitude is noted to be east longitude. The paper’s Table 1 lists the spectroscopy (0.3–2.5 lm, divided by wavelength region), longitudes of observations spanning 1992–1995, which are analogous structures on other planets, and temperature mea- consistent with decreasing ephemerides for Pluto observation surements. The paper mentions particular sub-Earth longitudes times given to the nearest day. It is noted whether Charon and describes the general brightness of the light-curve. A observations are taken at northern or southern elongation. footnote later in the chapter (page 91) defines the rotational The paper correctly identifies northern elongation as having a phase as zero at northern elongation and 90 sub-Earth longitude of 270 on Charon and southern elongation as having longitude (consistent with the decreasing system). Later a longitude of 90 on Charon. sections that speculate on surface features provide an overview The paper also references observations reported in Stern et al. of features on other Solar System moons. This article is part of (1991a) and notes that these observations were made from the Arizona Space Science Series book, Pluto and Charon. rotational phases 0.46–0.70. While these phases are an accurate Cross-listed in Appendix A.1. representation of what was reported in the original paper, these Tholen and Buie (1997a) describe bulk properties of Pluto and phases are not correct (see the Stern et al. (1991a) entry in Charon. Pluto’s light-curve is plotted in terms of sub-Earth east Appendix A.10 for corrected phases and sub-Earth longitudes). longitude with an additional axis for rotational phase. While not Sasaki et al. (2005b) give a sub-Earth longitude for an L band AO specified explicitly, the longitude is consistent with decreasing Subaru observation of Pluto and note that ‘‘on 2002 May 28 UT longitude. A rotation period of 6.38726 ± 0.00007 d is given near the opposition ... the sub-Earth longitude was 40–50’’. No for Pluto and an orbital period of 6.387223 ± 0.000017 d is given indication of the convention is given. The decreasing sub-Earth for Charon. This article is part of the Arizona Space Science longitude for that date was 90–34, so this observation is using Series book, Pluto and Charon. Cross-listed in Appendix A.1. the decreasing convention. Lellouch et al. (1998) present an IR thermal light-curve of Pluto Lellouch et al. (2011a) present 2.33–2.36 lm CRIRES spectra made from ISOPHOT observations at 60, 100, 150 and 200 lm. that show evidence for CO in Pluto’s atmosphere. The sub-Earth The sub-Earth longitudes of the maximum and minimum light longitudes for the two nights are noted to be ‘‘east’’ longitude are given as east longitude (though corresponding observation and are consistent with ephemerides to be decreasing in time. dates are not listed). It is noted that these features are nearly The paper notes that Grundy and Buie (2001) have evidence anti-correlated with features in Buie et al. (1997a), and the for a CO-rich region near 180 (consistent with figures in the visible light-curve minimum and maximum are given. These original paper, also in a decreasing system, though 180 is longitudes are consistent with a decreasing system, also used degenerate). in Buie et al. (1997a). This is a conference abstract. Buie et al. (1999) present 1.4–2.5 lm spectra of Pluto taken A.8. Increasing longitude with sub-Charon zero only with HST/NICMOS in spring 1998. The paper lists the four sub-Earth longitudes and dates (to the nearest day), which are Schmude (2005) describes observations made in 2003 of consistent with ephemerides in decreasing format. This paper Uranus, Neptune and Pluto, listing V-magnitudes of Pluto for is a companion to Grundy et al. (1999) (see Appendix A.5). five nights in March. Each night includes a sub-Earth longitude Douté et al. (1999) present 1.4–2.55 lm UKIRT spectra of Pluto in the increasing system that are consistent with ephemerides. Buie et al. (2006) report new orbits for Charon, S/2005 P1, and taken in May 1995 to search for CH4 segregation. The paper plots the time of observations versus sub-Earth longitude for S/2005 P2 based on precovery HST images of the satellites from the data presented atop a visible light curve from Buie et al. 2002–2003. The paper’s Table 1 assigns Visit ID numbers in (1997a), for the new observations in the paper as well three order of ‘‘increasing sub-Earth longitude’’. While the system additional points. All points are consistent with ephemerides used for sub-Earth longitude is not mentioned, the ordering is that follow the decreasing longitude system. A cartoon globe consistent with ephemerides for increasing longitude. Consulta- showing locations of sublimation, transport and deposits is tion with the author reveals that using the increasing system for given, but no orientation is provided. ordering was unintentional. Nakamura et al. (2000) present K-band Subaru spectra of Pluto and Charon at two times when Charon was near its greatest A.9. Ecliptic north and decreasing longitude with sub-Charon zero separation from Pluto. The sub-Earth longitudes given are in the decreasing system. The paper gives Pluto sub-Earth longi- Buratti et al. (2003) present B, V, R and 0.89 lm photometry of tudes for the two observations made and graphs Charon’s posi- Pluto from 1990–1993, 1999 and 2000. The ecliptic north/ tion along its orbit. The longitudes given and the Charon increasing longitude convention used for the majority of the positions are consistent with ephemerides for the decreasing paper is in accordance with the IAU, and it is noted that the system. A UKIRT observation from Douté et al. (1999) is rotational pole is at 90 south. This convention is used for tables reported as having a longitude of 200. This measurement is listing sub-Earth longitudes and latitudes for observations and one of three reported in that paper, and is also consistent with light curve plots in the paper’s Figs. 1, 3, 4, and 5. The paper’s the decreasing system. Fig. 7 shows a light curve model compared with data from pre- The paper notes that Charon spectra from Buie et al. (1987) vious observations as well as a model based on the HST maps of were taken at a sub-Earth longitude of 0. However, that paper Stern et al. (1997a). Because the HST maps use ‘‘east longitude’’, describes Charon spectra from a superior mutual event, which the data in the paper’s Fig. 7 were plotted in that format as well. A. Zangari / Icarus 246 (2015) 93–145 115

To contrast with the east longitude of the decreasing system, Table A.8 gives the published image time, the header mid times, increasing longitude is referred to as ‘‘west longitude’’ or simply the paper phase and the recalculated phase based on the header ‘‘longitude’’. Technically, increasing longitude is also east mid time. longitude in the ecliptic north system. This paper is not listed This work is expanded upon by Stern et al. (1991a). as having an error because the text is always explicit about Banks and Budding (1990) present the locations of spots on which system is being used in different parts of the paper, Pluto. The paper notes that north is defined in the direction of and the differing systems do not appear to be mixed up. Pluto’s angular momentum vector, opposite the IAU. The Cross-listed in Appendix A.4. light-curve is in rotational phase with zero at JD 24444240.59 (there should only be three 4s). Light curves are plotted accord- A.10. These papers contain errors or ambiguities ing to phase, which is given in degrees, instead of the standard 0 to 1. Longitudes and latitudes of spots are given according to the Note: Throughout this section, observation dates are given for spe- spin north/phase as degrees format. cific papers with longitude or phase errors. Each table may use a dif- Barker et al. (1991) present UV spectra of Pluto at several ferent date format to preserve the original text given in the different rotation phases, both from IUE and the ground. The respective papers. A summary of the papers in this section and their rotational phases given do not match calculated phases. This respective errors can be found in Table 4. is a conference abstract. See Table A.9 for corrected phases. Stern et al. (1991a) present several UV Pluto spectra taken with Bonneau and Foy (1980) report on speckle interferometry to IUE, some of which were previously published in Stern et al. determine orbits, albedos, mv difference, and diameters of Pluto (1989a). Both rotational phase and sub-Earth longitude are and Charon. The authors mention that they have chosen the given for each measurement. The images from Stern et al. nearest elongation point from Harrington and Christy (1980b) (1989a) have different phase values from the ones listed this as their zero, with JD 244409.991. This number is missing a paper, though the data are the same. The day of each measure- digit, and based on the surrounding text, the observation epoch ment is listed along with the exposure time, but the hour each should be JD 2444409.991, which corresponds to greatest south- image was taken is not included in the paper. However, image ern elongation on 1980-06-19 at 12 UT. However, there is no mid times from IUE data are available online (http://archive. mention of any particular rotational phase of Pluto. Rather the stsci.edu/iue/search.php), allowing the phases to be precisely rotational phase is used to calculate the orbital angle of Charon verified. Table A.10 lists the published image dates, the header with respect to Pluto. This article is in French with an English mid-times, the paper phases and re-calculated phase values. abstract. Note that three phase calculations differ substantially from Barker et al. (1989) present IUE UV spectra of Pluto at various the paper phase. While the first two spectra with incorrectly phases. Based on the dates listed, the phases given for each reported rotational phase did not figure into the analysis, a dif- observation match a zero point at the sub-Charon longitude, not the standard northern elongation, though no epoch or Table A.9 explanation is given. Note the reference for spectra is incorrect– Published and calculated longitudes for Barker et al. (1991). it refers to a Triton paper. This is a conference abstract. See Date Paper phase Calculated phase Table A.7 for corrected phases. 30 June 1989 0.64 0.76–0.91a Stern et al. (1989a) present IUE UV spectra of Pluto. The 16 July 1989 0.15 0.26–0.42 ‘‘rotational phases’’ given map out to sub-Earth longitude in 22–25 March 1989 0.47, 0.63, 0.78, 0.93 0.1–0.73 the increasing format, not phase defined at northern elongation 26 July 1989 0.7 0.83–0.98 1988, 1989 IUE spectra 0.46–0.70 See Stern et al. (1991a) (one time, the paper mixes up the months of 2 observations). Indeed, the observation nearest to 0.5 contains a mutual event a Bold-faced entries indicate calculations with significant disagreement with the (Pluto occults Charon), whereas standard notation puts Charon published values. transits at 0.25 and Pluto occultations of Charon at 0.75. As IUE images are stored online (http://archive.stsci.edu/iue/search. Table A.10 php), the original image mid-times were available, allowing Published and calculated phases for Stern et al. (1991a). for more accurate calculations for the phases given in the paper. Paper date Image header midtime Paper phase Calculated phase 87/169 1987–06-19 04:39:58 0.21 0.61a 87/170 1987-06-20 04:02:11 0.25 0.76 Table A.7 88/193 1988-07-11 16:34:13 0.46 0.44 Calculated and published phases for Barker et al. (1989). 88/193 1988-07-12 05:28:24 0.51 0.52 Date Paper phase Calculated phase 88/194 1988-07-12 10:37:07 0.58 0.56 89/205 1989-07-24 07:17:22 0.55 0.56 30 June 1989 0.64 0.75–0.91 89/205 1989-07-24 13:51:06 0.58 0.61 16 July 1989 0.15 0.26–0.42 89/206 1989-07-26 08:32:55 0.70 0.88 4 August 1989 0.12 0.23–0.42 26 July 1989 0.7 0.83–0.94 a Bold-faced entries indicate calculations with significant disagreement with the 1988 IUE spectra 0.16 See Stern et al. (1989a) published values.

Table A.8 Published and calculated phases for Stern et al. (1989a).

Paper start time plus half exposure time Image header mid time Paper phase Calculated phase 19 June 1987 22:37 + 162.5 min 1987-6-20 04:02:11 0.507 0.76 11 July 1988 2:20 + 67.5 min 1988-7-11 16:34:00 0.110 0.444 11 July 1988 5:05 + 360 min 1988-7-12 05:28:24 0.159 0.52 11 July 1988 17:30 + 120 min 1988-7-12 10:37:07 0.230 0.56 116 A. Zangari / Icarus 246 (2015) 93–145

ferent phase for the final image alters the paper’s conclusions Later in the paper, a rotation matrix is given and it is noted that substantially, specifically when measurements are compared the north pole is defined by the direction of the angular with a visible light curve from Marcialis and Lebofsky (1991) momentum vector, again citing the Astronomical Almanac. The (the paper notes that the peak of this light curve is at 0.65, 1994 Astronomical Almanac uses the ecliptic north system. and it is consistent with a curve defined with respect to The paper quotes two orbital periods for Pluto: 6.387246 ± rotational phase). 0.000011 d (Tholen and Buie, 1990) and 6.387223 ± 0.000017 d Sub-Earth longitude is also given for most measurements in the (Tholen and Buie, 1997b). The paper plots Charon’s light fraction paper. The sub-Earth longitude is not defined. However, it as a function of rotational phase according to the first northern increases in time, and the zero is not at the sub-Charon longi- elongation of 1980, as per Buie et al. (1997a). That particular tude, but rather the anti-Charon longitude, an unorthodox paper does not use rotational phase, but rather decreasing longi- convention. Table A.11 recalculates the sub-Earth longitude in tude. However, while the shape of the light curve of Charon light decreasing format with the prime meridian at the sub-Charon fraction is as expected against rotational phase. point. Sykes (1999) presents 60 lm and 100 lm thermal observations Schindhelm et al. (2015) re-evaluates the conclusion of the of Pluto and Charon with IRAS from 1983. In the paper’s Table I, 1991 paper in light of the recalculated coordinates, subtracts sub-Earth longitudes and latitudes are listed in the spin north, Charon’s contribution to the combined UV spectrum and com- decreasing longitude convention, based on dates of observation. pares the result with more recent UV observations of Pluto. These points are correct when compared to ephemerides. These Stern (1992) summarizes the current state of Pluto research, observations are also compared with a visual light curve from including history, orbit and rotation, Charon, mutual events, Buie et al. (1997a), as well as thermal curves that are bright bulk composition, interior structure, atmosphere occultations, where the thermal curve is dark due to albedo-based versions. solar wind, volatile transport, and system origin. Pluto light Marc Buie is thanked for providing sub-Earth longitudes. curves through time are given by phase. The pole for Pluto is However, the paper’s Table II compiles information from Stern given as B1950.0 declination 9, right ascension 312. One et al. (1993), Jewitt (1994) and Altenhoff et al. (1988). The coordinate is consistent with spin pole north (the negative sub-Earth longitudes given in the paper’s Table do not match declination) and the other is consistent with ecliptic north those predicted by the dates of the observation given for some (the right ascension). The north pole of Pluto is not specified. observations. In all cases, the original papers did not give longi- The paper notes that ‘‘superior events occur at 0.75 rotational tudes. The timings of each measurement, calculated longitudes phase, corresponding to Plutocentric longitudes centered and the paper longitudes can be found in Table A.12. around 0 degrees’’. A longitude of 180 corresponds to the Maps Grundy and Buie (2001) consider the spatial distribution location of superior events. of ices on Pluto based on 83 nights worth of spectra from Stern et al. (1995) describe the 1994 HST images that would 1.4 lm to 2.4 lm. The coordinate system is not explicitly provide the first direct image maps (not pictured in the abstract, defined, but the sub-Earth longitudes are consistent with these were later published in Stern et al. (1997a)). The abstract’s decreasing longitude ephemerides and the sub-Earth latitudes Fig. 1 notes ‘‘Pluto North at Top’’, though the north pole is not consistent with the right-hand rule. Sub-Earth points of each explicitly specified. Comparison with Figs. 16 and 17 from observation are plotted, in addition to band depths and a V light Stern et al. (1997a) shows that the paper’s images 16 and 19 curve as a function of east longitude. Several maps are repro- most likely correspond the ‘‘original binning’’ versions of the duced, including Grundy and Fink (1996), Stern et al. (1997a), 278 M and 410 M Pluto images shown in the abstract. However, and Lellouch et al. (2000a). Modified composition maps based the abstract’s images are rotated compared to the later-pub- on Grundy and Fink (1996) and Stern et al. (1997a) are pre- lished paper. Examination of the orbital position of Charon sented. All use the right-handed coordinate system. and other images shown in Stern et al. (1997a) indicate that The text has one minor error: the paper notes that the mutual those images genuinely reflect the spin north system. As no event maps were based on superior events. However, Charon system was officially designated, it is unclear whether the transited Pluto during inferior events, which were used to authors intended to use the ecliptic north system, though unli- create the Pluto maps. kely given the use of spin north in Stern et al. (1997a), and the Brown (2002) reviews recent research on Pluto’s formation, sea- widespread use of the spin-north system in the 1990s. The son and composition. The paper reviews and re-plots work from abstract also mentions that the authors hope to use the images Grundy and Buie (2001) and Stern et al. (1997a) keeping the to resolve a north–south albedo dichotomy with Charon. This is spin north, decreasing longitude convention. The paper also a conference abstract. presents data from Drish et al. (1995) in the paper’s Fig. 6, a Foust et al. (1997) use center of light astrometry to determine compilation of Pluto albedo versus time as a function of the Pluto/Charon mass ratio. The paper notes that sub-Earth lat- ‘‘sub-Earth latitude’’ [sic] from 0 to 360. The original plot itude and times of northern elongation are from a current had rotational phase as the x-axis. The shape of the light curve Astronomical Almanac. However, no specific latitudes are given. and examination of the original plot show that the abscissa has

Table A.11 Published and calculated longitudes for Stern et al. (1991a).

