UNIVERSITY of HAWAII at MANOA Institute for Astrononmy Pan-STARRS Project Management System

Pan-STARRS Document Control PSDC-xxx-xxx-00

UNIVERSITY OF HAWAII AT MANOA Institute for Astrononmy Pan-STARRS Project Management System

Appearance of and response to interesting and rare objects discovered by MOPS

Richard J. Wainscoat Pan-STARRS Solar System Group Institute for Astronomy October 28, 2006

c Institute for Astronomy 2680 Woodlawn Drive, Honolulu, Hawaii 96822 An Equal Opportunity/Afﬁrmative Action Institution Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00

Revision History

Revision Number Release Date Description 00 2006.10.20 First draft

Interesting and rare objects—deﬁnition and followup ii October 28, 2006 Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00

TBD / TBR Listing

Section No. Page No. TBD/R No. Description

Interesting and rare objects—deﬁnition and followup iii October 28, 2006 Contents

1 Overview 1

2 Referenced Documents 1

3 Facilities available for followup observations 1

4 Fuzzy objects—comets or outgassing asteroids 2 4.1 Introduction ...... 2 4.2 Signature ...... 2 4.3 Response ...... 2 4.4 Followup ...... 2 4.5 Naming of Comets discovered by Pan-STARRS ...... 3

5 Objects with high inclination, retrograde, or highly eccentric orbits 3 5.1 Introduction ...... 3 5.2 Signature ...... 3 5.3 Response ...... 4 5.4 Followup ...... 4 5.5 Dead comets ...... 4

6 Distant objects 4 6.1 Introduction ...... 4 6.2 Signature ...... 4 6.2.1 Scattered KBOs ...... 4 6.2.2 Distant planets ...... 4 6.2.3 Very nearby stars ...... 5 6.2.4 Additional efforts to detect very distant objects ...... 5 6.3 Response ...... 5 6.4 Followup ...... 6 6.5 Ambiguity between very nearby stars and very distant planets ...... 6

7 Trojan asteroids 6 7.1 Introduction ...... 6 7.2 Signature ...... 6 7.2.1 Trojans of Jupiter, Saturn, Uranus and Neptune ...... 6 7.2.2 Trojans of Mars ...... 7 7.2.3 Trojans of Earth ...... 7 7.3 Response ...... 7 7.4 Followup ...... 7

8 Objects not in heliocentric orbits—Interstellar comets 7 8.1 Introduction ...... 7 8.2 Signature ...... 8 8.3 Response ...... 8 8.4 Followup ...... 8

9 Objects not in heliocentric orbits—Planetary Satellites 8

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9.1 Introduction ...... 8 9.2 Signature ...... 8 9.3 Response ...... 9 9.4 Followup ...... 9

10 Asteroid Collisions 9 10.1 Introduction ...... 9 10.2 Signature ...... 10 10.3 Response ...... 10 10.4 Followup ...... 10

11 Near Earth Objects 10 11.1 Introduction ...... 10 11.2 Signature ...... 10 11.3 Response ...... 10 11.3.1 Potentially Hazardous Objects ...... 10 11.3.2 Death Plunge Objects ...... 11 11.4 Followup ...... 11

12 Objects with strange light curve variations or strange colors 11 12.1 Introduction ...... 11 12.2 Signature ...... 12 12.3 Response ...... 12 12.4 Followup ...... 12

13 Widely separated KBOs seen as binaries 12 13.1 Introduction ...... 12 13.2 Signature ...... 12 13.3 Response ...... 12 13.4 Followup ...... 12

14 Summary 13

Interesting and rare objects—deﬁnition and followup v October 28, 2006 List of Figures

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1 Overview

MOPS will find millions of objects in the Solar System. A small percentage of these objects (which will still be a large number of objects) will be of particular scientific or public interest. For the most interesting objects, very careful verification is needed before widespread or public release.

