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Five in the Signals, Two in the Habitable Zone WES KELLY, TRITON SYSTEMS, LLC

This January the American findings of this nature point to to be considered (e.g., Astronomical Society held its spacecraft missions for direct brown dwarfs) add into a wid- 221st meeting in Long Beach, imaging or atmospheric spec- er definition tally. CA. Comparable in size, at- tral analysis of extrasolar tendance or disciplinary scope planets. Which of the season’s or the to the AIAA Aerospace Sci- conference’s reports or dis- ences conferences held during For anyone tracking the annu- coveries is most significant? the same month elsewhere al AAS winter meetings, it is We hesitate to say with so (Dallas/Ft. Worth), interests clear that extrasolar much to examine. Yet in prel- of the two communities inter- sessions have increased re- ude to the 2013 conference, sect over satellite observato- markably over the last twenty the December 19th San Fran- ries launched into space re- ; from a few tentative cisco Chronicle reported, Above: Wes Kelly (at right) quiring close coordination papers to whole sessions “International , in an image from page 15 of between engineers and astron- (Table 1) on discoveries, de- including a leading planet the March and April 2012 omers. But what’s more, in- tection techniques, assessment hunter at UC Santa Cruz, say issue of Horizons (page 15). creasing concern in the astro- of atmospheres, size in com- they have detected five possi- At left is James C. McLane nomical community with de- parison to types ble planets circling a distant III. Image credit: Douglas tection and characterization of (“,” “,” much like Earth's - Yazell. “extrasolar” planets gives “Earths...”) types of stellar and that one of those planets form, character and specific primaries, formation process, is apparently in the famed targets for high aerospace habitability….(!) Planet con- ‘habitable zone’ where water aspirations: travel to planets firmations approach 1000 and could exist on its surface. The about other . At the least, thousands of objects too small (Continued on page 20)

Table 1. 221st American Astronomical Society Meeting Extrasolar Planet Sessions - January 2013

Session Title 104 Circumstellar Disks I 109 Extrasolar Planet Detection from and Micro-lensing 126 Interiors and Atmospheres 135 Scientific Opportunities for the James Webb Telescope 144 Circumstellar Disks 149 Extrasolar Planets: Detection 158 Stars, Cool Dwarfs, Brown Dwarfs

205 Circumstellar Disks II 220 Circumstellar Disks III 224 Exoplanet Atmospheres 231 Planets and Planetary Systems Identified by Kepler 236 Newton Lacy Pierce Prize: Hot on the Trail of Warm Planets Orbiting Cool M Dwarfs

308 Planetary Systems Orbiting White Dwarfs 315 Selection of Extra Solar Planets 324 Direct Detection of Exoplanets, Faint Companions and Protoplanetary Disks 333 Super Earths, M Dwarfs and Habitability 334 Survey and Catalogs of Extrasolar Planets 336 The Elemental Compositions of Extrasolar Planetesimals from Spectroscopy of Polluted White Dwarfs

343 Extra Solar Planet: Characterization, Theory and Detection 403 Dusty Debris in the Zone II (?) 407 Kepler Exoplanets 424 Planetary Systems Orbiting White Dwarfs and Neutron Stars 435 Extrasolar Planets

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(Continued from page 19) ia. The planet that is in the search software and technology. Exoplanets habitable zone is only five team led by Mikko Tuomi of times the of Earth, they As Figure 1 shows, Tau Ceti is a the University of Hertford- calculate.” Subsequent reports defining member of the constel- shire used a new technique to debate whether the discovery lation the Whale visible in find the planets around the consists of one habitable plan- the northern hemisphere. If the star Tau Ceti using telescopes et or two. can be discerned in Hawaii, Chile, and Austral- by an observer, then this specif- Detection methods for these ic nearby star can be pointed to planets were distinct from the as well as a possible to planets transit method employed by similar to the earth, worthy of the Kepler observatory, true; further study or exploration. but they are still based on Doppler meas- It is unavoidable to quote exten- urements, variations of ab- sively from the report of Tuomi sorption lines in the visual et al., posted on line at a Hert- spectrum of the primary star, fordshire University site. To like the original 1990s planet start, the authors provide the discoveries by pioneers defining parameters for Tau Mayor, Marcy and Butler. Ceti (Table 2) on which their What is different now is that observations are based. And in Bayesian statistical analyses conclusion they provide similar are being used, combining tables for five planets, the last spectrographic measurements two of which are of most imme- from several observatories: at diate concern due to their simi- Hawaii, Chile and Australia. larity to earth in thermal sur- If you have seen the term roundings, dimensions or mass Figure 1.  Ceti in the northern sky defining constellation. “rolling average” in a stock (Table 3). performance report, then there’s a big clue to what’s Beside parameters derived for new in extrasolar planet the five possible planets, Table 3 with its “sigma” measures give us an indication of the radi- al velocity sensitivities of the Table 2. Estimated Stellar Properties of Tau Ceti or HD 10700. three observatory instruments ------involved in the study: the Parameter Units Value Notes HIRES, AAPS and HARPS ------spectrographs located respec- Spectral Type G8.5 V tively at three separate observa- tories, the Keck (Hawaii), the log R′HK -4.995 Magnitude Anglo-Australian (Australia near Sydney) and the European π [milli-arcsecs] 273.96 ±0.17 measure (ESO) in Chile.