Paper date Image header mid time Paper longitude () Calculated longitude (decreasing ) 87/169 1987-6-19 04:39:58 – 230 87/170 1987-6-20 04:02:11 – 175 88/193 1988-7-11 16:34:13 256 292a 88/193 1988-7-12 05:28:24 276 262 88/194 1988-7-12 10:37:07 299 249 89/205 1989-7-24 07:17:22 288 248 89/205 1989-7-24 13:51:06 297 232 89/206 1989-7-26 08:32:55 342 131

a Bold-faced entries indicate calculations with signiﬁcant disagreement with the published values. A. Zangari / Icarus 246 (2015) 93–145 117

Table A.12 Calculated and paper sub-Earth (decreasing) longitudes for measurements compiled in Sykes (1999).

Date Wavelength (lm) Paper longitude () Calculated longitude (decreasing ) For measurements compiled from Altenhoff et al. (1988) 25.2.86 1200 356 238–182a 27.3.86 1200 321 348–291 28.3.86 1200 17 235–291 16.4.86 1200 293 301–244 For measurements compiled from Stern et al. (1993) 1993 January 26.8 0450 315 317 1993 January 26.8 0800 315 317 1991 October 08.2 1100 293 182a 1993 January 26.8 1100 315 317 1993 January 26.8 1300 315 317 1993 February 19.4 1300 65 67 For measurements compiled from Jewitt (1994) UT 1992 May 2.4–2.48 800 – 23–18 UT 1992 May 3.4–2.47 800 330 326–322 UT 1992 May 4.35–4.47 1300 213 273–266a

a Bold-faced entries indicate calculations with signiﬁcant disagreement with the published values.

substituted without conversion for this paper. However, the longitude. In general, Charon’s longitude should simply be off- paper does not mention the shift in longitude, nor that these set 180 from Pluto’s longitude, and three out of the four mea- longitudes differ from the other data presented in the paper surements are consistent with Charon ephemerides. in decreasing longitude format. Consultation with the author (Cook, personal communication, Grundy and Buie (2002) present 1.4–2.55 lm HST/NICMOS 2013) revealed the actual start of imaging for each night’s spectra of Pluto, separate from Charon. The coordinate system observations, as well as that night’s total integration time. The used is not explicitly identiﬁed, but the sub-Earth longitudes date listed in the paper for the third measurement, 2005-09- for each observation are given and are consistent with decreas- 09, should actually be 2005-09-08. With the increased precision ing longitude. The IR light curves are plotted in comparison with for the times and the proper dates, the longitudes given are con- a visible light curve against longitude (not ‘‘east’’ longitude). It is sistent with decreasing ephemerides for Charon. Table A.14 mentioned in the text that the northern polar cap is coming into gives the original dates, the corrected dates, total exposure time view, and less of the southern hemisphere is visible as time goes and the decreasing Charon longitudes originally presented in on. One of the longitudes differs from calculations by about the paper, as well as more-precise longitudes calculated for 10 – about a four hour error in time. See Table A.13. the start of the exposure series. Elliot et al. (2003a) present results from the August 2002 Pluto Olkin et al. (2007) present 1–2.5 lm spectra of Pluto from the occultation (P131.1). Sub-Earth coordinates are given in the IRTF and 2.8–4.2 lm spectra from Keck. It is noted that the ‘‘IAU rules’’, and it is noted that the north pole is not visible sub-Earth longitudes and latitudes are ‘‘based on the IAU’s from Earth, consistent with the ecliptic north system. The deﬁnition of the north pole’’. The longitudes and latitudes for sub-Earth longitude is described as ‘‘east longitude’’, a term each observation are consistent with ecliptic north and increas- often used with decreasing longitude. However, in the ecliptic ing longitude. Later in the paper the sub-Earth positions are north paradigm, increasing longitude increases to the east as plotted atop Stern et al. (1997a) maps, but the system change well, since planetographic coordinates are also right-handed to spin north, decreasing longitude is not fully realized. The lati- in that system. The sub-Earth latitude and longitude are given tude of the points are switched to spin north, but the increasing as 28.1 and 38.1 and are consistent with ephemerides. longitude is wrongly preserved. In addition to the sub-Earth points Cook et al. (2007) present H and K band AO spectra of Charon of the new observations presented in the paper, an additional taken in August–September 2005. The authors identify the datum from Sasaki et al. (2005b) is plotted at 45 longitude. The sub-Earth latitude of Charon (which is the same as Pluto’s) as sub-Earth longitude of this datum was copied exactly from its negative, consistent with the ecliptic north system. In the original paper, and follows the opposite convention (decreasing) paper’s Table 1, longitudes are given for Charon with dates to and is therefore plotted correctly in the paper’s Fig. 13. the nearest day. However, the longitudes given were very near Schmude (2008) is a popular science book that does an excel- the sub-Pluto and anti-Pluto meridians and rounded to the lent job of summarizing the state of Pluto research for the inter- nearest 10. With the one-day time resolution and measure- ested lay person. At the beginning of Chapter 3, the author ments close to the sub-Pluto and anti-Pluto meridians, it is states that he will use the ‘‘IAU convention’’ throughout, and not immediately apparent which system is used. The longitudes the description of Pluto’s seasons is completely consistent with are given as ‘‘east longitude’’ which usually indicates decreasing the ecliptic north paradigm. Later in the chapter, the maps from Stern et al. (1997a) are presented and it is noted that ‘‘positive Table A.13 latitudes refer to the northern hemisphere’’, which is only true Grundy and Buie (2002) longitudes and calculated longitudes. for the map in the spin north paradigm. The sub-Earth longitude

Date Paper longitude () Calculated longitude (decreasing ) is brought up in the context of Pluto’s light-curve in the 1950s. The chapter identiﬁes 230 as the dimmest point in the light- 1998/03/17.8 50 54 1998/03/27.5 223 227 curve and 100 at the brightest. However, these longitudes do 1998/05/28.8 311 316 not match the light curve in any coordinate system for Pluto. 1998/06/07.3 128 141a DeMeo et al. (2010) present VLT and UKIRT spectra of Pluto and Charon (and Triton) from 1.4 to 2.45 m (H and K) as part of a a Bold-faced entries indicate calculations with signiﬁcant disagreement with the l published values. search for ethane on their surfaces. The paper states that it uses 118 A. Zangari / Icarus 246 (2015) 93–145

Table A.14 Published and calculated dates for Cook et al. (2007).

Date (from paper) First image start timea Total time (min) Paper Charon longitude () Calculated Charon longitude (decreasing ) 2005/08/10 August 10, 06:26 UT 72 190 186 2005/08/26 August 26, 05:19 UT 123.5 0 7 2005/09/09 September 08b, 05:15 UT 84 350 354 2005/09/11 September 11, 05:16 UT 114 180 185

a Times based on communication with author (Cook, personal communication, 2013). b Bold-faced entry indicates date that differs from the paper’s Table 1.

the ‘‘IAU definition’’, and the longitudes and latitudes provided Zalucha and Gulbis (2012) present a global circulation model for are consistent with ephemerides for ecliptic north and increas- Pluto based on stellar occultation light-curves. The authors ing longitude. Later in the paper, the sub-Earth points are plot- choose the ‘‘IAU convention’’, here saying that Pluto rotates in ted atop a map from Stern et al. (1997a), which uses the original the opposite sense that it revolves, and the north pole is on spin north, decreasing system axes. The figure caption notes the the same side of the ecliptic. Latitudes for each occultation longitude is now plotted ‘‘as 360 minus the IAU longitude’’ and immersion and emersion points are marked. All are consistent these new longitudes have been correctly given for each mea- with Zangari (2013), save for 1988, in which the immersion surement (the two points from the same night were averaged), and emersion latitudes are flipped. and the points have been properly plotted at those longitudes. The same figure caption also notes that the ‘‘rotational north Appendix B. Pluto articles without references to cartographic pole is +90’’, however, the sub-Earth latitudes of the points coordinates have not been altered to be in the northern hemisphere. A later table lists prior observations to report the presence of a B.1. UV spectra 2.4 lm feature in other published data, and includes longitudes and latitudes from Verbiscer et al. (2007), Douté et al. (1999) Stern et al. (1988a) describe IUE UV spectra of Pluto, and plan to and Nakamura et al. (2000). In the latter two cases, the publish UV geometric albedos. Dates, but no phases are given coordinates have been recalculated from spin north, decreasing for the data. These spectra are later published as Stern et al. into the ecliptic north, increasing system, and are consistent (1989a). This is a conference abstract. with ephemerides. The Verbiscer et al. (2007) longitude is Stern et al. (1989b) compare IUE UV spectra of Pluto and Triton presented as written, and it is noted that there is not enough from 2600–3200 Å, and report UV albedos for both. No dates or information to confirm the longitude, however, this longitude rotational phases are given for the spectra. This is a conference is increasing, see entry in Appendix A.4. abstract. Merlin et al. (2010) present 0.6 lm to 2.45 lm spectra and note Stern et al. (1990) present IUE 2600–3150 Å UV spectra of Pluto the sub-Earth (‘‘east’’) longitude and latitude. Their convention and Triton. No timings or phases are given, though it is noted description only states that the paper follows the conventions of that observations correspond to minimum and maximum light, Olkin et al. (2007), which ostensibly uses the ecliptic north and and are to be compared with visible light curves. This is a con- increasing convention (see entry in this section). However, the ference abstract. sub-Earth longitudes and sub-Earth latitudes of the spectra Clarke et al. (1992) report IUE observations from July 1989 in an are consistent with the left-handed ecliptic north, decreasing effort to find Lyman a lines from Pluto’s atmosphere. longitude convention. Stern et al. (2012) report new mid-UV spectra of Pluto and Charon B.2. Visible spectra from the HST Cosmic Origins Spectrograph. The paper text notes that east longitudes are used and the north pole points in the Benner et al. (1977) report 0.68–0.9 lm spectra. The authors direction of the angular momentum vector. The paper also notes promise to analyze the Pluto spectra for an atmosphere. This that this is contrary to the angular-momentum-violating IAU def- is a conference abstract. inition. Sub-Earth Pluto longitudes are listed in a table, and are Benner et al. (1978) report spectra from 0.68 to 0.9 lm of Pluto

consistent with ephemerides for decreasing longitude. However, and Triton and put an upper limit on the CH4 found. in the conclusions section, the pole is described as moving from Cochran and Cochran (1978) present 0.5–0.8 lm spectra ‘‘9 at the mid-point of the 1992–1993 Trafton & Stern data of Pluto and note CH4 abundances. This is a conference set, to 43 at our observing epoch in 2010’’. However, those abstract. sub-Earth latitudes follow the ecliptic north convention, opposite Bell et al. (1979) report spectra of Pluto from 0.32 to 0.95 lm. what is mentioned in the text. This is a conference abstract. The observations are grouped into two sub-Earth longitudes: 95 Barker et al. (1980) take spectra of Pluto from 0.350 to 0.735 lm and 273. The data are also compared with observations of and ﬁnd it has a slope resembling an S-type asteroid.

Charon by Krasnopolsky (2001) and it is noted correctly that Fink et al. (1980a) report CH4 absorption in 0.5–1 lm spectra, 270 is northern elongation and 90 is southern elongation. These and suspect the CH4 is from an atmosphere, not frost. longitudes are consistent with decreasing longitude on Charon, Fink et al. (1980b) present a spectrum of Pluto from 0.58 to which is offset 180 from Pluto’s longitude. However, the sub- 1.06 lm. The authors ﬁnd CH4 in Pluto’s spectrum and suggest Earth longitudes given for the new Pluto observations are also a gaseous origin.

directly applied to Charon. The paper’s Fig. 2 caption states that Buie and Fink (1985) attempt to model the distribution of CH4 the data were taken at 95 and 270, but these Charon longitudes gas and frost for 0.56–1.06 lm spectra at four different, should be 275 and 93. Fortunately, in the paper’s Fig. 2, Charon unspeciﬁed rotational phases. While the model reproduced COS data are averaged together instead of compared separately absorption strength for different phases, it did not reproduce to the two Krasnopolsky (2001) observations. band shapes. This is a conference abstract. A. Zangari / Icarus 246 (2015) 93–145 119

Sawyer (1989) presents 0.5–1.0 lm spectra covering the range Sasaki et al. (2005a) present AO L-band (2.9–3.9 lm) spectra of of Pluto’s rotation. This is a conference abstract. Pluto from Subaru on 2002 May 28 UT. This is a conference Grundy and Fink (1993) present 0.65–1 lm spectra of Pluto abstract. dating from 1982. The spectra are to be analyzed for variations Young et al. (2006) present 1–4 lm IR surface spectra of Pluto based on the sub-Earth point, season, etc. in the poster, but no from the IRTF, Keck and Subaru. This is a conference abstract. features are identiﬁed in this conference abstract. Protopapa et al. (2007) present 1–5 lm VLT AO spectra of Pluto. Tegler et al. (2010) present a single spectrum taken on 2007- Protopapa et al. (2008a) present 4–5 lm spectroscopy from 06-21 UT from 0.71 to 0.94 lm, along with spectra of Eris, and ESO’s VLT. These spectra appear in Protopapa et al. (2008b)

calculate CH4 and N2 abundances for each. The authors suggest discussed in Appendix A.4. This is a conference abstract. looking for spectral variations on Pluto and Eris with longitude, Protopapa et al. (2009) present resolved L-band spectral but do not report sub-Earth positions in their paper. These data observations of Pluto up to 5 lm. The paper notes that are later used in Tegler et al. (2012). differences between these spectra and spectra taken in 2001 (Grundy et al., 2002) could be due to either a sub-Earth latitude B.3. IR spectra change or surface processes. No sub-Earth points are presented. The data presented were taken from 2005-08-03 to 2005-08-07. Cruikshank and Silvaggio (1978) report 1.4–1.9 lm spectra of This is a conference abstract.