The predicted 5σ sensitivities to point sources in the Pan-STARRS 1 (PS1) opposition survey are gAB = 23.24, rAB = 22.70, iAB = 22.59, zAB = 21.59, and yAB = 20.12 (see PSDC-230-002-04 for more details). The sensitivities in the gri passbands are well matched for typical solar system colors. Sensitivities in the z and y passbands are significantly poorer for objects with typical solar system colors. Predicted 5σ sensitivities to an NEO moving at 0.5 deg/day are gAB = 23.06, rAB = 22.62, iAB = 22.48. Sensitivities in the sweet spot regions will be lower due to increased sky brightness (the sky is approximately a factor 2 brighter at 2 airmasses than at the zenith), poorer seeing (about 50% worse), and higher extinction (color dependent loss of 5–15% per airmass). MOPS will detect objects with motions as small as 0.1 arcsec in 10 days for objects detected at a signal-to-noise ratio of 5. Variations in seeing may limit detections of very slow motions. The maximum rate of motion that MOPS can detect will be limited by the Air Force streak removal, currently expected to be approximately 10 degrees per day. This document identifies many of the more interesting and rare objects that Pan-STARRS will (or may) discover. For some of these objects, immediate or rapid followup will be necessary. The document also discusses those cases for which rapid release of object discovery is necessary or desirable. In many cases, extensive precovery efforts will also be warranted, including searches of the 3σ database of transients when warranted. The precovery observations will be extremely valuable in refining orbits.

2 Referenced Documents

PSDC-230-002-04 Mission Concept Statement for PS1 PSDC-002-014-00 Death Plunge Objects

3 Facilities available for followup observations

The University of Hawaii has access to all telescopes on Mauna Kea. These are the twin Keck telescopes, the Subaru and Gemini telescopes, the United Kingdom Infrared Telescope (3.8-meters), the Canada-France-Hawaii 3.6-meter telescope, the NASA Infrared Telescope Facility (3.0 meters), the UH 2.2-meter telescope, the UH 0.6-meter telescope (soon to be replaced by a 0.9-meter telescope), the Submillimeter Array (SMA), the James Clerk Maxwell Telescope, and the Caltech Submillimeter Observatory. The Smithsonian Astrophysical Observatory (SAO) has access to the MMT, the Magellan telescopes, and the SMA, as well as its own 1.2-m and 1.5-m telescopes. Some followup observations will be passed on to collaborating institutions, including Spacewatch, Magdalena Ridge Observatory (MRO), and Las Cumbres Observatory (LCO).

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4 Fuzzy objects—comets or outgassing asteroids

4.1 Introduction

Any moving objects discovered by MOPS that have a non-stellar PSF are expected to be comets or outgassing asteroids. Any non-stellar moving object should first be checked against an up to date database of known comets with reliable orbits, and also checked for possible matches with previously discovered, and subsequently lost comets. The discovery rate for comets will be small enough that each discovery should be carefully checked by hand. In particular, because the area being surveyed is so large, there is a possibility for an asteroid be located on top of a galaxy (or bright star) on the first observation, then located on top of a different galaxy (or bright star) on a subsequent observation. Imperfect subtraction of the static sky in such cases potentially could lead to a false identification of a comet. Until the static sky subtraction is better understood from real data, careful checking of rare discoveries seems warranted. Ghost images resulting from the Pan-STARRS optics or from reflections inside the camera are also possible. It is possible that some of these may manifest themselves as comet-like objects. It will be important to properly understand these during the commissioning period.

4.2 Signature

Moving object with a non-stellar point spread function.

4.3 Response

It is expected that Pan-STARRS will provide discovery and confirmation of new comets with the confirmation observations occurring automatically (but in a different filter) a few nights after the discovery observations. Within the same lunation, the survey strategy (see PSDC-230-002-04), will normally provide observations in the g, r, and i filters to similar depths. These observations will be centered on new moon. Subsequent observations in the z filter during gray time will be slightly less deep, but in many cases will provide additional confirmation and will be useful to refine the orbit. For brighter objects, observations taken through the y filter in bright time will likewise be useful. In general comets discovered by Pan-STARRS will be reported quickly to the Central Bureau for Astronomical Telegrams (CBAT), to claim discovery rights. As part of the discovery and reporting process, preliminary estimates of likely brightness of the comet seen from Earth will be made. For any comets discovered that will become bright comets seen from the Earth (e.g., C/1995 O1 Hale-Bopp, C/1996 B2 Hyakutake), a major press release is warranted, which should be issued only after careful review. This press release should be issued by Pan-STARRS.