Lstar [L0 ] 0.488 ±0.010 HIRES is a grating echelle spec- trograph capable of operating Rstar [R0 ] 0.793 ±0.004 Stellar Radius between 0.3 and 1.0 microns (UV to IR) attached to the Keck Mstar [M0 ] 0.783 ±0.012 Observatory on Mauna Kea on

o the island of Hawaii. Teff [ ] 5344 ±50 The AAPS is the Anglo- [Fe/H] [vs. Solar] -0.55 ±0.05 Australian Planetary Search program undertaken with the Age [Giga-years] 5.8 Australian Astronomical Obser-

−1 vatory. The AAPS exploits the v sin i [kms ] 0.90 Stellar Radial Velocity - Nominal high stability of what was the University College of London P [days] 34 Stellar Rotational Period rot (Continued on page 21)

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Table-3 System Summary – Nominal Orbital Solution of HD 10700 Radial Velocities Exoplanets Tau Ceti b c d e f

Minimum Mass * (Earths) 2.0 3.1 3.6 4.3 6.6 Semi-Major Axis (AUs) .105 .195 .374 .552 1.35 Period (Days) 13.95 35.36 94.11 168.1 642 Eccentricity - 0.16 0.03 0.08 0.05 0.03  (radians) 1.5 3.0 4.0 5.5 3.9 t0 ** (days) 4.17 20.62 2.31 37.42 168.49 M0 (radians) 2.6 3.2 5.8 0.5 1.6 K (m/sec) 0.64 0.75 0.59 0.58 0.58

Instrument Sensitivities ) σJ,1 (HIRES) (m/sec 2.14 σJ,2 (AAPS) (m/sec) 2.13 σJ,3 (HARPS) (m/sec) 1.06

* MPL sin i (inclination to perpendicular to line of sight) ** - argument of periastron,t0 - time of periastron, M0 - Mean Anomaly,

(Continued from page 20) they were in isolating and model- can be said about this? Perhaps a ing the jitter effects surrounding simple situation comparison Echelle Spectrograph (UCLES) the planetary search process. Sift- helps. to obtain the few meter per ing through the three observatories second measurement precision cumulative measurements and I have two coins with heads and in radial (line-of-sight) veloci- comparing them, their statistical tails, and then also I have two ties of stars, i.e., the necessary processing did much to clear away keys: one to an office building minimum to detect the reflex the noise. If polluting sonic fre- and then one to my office with- stellar Doppler motion induced quencies can be erased by coun- in. The keys are each difficult to by the presence of a terrestrial tering noise 180 degrees out of distinguish from each other, es- mass planet. phase, then much the same can be pecially in the dark. But the done with light noise. In examin- point is that likelihood of calling The HARPS high accuracy ing the sources of noise, it was heads and tails with the two radial velocity planet searcher necessary as well to adjust the coins will have a different distri- is attached to the 3.6 meter filters with time for effects such as bution than the likelihood of European Space Observatory, natural stellar overtones on other selecting the second key to the located in the high deserts at La cycles. But when all of these office door. This is because there Silla, Chile. Since October of measures were taken, the re- are different underlying assump- 2012, it has built to a capability searchers were startled to find tions. Even if the wrong key is of detecting a 0.96 meter sec- remaining Keplerian motions that selected for the office building, ond variation in visible spectral had not been identified before. the likelihood of selecting the lines, perhaps currently the best right key for the second door is such instrument on earth or in Much of the argument in behalf of very high – unless one misplaces space. the detections is based on Bayesi- the keys all over again in the an statistics and “posterior distri- hallway dark. Rolling Averages bution” parameters. As others and Spectral Lines have observed, some of these Now what if the keys are not techniques have been used to sig- held in one’s right and left hand, As reported in an earlier Hori- nificant effect by mathematicians eliminating uncertainty about zons, radial velocity measure- and physicists working on Wall which key was first used? And ment detection of planets is Street, the tools of the trade for then what happens if the keys hindered by background noise “quants.” For a non-statistician, are dropped and the background from both instrumentation and such as this reporter, “a priori” light is adjusted down to a stellar targets. Tuomi and the sounds more familiar than proba- threshold where murk affects rest of the team, in targeting bility measures “posterior;” and things much the same as full Tau Ceti were not so much the qualifier “Bayesian” often darkness? The certainty about intent on discovering planets as leaves one with dread. So, what (Continued on page 22)