Pluto and ﬁnd CH4 features consistent with previous work. Lellouch et al. (2010) discuss atmosphere-surface interactions on Lebofsky et al. (1979) report 1.5–3.7 lm spectra as well as J, H, Pluto based on 1.64–1.68 lm spectra (Triton spectra were also K, and L IR photometry of Pluto. The authors conﬁrm the pres- observed at different wavelengths). This is a conference abstract

ence of CH4. Protopapa et al. (2011) present VLT NACO spectra of Pluto from Cruikshank and Silvaggio (1980) report 1.4–1.9 lm spectra of 2.9 and 3.7 lm. The authors ﬁnd no sub-Earth longitude based

Pluto and model CH4 absorption. differences in spectra between these images and ones published Soifer et al. (1980) report 1.2–2.5 lm observations of Pluto that by Protopapa et al. (2008b), nor do they ﬁnd changes in the ratio

conﬁrm the presence of CH4. between pure and diluted CH4. No speciﬁc longitudes or Marcialis et al. (1988) plan to present a status report on coordinates are mentioned. This is a conference abstract. 1.0–2.5 lm IRTF spectra of Pluto and Triton for which observations are in progress. This is a conference abstract. B.4. Far-IR spectra, sub-mm, mm and radio Spencer and Buie (1988) report 3–4 lm spectra of Triton taken with the IRTF and plan to present the results of the Pluto– Altenhoff and Wendker (1982) report Pluto’s temperature based Charon spectra at the meeting. This is a conference abstract. on radio measurements from 14.5 and 22.8 GHz. No reference Spencer et al. (1990) present spectra of Pluto/Charon and Triton to coordinates. This is a conference abstract. In German.

in the 1–4 lm region, and identify a CH4 absorption feature at Lebofsky et al. (1982) report attempts to measure Pluto’s diam- 3.25 lm. eter at 22.5 lm. They do not detect Pluto and are independent Coustenis et al. (1991) report on 2.15–2.35 lm spectra of Pluto of Morrison et al. (1982a). This is a conference abstract.

obtained with the IRTF, and suggest that a pure CH4 atmosphere Morrison et al. (1982a) report attempts to measure Pluto’s cannot account for the absorption seen. This is a conference diameter at 20 lm. This is a conference abstract. abstract. Morrison et al. (1982b) use Q band (16–26 lm) thermal IR mea-

Owen (1992) reports on ﬁnding CH4,N2 and CO on Pluto based on surements to create an upper limit on Pluto’s diameter. Triton observations using the Cooled Grating Spectrometer on UKIRT. A was also observed. wavelength range is not given, though the paper mentions an Aumann and Walker (1987) use IRAS to observe Pluto and absorption band at 2.15 lm on Triton. Similar to Owen et al. Charon and estimate radius and emissivity. (1992b) and Owen et al. (1992a). This is a conference abstract. Sykes et al. (1987) report 60 and 100 lm IRAS measurements of

Owen et al. (1992a) report CH4 as well as CO and N2 ice in a 1.45– Pluto and Charon. While the sub-Earth point is mentioned in an 2.40 lm region spectrum of Pluto taken from UKIRT on UT dates equation, it is deﬁned to be a zero point for a ﬂux equation. 1992-05-27 and 1992-05-28. This is a conference abstract. Polar caps and latitudes are discussed symmetrically.

Owen et al. (1992b) report detection of CH4,N2 and CO on Pluto Tedesco et al. (1987) use 25 lm, 60 lm and 100 lm measure- in spectra from 1.45 to 2.40 lm region from UKIRT on UT dates ments from IRAS to measure the sizes of Pluto and Charon at 1992-05-27 and 1992-05-28. Similar to Owen et al. (1992a). 60 lm. The low IR ﬂux suggests an atmosphere for Pluto but Owen et al. (1993a) present new 1.2–2.5 lm UKIRT spectra of not for Charon. Pluto, taken on UT dates 1993-05-20, 1993-05-22, and 1993- Altenhoff et al. (1988) detect Pluto in the radio with IRAM and 05-24. This is a conference abstract. report its ﬂux density. Dates, but no UT hours or sub-Earth lon-

de Bergh (1993) lists the detection of N2 ice in spectra of Pluto gitudes are given for the measurements. as one of the major breakthroughs of IR spectroscopy for the Stern and Weintraub (1992) report on millimeter-wave mea- planets. This is a conference abstract. surements of Pluto. This is a conference abstract. Roush (1994) compares observed spectra of Charon from 1.5 to Barnes (1993) describes an unsuccessful search for CO on Pluto 2.5 lm with calculations of various ice mixtures. with Haystack radio telescope at 115 GHz. Young et al. (1997) report on 1.6 lm spectra taken on 1992-05- Festou et al. (1993) present mm-wave measurements that sug-

25 to 1992-05-26. No mention of longitude or latitude is made. gest any CH4 seen on Pluto is in solid form. Brown and Calvin (2000) do not mention location on Pluto Stern et al. (1993) present 1100 lm measurements of Pluto’s sur- when presenting well-separated 1.0–2.5 lm Keck spectra of face temperature made with the James Clerk Maxwell Telescope Pluto and Charon taken on 1999 May 28 that suggests the pres- in 1991 as well as 450 lm, 800 lm, 1100 lm and 1300 lm ence of ammonia and water ices. measurements made in 1993. Also included are 1300 lm IRAM Young et al. (2001b) present NIR echelle 2.33636–2.34206 lm measurements from 1993. The paper assumes that Pluto is iso- spectra from the IRTF from April 1996 (July 1996 observations thermal. Equations involving sub-solar longitude and latitude correspond to Triton) in an unsuccessful attempt to detect CO. were presented, but these equations are not specialized to any No position information on Pluto is given. particular measurements and refer to temperatures on Charon. 120 A. Zangari / Icarus 246 (2015) 93–145

Jewitt (1994) presents 800 lm and 1300 lm thermal Null et al. (1992) plan to report masses and densities for Pluto measurements of Pluto from the James Clerk Maxwell Tele- and Charon based on HST results. This is a conference abstract. scope. While the paper suggests there are cold and warm Null et al. (1993) present a new Pluto–Charon mass ratio based regions that are anti-correlated with Pluto’s light curve, and on HST images. mentions a latitude-based temperature scheme, no reference Marcialis and Merline (1998) revisit measurements made by to explicit coordinates is made. Kuiper (1950) of Pluto’s disk diameter and calculate that despite Barnes (1996) predicts CO line flux densities for Pluto’s atmo- the fact that the results were much greater than Pluto’s actual sphere at radio wavelengths. size, the measurements were reasonable, allowing for Charon’s Bockelée-Morvan et al. (2001) tentatively detect the J(2–1) CO unseen influence. This is a conference abstract. line for Pluto in the radio. Bertoldi et al. (2006) present millimeter-wavelength observa- B.6. Mutual events tions of Eris to compare its size to Pluto. No mention of features on Pluto. Many of the following papers may include depictions of mutual Butler et al. (2011) report on seven 0.9 cm ELVA observations of event geometry. These papers are listed in this section because neither Pluto and Charon (among other TNOs). The month and day are pole is explicitly identified as north or south, or events are not identi- given for each object’s observations, but no year. No sub-Earth fied by rotational phase (or longitude). The poles discussed are not positions are given. This is a conference abstract. indeterminate, rather the authors did not name them. The spin north Gurwell et al. (2011) present resolved 1.1 mm and 1.4 mm pole is to the right (WSW), while the ecliptic north pole is to the left observations of Pluto and Charon from the Submillimeter Array (ENE) in all north-up, east-left depictions of event geometry. Early from May 2005, July 2009 and July 2010. This is a conference Charon inferior events blocked latitudes nearest to the spin-north pole, abstract. while later events blocked latitudes nearest to the ecliptic north pole. Inferior events (Charon in front of Pluto) occur at a rotational phase B.5. Charon of 0.25, and the sub-Earth longitude of Pluto in both systems is 0 (180 on Charon). Superior events (Pluto in front of Charon) occur at Christy and Harrington (1978) report the discovery of Charon a rotational phase of 0.75, and the sub-Earth longitude of Pluto in both and note that mutual events could occur in the 1980s if the pole systems is 180 (0 on Charon). of Charon’s orbit is at a ¼5; d ¼ 8h or already occurred from 1968–1972 if the pole is at a ¼ 35; d ¼ 19h. Andersson (1978) notes that the ambiguity of Charon’s orbit Smith et al. (1978) report the discovery of 1978 P1 by Christy. suggest that eclipses of the system may occur in the 1980s. This It is noted to have a revolution period equal to Pluto’s is a conference abstract. rotation of 6.3867 d. A list of position angles and separations Harrington and Christy (1980a) report improvements on the are given. orbit of Charon, and now predict mutual events to begin in Thomsen and Ables (1978) report the detection of Charon in 1984. additional images taken at the US Naval observatory. A separa- Mulholland and Binzel (1983) report that mutual events of tion for the pair is derived. This is a conference abstract. Pluto and Charon have not yet been detected, contrary to the Harrington (1979) requests additional help observing Charon, reports of Lyutyi and Tarashchuk (1982). which is not yet confirmed. Hege and Drummond (1984) report speckle interferometry mea- Christy and Harrington (1980) discuss the discovery of Charon surements of Charon that confirm its orbit is becoming more and present orbital elements. edge-on and that mutual events should be happening soon. Harrington and Christy (1980b) report the orbit of Charon and Dunbar (1985) describes a mutual event model that includes note that the satellite rotation and what was thought to be the contribution of shadows. This is a conference abstract. Pluto’s rotation seem to line up. Times of northern and southern Tedesco (1985a) provides depth estimates for the upcoming elongations of Charon are given to the nearest hour, however, 1986 mutual events. the rotational phase system is not used. Tedesco (1985b) sends out a call to amateur astronomers to Harrington and Christy (1981) report a semi-major axis and observe the mutual events. total mass for the Pluto–Charon system. Tholen (1985a) provides circumstances for the 1986 mutual van Flandern et al. (1981) report a period for Charon’s orbit of events. Longitude refers to the optimum longitude on Earth 6.3871 ± 0.0002 d based on barycentric motion of Pluto from for observation of each event. 1930 to 1979. Binzel and Frueh (1986) describe 1986 B and V mutual event Baier et al. (1982) describe speckle interferometry measure- observations from McDonald observatory. It is mentioned that ments of Charon. the albedo of Charon may be darker than Pluto. This is confer- Hege et al. (1982) use speckle interferometry to pin down Char- ence abstract. on’s orbit. Hildebrand (1986) describes tests for an impact origin for Pluto Hetterich and Weigelt (1983) use speckle interferometry to find and Charon and emphasize the importance that future mutual the separation of Pluto and Charon. events, HST observations, and occultations by Pluto and Charon Tholen (1985b) improves Charon’s orbit based on speckle will have on constraining size, atmospheres and ultimately the interferometry. No mention of poles on Pluto. A period of impact model. This is a conference abstract. 6.38764 ± 0.00018 d and an epoch of JED 2445000.5 is given Marcialis (1986) plans to present photometric results from among many fits. three mutual events in 1986. This is a conference abstract. Wildey (1985) provides a method for determining orbital ele- Mulholland and Gustafson (1986) calculates Fraunhofer diffrac- ments of Pluto–Charon from images. tion for the mutual events. This is a conference abstract. This Marsden (1986) reports that 1978 P1 is officially named work is expanded upon in Mulholland and Gustafson (1987). Charon! Reinsch and Pakull (1986) report detection of another Baier and Weigelt (1987) report on speckle interferometry mutual event by 2.2-m and Danish 1.5-m telescopes at ESO measurements of Pluto and Charon, finding diameters of and the resulting Pluto/Charon radii and sidereal orbital period 2710–3460 km and 1050–1520 km, respectively. (6.38718 ± 0.00013 d). A. Zangari / Icarus 246 (2015) 93–145 121

Tedesco and Dunbar (1986) compile mutual event data to give a the ‘‘equatorial north’’ that is noted to be up in the caption of radius, density and description of a ‘‘first order model’’ (includes the paper’s Fig. 1 refers to the geometry on the sky. An shadow) as well as times to observe inferior and superior orbital period of 6.387204 d with an epoch of JD 2446600.5 is events. This is a conference abstract. given. Tholen (1986) reports successful observations of a mutual event Vasundhara and Bhattacharyya (1987) report observations of (partial transit of Charon) on 1985-12-14 from the 2.24-m tele- the 1986-03-06 mutual event from Vainu Bappu Observatory scope on Mauna Kea. A steeper rise from minimum light than in Kavalur, India. They note that the observations matched expected was seen, and improved magnitudes for comparison expectations. This is an abstract. stars were found. However, a correction to the timing for the Buie and Polk (1988) want to see if a polarimeter will show that 1986 events was not apparent from these measurements. light from an occulted Charon could be refracted around Pluto’s Tholen et al. (1986) reports new radii for Pluto and Charon, and atmosphere during a mutual event on 1988-06-05 UT. The data an orbital period of 6.38720 d among other physical parameters have been taken and the authors promise they will analyze it based on the mutual events. This is a conference abstract. before the meeting. This is a conference abstract. Binzel et al. (1987) present mutual event results from 1985 to Fink and Disanti (1988) observe 0.5–1 lm spectra of Pluto while 1987. This is a conference abstract. it occults Charon on 1987-03-03 to obtain separate measure- Buie and Tholen (1987a) promise to present geometric visual- ments of the two. izations for the 1988 events, as well as past and future events. Marcialis and Lebofsky (1988) report wavelength-dependent No specific geometric details are given. Similar to Buie and albedos of Pluto and Charon based on mutual event results. This Tholen (1987b). This is a conference abstract. is a conference abstract. Buie and Tholen (1987b) promise to present geometric visual- Stern (1988) constrains Pluto and Charon’s density with mutual izations for the 1988 events, as well as past and future events. event and IRAS observations. No specific geometric details are given. Similar to Buie and Tholen and Buie (1988a) present circumstances for the 1989 Tholen (1987a). This is a conference abstract. mutual events of Pluto and Charon. East longitude in the paper’s Buie et al. (1987) infer the spectrum of Charon by calculating it Table 1 refers to east longitude on Earth. Although the geometry from a spectrum taken on 1987-04-23 when Charon was com- of the mutual events are drawn in the figures, no pole on Pluto pletely occulted by Pluto during mutual events and comparing is specified as north or south: the ‘‘equatorial north’’ that is it to the combined spectra of the two objects. The spectra were noted to be up in the caption of the paper’s Fig. 1 refers to the discrete measurements from 1.5 to 2.35 lm. No coordinates geometry on the sky. An orbital period of 6.38730 d with an were assigned to the data as part of this write-up. epoch of JD 2446600.5 is given. Fink and Disanti (1987) report Charon-less 0.54–1.02 lm Pluto Tholen and Buie (1988b) report physical parameters such as spectra from the 1987-03-03 superior mutual event. They also radius and albedo, as well as orbital parameters from the

note that the 7200 Å CH4 band has weakened in comparison Pluto–Charon mutual events. An orbital period of 6.38730 d to 1983 measurements published in Buie and Fink (1987) and with an epoch of JD 2446600.5 is given.

