Distant EKOs, Issue #88  (August 2013)


News & Announcements
Abstracts of 8 Accepted Papers
Abstracts of 1 Thesis
Newsletter Information


Names of the two most recently-discovered satellites of Pluto were announced in IAU Electronic Telegram #3575 based on approval from the IAU's Working Group for Planetary System Nomenclature and the Working Group on Small-Body Nomenclature:
$\bullet$ Kerberos = Pluto IV = S/2011 (134340) 1
$\bullet$ Styx = Pluto V = S/2012 (134340) 1

CBET 3575: http://www.cbat.eps.harvard.edu/iau/cbet/003500/CBET003575.txt

Dear Distant EKOs Readers,

With the support and encouragement of Dr. James L. Green, Director of Planetary Science, NASA Headquarters, we are making a call for observations in support of the New Horizons mission.

We make this request because:
The July 2015 New Horizons encounter with Pluto presents a once-in-a-lifetime opportunity to directly link our Earth-based view of Pluto with `ground truth' provided by in situ measurements.

To support the New Horizons encounter, our Campaign Goal is straightforward:
Establish an extensive Earth-based measurement context for the state of the Pluto system at the time of the flyby, including evolving trends in the system for at least one year prior- and post-flyby.

While near-simultaneous measurements at the highest possible resolution near the time of the July 14, 2015 flyby most directly complement New Horizons' measurements, there is a longer-term temporal context that must be addressed. A long record of observations shows Pluto to be a changing world, likely due to the insolation it receives decreasing by $\sim$2% per year on account of its eccentric orbit now carrying it rapidly away from perihelion. What's more, the obliquity of Pluto also causes a change of sub-solar latitude by more than 1 degree per year, bringing 105 km2 of new surface area into sunlight for the first time in a century (while casting an equal and opposite polar area into arctic winter). These orbit-related effects on the atmosphere and surface of Pluto are on top of the well-known longitudinal variations measurable over the course Pluto's 6.387 day rotation.

A chart showing the New Horizons Earth-Based Campaign's Phases and a brief outline of priorities for a wide range of critically needed measurements is show below and is available on the "Campaign Objectives" tab on the website at http://www.boulder.swri.edu/nh-support-obs/ . (click to embiggen)

We invite you to participate in this campaign. Please register your interest by sending an email to: nhobs "at" boulder.swri.edu In addition, informal workshops (information sessions) are being planned during the European Planetary Science Conference (EPSC)London 8-13 September and during the Division for Planetary Sciences Meeting (DPS) Denver 6-11 October.

For more information, please visit the Earth-Based Campaign website:

With thanks for your support and consideration,
Richard P. Binzel (Professor of Planetary Science (MIT), New Horizons Lead, Earth-Based Campaign)
S. Alan Stern (New Horizons Principal Investigator)
nhobs "at" boulder.swri.edu

There were no new TNO discoveries announced since the previous issue of Distant EKOs and 1 new Centaur/SDO discoveries:

2013 PH44

Objects recently assigned numbers:

2002 PQ145 = (363330)
2003 LB7 = (363401)
2006 JZ81 = (364171)

Objects recently assigned names:

2009 QV38 = Rhiphonos

Re-identified objects:

1996 TC68 = 2003 UY413
2002 JR146 = 2010 HE79

Deleted objects:

2004 PR107
2005 VD

Current number of TNOs: 1258 (including Pluto)
Current number of Centaurs/SDOs: 376
Current number of Neptune Trojans: 9

Out of a total of 1643 objects:
   649 have measurements from only one opposition
     634 of those have had no measurements for more than a year
       323 of those have arcs shorter than 10 days
(for more details, see: http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)


The Size, Shape, Albedo, Density, and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations
F. Braga-Ribas 1,2, B. Sicardy2,3, J.L. Ortiz 4, E. Lellouch 2, G. Tancredi5, J. Lecacheux2, R. Vieira-Martins1,6,7, J.I.B. Camargo1, M. Assafin7, R. Behrend8, F. Vachier6, F. Colas6, N. Morales4, A. Maury9, M. Emilio10, A. Amorim11, E. Unda-Sanzana12, S. Roland5, S. Bruzzone5, L. A. Almeida13, C. V. Rodrigues13, C. Jacques14, R. Gil-Hutton15, L. Vanzi16, A. C. Milone13, W. Schoenell11,4, R. Salvo5, L. Almenares5, E. Jehin17, J. Manfroid17, S. Sposetti18, P. Tanga19, A. Klotz20, E. Frappa21, P. Cacella22, J.P. Colque12, C. Neves10, E. M. Alvarez23, M. Gillon17, E. Pimentel14, B. Giacchini14, F. Roques2, T. Widemann2, V. S. Magalhães13, A. Thirouin4, R. Duffard4, R. Leiva16, I. Toledo24, J. Capeche5, W. Beisker25, J. Pollock26, C. E. Cedeño Montaña13, K. Ivarsen27, D. Reichart27, J. Haislip27, and A. Lacluyze27