4.4 Followup

In many cases, it is expected that comet discoveries will be made sufﬁciently far in advance of close passage to Earth or perihelion that requests for observing time through the normal telescope time allocation process are appropriate. Since Pan-STARRS is likely to discover comets fainter than many of the present searches, they will be discovered earlier, and therefore with more lead time.

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For important comets discovered with insufﬁcient lead time for the normal telescope time allocation process, alternate methods of access to observing time must be developed. For the Mauna Kea telescopes, only the Gemini Northern 8- meter telescope has a formal Director’s Discretionary Time process. Some of the other telescopes have a small amount of discretionary time (e.g., CFHT), but this is commonly earmarked for special purposes (e.g., observing time for staff). The University of Hawaii could reserve a part of its own observing time on the classically scheduled Mauna Kea telescopes for allocation within the semester, on shorter lead times. For the queue operated telescopes, such as JCMT and SMA, it would be possible, at the Institute for Astronomy’s Director’s discretion, to insert a new program into the queue part way through the semester. Finally, some observations could presumably be taken in other people’s observing time, but this would rely on goodwill. Overriding of existing classically scheduled nights is unlikely to be a popular approach. In the past, the Subaru Director has shown willingness to make additional nights available to UH on very short notice for important discoveries. The understanding has been that this time will be paid back in future semesters. This is another avenue for access to large telescopes on short notice. Many of the more interesting observations of comets discovered by Pan-STARRS are likely to be done with the submillimeter telescopes on Mauna Kea (JCMT, CSO, and SMA). Optical and infrared observations will also be performed, including spectroscopy in the ultra-violet region above 310 nm with UV sensitive spectrographs such as HIRES and LRIS.

4.5 Naming of Comets discovered by Pan-STARRS

Comet discoveries are announced by the CBAT on behalf of the International Astronomical Union (IAU). The IAU ap- proved guidelines for naming comets are available at http://www.ss.astro.umd.edu/IAU/csbn/cnames.shtml. Comets automatically discovered by the Pan-STARRS solar system team using MOPS would be expected to get names such as C/2007 T1 (Pan-STARRS). Comets discovered from Pan-STARRS data mainly from the work of one or two individuals, rather than the team, would take the last name of the discoverer(s) (e.g., C/2008 F3 (Lastname)). Pan-STARRS can be expected to discover a substantial fraction of new comets, but will certainly not discover all. Its survey strategy will focus on the opposition regions, and the sweet spot regions; it will miss comets that appear outside of these regions and comets that ﬁrst become apparent in the southern sky south of −30◦. Because it will become the dominant discoverer of comets, there is a danger of Pan-STARRS breaking the current naming scheme for comets. Although the IAU naming scheme gives a unique name to comets, they are usually referred to by the discoverer’s name (e.g., Shoemaker, Pan-STARRS). There will be many ”Comet Pan-STARRS.” Although good publicity for the project, public confusion seems likely.

5 Objects with high inclination, retrograde, or highly eccentric orbits

5.1 Introduction

Although high-inclination, retrograde and highly eccentric orbits are common for comets, they are unusual for non- cometary objects, such as main-belt asteroids, Centaurs, and KBOs. Objects detected with high-inclination or retrograde or highly eccentric orbits are interesting because it is important to understand how these objects attained such orbits.

5.2 Signature

Objects with high inclination, high eccentricity, or retrograde orbits that are not known comets.

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5.3 Response

Discovery of such objects will generate an automatic alert. Discoveries will be passed on to partner institutions and/or collaborating institutions.

5.4 Followup

Additional astrometry will help reﬁne orbits. Targeted photometric observations with 2-meter class telescopes will reveal color and rotational information. Larger telescopes will be required for spectroscopic observations.