attribute the band difference to a change in atmospheric CH4. Tholen and Hubbard (1988) respond to the charge by This is a conference abstract. Mulholland and Gustafson (1987) that Fresnel or Fraunhofer Marcialis et al. (1987) identify water ice on Charon when it is diffraction could interfere with mutual event results and ﬁnd completely blocked by Pluto from 1.5, 1.7, 2.0 and 2.35 lm through calculation that they should not have an effect. measurements on 1987-03-03. The paper’s Fig. 1 shows geom- Barbieri et al. (1989) report V and R observations of two 1987 etry of the superior event in approximately north-up east-left mutual events (1987-02-08 to 1987-02-08 and 1987-04-29 to on the sky, but does not identify the poles. 1987-04-30 UT) and astrometry from 1978 to 1987. Abstract Mulholland and Gustafson (1987) argue that Fraunhofer diffrac- is in Italian. tion should matter in the case of the mutual events. Addressed Binzel (1989) summarizes the mutual events without reference by Tholen and Hubbard (1988). to locations on Pluto. A period of 6.387245 ± 0.000012 d is given Sawyer et al. (1987a) report results of a superior mutual event as part of a table of system parameters. The paper’s Fig. 1 shows on 1987-04-04 UT at McDonald observatory and ﬁnd that Plu- Charon’s orbit plane approximately north up, east left on the

to’s spectrum accounts for all the CH4 absorption. Results are sky at different years during the mutual event season. Viewing also given for an inferior event observed at Yunnan Observatory geometries along the plane of the sky are given for various on 1987-04-26 UT. events in the paper’s Figs. 2 and 3, without pole identiﬁcation. Sawyer et al. (1987b) report Charon-less 0.5–1.0 lm Pluto spec- Blanco et al. (1989a) report seven B and V mutual event tra from two superior mutual events and ﬁnd Charon to be gray. observations in 1986 and 1987. This is a conference abstract. Blanco et al. (1989b) report seven U, B and V mutual event Sawyer et al. (1987c) present 0.55–1.0 lm separate spectral results from 1986 and 1987. This is an expanded version of observations of Pluto and Charon from superior mutual events Blanco et al. (1989a). on 1987-03-03 and 1987-04-04. Buie et al. (1989) describe an IR mutual event data set that Tholen (1987) reports successful observation of the 1986-12-29 includes observations at 1.53, 1.75 lm (1986–1987) and 1.53, superior mutual event, noting that the third contact time was 1.72, 2.00, 2.35 lm (1988–1989). These IRTF data should allow

later than expected by 10 min. for the mapping of CH4 on Pluto. This is a conference abstract. Tholen and Buie (1987) report new basic parameters for Pluto Young and Binzel (1989) describe efforts to make surface maps and Charon from mutual event data. An orbital period of of Pluto and Charon based on mutual event data. This is a con- 6.387217 d with an epoch of JD 2446600.5 is given. This is a ference abstract. conference abstract. Buie et al. (1990) promise an albedo map of Pluto from mutual Tholen et al. (1987b) report circumstances for the 1987 mutual event observations. This is a conference abstract. events. The ‘‘Long. Range’’ in the paper’s Table I refers to the east Marcialis (1990c) presents results from the mutual events. This longitude of Earth observers who will be able to view each is a dissertation abstract (see Marcialis (1990b)). event. Although the geometry of the mutual events are drawn Tholen and Buie (1990) add in 1990 data to the mutual in the ﬁgures, no pole on Pluto is speciﬁed as north or south: event models and report that no changes from the predictions 122 A. Zangari / Icarus 246 (2015) 93–145

resulted. A Charon orbital period of 6.387246 d and epoch of JDE amplitude varies with sub-Earth latitude and rotational phase, 2446600.5 is reported. This is a conference abstract. however, there is no mention of specific coordinates on Pluto. Blanco et al. (1991) report B and V photometric observations of An orbital period of 6.3872464 d is given for Charon. mutual events in 1987 and 1988. While both inferior and Buie et al. (2004) describe the mathematical process for superior events are reported, no phases are assigned. creating a new map of Pluto using HST images. The description Young and Binzel (1991) discuss the process of turning mutual of the observations and a qualitative outline of the fitting event light curves into maps. This is a conference abstract. mentions neither the orientation of the map, nor any specific Blanco et al. (1994) present B and V light-curves from mutual Plutonian features. This is a conference abstract. events in 1989 and 1990. Schmude (2004) details observations by ALPO of the outer Young and Buie (2008) discuss combining HST maps, mutual planets made in 2002. While the paper states that IAU defini- event data and Charon stellar occultations to revisit Pluto’s tions of the poles will be used, no mention of coordinates on radius. The view of Pluto and Charon during three mutual Pluto is made for the single observation made that year. events is plotted, but north or south is not explicitly identified. Clancy et al. (2005) summarize work to fit PSFs to determine the This is a conference abstract. Charon–Pluto light ratio. This is a conference abstract. NA (2007) shows new Keck adaptive optics images of Pluto. B.7. Photometry and Imaging Andrei et al. (2008) discuss the reliability of fitting PSFs for Pluto/Charon. This is a conference abstract. Mulholland and Binzel (1982) will report photometry of Pluto’s Howell et al. (2012) present 0.693 and 0.880 lm speckle images light curve. This is a conference abstract. of Pluto from Gemini North and reconstruct diameters, Reitsema et al. (1983) present a very early attempt at separation and position angle for Pluto and Charon. calculating the Pluto to Charon light ratio via PSF subtraction (pre-DAOPHOT) with data taken on 1980-02-03.559. B.8. Occultation reports Tholen (1983) presents light curves of Pluto in an effort to establish a good reference curve in preparation for the mutual Moore et al. (1980) did not see an occultation by Pluto or events. This is a conference abstract. Charon on 1980-04-06. Tholen and Tedesco (1984) present new precise photometry Walker (1980) recounts successful observations of the first and a new sidereal rotation period for Pluto of 6.38755 ± stellar occultation by Charon. 0.00007 d in preparation for mutual events. Candy and O’Meara (1982) did not see a Pluto occultation at Jones et al. (1988) present PSF-fit B and I photometry of Pluto Harvard, but suspect the track went south. and Charon taken in June 1987. Maley et al. (1983) did not see an occultation by Pluto on Albrecht et al. (1990) report the first HST images of Pluto. This is 1983-04-04. a conference abstract. Brosch (1985) corrects the misconception that the 1985-08-19 Albrecht et al. (1991) present the first published HST images of occultation could have involved Charon. Pluto (the first data on any Solar System object) and return the Brosch and Mendelson (1985) report a detection of an occulta- relative brightnesses of a separated Pluto and Charon. tion by Pluto (or Charon) and suspect that an atmosphere was NA (1991) presents CCD astronomical images taken by Maurice seen and the event was grazing. Gavin, one of which is of Pluto, taken on 1991-05-10. Bosh et al. (1988) put an upper limit on Pluto’s surface radius Olkin et al. (1993b) present separate light-curves for Pluto and based on occultation results. This is a conference abstract. Charon. This is a conference abstract. Dunham et al. (1988) discuss the thermal gradient/haze layer in Young et al. (1994) use ground based telescopes to make B PSF Pluto’s atmosphere and its implications. models of Pluto and Charon using DAOPHOT. V, R and I images Elliot et al. (1988b) report successful observations of P8 by the were also acquired, but not analyzed. KAO and other Australian observatories. A miss was recorded at Null and Owen (1996) use HST to calculate the Charon-Pluto Mauna Kea. mass ratio. There is no mention of geographic features. A Elliot et al. (1988a) present results from the KAO light-curve, Charon orbital period of 6.387452(138) d is found when no a including a temperature to mean molecular weight ratio. This priori conditions are used. is a conference abstract. Reichhardt (1996) provides a brief note about new Hubble sur- Hunten et al. (1988) discuss Pluto’s atmosphere based on the face maps (not cited, but from Stern et al. (1997a)), and show Hobart light curve of P8. small thumbnails of Pluto and Charon globes from two views. Hubbard et al. (1988) report detection of an atmosphere in the While equatorial spots and polar caps are described, no orienta- P8 occultation. tion for the globes is given. Kilmartin et al. (1988) report successful observations of P8 for Close et al. (1999) report on 2.02 and 2.26 lm AO images of several ground-based sites in New Zealand and Australia. Pluto with the CFHT. This project is described in more detail Millis et al. (1988) describe successful observations of P8 in in Close et al. (2000). This is a conference abstract. Charters Towers, Australia. This is a conference abstract. Melillo (1999) reports a partial unfiltered differential light- Walker et al. (1988) update the timings for their successful curve of Pluto, taken by an amateur astronomer. The data are observations of the 1988-06-09 occultation by Pluto (P8) in plotted as a function of time, and rotations are marked based Auckland. on the start of the first observation. A larger-than-normal Bosh and Elliot (1989) use mutual event results to constrain the amplitude is reported for the light curve. Pluto occultation result radius. This is a conference abstract. Close et al. (2000) present AO resolved photometry of Pluto and Elliot and Bosh (1989) wonder if Pluto has a haze layer or ther- Charon. mal gradient based on its occultation data. This is a conference Schmude (2002) reports ALPO observations of the outer planets. abstract. While the paper states that the IAU conventions will be used for Elliot et al. (1989) present the KAO observations of the P8 Pluto results, only locations on Uranus are described. occultation. While a map of Pluto, its equator and the occulta- Olkin et al. (2003) use HST to calculate the mass ratio of tion tracks is shown and Charon is noted as being at southern the Pluto–Charon system. It is mentioned that light-curve elongation, no coordinates or positions on Pluto are specified. A. Zangari / Icarus 246 (2015) 93–145 123

Eshleman (1989) models the ‘‘bite’’ in Pluto’s light curve. Rannou and Durry (2009) discuss an extinction layer found in The inversion is compared to inversions near the polar regions Pluto occultation observations from ‘‘August 2003’’. Based on on Mars. the citations, the authors are referring to the 2002-08-21 Slivan and Dunham (1989) constrain Pluto’s atmosphere based occultation of the star P131.1. on observations of the P8 occultation. This is a conference Assaﬁn et al. (2010) publish Pluto occultation predictions from abstract. 2008 to 2015. The sub-planet point described herein is Earth as Stansberry et al. (1989) model haze on Pluto based on occulta- seen from Pluto. tion results. Gulbis et al. (2011) discuss occultation P571 (2008-06-24) with Whipple et al. (1989) describe a model of Pluto’s upper atmo- an emphasis on the instrument (MORIS on the IRTF) that was sphere. This is a conference abstract. used to observe the occultation. Yelle and Lunine (1989) posit that the atmosphere of Pluto must Olkin et al. (2011) discuss the central ﬂash observed during the

support a molecule heavier than CH4 based on the recent P8 2007-07-31 occultation by Pluto. This is a conference abstract. 1988-06-09 occultation. Pasachoff et al. (2011a) report on occultation observation Dunham et al. (1990) discuss a strip scan search for Pluto– attempts for the 2011-06-23 and 2011-06-27 occultations by Charon occultation candidates. This is a conference abstract. Pluto and Charon and Pluto and Hydra. This is a conference Hubbard et al. (1990) create a non-isothermal model for Pluto’s abstract. atmosphere. Pasachoff et al. (2011b) report on observations for the 2011-05-22 Elliot and Young (1991) report on atmospheric modeling of the occultation by Pluto. This is a conference abstract. 1988-06-09 P8 occultation data. This is a conference abstract. Sicardy et al. (2011b) use Pluto as a barometer to describe the Wasserman et al. (1991) calculate Pluto’s radius from the 1988- first observed stellar occultation by dwarf planet Eris. Neither 06-09 P8 occultation. This is a conference abstract. the original article nor the supplementary information men- Young and Elliot (1991) test a model to fit Pluto’s lower atmo- tions surface features on Pluto. sphere. This is a conference abstract. Throop et al. (2011) re-analyse the P384.2 (2006-06-12) Pluto Elliot and Young (1992) create a model for Pluto’s atmosphere occultation for stray particles. There is no mention of coordi- as seen during a stellar occultation. nates on Pluto. This is a conference abstract. Sybert et al. (1992a) present magnitudes for Pluto occultation Young et al. (2011a) report on the 2011-06-23 and 2011-0-627 stars. occultations by Pluto and Charon and Pluto and Hydra. This is a Gilmore and Kilmartin (1993) report failure to observe an conference abstract. occultation of P20 by Charon at Mt. John Observatory. Young et al. (2011b) report on the 2011-06-23 and 2011-06-27 Millis et al. (1993a) use the 1988-06-09 P8 occultation to calcu- occultations by Pluto and Charon and Pluto and Hydra. This is a late Pluto’s radius. This is a conference abstract. conference abstract. Lellouch (1994) models Pluto’s atmosphere with and without Zuluaga et al. (2011) report the location of the shadow path for haze. the 2011-06-23 occultation by Pluto and Charon. This is a con- Stansberry et al. (1994) model Pluto’s atmosphere based on the ference abstract. 1998-06-09 P8 data. Rogozin (2012) discusses the diameters of Pluto and Eris. There Brosch (1995) presents the Wise Observatory light curve for is no mention of longitude and latitude. ArXiv only. the 1985-08-19 stellar occultation by Pluto. Comparisons with the 1988-06-09 P8 event are made. There is no mention of B.9. Composition/formation longitude or latitude on Pluto, but it is mentioned that Charon was 7 h from its greatest northern elongation at the Arnold et al. (1979) make speckle interferometry measurements time. of Pluto to measure its diameter. Elliot et al. (1995) review the state of stellar occultation Lupo and Lewis (1979) model Pluto’s radius and composition. research as of the mid-1990s and include a section on the This is a conference abstract. KAO observations of Pluto in 1988. There is no mention of lon- Hughes (1980b) describes speckle interferometry measure- gitude or latitude on Pluto. ments of Pluto by Arnold et al. (1979). Elliot et al. (2003b) provide a detailed description of the atmo- Lupo and Lewis (1980a) make ternary diagrams and try to spheric inversion for occultation light curves. Second in a series constrain the mass and radius of Pluto. after Elliot and Young (1992). Lupo and Lewis (1980b) use mass estimates of Pluto to consider Elliot (2005) describes the differences in the light-curves its composition. between the 1988 and 2002 stellar occultations by Pluto. This Cole (1984) describes the interior and general features of Pluto is a conference abstract. (and the Solar System’s icy satellites). Pasachoff et al. (2005) present a detailed analysis of spikes from Tholen (1985c) sets a limit on Pluto’s density based on speckle the 2002-08-21 stellar occultation by Pluto (P131.1). Latitude interferometry images of Charon. This is a conference abstract. and longitude on Pluto are not mentioned. Stern (1987a) constrains Pluto’s density. This is a conference Young et al. (2005) announce successful observations of a stellar abstract. occultation by Charon. McKinnon and Mueller (1988a) use Pluto’s density results to Person et al. (2007a) report observations of P445.3. Same as consider different formation scenarios. This is a conference Person et al. (2007b). abstract. Assafin et al. (2008) present occultation predictions for TNOs, McKinnon and Mueller (1988b) suggest that Pluto formed in the including Pluto. solar nebula. McCarthy et al. (2008) model the MMT observations of the Simonelli and Reynolds (1989) discusses the interior structure 2007-03-18 Pluto occultation. There is no mention of of Pluto and Charon. coordinates on Pluto. Stern (1989a) considers differentiation on Pluto. Hubbard et al. (2009) present models of Pluto’s upper Prentice (1992) models the protosolar cloud to re-create the atmosphere based on the P445.3 (2007-03-18) data set. The compositions of Pluto, Charon and Triton. This is a conference data are described in terms of km from Pluto’s center. abstract. 124 A. Zangari / Icarus 246 (2015) 93–145

Prentice (1993b) discusses modeling Pluto and Charon as rem- Trafton (1987) analyzes CH4 in Pluto’s atmosphere. This is a nants from the solar cloud. conference abstract. McKinnon and Mueller (1993) consider internal geologic activ- Trafton et al. (1987) follow the paths of molecules that escape ity on Pluto. This is a conference abstract. Pluto’s atmosphere. This is a conference abstract. Dobrovolskis et al. (1997) look at Pluto and Charon’s mutual Trafton et al. (1988) look at atmospheric escape on Charon. Net orbits and formation history. This article is part of the Arizona sublimation as a function of latitude is calculated symmetrically. Space Science Series book, Pluto and Charon. McKinnon (1989a) analyzes water ice jetting on Pluto. McKinnon et al. (1997) discuss possibilities for the composition McNutt (1989) examines loss in Pluto’s atmosphere. No regard of the interior of Pluto and possible equations of state. This arti- is made to location on Pluto. cle is part of the Arizona Space Science Series book, Pluto and Trafton (1989) explores Pluto’s atmosphere and how it is Charon. affected by perihelion passage. The article avoids speciﬁc loca- Stern et al. (1997b) describe theories for Pluto and Charon for- tions, talking about high and low latitudes or bright and dim mation – new, old and discarded. This article is part of the Ari- longitudes. zona Space Science Series book, Pluto and Charon. Trafton (1990) models seasonal and volatile escape on Pluto. Summers et al. (1997) analyze the chemical composition and While a winter pole is mentioned, and plots of ice deposits over reactions in Pluto’s atmosphere. This article is part of the Ari- the most recent Plutonian year are given, there is no mention of zona Space Science Series book, Pluto and Charon. speciﬁc features or coordinates on the planet.