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(Continued from page 21) And now suppose we have a the rings were observed from Exoplanets hundred coins that we flip and a surface normal, then no nor- which key is correct for the a hundred embedded door and mal radial velocities could be second lock is altered accord- safe locks that generate heads obtained from their light. Yet ingly. or tails and yes or no deci- although the Tau Ceti planets sions respectively. The statis- and their orbital plane might tics of the hundred coins with be invisible, the stellar spec- each successive trial will gen- tral line shifts that they cause erate a distribution of results can be observed even if the that will spread symmetrically line of sight to the star is par- about a 50-50 distribution of allel to the plane. In that case, heads and tails. But the replay with each orbit there would be of the lock and key distribu- two points at which non- tion will alter from these sta- radial velocities would be tistics as knowledge assump- reduced to zero with each tions about the successive circular orbit. Using the con- lock and key operations are vention of “inclination” changed, as Figure 2 suggests. adopted by astronomers for Now suppose that beside a studying binary stars, zero sequence of doors and safes to inclination is observation of lock in dim light, one is also the system perpendicular to wearing night goggles sensi- its plane. Hence, inclination tive to light within certain of 90 degrees would be obser- wavelengths and the system vation “edge on.” If this can experiences jitter… be demonstrated by transit events (such as observed with The point here is that the Kepler observatory), then Figure 2. Altered distribution of results based on knowledge knowledge about seemingly there is no uncertainty in mass of keys vs. coins. random processes surround- due to inclination uncertainty ing stars and instrumentation and mass is well pinned is not entirely without clues to down. their nature – and that these processes can be modeled But if inclination is unknown enough to clear away much and a mass is derived from fog. the apparent Doppler shifts of the star due to radial velocity Yet what is striking about the variations, actual planetary reported result is that if the mass would vary as a function values of K in Table 3 are M = M0/cos(i), where i is an considered as velocity magni- inclination between 0 and 90o. tudes for the planet induced For “line of sight offsets” of cyclic motions of Tau Ceti, all 45 to 60o, the mass increases the values are well below the by 40 and 100%, of course, as nominal sensitivities of the Figure 4 indicates. Conse- three instrument detection quently, if a nearly earth like systems. Curious about planet has a density much like Bayesian statistics and Mar- Earth’s (~5 gm/cm3), then we kov chains now? could also derive changes in diameter with mass as well as Planets as a differences in . Function of Inclination – , Earth and And Then Density have similar densities; but yet the Moon and have den- Paradoxically, the best angle sities closer to 3/5 that of to get a reading on the orbital these terrestrial planets. Do velocities of ’s rings is we know whether these plan- Figure 3.  Ceti system of planets derived from radial veloci- when they are hardly visible ets would have either density? ty measurements showing that between planets “e” and “f” at all – when they are ob- No, not yet, but we can show there exists a large gap. served on edge. Then again, if (Continued on page 23)