5.5 Dead comets

A possible class of high-inclination objects might be dead (inactive) cometary nuclei. Such objects may have very low albedos, with their dark surfaces allowing them to escape detection. Their sizes will be typical of cometary nuclei (or smaller) making them very faint unless they are close to us. They may be quite numerous, and may represent a poorly understood risk as potentially hazardous objects. The Pan-STARRS 1 survey should help to quantify how common these objects are, and what risk they represent. Followup mid-infrared photometry, with instruments such as Michelle on Gemini, will allow the albedo and size of such objects to be calculated.

6 Distant objects

6.1 Introduction

Distant objects with orbits outside the classical Kuiper Belt region (about 30 to 50 AU, low inclination), or with large aphelion distance, are rare. The number of known scattered disk objects (typically with perihelion q≈35 AU, and higher inclination and eccentricity) is still small and PS1 will dramatically increase the known population.

6.2 Signature

6.2.1 Scattered KBOs

Scattered KBOs are Kuiper Belt Objects with higher inclination orbits typically with perihelion greater than 35 AU.

6.2.2 Distant planets

Any object detected at a large distance that is relatively bright must be carefully evaluated as a possible planet. Any such discovery would be one of the most important to come from PS1, and the subject of a major press release; it is one of the “holy grails” of contemporary planetary astronomy. The media frenzy over the recent deﬁnition of a planet by the IAU hints at the interest such a discovery would attract. An object with semi-major axis of 100 AU will have a period of 1,000 years; an object with a semi-major axis of 900 AU will have a period of 27,000 years. For the object at 100 AU, the motion of the object due to the Earth’s orbit around the

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Sun will be 0.37 arcsec in 30 minutes, which is expected to be the typical spacing between pairs of exposures. This is detectable for brighter objects, but for the case of the more distant 900 AU object, it will be 0.04 arcsec in 30 minutes, which is unlikely to be detectable. During an observation spacing of 4 nights, the 100 AU object will move by about 72 arcsec, and the 900 AU object will move by about 8 arcsec. The signature of such distant objects will therefore be very slow or undetected motion on a single night, and slow, but easily detected motion over the space of a few nights. These may therefore manifest themselves as non-moving transients (which may look like supernovae) on a single night that move signiﬁcantly by the time of the next observation. A distant planet, if it exists, might be expected to orbit the Sun close to the ecliptic plane, where it would be expected to have formed. However, subsequent close encounters by our Solar System with other stars may well have disturbed such an object from the ecliptic, so searches for distant planets should not be restricted to close to the ecliptic.

6.2.3 Very nearby stars

MOPS will also detect very nearby stars through their proper motion. The star with the highest proper motion is Barnard’s star, at a distance of 1.8 pc, and with a proper motion of 10.3 arcsec/year; it is the second closest star system to the Sun (and the fourth closest star, after the three stars in the Alpha Centauri system). There are two types of stars that could be faint enough to have escaped detection despite being very close to us—cool brown dwarfs and cool white dwarfs. Cool white dwarfs may have high proper motions if they are halo members (and thus have high velocities compared to disk stars). Stars with proper motions similar to or greater than Barnard’s star will show up as slow moving transients which MOPS will attempt to link. We expect that with the planned observing strategy, MOPS will be efﬁcient in detecting proper motions of about 1 pixel (0.3 arcsec) per week, or about 15 arcsec/year.

6.2.4 Additional efforts to detect very distant objects

Detection of very faint moving objects is so important that additional efforts are warranted. Much of the automated processing done by MOPS will be based on 5σ detections. The 3σ database of non-moving transients (most of which will be either noise or supernova) will be searched for possible linkages, to try to ﬁnd any possible distant objects that are lurking just below the normal threshold for MOPS.

6.3 Response

Discovery of any such objects should generate an alert to all team members. Any discovery of this class will be one of the most important made by the project; it warrants immediate attention by as many team members as possible. Strict conﬁdentiality is essential. Careful but rapid publication of such discoveries is advisable, since some details seem likely to leak out through the pro- cesses required to acquire the observing time on the 8–10 meter class telescopes that will be needed for the spectroscopy. Any such discovery will warrant a major press release, and is likely to create an immediate media frenzy. We need to be well prepared to fully capitalize on the interest that it creates.