Ip et al. (2000) calculate the ion composition and density profile Hansen and Paige (1993) adapt a seasonal N2 cycle model for of Pluto’s atmosphere. Pluto. There is no mention of specific sub-Earth features. This Robuchon and Nimmo (2011) provide a theoretical basis for tec- is a conference abstract. tonics and a subsurface ocean on Pluto. Hubbard et al. (1993) investigate the possibility of a multi-layer Maps Matsuyama and Nimmo (2013) predict tectonic patterns atmosphere for Pluto. for Pluto’s surface. No coordinates are defined, as patterns are Lunine and Nolan (1993) model Pluto’s atmosphere as originally symmetric about the equator and the prime meridian. This is thin and rapidly escaping. This is a conference abstract. a conference abstract. Stansberry et al. (1993) discuss the implications of non-equilib- Mousis et al. (2013b) discuss the existence of noble gas clath- rium conditions for Pluto’s atmosphere. This is a conference rates on Pluto’s surface. This is a conference abstract. abstract. Sykes (1993) argues Pluto’s surface is not isothermal. This is a B.10. Atmosphere and weather conference abstract. Tryka et al. (1994a) determine the temperature on Pluto by Trafton (1979) asserts that Pluto is not massive enough to retain combining information about lab spectra and 2.148 lm mea-

aCH4 atmosphere. This is a conference abstract. surements. Insolation and thermal inertia are considered. The Trafton (1980) calculates that if Pluto has an atmosphere, it paper notes that maps by Buie et al. (1992) and Young and would blow away. Binzel (1993) have a north–south asymmetry, but no system Stern and Trafton (1981) model Pluto’s atmosphere and con- is mentioned – latitude and the extent of the polar caps are sider seasonal effects. This is a conference abstract. treated symmetrically in plots. The temperature of a single Trafton (1981) argues that for Pluto’s atmosphere NOT to go meridian on Pluto at different times of day is plotted.

away, it would also have to contain heavy gasses in addition Tryka et al. (1994b) calculate the N2 temperature on Pluto. The to CH4. There is some discussion on seasons and Pluto’s obliq- polar caps are noted as extending down to ±20 to ±25 latitude. uity, but no speciﬁed locations. This is a conference abstract.

Hunten and Watson (1982) ﬁnd that suggestions by Trafton Stansberry et al. (1996a) look at N2 emissivity on Pluto. Polar (1980) that Pluto’s atmosphere is unstable are exaggerated. regions are only mentioned generally.

Instead, the predicted blow-off CH4 flux can be greatly Stansberry et al. (1996b) discusses CH4 on Pluto. A specific sub- reduced by assuming that the upper atmosphere is non- solar latitude is mentioned on Triton. For Pluto, the sub-solar isothermal, and that the remaining gas is cooled by adiabatic latitude is described as being ‘‘near the equator’’ and transport expansion. is ‘‘toward the poles’’, but no specifics are mentioned. Trafton and Stern (1982) try to explain the elevated surface Strobel et al. (1996) model Pluto’s atmosphere. No discussion of temperature on Pluto. This is a conference abstract. geographic features.

Buie and Fink (1983) assert that CH4 lines of varying strength Lara et al. (1997) model Pluto’s atmosphere and determine its with phase suggest solid, not gaseous CH4. This is a conference most common constituents. abstract. Krasnopolsky (1999) makes an analytic model of atmospheric Trafton and Stern (1983) consider diurnal and seasonal effects ﬂow based on Pluto. No mention of longitude or latitude is on Pluto’s atmosphere. Latitudinal tides are considered, but no made. pole or coordinates are assigned. Krasnopolsky and Cruikshank (1999) create models of Pluto’s

Buie and Fink (1984) ﬁnd that the rotationally varying CH4 in atmosphere. No mention of longitude or latitude is made. Pluto’s spectrum does not need to be from an atmosphere. No Young and Stern (2000) look at the amount of light from Charon wavelength is mentioned. This is a conference abstract. that Pluto’s sub-Charon hemisphere receives as it travels away Owen (1984) suggests that Pluto has a trapped reservoir of vol- from equinox. North and south are not assigned, and it is noted

atiles. If Pluto has no N2 then it may have formed in the solar that the maximum amount of light received from Charon during nebula, as opposed to Neptune’s protoplanetary nebula. This is arctic night occurs at 58 latitude. Charon ﬂux is plotted at a a conference abstract. function of Pluto latitude, but the graph is symmetrical about Stern and Trafton (1984) constrain Pluto’s atmosphere. Though the equator. This is a conference abstract. seasonal and diurnal changes are considered, no speciﬁc points Rao (2001) creates gray models for Pluto’s atmosphere. The are mentioned. tidal and non-tidal models are found to be indistinguishable.

Marcialis (1985) considers a CH4 lithosphere for Pluto. This is a No mention of coordinates on Pluto was found. This is a PhD conference abstract. thesis. A. Zangari / Icarus 246 (2015) 93–145 125

Elliot and Kern (2003) discuss Pluto’s atmosphere and the McNutt et al. (2008) describe PEPSSI, a New Horizons instrument possibility of other KBOs having an atmosphere. designed to probe the particle environment around Pluto and

Atreya et al. (2006) discuss the role of N2 on various major outer Charon. The paper’s erratum corrects only errors with the Solar System moons and Pluto. author list (McNutt et al., 2009). Mousis et al. (2010) look at compounds in Pluto and Triton’s Reuter et al. (2008) describe Ralph, a visible/infrared imaging atmosphere. This is a conference abstract. spectrometer aboard New Horizons. NIR spectra of Pluto and Schaufelberger et al. (2010) model Pluto and Titan’s exosphere. Charon are presented as part of the science case for Ralph, but No mention of longitudes or latitudes. This is a conference no location-based science case is made. abstract. Stern (2008) provides an overview of the New Horizons mission. Erwin et al. (2011) discuss models of Pluto’s atmosphere. This is Mapping is mentioned as a priority, but no coordinates are a conference abstract. mentioned. Michaels and Young (2011) describe early results from a Pluto Stern et al. (2008) describe ALICE, a UV imaging spectrograph GCM. No mention of coordinates. This is a conference abstract. which will take solar occultation data aboard New Horizons. Zalucha et al. (2011b) fit immersion and emersion models for No mention of coordinates on Pluto’s surface is made. atmospheric pressure without regard to specific differences. Weaver et al. (2008) provide an overview of the New Horizons Rather it is decided that there are no longitude/latitude science payload. No mention of coordinates on Pluto’s surface differences due to the similarity of the immersion/emersion is made. light curves. NA (2010a) reports on the health of the New Horizons Sillanpää et al. (2012) model Pluto’s plasma tail. instruments. Tucker et al. (2012) create a global average profile of Pluto’s Randol et al. (2010) compare lab data from the SWAP instru- extended atmosphere. One figure shows a column density plot ment (currently aboard New Horizons en route to Pluto) to that collapses the northern and southern hemispheres of quantum mechanical simulations of how the instrument is Charon into the z axis, so no distinction is made between the expected to behave. two. Ebert et al. (2010) present calibration data for the SWAP instru- Jessup et al. (2013) consider the detectability of 14N15N in Plu- ment on New Horizons. to’s atmosphere. Young and Stern (2010) discuss the scientific goals and the Zhu et al. (2014) add radial velocity terms to the models for Plu- phases of the New Horizons mission at Pluto. Specific longitudes to’s stratospheric density and thermal structure. and latitudes are not specified. Instead, the authors mention goals such as imaging Pluto’s night/dark pole (the pole that is B.11. New Horizons north of the invariable plane) and imaging CO-rich longitudes and longitudes ‘‘other than the ones at closest approach’’. Stern and Cheng (2002) discuss the selection of New Horizons Beauvalet et al. (2012) predict to what degree New Horizons and the significance of the mission. Prior mapping of the system measurements will constrain the mass of Nix and Hydra as well is discussed in generalities, but no orientation is given. as what constraints could be made without New Horizons. Brumfiel (2004) worries that security issues at Los Alamos could Iorio (2013) investigates whether New Horizons could detect a delay the launch of New Horizons and cause it to miss its crucial massive hypothetical trans-Plutonian planet. winter 2006 launch window. Deboy et al. (2005) detail the New Horizons RF antenna. B.12. Impacts, magnetic field, solar wind Hegge et al. (2005) discuss the IR-optimized telescope aboard New Horizons. Bagenal and McNutt (1989a) describe the interaction between Kusnierkiewicz et al. (2005) detail the New Horizons spacecraft Pluto’s escaping atmosphere and the solar wind. This is a con- itself and focus on parts that do not involve the major ference abstract. instruments. Bagenal et al. (1989b) characterize Pluto’s interaction with the Reuter et al. (2005) provide a technical description of Ralph, a solar wind. There is an image that shows Pluto and Charon visible/IR imager aboard New Horizons. orbiting clockwise with a left-handed pole, but no discussion Stern et al. (2005a) provide a technical description of ALICE, an of this was found in the text. imaging spectrometer aboard New Horizons. Johnson (1989) looks at cosmic rays and other sources of Tyler et al. (2005) summarize the current state of the New Hori- irradiation on Pluto. zons mission and its instruments. This is a conference abstract. Weissman et al. (1989b) note that Charon’s eccentricity must be Enright (2006) reflects on the New Horizons mission immedi- better defined in order to fully understand the impactor flux on ately after launch. Pluto and Charon. Hogue (2006) reports on the fallout from the New Horizons Kecskemety and Cravens (1993) calculate trajectories for ions launch. This article is about aeronautical engineering. that escape Pluto’s atmosphere and are picked up by the solar NA (2006b) reports the renaming of the Student Dust Counter wind. (SDC) on New Horizons to the Venetia Burney Student Dust Weissman and Stern (1994) estimate the impactor flux on Pluto Counter (SDC) in honor of Venetia Burney Phair. and Charon, estimating that most impactors will be from the Moore (2007) discusses backup features on the New Horizons Kuiper Belt or Oort Cloud, and that the surfaces should not be spacecraft. saturated. Cheng et al. (2008) describe LORRI, an imager on the New Hori- Bagenal et al. (1997) map out solar wind interactions with zons spacecraft. No coordinates are mentioned. Pluto. In the paper’s Fig. 4, Pluto’s rotation is marked in a left- Fountain et al. (2008) provide an overview of the New Horizons handed manner, but no north/south distinction seems to be spacecraft. made. This article is part of the Arizona Space Science Series Horányi et al. (2008) describe the Student Dust Counter (SDC), a book, Pluto and Charon. dust measuring instrument aboard New Horizons. Sauer et al. (1997) describe Pluto’s interaction with the solar McComas et al. (2008) describe SWAP, an instrument aboard wind. New Horizons designed to measure the solar wind. Shevchenko et al. (1997) discuss MHD activity near Pluto. 126 A. Zangari / Icarus 246 (2015) 93–145

Kosarev et al. (2002) calculate the effect of impactors on Pluto’s Bell (1983) reports scientists’ discovery of CH4 on Pluto and atmosphere. This is a conference abstract. Triton. Thiessenhusen et al. (2002) suggest an ejecta-created dust envi- Fink and Ip (1983) summarize the discovery of the outer planets ronment around Pluto that could be detected by an in situ dust and the current, pre-Voyager knowledge about Uranus, and detector on a spacecraft ﬂyby mission of Pluto. Neptune. The sections on Pluto describe the discovery at Lowell Delamere and Bagenal (2004) discuss how escaped particles Observatory, report basic physical parameters and show a 0.3– from Pluto interact with the solar wind. 2.5 lm spectrum. In German. Harnett et al. (2005) simulate Pluto’s magnetosphere. O’Hora (1984) reports how Venetia Burney was not the ﬁrst per-

Tian and Toon (2005) discuss N2 escape from Pluto. son to suggest the name Pluto. Strobel (2008) calculates N2 escape rates from Pluto’s Brown and Cruikshank (1985) summarize the mutual events atmosphere. and the current state of knowledge about Pluto. Delamere (2009) uses a right-handed x, y and z coordinate Reaves (1985) recounts how PL was chosen as the Pluto symbol. system based on the direction of the Sun’s magnetic ﬁeld to This is conference abstract. model the interaction of Pluto’s atmosphere and the solar Cruikshank (1987) reviews current knowledge of the physical wind. parameters of Pluto, Charon and Triton, noting that it is sus- de Elía et al. (2010a) make predictions about cratering on Pluto. pected that Pluto has an atmosphere and there is water ice on de Elía et al. (2010b) look at the impactor ﬂux in the Pluto/ Charon. This is a conference abstract. Charon system. Henbest (1987) reports on new diameters and densities drawn Poppe and Horányi (2011a) update predictions on a Pluto– from scientists’ measurements of the mutual events. Charon dust cloud in light of the discoveries of Nix and Hydra. Hughes (1987) updates readers on the results from the mutual Poppe and Horányi (2011b) discuss the Pluto–Charon dust envi- events, then introduces Tedesco et al. (1987). ronment. This is a conference abstract. NA (1987a) introduces Tholen et al. (1987a), noting that the next two years will have full, not partial, mutual events (unlike Appendix C. Additional Pluto articles without references to 1986 and 1985). cartographic coordinates NA (1987b) introduces Sykes et al. (1987) and Marcialis et al. (1987).