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(Continued from page 22) inhabitable, but comparative starting with the Earth-Sun interstellar planetology requires relationship, the 700,000 km Exoplanets the effect of reduced density examining many stellar and radius sun with a 5800o Kel- on radius and surface gravi- planetary characteristics to vin surface temperature (TEFF) ty (Figs. 5 and 6). Reasons mount a case for habitability would diffuse to a tempera- for reduced density might elsewhere – and the data is not ture of about 400 o K at include less relative to necessarily all there. To start Earth’s orbital radius of 1 AU silicon – or more water con- with, thermal flux from Tau Ceti (149.95 million km). densation in formation. But or another star must be calibrat- depending on the surface ed with the sun before consider- 0.5 o , greenhouse effects ing how that thermal flux is ab- T(RPL) =(RPL/RSURF) TEFF = 396.7 K and location within the pre- sorbed or reflected back into sumed habitable zone, low space by a planet we will even- density could solve the high tually have to describe as well. Since Mars (R=1.52) and Ve- gravity problem in the event Considering that total flux from nus (R=.67 AU) might pro- of human visitation, but a stellar spherical surface re- vide rough bounds for habita- there would remain an issue mains constant between its sur- bility if their surface and at- 2 of whether the resulting face radius (4  RSURF ) and the mospheric reflectances were planets would resemble orbital radius of the planet, then tuned rather well to sustain or Venus more we know that effective tempera- near room temperature (300o than the Earth with thick tures in space decrease with dis- K) conditions in the temperate blankets of atmosphere tance. That is, luminosity is con- zones, as with the Earth, then merging into bottomless stant. control volume temperatures seas. at those regions would be rough bounds for the solar 2 4 2 4 Habitability L* = 4  RSURF TEFF =  4 RPL T(RPL) system’s habitability belt. The cooler, smaller and therefore Of course, we assume for Allowing for some round-off or less luminous (0.488) Tau starters that the Earth is measurement uncertainties, and (Continued on page 24)

Figure 4. Tau Ceti planets b through f – mass as a function of inclination from line of sight.

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(Continued from page 23) um temperatures of a thick tacular in comparison to Exoplanets cloud cover or other elaborate events in our system’s Ceti produces the same tem- heat transport mechanisms, plane. perature at a radius of about the planetary surface reflec- 0.698 AU. The “Venus-Mars” tance (inverse: albedo) would Wrap Up bounds can be redrawn for give us an estimate of how Tau Ceti accordingly as 0.48 much of that stellar flux is Just last August this writer and 1.06 AU the limits of radiated back into space. had the occasion to see the habitability. Greenhouse effects near the Discovery Channel video outer limit would be more Alien Planet which described So, do we have any possibil- supportive for the case of a visit to a nearby extrasolar ity of winners? The planets habitability there. planet by a future robotic “e” and “f” are located at or- spacecraft. Many of the fea- bital distances (semimajor Then there might still be an as tures of the story seemed to axes) of 0.552 and 1.35 re- yet undetected planet between suggest they were describing spectively (illustrated in Fig. “e” and “f” with a mass more Tau Ceti, or a similar nearby 3). By the rules described so near that of Earth’s. Our cal- star. far, “e” would qualify as a culations of spheres of influ- habitable planet and “f” at ence with increase of plane- I believe the destination star first glance would be consid- tary mass do not rule this out. was fictional. But had the ered more hostile than Mars. Examining spacing (.105, writers and contributing sci- And yet the prospects in our .195, .374, .552, 1.35 AUs), entists known! own solar system for present mass (2.6, 3.0, 5.8, 4.3, 6.6) “habitability” for Mars and period (13.95, 35.36, References and Figure 6 are far greater than that of 94.11, 168.12, 642 days), Venus, though perhaps bil- there is no obvious reason lions of years back, water and there should not be a planet or earth-like temperatures or two between detected “e” and (Continued on page 25) atmospheric pressures might “f.” And habitable or not, once have prevailed on both. observing the other planets from that point in the mid Ignoring the layered equilibri- habitable zone would be spec-

Figure 5. Tau Ceti planets surface radii assuming Earth density & inclination effect.

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(Continued from page 24) Exoplanets

References and Links

http://www.centauri-dreams.org/?p=25935#comments

http://star-www.herts.ac.uk/~hraj/tauceti/paper.pdf

http://aas.org Abstracts for the 221st meeting are no longer available on line, but this sight provides information about coming astronomical conferences and astronomical news.

Figure 6.  Ceti planets “e” and “f”: surface radii & gravity for nominal & “3/5” densities mass calculations for 0 o, 30o and 45o inclinations of orbital plane to line of sight.

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