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6.4 Followup

Immediate strong followup of any discovery of a distant planet or nearby star is essential. Access to 8–10-meter class telescopes will be essential for spectroscopic followup. Infrared photometry from 2–4-meter class telescopes will provide strong clues to the nature of the object that has been discovered, and should be followed by infrared spectroscopy which will show absorption bands from gases such as methane (expected to be present in a very dim star, but might be frozen out in a very cold planet). Laser Guide Star adaptive optics (LGSAO) is an excellent tool for obtaining infrared spectroscopy of faint objects, because a very narrow slit or an Integral Field Unit (IFU) can be used to increase the signal-to-noise ratio by reducing the background from the sky. LGSAO is also a powerful tool to check for possible binarity. The process by which UH astronomers can access the Mauna Kea telescopes on short notice is detailed in the section on comets above.

6.5 Ambiguity between very nearby stars and very distant planets

In the event that a very slow moving object is discovered, it may be initially difﬁcult to distinguish whether the object is a very nearby very dim star, or a very distant planet. It is likely that several month’s of astrometry will be needed to distinguish between the two cases. Spectroscopy in the optical and near-inrared (if practical) should be immediately acquired for any such objects. Although formally we do not know what the spectrum of a very cool brown dwarf, or a Neptune sized planet at 1000 AU might look like, since no such objects are known, some modeling of cool brown dwarfs has been done which could be compared to the spectrum acquired. Mid-IR observations will also be useful.

7 Trojan asteroids

7.1 Introduction

Pan-STARRS will survey regions of the sky that should lead to discovery of Trojan asteroids for the planets from Earth out to Neptune. Pan-STARRS will not look close enough to the Sun to detect any possible Trojan asteroids of Venus.

7.2 Signature

7.2.1 Trojans of Jupiter, Saturn, Uranus and Neptune

Pan-STARRS should discover all of the Trojan asteroids of Jupiter, Saturn, Uranus and Neptune down to its limiting magnitude. These will appear as objects with similar orbits to the giant planets, but lagging or leading them by approximately 60 degrees in their orbits. There are some limitations, however, for the slower moving outer planets Uranus and Neptune. Uranus will be located near 23.3h RA and Neptune near 21.6h RA at the start of the Pan-STARRS 1 survey. This means that for both of these planets, one of their Trojan clouds will be located close to where the ecliptic crosses the Galactic plane (near 18h, −23◦), which is close to the Galactic center and a region of extremely high star density. This will be an extremely challenging

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7.2.2 Trojans of Mars

There are not any known Mars Trojans. If there are any down to the Pan-STARRS limiting magnitude, the normal observing strategy should reveal them as objects with similar orbits to Mars, but lagging or leading Mars by approximately 60 degrees. It may be difﬁcult to distinguish Mars Trojans from inner main-belt asteroids, and require a longer baseline of observations to reﬁne the orbit.

7.2.3 Trojans of Earth

There are no known Earth Trojans. The proposed sweet spot observing strategy, which will search at solar elongations between 60 and 90 degrees, will sample about half of the area where such objects would be located, and will miss objects at lower solar elongation than 60 degrees. Earth Trojans would appear as objects with similar orbits to the Earth, but leading or trailing by 60 degrees.

7.3 Response

Trojans of Jupiter are relatively common, and should generate an appropriate alert to interested parties. Trojan satellites of Neptune are rare. There are no known Trojan satellites of the other planets, so any discovery would be important and likely warrant a press release. Discovery of an Earth Trojan would warrant a major press release. If the survey does detect Earth Trojans, it may be warranted to extend the survey to slightly lower solar elongation (which perhaps could be does as a campaign during a few months when lower solar elongations can be optimally observed) to obtain a more complete census of such objects.