C.1. Article introductions – secondary sources – memoirs – letters Wace (1987) reports that astronomers discovered a CH4 atmosphere on Pluto using IRAS. Mulholland (1978), who states he had gone on prior record Hughes (1988) introduces the paper by McKinnon and Mueller doubting Pluto’s moon, admits there is evidence of Charon in (1988b). some of the old plates of Pluto he examined and concedes that Kerr (1988) introduces Sussman and Wisdom (1988), noting a satellite could be there. that Pluto is the most likely of any Solar System body to be Hughes (1978) reports the discovery of a satellite of Pluto in chaotic. Smith et al. (1978). The author suggests 1978 P1 should be NA (1988) introduces Binzel (1988a), which showed that named Persephone. Charon is blue. Öpik (1978) comments on Charon’s discovery. Stern (1989b) introduces a special issue of Geophysics Research Sharma (1978) reports that V.B. Ketakara predicted Pluto’s exis- Letters featuring papers about Pluto and Charon: Binzel (1989), tence using the equilibrium of moments. Simonelli and Reynolds (1989), Trafton (1989), Dobrovolskis Bodifee (1979) reports the discovery of Charon. The article (1989), Stansberry et al. (1989), McNutt (1989), Bagenal et al. reports the north pole of the orbit of Charon as 18h26m, 12 (1989b), Johnson (1989), McKinnon (1989a), Weissman et al. 200, but no epoch is given. In French. (1989b). Dowdell (1979) reports his personal experiences observing Cruikshank (1990) describes the current state of research about Pluto. Triton, Pluto and Charon. Charon is described as moving south Beebe and Beebe (1980) recount a special meeting to commem- to north on the sky. Polar caps, spots and equatorial regions orate the ﬁftieth anniversary of Pluto’s discovery at New Mexico are mentioned, but no coordinates are assigned. An orbital per- State University. This issue of Icarus features many Pluto-cen- iod of Charon of 6.387230 ± 0.000021 d is given. tric articles (Tombaugh, 1980; Giclas, 1980; Duncombe and Kemp (1990) compares the discovery of Pluto with that of Nep- Seidelmann, 1980; Seidelmann et al., 1980; Marsden, 1980; tune and Uranus. Christy and Harrington, 1980; Lupo and Lewis, 1980b; Barker McKinnon (1991) compares Pluto and Triton. This is a confer- et al., 1980; Trafton, 1980; Fink et al., 1980b; Cruikshank, ence abstract and invited review talk. 1980; Harrington, 1980). Stern (1991) provides an overview of the current state of Pluto Dessler and Russell (1980) extrapolate that Pluto will disappear science. This is a conference abstract. by the year 2000. Kerr (1992) describes Wisdom and Sussman’s calculations that Duncombe and Seidelmann (1980) discuss the history of Pluto’s all nine planets have chaotic orbits. mass and its downward trend, noting that it could not perturb Lunine (1993) introduces Owen et al. (1993b) and discusses the Neptune’s orbit enough to produce the residuals that motivated role Pluto and Triton play in unlocking how the outer Solar Sys- the search for Planet X. tem formed. Giclas (1980) describes the history of the Pluto Discovery Marcialis (1993b) introduces PLUBIB, a database of Pluto and Telescope. Charon papers. This is a conference abstract. Hoyt (1980b) recounts the discoveries of Uranus, Neptune, Peale (1993) introduces an article by Malhotra (1993b) about Pluto and Charon. This is a book. Pluto’s orbital evolution. Hughes (1980a) introduces Walker (1980). Burns (1994) introduces a special issue of Icarus featuring 10 Tombaugh (1980) recounts some mechanical issues with the papers about Pluto and Charon: Gemmo and Barbieri (1994), Pluto Discovery Telescope. Standish (1994), Young et al. (1994), Tholen and Tedesco (1994), Tombaugh and Moore (1980) recount the discovery of Pluto. Reinsch et al. (1994), Young and Binzel (1994a), Buie and This is a book. Shriver (1994), Stern et al. (1994), Roush (1994), Lellouch (1994). A. Zangari / Icarus 246 (2015) 93–145 127

NA (1994) announces the first Pluto–Charon images from HST Mink and Klemola (1985) present occultation predictions for post refurbishment. This is a press release from ESO. Pluto and the ice giants. Binzel and Marcialis (1996) write to Physics Today to comment Mink and Tedesco (1986) note that P4 should include a Charon that HST had imaged Pluto’s surface previously, and maps had occultation. been created by the mutual events – the new images confirm Mink et al. (1986) request that astronomers in Hawaii, Japan these results, and help model seasonal variation. It is also noted and China attempt to observe the occultation by Pluto called P4. the maps of Pluto are merely a model derived from the Mink and Klemola (1989) present occultation star search much-lower resolution Hubble images. results. This is a conference abstract. Christy (1997) writes about Charon’s discovery. It is noted that Dunham et al. (1991) list potential Pluto–Charon occultation the ‘‘bright pole’’, of Pluto is on the ‘‘wrong side’’. This article is stars for 1990–1995. part of the Arizona Space Science Series book, Pluto and Charon. Mink et al. (1991) report Pluto–Charon occultation candidates Marcialis (1997a) discusses PLUBIB, a TeX file containing all ref- from 1990 to 1999. erences on Pluto, which numbered about 1500 at that time. This Sybert et al. (1992b) report that the predicted occultation track article is part of the Arizona Space Science Series book, Pluto and of P17 has moved off the Earth. Charon. Olkin et al. (1993a) report Pluto will not occult P20 over the Reaves (1997) discusses Pluto and Charon’s discovery. This arti- Earth, as the predicted shadow has moved above the north cle is part of the Arizona Space Science Series book, Pluto and pole.However, an occultation by Charon may be possible in Charon. the southern hemisphere. Tombaugh (1997) writes about Pluto’s discovery. This article is McDonald and Elliot (1996) provide a list of Pluto–Charon part of the Arizona Space Science Series book, Pluto and Charon. stellar occultation candidates for 1996–1999. (None were Silverberg (2000) writes a science-fiction story about the dis- observed.) covery of life on Pluto in 2668 for Nature. McDonald and Elliot (2000a) present Pluto–Charon stellar Chapman (2003) recounts the story of the discovery of Charon. occultation candidates from 2000–2009. Here, east longitude Hubbard (2003) introduces dual papers on the 2002 Pluto occ- refers to the sub-star longitude on Earth. This paper is super- ultations by Elliot et al. (2003a) and Sicardy et al. (2003). seded by McDonald and Elliot (2000b) which corrects the Kourganoff (2003) reviews the discoveries of Neptune and ephemeris used and re-plots the occultation globes and tables. Pluto. In French. Waagen (2012) alerts astronomers about a potential Pluto Chapman (2005) provides a biographical sketch of Percival Low- occultation on 2012-06-14. ell, and a history of Lowell Observatory and Pluto’s discovery. Cruikshank (2005) provides an inventory of the outer Solar C.3. Space missions to Pluto besides New Horizons System. Haag (2005) profiles the early life of Alan Stern and the creation Bagenal et al. (1990) discuss plans for a mission to Pluto arriving of SwRI Boulder. in 2015. This is a conference abstract. Binzel (2006) introduces Weaver et al. (2006) and Stern et al. Cole (1991) discusses which Cassini instruments could be used (2006b), discovery papers for new moons of Pluto. for a Pluto flyby. This is a conference abstract.

Brosch et al. (2006) summarize UV observations of Solar System Bailey et al. (1993) use knowledge of CO, CH4 and N2 in Pluto’s bodies, including Pluto. While mapping is mentioned, no data atmosphere from IR spectra to create models of what Pluto’s are presented. spectrum should look like in the UV for a Pluto Fast Flyby UV James (2006) announces a correction about limiting magnitudes spectrometer. in a previously published ﬁnder chart for Pluto. Fink et al. (1993) discuss the speciﬁcations for an IR mapping NA (2006a) provides a bullet-point history of important discov- spectrometer for the Pluto Fast Flyby mission. eries in the Pluto system. Glenar and Hillman (1993) describe an IR imaging spectrometer NA (2006d) recounts Pluto’s discovery and naming. The article for the Pluto Fast Flyby. This is a conference abstract. misinterprets ‘‘Planet X’’ as the tenth planet. A second article Gurrola et al. (1993) calculate whether a radio occultation recounts the discovery of S/2005 P1 and S/2005 P2. would prove useful with the Pluto Fast Flyby using experiences Russell (2008) introduces the Space Science Review issue on New from Triton and Voyager. This is a conference abstract. Horizons. This book also contains Stern (2008), Fountain et al. Jennings et al. (1993) describe the creation of a spectrometer for (2008), Guo and Farquhar (2008), Weaver et al. (2008), Young a Pluto Fast Flyby mission, LEISA. This is a conference abstract. et al. (2008b), Reuter et al. (2008), Stern et al. (2008), Cheng Malin (1993) discusses the challenges of creating a visible ima- et al. (2008), Tyler et al. (2008), McComas et al. (2008), ger for the Pluto Fast Flyby mission. McNutt et al. (2008), Horányi et al. (2008). Stern (1993a) summarizes the Pluto Fast Flyby mission design. Stern (2010) provides context for the observations reported in This is a conference abstract.

Tegler et al. (2010) and questions why some bodies have N2 Stern and Marshall (1993) correct some misconceptions about a and CH4 on their surfaces, while other bodies contain H2O, but mission to Pluto. no trace of N2 and CH4. Reichhardt (1994) reports on the cancellation of the Pluto Fast NA (2012) reports that the New Horizons team underwent a dry Flyby mission. run for the 2015 Pluto encounter. Minovitch (1994) works out several launch windows for direct Pluto trajectories and Jupiter gravity assist missions. Atmo- C.2. Occultation prediction papers spheric concerns are discussed for timing planning purposes, but not geographic concerns. Kiemola and Elliot (1980) report that the 1980-04-06 occulta- Sims et al. (1997) analyze possible trajectories to bring a space- tion will probably miss the Earth. craft to Pluto. Candy (1982) alerts of a possible Pluto occultation on 1982-04- Trujillo and Jewitt (1998) create a method for searching for 15. post-Pluto encounter KBOs for the Pluto–Kuiper Express. Millis et al. (1983) ask astronomers to observe a Pluto occulta- El-Genk et al. (1999) describe the AMTEC cells designed for the tion miss that just might pass over the Earth on 1983-04-04. Pluto–Kuiper Express. 128 A. Zangari / Icarus 246 (2015) 93–145

Henry et al. (1999) discuss the trajectory of the Pluto–Kuiper Christensen (2007) gives an account of the Pluto demotion from Express and estimates the number of KBOs that might be in the Press Room of the IAU, and asks what science communica- the cone of accessibility after Pluto. tors can learn from the incident. Leipold (1999) proposes Pluto be reached by solar sails and a Sykes (2007) discusses the recent reclassification of Pluto solar flyby instead of a Jupiter gravity assist. (introduced by Brissenden and Noel-Storr (2007a)). Stern (1999) discusses the Pluto–Kuiper Express mission Tyson (2007) discusses the recent reclassification of Pluto planning. This is a conference abstract. (introduced by Brissenden and Noel-Storr (2007b)). Terrile (1999) discusses the science objectives of the Pluto– Zielinski (2007) reports New Mexico’s declaration that Pluto is Kuiper Express. This is a conference abstract. still a planet. Terrile et al. (1999) describe the Pluto–Kuiper Express. This is a Broughton (2008) explores the connection between emotion conference abstract. and scientific belief in elementary school children using the Tournier and El-Genk (1999) describe the AMTEC cells designed reclassification of Pluto. None of the background information for the Pluto–Kuiper Express. discusses Pluto mapping. This is a PhD dissertation. Feder (2000) reports the cancellation of the Pluto–Kuiper Weintraub (2008) explores the historical evolution of the word Express. ‘‘planet’’ to explore the issue of whether Pluto is a planet. While Reichhardt (2000) reports a Pluto mission may happen after all. the 1994 HST images are included and it is noted that Pluto can Triplett (2000) reports the enormous public outcry in the wake be considered to be either upside down or rotating backwards, of the cancellation of the Pluto–Kuiper Express. Pluto’s pole is not discussed. Oleson et al. (2001) show how a spacecraft could get to Pluto without a Jupiter gravity assist. C.5. Book reviews Rathke (2004) hopes a possible ESA mission to Pluto would include provisions to test the Pioneer Anomaly as the craft Cruikshank (1980) reviews Hoyt (1980b). leaves the Solar System. Hoyt (1980a) reviews Hoyt (1980b). Harrington (1980) reviews Whyte (1980). C.4. Planethood Hoyt and Lang (1980) review Hoyt (1980b). Hoyt and Meadows (1980) review Hoyt (1980b). Marsden (1980) recounts the story of discovery of many bodies Hoyt and Morgan (1980) review Hoyt (1980b). in the Solar System and proposes Pluto’s demotion to minor pla- Veverka (1980) reviews Whyte (1980). net status. Whyte and Beer (1980) review Whyte (1980) and Tombaugh Moore (1984) provides an update of the current status of Pluto and Moore (1980). research and questions its planethood. Hoyt and Reaves (1981) review Hoyt (1980b). Hollis (1999b) weighs in on a recent proposal to make Pluto NA (1981) reviews Hoyt (1980b). In French. asteroid number 10000 instead of a planet, and closes by brand- Whyte (1981) reviews Whyte (1980). ing all of the speculation on Pluto’s planethood as ‘‘pretty silly’’. Whyte and Morgan (1981) review Whyte (1980). Millis et al. (1999) reassure the public that the IAU has no plans Tombaugh et al. (1982) review Tombaugh and Moore (1980). or authority to declare that Pluto is not a planet, and that Pluto Whyte and Reaves (1984) review Whyte (1980). has little in common with the newly-discovered KBOs. Hollis (1998) reviews Stern and Tholen (1997). A’Hearn (2002) suggests Pluto be considered both a planet and a NA (1998a) reviews Stern and Tholen (1997). TNO. NA (1998b) reviews Stern and Mitton (1998). Reichhardt (2002) discusses the possibility that Pluto might be Cruikshank et al. (1999) review Stern and Tholen (1997). a KBO after the discovery of Quaoar, the largest discovered KBO Miles and Davies (2001) review Davies (2001). to date. NA (2001) reviews Davies (2001). Pasachoff and Elliot (2004) urge readers to look beyond the Spencer Jones (2001) reviews Stern and Mitton (1998). controversy over Pluto’s planethood and learn about the Bond (2006) reviews Stern and Mitton (2005). interesting occultation science results about Pluto’s atmosphere Weintraub and Bottke (2007) review Weintraub (2008). instead. Shiga (2009) reviews Tyson (2009). Abbott (2005) muses about what the IAU might do in response Tyson et al. (2009) review Tyson (2009) and Schilling (2009). to the discovery of Eris. Miles and Jones (2010) reviews Jones (2010). Gehrels (2005) hopes that the IAU will allow Pluto to keep its Consolmagno (2011) reviews Jones (2010). planetary status during the upcoming 2006 meeting, but sup- ports assigning Pluto a minor planet number. C.6. Astrometry Christensen (2006) provides a timeline of the IAU events. Green (2006a) announces the IAU’s decision and a minor planet Barbieri et al. (1979) report astrometry of Pluto. number for Pluto: (134340). Jensen (1979) reports astrometry of Pluto. Hogan (2006) reports the backlash against the IAU definition Seidelmann et al. (1980) discuss the history of ephemerides of that reclassified Pluto as a dwarf planet. Pluto and present a new ephemeris. Lopresto (2006) finds that post-secondary Astronomy students Zappala et al. (1980) report astrometry of Pluto from 1973 to 1979. reacted more favorably to the IAU’s reclassification of Pluto Debehogne et al. (1981) report astrometry of Pluto (and the after completing a unit on the Solar System. Gallilean satellites). NA (2006c) presents reactions from the scientific community to Zappala et al. (1983) present astrometry of Pluto from 1980 to the IAU decision about Pluto. 1982. Nath (2006) writes a magazine article where two characters Debehogne et al. (1984) provide new astrometry on Pluto. discuss the events at the IAU meeting. Though Pluto’s obliquity Hardie et al. (1985) present astrometry of Pluto from 1965 to 1981. is given as 119.6, no mention of coordinates is made. In French. de Sanctis and Massone (1986) pre-create a catalog of stars in Consolmagno (2007) narrates the history behind Pluto’s Pluto’s future path to aid in astrometric measurements of the discovery and the IAU’s processes in 2006. system. This is a conference abstract. A. Zangari / Icarus 246 (2015) 93–145 129

Goffin et al. (1986) provide a method for improvement of long- Nacozy and Diehl (1978) compare a long term solution for Plu- term calculations in Pluto’s orbit. to’s motion with other solutions, resonances and librations. Roberts (1987) finds that the cosmological constant is NOT Farinella et al. (1979) consider how tides made the Pluto and responsible for Pluto orbital irregularities. Charon system evolve. Barbieri et al. (1988) report astrometric positions of Pluto. Harrington and van Flandern (1979) model the hypothesis that Debehogne and de Freitas Mourao (1988) present astrometric Pluto is an escaped satellite of Neptune and the product of a positions of Pluto. massive collision. Wasserman et al. (1988) promise new Pluto–Charon astrome- Piraux (1979) reports on perturbations by Pluto on Neptune. In try. This is a conference abstract. French. Lopez et al. (1989) present astrometric results for Pluto and a Dormand and Woolfson (1980) consider the theory that Pluto is selection of bright asteroids. an escaped satellite of Neptune. Tholen and Buie (1991) calculate Pluto’s radius from the mutual Farinella et al. (1980) discuss the origin of Pluto as an escaped event data and provide an estimate of Charon’s orbital semi- Neptunian satellite and argues for capture of Triton. major axis based on the first HST images. This is a conference Ries and Duncombe (1980) search for periodicity in Pluto’s abstract. motion. This is a conference abstract. Morrison et al. (1992) compare meridian circle observations of Nacozy (1980) discusses the irregularities of Pluto’s orbit Pluto with the JPL ephemeris. around the Sun. Abrahamian et al. (1993) present astrometric measurements of Zhou (1980) looks at orbital elements of the outer planets. Pluto and the other outer planets. Lin (1981) proposes that Pluto and Charon were formed by bin- Dolganova et al. (1993) present astrometric measurements of ary fission and constrains a mass ratio for the pair to 0.25. Pluto from 1969, 1970, 1989 and 1990. Harris (1982) suggests the equinox/perihelion coincidence for Gemmo and Barbieri (1994) present astrometric measurements Pluto is a rare and temporary condition. of Pluto from 1969 to 1989. Chapront (1984) uses approximations to create a two century Standish (1994) provides a history of Pluto ephemerides as pro- ephemeris for Pluto. vided by the Jet Propulsion Laboratory, and the improvements Chapront and Vu (1984) present numerical approximations for made throughout the years. The longitude and latitude errors ephemerides, and applies these methods to present a new plotted in the paper’s Figs. 5–7 refer to ‘‘position fix on place 225 year ephemeris for Pluto. of the sky’’. Kinoshita and Nakai (1984) present a five million year integra- Rylkov et al. (1995) present astrometric measurements of Pluto tion of the orbits of the outer planets. Pluto’s argument of peri- from 1930 to 1992. helion is found to librate around 90, and Neptune’s perihelion Yoshizawa et al. (1995) provide astrometric comparisons of is found to be sensitive to Pluto’s mass. Pluto’s position and two JPL ephemerides (DE200 and DE245). McKinnon (1984) rejects the escaped satellite of Neptune the- Ryl’Kov et al. (1996) present four years of Pluto astrometric ory for Pluto on the basis that there was not enough energy or observations. momentum to turn Triton retrograde. Instead, it is proposed Standish (1996) discusses problems with the Pluto ephemeris that Pluto and Triton are independent bodies. and gives advice to future observers. All (then known) pre- Steel (1985) finds that a Pluto-like object in a non-protected discovery images are listed. orbit around Neptune could not survive. Ryl’Kov et al. (1997)describe a large catalog of Pluto astrometric Jackson and Killen (1987) try to constrain the orbit of a measurements taken by Pulkovo astronomers, spanning hypothetical planet X based on the orbits of the other five outer 1930–1994. Solar System planets and find that the Pluto–Neptune reso- Ratcliffe (1998) discusses inconsistencies in published books nance must be maintained for 100,000 years. This is a confer- about the date Pluto crosses beyond Neptune’s orbit. ence abstract. Wild et al. (1998) report the discovery of images from 1909 that Jackson and Killen (1988) look for resonances where a hypo- contain Pluto. This is a conference abstract. thetical Planet X could hide. Owen and Meeus (1999) try to reconcile a two-day discrepancy Olsson-Steel (1988) calculates that if Pluto’s orbit were chaotic, in ephemerides on the date that Pluto becomes further away it would not be protected from encounters with Neptune. from the Sun than Neptune. Sussman and Wisdom (1988) find that Pluto’s orbital elements Buchwald et al. (2000) report the discovery of pre-discovery change chaotically. images of Pluto taken at Yerkes Observatory in 1909. Dobrovolskis (1989) reviews the dynamics of the Pluto and Rapaport et al. (2002) compare new astrometry of Pluto to pre- Charon system. The paper discusses how Pluto’s orbit has dictions made by the DE403 and DE405 ephemerides. evolved to avoid an encounter with Neptune, how tides Veiga (2008) presents nine years of Laboratório Nacional de circularize Charon’s orbit, that Pluto’s orbit around the Sun is Astrofísica (LNA/MCT) Itajubá-Brazil 1.6-m and 0.6-m astrome- chaotic, and its obliquity varies in time such that Pluto may tric measurements of Pluto spanning from 1995 to 2004. become prograde at certain points of its orbit. The paper Kudryavtsev and Kudryavtseva (2009) explain the processes mentions that the amplitude of Pluto’s light curve has that went into the calculation of Pluto’s ephemeris. increased, and Pluto has dimmed over time due to bright polar Khrutskaya et al. (2013) publish UCAC 4 positions of Pluto caps visible during discovery. The paper avoids identifying a extracted digitally from the Pulkovo plates taken from 1930– specific pole. 1963. ArXiv only. Innanen and Mikkola (1989) report that the planets in the outer Solar System have stable orbits. This is a conference abstract. C.7. Dynamics McKinnon (1989b) discusses the formation of the Pluto–Charon binary, looking at density and angular momentum. The paper’s Dermott (1978) looks at the spin–orbit configuration of Pluto erratum (McKinnon, 1989c) was unavailable. and Charon (and compares it to Mercury, Venus and Milani et al. (1989) reports the changes in Pluto’s orbit as part of Herculina).This is a conference abstract. at 100 Myr Solar System integration. 130 A. Zangari / Icarus 246 (2015) 93–145

Weissman et al. (1989a) try to constrain intervals of comet/KBO Durda and Stern (2000) estimate collision rates in the Kuiper impacts with Pluto and Charon based on Charon’s low orbital Belt. eccentricity around Pluto. This is a conference abstract. Gladman et al. (2000) calculates what dynamical effect Pluto Neubert (1990) reports on Pluto and chaos in the Solar System. would have on other bodies in the Kuiper Belt. In German. Nesvorny´ et al. (2000) argue that Pluto is a necessary compo- Dobrovolskis (1991) reports on the configuration of Pluto’s nent to trans-Neptunian dynamical models, in addition to the ‘‘Laplace plane’’. This is a conference abstract. four giant planets, as it can destabilize objects during close Dobrovolskis (1993) calculates the Laplace plane for Pluto (and encounters. Uranus), which could predict locations of as yet unfound Rubincam (2001) discusses whether volatiles on Pluto would satellites. affect its dynamics. Poles are not discussed in terms of specifics. Levison and Stern (1993a) map out regions of stability for par- This is a conference abstract. ticles in the 3:2 resonance with Neptune. This is a conference Wan et al. (2001) explore Pluto and Charon’s 1:1 abstract. superresonance. Levison and Stern (1993b) suggest an impact brought Pluto into Bottke et al. (2003) discuss the implications of a non-zero its stable orbit in the 3:2 resonance. This is a conference eccentricity for Charon. abstract. Canup and Asphaug (2003) simulate the formation of Pluto and Malhotra (1993a) suggests Pluto was captured into its 3:2 reso- Charon. nance as Neptune migrated outwards. This is a conference Wiegert et al. (2003) simulate the accretion of Neptune and the abstract. capture of Pluto and Plutinos into the 3:2 resonance. Malhotra (1993b) presents a model of the evolution of Pluto’s Canup (2005) presents hydrodynamical simulations that sup- orbit. port the collision hypothesis for the formation of the Pluto– Prentice (1993a) suggests the relative densities of Pluto and Charon binary. Charon indicate that Charon formed through rotational fission Kalinicheva and Tomanov (2009) check to see if any comets are after Pluto shed its mantle. This is a conference abstract. influenced by Pluto, but find that none of the 59 near-parabolic Bursa (1994) estimates tides on Pluto and Charon. comets surveyed passes through its sphere of influence from Levison and Stern (1995a) suggest that encounters with KBOs 3000 to 2000. could excite Charon’s orbital eccentricity. Eroshkin and Pashkevich (2010) discuss geodetic rotation for Levison and Stern (1995b) discuss formation theories for the the Sun, planets, and the Moon. The paper finds that geodetic Pluto–Charon binary. rotation of Pluto (along with the Sun and the gas giants) is Malhotra (1995a) uses resonance capture to explain Pluto’s irrelevant. eccentricity and inclination and the distribution of KBOs. Winter et al. (2010) explore the location of stable orbits in the Malhotra (1995b) theorizes that the resonance sweeping model Pluto–Charon system. could account for the origin of Pluto’s inclination and eccentric- Pires dos Santos et al. (2011) examine the dynamical stability in ity. This is a conference abstract. the region external to Nix and Hydra. Dvorak and Lohinger (1996) determine the extent of the stable region for Pluto’s orbit. C.8. Ice in the Lab Gallardo and Ferraz-Mello (1996) find Pluto’s libration to be chaotic. Strazzulla et al. (1984) suggest solar cosmic rays could build up Kinoshita and Nakai (1996a) integrate Pluto’s orbital elements carbonaceous material on Pluto and Triton based on laboratory over 5.5 billion years to map about the long-term behavior of experimentation.

its orbital elements. Schmitt et al. (1993) present lab spectra of CH4 and N2 bands in Kinoshita and Nakai (1996b) ﬁnd Pluto’s orbit is chaotic, but different transitions. This is a conference abstract.

stable. Tryka et al. (1993) show that the N2 bands at 2.148 lm have a Malhotra and Williams (1997) look at the long term fate of Plu- region at 2.162 lm which changes with temperature in the

to’s orbital elements with respect the Sun. This article is part of lab, allowing for determination of the temperature of the N2 the Arizona Space Science Series book, Pluto and Charon. from Pluto’s spectrum taken with UKIRT in 1993. This is a con- Malhotra (1998) uses resonance sweeping to explain Pluto’s ference abstract. inclination and proposes an outward migration of Neptune Bohn et al. (1994) create ices in the lab that will reproduce spec- swept Pluto and other KBOs into the 3:2 resonance. This is a tra of Pluto and Triton. conference abstract. Quirico and Schmitt (1997a) present laboratory spectra of CO

Roig et al. (1999) show how Pluto clears its immediate orbit of diluted in N2. No mention of positions on Pluto are made. Plutinos, and has an inﬂuence on the orbits of other KBOs in the Quirico and Schmitt (1997b) present laboratory spectra of sim-

2:3 resonance region. Later published as Nesvorny´ et al. (2000). ple hydrocarbons diluted in N2. No mention of positions on This is a conference abstract. Pluto are made. Stern et al. (1999a) posit that other objects that share the 2:3 Moore and Hudson (2003) discuss lab measurements and Neptune resonance with Pluto are debris from a Pluto–Charon experiments with ices that could be on Pluto. No mention of forming impact. longitude or latitude is made. Stern et al. (1999b) discuss whether Plutinos are debris from the Morales et al. (2010) look at laboratory CN radical reactions event that created Pluto and Charon. applicable to cold atmospheres. Woolfson (1999) proposes that Pluto was originally a natural satellite of Neptune and escaped after having collided with C.9. Moons beyond Charon Triton. Collins and Pappalardo (2000) describe models about the sort of Stern (1987b) looks at the Bouet’s mass-rotation period relation surface stresses we would see if Pluto and Charon were not and compares it with Pluto, ﬁnding Pluto either does not ﬁt or rotating synchronously. This is a conference abstract. must have more satellites/rings. A. Zangari / Icarus 246 (2015) 93–145 131