7.4 Followup

Followup observations of new Trojan satellites of Jupiter would yield improved orbits, and photometry would yield colors; 2-meter class telescopes are appropriate. Followup observations of new Trojan satellites of the other planets are more important. Because press releases are likely, conﬁrming observations from other telescopes and partners are important, including colors, and low-resolution optical spectroscopy (2–4-meter telescopes) and infrared spectroscopy (8–10-meter telescopes) to examine the composition of the surface.

8 Objects not in heliocentric orbits—Interstellar comets

8.1 Introduction

When our solar system formed, the giant planets should have ejected many comet-like planetesimals from our Solar System. Similarly, when other stars formed, if those stellar systems contained Jupiter-like planets, comets should have

Interesting and rare objects—deﬁnition and followup 7 October 28, 2006 Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00 been ejected from those stellar systems also. If one of those comes close enough to our Solar System and Sun, it will become an interstellar comet. No interstellar comet has yet been discovered. Pan-STARRS will discover either zero or one interstellar comet.

8.2 Signature

It would appear as an object not in orbit around the Sun (in a hyperbolic orbit), perhaps initially as a point source, then developing a coma/non-stellar appearance if it approaches close enough to the Sun.

8.3 Response

Because of its rarity and importance, many telescopes throughout the Earth will study it. It is reasonable to obtain some early observations to conﬁrm the nature of such a discovery, but then the discovery should be publicly released so that telescopes across the Earth can study such an important object. A major press release is warranted because of the importance and rarity of such a discovery.

8.4 Followup

Isotopic measurements will form an important component of the observations, and the submillimeter telescopes on Mauna Kea will play a major role in these observations. These measurements will be key to determining whether this is indeed an object that formed around a different star than the Sun.

9 Objects not in heliocentric orbits—Planetary Satellites

9.1 Introduction

Most of the satellites of JSUN should have already been discovered down to the Pan-STARRS detection limits. Pan- STARRS will, however, provide a multitude of observations to improve the orbits of these satellites. There are only two known satellites of Mars. There have been some unsuccessful attempts to search for additional (smaller) satellites. One of the problems with searching for satellites of Mars is that their motions on the sky will be similar to asteroids in the inner main-belt. A long series of observations, such as will be obtained by Pan-STARRS will be ideal for separating possible satellites from the huge number of asteroids in the background. Discovery of any object in orbit around the Earth will be extremely important. Pan-STARRS will not observe at low enough solar elongation to search for satellites of Venus or Mercury.

9.2 Signature

The planetary satellites will have orbits that initially appear to be very similar to the parent planet, but over time diverge from a heliocentric orbit solution as the satellite orbits around its parent planet. Any Earth satellite discovered by PS1 will have rapid motion, particularly when it is close to the Earth. Their motion may be rapid enough to be removed by the Air Force. Initial orbit solution using heliocentric models will fail, so geocentric

Interesting and rare objects—definition and followup 8 October 28, 2006 Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00 solutions should be attempted. Any objects with rapid motions/long streaks are expected to be very nearby, and warrant careful scrutiny by an astronomer. Trojans of the Earth-Moon system would have orbits similar to the Moon, but lagging or leading by 60 degrees. It is unclear whether the streaks left by such nearby objects (about 16 arcsec in a 30 second exposure) will be available to astronomers. The rapid motion will smear the object’s light over many pixels, and will significantly reduce the sensitivity to such objects (even though they are close). Any such objects will be in specific areas of the sky (lagging/leading the Moon); observations of such areas will tend to avoid the g and r passbands in particular, because these observations will be taken when the moon is set. Careful searches could be conducted looking for streaks of this size in appropriate i and z band data. Given the rapid motion of such objects, a directed search tracking at the predicted motion rate for such objects may be more successful.

9.3 Response

Discovery of any possible planetary satellites by MOPS should trigger an immediate alert to all team members for immediate followup. Discovery of any new planetary satellite by Pan-STARRS warrants a press release. For JSUN, the discovery would be somewhat surprising, since extensive searches of the Hill sphere have already been made. Discovery of new satellites of Mars and the Earth would warrant a major press release because of the importance of these discoveries.