Stern et al. (1987) constrain the locations and magnitudes of Tholen et al. (2008a) discuss the dynamics of Pluto and its additional satellites of Pluto. This is a conference abstract. moons. This is a conference abstract. Stern et al. (1991b) use deep ground-based images to search for Tholen et al. (2008b) present masses of Nix and Hydra based on distant satellites of Pluto. This is a conference abstract. a four body dynamical solution. Stern et al. (1991c) search for additional satellites besides Stern (2009) discusses whether ejecta from Pluto, Charon, Nix Charon using ground-based imaging. and Hydra influence each other’s albedos. The paper notes that Marchal (1993) hypothesizes a ring system around Pluto. the only structure in Charon’s light-curve is at the sub-Pluto Stern et al. (1994) assess the likelihood of Pluto having satellites hemisphere, avoiding the need to work in terms of coordinate besides Charon. systems. Stern (2003) describes efforts to search for satellites of Pluto Zsigmond and Süli (2010) look at the stability around Nix and besides Charon before New Horizons’ 2006 launch. Hydra. Stern et al. (2005b) discuss the formation of Nix and Hydra. Canup (2011) creates computer simulations to describe the ArXiv only. Published officially as Stern et al. (2006b). formulation of Charon, Nix and Hydra (P4 had not yet been dis- Fuentes and Holman (2006) report detection of Nix and Hydra covered). Nix and Hydra are described having prograde orbits with IMACS on Magellan. ‘‘with respect to Pluto’s rotation’’. However, no Pluto-centric Green (2006b) announces the naming of Nix and Hydra coordinates appear. (formerly Pluto II = S/2005 P2 and Pluto III S/2005 P1, Peale et al. (2011) discuss the formation of Nix and Hydra and respectively). the Pluto–Charon system. This is a conference abstract. Lee and Peale (2006a) look at the orbits and masses of Nix and Showalter et al. (2011) report the discovery of P4. Hydra. ArXiv only. Later published as Lee and Peale (2006b). Buie et al. (2012b) provide new orbits for Pluto, Charon, Nix, Lee and Peale (2006b) look at the orbits and masses of Nix and Hydra and P4. This is a conference abstract. Hydra. Pires dos Santos et al. (2012) explore the possibility of Pluto’s Nagy et al. (2006a) discuss simulations that suggest Nix and moons as captured planetesimals in the very early stages of for- Hydra formed in situ. Similar, but not identical to Nagy et al. mation later disrupted by collision but finds that their origin (2006b,c). cannot be explained in this way. Nagy et al. (2006b) discuss the simulations that suggest Nix and Showalter et al. (2012a) report on the search for additional rings Hydra formed in situ. Similar, but not identical to Nagy et al. and moons of Pluto. This is a conference abstract. (2006a,c). Showalter et al. (2012b) report the discovery of P5. Nagy et al. (2006c) survey the phase-space around Pluto and Tholen et al. (2012) provide masses for Pluto, Charon, Nix and Charon and find that a capture origin of S/2005 P1 and S/2005 Hydra. P2 is unlikely. This paper is available on the ArXiv. Later pub- Youdin et al. (2012) use P4 to constrain the masses of Nix and lished as Nagy et al. (2006a,b). Hydra. No mention of coordinates on Pluto’s surface is made. Nicholson and Gladman (2006) carry out a ground-based search Giuliatti Winter et al. (2013) find a stable ‘‘sailboat’’ region using the Palomar 200-in. for satellites of Pluto beyond Charon. around Pluto. The search was unsuccessful. The paper notes that Nix and Pires dos Santos et al. (2013) examine the fates of ejecta from Hydra were discovered using HST while the paper was in press, small satellites of Pluto and Charon. and that they were beyond the detection limits presented in Showalter et al. (2013) report preliminary orbital elements for this paper due to saturation. P5. This is a conference abstract. Steffl et al. (2006) provide constraints on additional discoveries Kenyon and Bromley (2014) model the formation of the four of satellites of Pluto after the discovery of Nix and Hydra. A 90% known small satellites beyond Charon’s orbit, and predict the confidence interval is placed upon satellites brighter than existence of small satellites beyond the orbit of Hydra. 00 00 mv = 25.7 between 1 and 3 . With the eventual discovery of P4, Showalter et al. (2011) report its positions and magnitudes C.10. Not about Pluto from a variety of HST images. P4 was found between 200 and 2:500 from Pluto with magnitudes ranging from V = 25.71 ± 0.3 to Bailey (1983) theorizes about a cloud of comets beyond Pluto. V = 26.1 ± 0.3. This paper is not about Pluto. Sicardy et al. (2006) announce successful detection of Hydra Simpson et al. (1990) look for dust in the outer Solar System using ground-based AO with the ESO 8.2-m telescope. beyond Pluto. This paper is not about Pluto. This is a conference Stern et al. (2006a) report HST photometry and astrometry of abstract. Nix and Hydra. ArXiv only. Guliev (1992) suggests a search for trans-Plutonian planets. This Stern et al. (2006b) postulate that the impact hypothesis pro- paper is not about Pluto. vides a reasonable explanation for the near-circular and co-pla- Hainaut and West (1993) report the discovery of 1993 FW, the nar orbits of Charon, Nix and Hydra. second KBO. This paper is not about Pluto. Stern et al. (2006c) argue that P1 and P2 (Hydra and Nix) had Weissman and Levison (1997) describe the uncleared region of formed in situ based on circular, planar orbits and mean motion space around Pluto and the 32 known KBOs at time of publica- resonances. This is a conference abstract. tion, hypothetical Neptune Trojans, and comets in the Oort Ward and Canup (2006) discuss how Nix and Hydra are in res- cloud. This article is part of the Arizona Space Science Series onance with Charon. book, Pluto and Charon. This paper is not about Pluto. Weaver et al. (2006) present the discovery of Nix and Hydra. Davies (2001) focuses on the Kuiper Belt and disks beyond stars. Steffl and Stern (2007) put constraints on Pluto’s ring system This is a book. and make recommendations for a safe location for a spacecraft Melita et al. (2002) discuss perturbations at the edge of the to travel through Pluto’s orbital plane. Kuiper Belt. This paper is not about Pluto. This is a conference Stern et al. (2007) present astrometric positions of Nix and abstract. Hydra from HST. Stober and Bucher (2005) refer to the Greek gods when using Lithwick and Wu (2008) propose origin theories for Nix and ‘‘Neptune meets Pluto’’ as a title. This paper is about deep fluids Hydra. ArXiv only. on planet Earth. 132 A. Zangari / Icarus 246 (2015) 93–145

Kuz’Michev and Tomanov (2006) look at cometary obits to For the stable version, GeoViz Pluto calculations are based off of search for KBOs (called Transplutonian planets). This paper is SPICE kernels plu017.bsp and pck00008.tpc (ecliptic north, not about Pluto. increasing longitude), and the ephemerides reflect that system Licandro et al. (2006) compare spectra of Makemake to spectra as well. The kernels used in GeoViz calculations can be of Pluto’s spectrum in both visible and IR wavelengths. No men- displayed by selecting the ‘‘List kernel info’’ checkbox in the tion of coordinates on Pluto. GeoViz interface. For the development version, GeoViz Pluto Rabinowitz et al. (2006) discuss the rotation of Haumea and calculations are based off of SPICE kernels plu017.bsp and compare it to physical characteristics of Pluto. pck00008.tpc (ecliptic north increasing longitude), and the Sheppard (2007) presents light-curves of several large KBOs and ephemerides reflect that system as well. The kernels used in compares them to Pluto. No mention of geography. GeoViz calculations can be displayed by selecting the ‘‘List ker- Davis and Miller (2008) discuss the light-curve of Makemake. nel info’’ checkbox in the GeoViz interface. The addition of cus- This paper is not about Pluto. This is a conference abstract. tom kernel uploads is in beta. Spin north, decreasing longitude Lykawka and Mukai (2008) discuss the possibility of planets coordinates can be mapped by choosing ‘‘Pluto RHR’’ from the beyond Pluto. This paper is not about Pluto. ‘‘Surface Style’’ drop-down menu. ‘‘Pluto LHR’’ (and every other de la Fuente Marcos and de la Fuente Marcos (2012) report the skin) enables ecliptic north, increasing coordinates to be dis- discovery of a ‘‘quasi-satellite’’ of Pluto (i.e. a plutino that orbits played on the map. In the table of ephemeris information below, the Sun outside the Pluto’s Hill Sphere and shares a mean lon- an additional row is added for Pluto that contains the right- gitude and semi-major axis, but not eccentricity or inclination). hand rule. The status of the development version, and inclusion This paper is not about Pluto. of any of the above aspects into the stable version are subject to Randol (2012) discusses measurements of pick up ions made by change. the SWAP instrument at 11 and 12 AU. This paper is not about ISIS (http://isis.astrogeology.usgs.gov/index.html) is a special- Pluto. ized digital image processing software package designed by Croswell (2013) discusses the search for a post-Pluto encounter the United States Geological Survey for NASA. The software cen- target for New Horizons. This paper is not about Pluto. ters around placing spacecraft images of planetary bodies in the Parker et al. (2013) report the discovery of a Neptune Trojan as proper cartographic location for analysis, and ISIS is used to cre- part of the effort to find a target for New Horizons after the Pluto ate USGS map products. Currently in its third major version, encounter. This paper is not about Pluto. Keszthelyi et al. (2014) report that ISIS will be modified to ingest the New Horizons data products. The positions deter- Appendix D. Tools mined by ISIS depend on SPICE kernels (see the SPICE entry for a listing of which files use which system). SPICE kernels The Astronomical Almanac is published annually by the U.S. are added to images via the ‘‘spiceinit’’ function and each kernel Nautical Almanac Office, United States Naval Observatory used is listed in the text output for confirmation. Users should (USNO) in the United States and Her Majesty’s Nautical Alma- confirm the desired pole was assigned based on spiceinit’s out- nac Office (HMNAO), United Kingdom Hydrographic Office put kernel listing. (UKHO), in the United Kingdom. The Astronomical Almanac lists To customize the pck file used by the spiceinit command and the sub-Earth point and north pole angle for Pluto, and the override the default pck file, a user can simply include ‘pck=’ times of northern elongation for Charon, as well at the orbital and the file path to the desired pck file in the spiceinit composition of Charon at specified times. The Pluto longitudes mand statement. Similar override commands exist for other and latitudes followed the ecliptic north, increasing longitude types of kernels; read the USGS documentation for more details. convention until 2012. In 2013, the designation of the north In general, ISIS always choses the latest kernel file from the New pole was reversed to match the spin north convention, and lat- Horizons mission kernels, (isis3/data/newhorizons/kernels/pck/) itudes and north pole angle were adjusted. However, the longi- or, failing to find one, ISIS selects the latest file from the base tude remained the same – The Astronomical Almanac publishes kernel set (isis3/data/base/kernels/pck). Modifying these ker- planetographic (increasing) longitudes only (Hilton, personal nels or the files in the kernel folder is not recommended, as communication, 2012). an update to ISIS may overwrite or eliminate any changes made. GeoViz (http://soc.boulder.swri.edu/nhgv/ or http://soc.boul- JMars (http://jmars.asu.edu/) is a mission planning and analysis der.swri.edu/gv-dev/) is a online tool designed by Henry Throop tool designed by Arizona State University. Users may select a for spacecraft observation planning created specifically for the map of Pluto from the ‘‘Select Body’’ option in the ‘‘Body’’ file New Horizons mission, but with capabilities for other missions. menu. The Pluto map in the current version is from Buie et al. Users can choose from a list of planets, moons and spacecraft (2010b), and is displayed in the spin north, decreasing longitude and map out the orientations of a variety of targets, overlain system. with instrument FOVs. With Pluto, several maps are available, JPL Horizons (http://ssd.jpl.nasa.gov/horizons.cgi) is one of the including the maps from Grundy and Buie (2001), Stern et al. most well-known and user-friendly sources of ephemerides for (1997a) and several Pluto B and V I/F maps from Buie et al. Solar System bodies. The sub-observer as well as sub-solar (2010b). The maps include a grid with labelled longitudes and longitudes and latitudes are available as an output option, latitudes, and an ephemeris readout is given for the measure- calculated using the latest ephemerides. Ephemerides can be ment time. Because GeoViz is used by certain mission opera- printed out in html, or downloaded as plain text. Major system tions, there is an aversion to replacing the output before the updates can be found at (http://ssd.jpl.nasa.gov/?horizons_ completion of the New Horizons mission, and potentially intro- news). The IAU 1991–2003 pole was used until March 11, ducing bugs into mission operations that depend on GeoViz 2010, at which point it was replaced with the 2006 IAU pole. (Throop, personal communication, 2012). As a result, GeoViz This pole was in place until August 23, 2013 until it was has been split into two versions: a ‘stable’ version (http:// replaced by the IAU 2009 pole and its errata. See Table 1 for a soc.boulder.swri.edu/nhgv/) and a development version list of report values. (http://soc.boulder.swri. edu/gv-dev/). Approved changes in SPICE (http://naif.jpl.nasa.gov/naif/) is a space geometry infor- the development version will later be merged into the stable mation system. Toolkits are currently provided for IDL, MATLAB, version. F77 and C. Users compute observation circumstances from a A. Zangari / Icarus 246 (2015) 93–145 133

series of input kernels. The end user choice of kernel input Atreya, S.K., Niemann, H.B., Mahaffy, P.R., Owen, T.C., 2006. Origin and evolution of allows one to recreate both the most up-to-date ephemerides nitrogen on Titan, Enceladus, Triton, and Pluto. In: European Planetary Science Congress 2006, p. 86 (abstract). as well as circumstances for Solar System bodies as they were Aumann, H.H., Walker, R.G., 1987. IRAS observations of the Pluto–Charon system. known at previous points in (recent) history. The coordinates Astron. J. 94, 1088–1091. http://dx.doi.org/10.1086/114545. of Pluto are determined from the pole positions listed in the Bagenal, F., McNutt Jr., R.L., 1989a. Pluto’s interaction with the solar wind. Bull. Am. Astron. Soc. 21, 986 (abstract). plaintext, human-readable ‘‘pck’’ files. There are currently 5 Bagenal, F., McNutt Jr., R.L., 1989b. Pluto’s interaction with the solar wind. Geophys. pck files available. They all use the IAU conventions and con- Res. Lett. 16, 1229–1232. http://dx.doi.org/10.1029/GL016i011p01229. stants from Table 1, so Pluto coordinates evolve with the IAU. Bagenal, F., Stern, S.A., Farquar, R., 1990. Flyby missions to Pluto/Charon. Bull. Am. Astron. Soc. 22, 1129 (abstract). All files use the ecliptic north, increasing longitude system, Bagenal, F., Cravens, T.E., Luhmann, J.G., McNutt Jr., R.L., Cheng, A.F., 1997. Pluto’s except for the most recent file (pck00010.tpc) which has been Interaction with the Solar Wind. In: Stern, S.A., Tholen, D.J. (Eds.), Pluto and updated to reflect the updated IAU convention (spin north, Charon. University of Arizona Press, Tucson, pp. 523–556. Baier, G., Weigelt, G., 1987. Speckle interferometric observations of Pluto and decreasing longitude). its moon Charon on seven different nights. Astron. Astrophys. 174, 295– The following is a list of pck files and pole conventions used: 298. Baier, G., Hetterich, N., Weigelt, G., 1982. Digital speckle interferometry of Juno, Amphitrite and Pluto’s moon Charon. The Messenger 30, 23–26. pck file IAU report years Bailey, M.E., 1983. Is there a dense primordial cloud of comets just beyond Pluto?. In: pck00006.tpc 1991–2003 Lagerkvist, C.I., Rickman, H. (Eds.), Asteroids, Comets, and Meteors, p. 383–386 Bailey, S.M. et al., 1993. Theoretical models of Pluto’s UV spectrum. Bull. Am. Astron. pck00007.tpc 1991–2003 Soc. 25, 1131 (abstract). pck00008.tpc 1991–2003 Banks, T., Budding, E., 1990. Information limit optimisation techniques applied to pck00009.tpc 2006 recent photometry of Pluto. Earth Moon Planets 49, 15–23. http://dx.doi.org/ 10.1007/BF00053995. pck00010.tpc 2009 Barbieri, C., Benacchio, L., Capaccioli, M., Pinto, G., Schoenmaker, A.A., 1979. Accurate positions of the planet Pluto from 1974 to 1978. Astron. J. 84, 1890– 1893. http://dx.doi.org/10.1086/112620. Barbieri, C., Benacchio, L., Capaccioli, M., Gemmo, A.G., 1988. Accurate positions of the planet Pluto from 1979 to 1987. Astron. J. 96, 396–399. http://dx.doi.org/ 10.1086/114818. References Barbieri, C., Benacchio, L., Capaccioli, M., Gemmo, A.G., 1989. Studies of the planet Pluto at Asiago Observatory. Memorie della Società Astronomia Italiana 60, 79– Entries without an author can be found listed under ‘‘NA’’ (no author). 90. Barker, E.S., Cochran, W.D., Cochran, A.L., 1980. Spectrophotometry of Pluto from Abbott, J., 2005. The status of Pluto. J. British Astron. Assoc. 115, 295–296. 3500 to 7350 A. Icarus 44, 43–52. http://dx.doi.org/10.1016/0019- Abrahamian, H.V., Gigoian, K., Kisselev, A.A., Kisseleva, T.P., Shakht, N.A., 1993. 1035(80)90053-6. Positional photographic observations of Saturn, Uranus, Neptune, their Barker, E.S. et al., 1989. Near UV reflectivity of two hemispheres of the Pluto– satellites and Pluto in 1990 with the telescope ZTA-2.6 m at Byurakan in Charon system. Bull. Am. Astron. Soc. 21, 986 (abstract). Armenia. Astron. 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