9.4 Followup

In many cases, followup astrometric observations will be needed to constrain orbits and provide the further conﬁrmation needed before issuing a press release. These observations could come from a 2-meter class telescope. PS1 will provide some followup observations automatically, but more rapid response and faster cadence is needed for important discoveries such as these. Spectroscopy of the satellites will provide information about their composition. This does not need to be done instantly for JSUN satellites, but would be particularly urgent for any Earth satellite discovered. For objects in orbit around the Earth, observations tracked at the object’s rate of motion may prove very useful for photometry and rotation studies. The orbital stability of any object orbiting the Earth will need to be studied so that the likelihood of possible lunar or Earth impact in the future can be understood. One such object is J002E3 which is now believed to be the third stage of the Apollo 12 mission. Anther similar object has been discovered by Tholen who believes that it could be a piece of the Moon ejected by an impact.

10 Asteroid Collisions

10.1 Introduction

Asteroid collisions could occur in the main belt, Trojan clouds, or in the Kuiper belt. The frequency of such collisions will help us to better understand the numbers of very small objects in these regions—because they are likely the most numerous, they are also the most likely to be involved in collisions.

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10.2 Signature

The signature of such a collision will be a sudden bright source that appears, and moves in a heliocentric orbit characteristic of the parent population. Over time the resultant cloud of dust would expand, causing the transient to slowly soften in shape from a point source to a diffuse object, but not necessarily become fainter in integrated brightness. As the cloud expands, its surface brightness would become fainter and fainter, meaning that it would eventually become undetectable by Pan-STARRS. The time evolution of the resultant dust cloud will reveal information about the dust velocity and the collision circumstances. If the collision is with a known or detectable asteroid, then instead, its brightness will be seen to suddenly increase, then slowly fade, with the dust diffusing away from the impacted asteroid.

10.3 Response

Detection of an asteroid collision should trigger an alert to all observatories interested in and capable of followup. A 2-meter class telescope is appropriate to followup such a collision.

10.4 Followup

Followup of such collision signatures would be needed on other telescopes because the cadence of Pan-STARRS observations is unlikely to be fast enough to properly watch the evolution of the collision signature. The three deep visits to each field in a lunation will be in separate filters (gri), meaning that color effects may make interpretation more difficult. Targeted observations every few nights with a separate telescope (e.g., UH 2.2-meter) would be appropriate to study the remnants of these collisions.

11 Near Earth Objects

11.1 Introduction

Near Earth Objects will be discovered in the evening and morning sweet spot surveys as well as the opposition survey. The objects discovered will be broadly classiﬁed into two categories—those that are Potentially Hazardous, and those that are not.

11.2 Signature

Objects that are discovered that have orbits that cross the Earth’s orbit—i.e., perihelion < 1 AU, and aphelion > 1 AU.

11.3 Response

11.3.1 Potentially Hazardous Objects

A minimum orbital intersection distance of < 0.05 AU can be used to identify objects that warrant special treatment. For these objects, we need to alert the astronomers who are expert in calculating impacts. There need to be extra efforts

Interesting and rare objects—deﬁnition and followup 10 October 28, 2006 Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00 to obtain astrometry. The UH 2.2-meter telescope has been a very productive tool for obtaining astrometry because it has excellent seeing and simple optics (and thus minimal and well-understood distortions). External efforts to obtain astrometry of PHOs are also essential. For any objects for which an impact seems likely, it is essential that external review is done before public release of information (unless there is insufﬁcient time). It is important for the credibility of the NEO program of Pan-STARRS that we do not “cry wolf.”

11.3.2 Death Plunge Objects

Small objects that are likely to collide with the Earth during the project lifetime have been considered in a separate document—PSDC-002-014-00. The observing strategy for PS1 is not ideal for detection of these objects, because the diurnal parallax from a pair of observations separated by about 30 minutes will make linking difficult. In the event that such an object is detected, and provided that there is reasonable certainty that an impact is imminent, government authorities should be notified. Opening a dialog with the Pacific Tsunami Warning Center ahead of PS1 operations is advisable. The Pacific Tsunami Warning Center may be the ideal conduit for such a warning, since they already have developed the appropriate communications channels, and are a respected source for this type of disaster prediction.

11.4 Followup

Initially, additional astrometry is the most important followup observation needed for Potentially Hazardous Objects. Low-resolution spectroscopy, spanning optical to near-infrared wavelengths will be useful to characterize the population of Near-Earth Objects. 2–4-meter class telescopes will be appropriate for these objects when they are close to the Earth, but larger telescopes will be needed for infrared spectroscopy and when the objects are faint. It is worth noting that of the 8–10-meter telescopes on Mauna Kea, the two Keck telescopes handle objects moving at non-sidereal rates far better than Subaru or Gemini. Gemini is able to handle infrared observations reasonably well (but less efﬁciently than Keck), but is unable to track fast-moving objects with its optical imager/spectrograph.

12 Objects with strange light curve variations or strange colors

12.1 Introduction

Objects with strange light curve variations may include asteroids with highly elongated shapes, with their rotation causing large variations in brightness from when they are seen end-on compared to face-on. Such objects are of interest because their shape gives clues about their formation and strength. Objects with strange colors are of special interest, because these colors suggest special surface compositions that are uncommon. A noteworthy case where strange colors are be expected will be the potentially very distant objects (planets or nearby stars) discussed earlier.

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12.2 Signature

Because of the nature of the opposition survey, in which fields will be visited on separate nights in each of the filters, it may be initially difficult to distinguish between objects that have strange light curve variations and objects that have strange colors. Light curve variations of 1 magnitude or greater may warrant further study. Objects with colors that are at least 5σ different from typical solar system object colors may warrant followup.

12.3 Response

We will create an alert for objects detected that have strange light curve variations or strange colors. It likely will require data from several months to be able to distinguish whether an object has anomalous colors or variable brightness.

12.4 Followup

Followup will depend on whether the object has strange light curve variations or strange colors. For objects with strange light curve variations, acquisition of a more frequently sampled light curve will be needed for interpretation. For objects with strange colors, spectroscopy in the optical (2–4-meter telescopes) and infrared (8–10-meter telescopes) will be needed to understand the nature of the object. The urgency of such observations will depend on what the object is suspected to be.

13 Widely separated KBOs seen as binaries

13.1 Introduction

There may be some widely separated KBOs that are binaries. These are important objects because they allow mass and density estimates to be made.

13.2 Signature

The signature of binary KBOs will be a pair of objects for which linkages of tracks deliver orbits for adjacent KBOs that are very similar. Over time, rotation of the binary around a common center of mass should be seen.

13.3 Response

Detection of suspected binary KBOs should generate an alert to all interested parties.

13.4 Followup

Followup on 2-meter class telescopes will help follow the rotation of the binary objects around each other to properly constrain the orbit. For widely separated binaries, PS1 may provide sufﬁcient cadence to follow the orbit. Targeted observations will be needed to obtain colors.

Interesting and rare objects—deﬁnition and followup 12 October 28, 2006 Pan-STARRS Moving Object Processing System PSDC-xxx-xxx-00

14 Summary

The table below brieﬂy summarizes the interesting and rare objects described in detail above, and the responses required.

Object Signature Response time Followup Press Release Comet non-stellar moving objects hours/days Optical/IR/Submm yes Unusual orbit high inclination/high eccentricity days/weeks Optical no Distant planets very slow motion days/weeks/months Optical/IR yes Very nearby stars very slow motion weeks/months Optical/IR yes Trojan asteroids 60◦ from planet weeks Optical yes except Jupiter Interstellar comet hyperbolic orbit days Optical/IR/Submm yes Planetary satellites orbit planet days/weeks Optical yes for new Asteroid collisions sudden brightening days Optical yes Near Earth Objects passes close to Earth days Optical sometimes Death Plunge Objects will hit Earth hours Optical yes Unusual object strange light curve/color days/weeks Optical no KBO binaries pair of similar orbits days/weeks Optical no

Table 1: Summary of interesting and rare objects that may be found by Pan-STARRS.

Interesting and rare objects—deﬁnition and followup 13 October 28, 2006