1 Observatório Nacional, Rio de Janeiro, Brazil
2 Observatoire de Paris, LESIA, Meudon, France
3 Université Pierre et Marie Curie, Paris, France
4 Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain
5 Observatorio Astronomico Los Molinos, Uruguay
6 Observatoire de Paris, IMCCE, Paris, France
7 Observatório do Valongo / UFRJ, Rio de Janeiro, Brazil
8 Observatoire de Genève, Switzerland
9 San Pedro de Atacama Celestial Explorations, San Pedro de Atacama, Chile
10 Universidade Estadual de Ponta Grossa, Ponta Grossa, Brazil
11 Universidade Federal de Santa Catarina, Florianópolis, Brazil
12 Unidad de Astronomía, Universidad de Antofagasta, Antofagasta, Chile
13 Instituto Nacional de Pesquisas Espaciais, DAS, São José dos Campos, Brazil
14 Centro de Estudos Astronômicos de Minas Gerais (CEAMIG), Belo Horizonte, Brazil
15 Complejo Astronómico El Leoncito & San Juan National University, Argentina
16 Dept. of Electrical Engineering and Center of Astro-Engineering, Pontificia U. Católica de Chile, Santiago, Chile
17 Institut d'Astrophysique de l'Université de Liége, Belgium
18 Gnosca Observatory, Switzerland
19 Laboratoire Lagrange, Université de Sophia Antipolis, Observatoire de la Côte d'Azur, CNRS UMS7293
20 Université de Toulouse, UPS-OMP, IRAP, France
21 Euraster, 1B cours J. Bouchard, St-Etienne, France
22 Rede de Astronomia Observacional, Brasilia, Brazil
23 Observatorio Los Algarrobos, Salto, Uruguay
24 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
25 International Occultation Timing Association - European Section, Munich, Germany
26 Department of Physics and Astronomy, Appalachian State Univ., Boone, NC 28608, USA
27 Physics and Astronomy Department, University of North Carolina, Chapel Hill, USA

We present results derived from the first multi-chord stellar occultations by the transneptunian object (50000) Quaoar, observed on 4 May 2011 and 17 February 2012, and from a single-chord occultation observed on 15 October 2012. If the timing of the five chords obtained in 2011 were correct, then Quaoar would possess topographic features (crater or mountain) that would be too large for a body of this mass. An alternative model consists in applying time shifts to some chords, to account for possible timing errors. Satisfactory elliptical fits to the chords are then possible, yielding an equivalent radius $R_{\rm
equiv}=555 \pm 2.5$ km and geometric visual albedo $p_V= 0.109 \pm
0.007$. Assuming that Quaoar is a Maclaurin spheroid with indeterminate polar aspect angle, we derive a true oblateness of $\epsilon=
0.087^{+0.0268}_{-0.0175}$, an equatorial radius of 569+24-17 km and a density of $1.99 \pm 0.46$ g cm-3. The orientation of our preferred solution in the plane of the sky implies that Quaoar's satellite Weywot cannot have an equatorial orbit. Finally, we detect no global atmosphere around Quaoar, considering a pressure upper limit of about 20 nbar for a pure methane atmosphere.

Published in: The Astrophysical Journal, 773, 26 (2013 August 10)

For preprints, contact ribas@on.br
or on the web at

Limits on Quaoar's Atmosphere
Wesley C. Fraser1, Chad Trujillo2, Andrew W. Stephens2, German Gimeno3, Michael E. Brown4, Stephen Gwyn1, and JJ Kavelaars1

1 Herzberg Institute of Astrophysics, 5071 W. Saanich Rd. Victoria, BC V9E 2E7 Canada
2 Gemini Observatory, Northern Operations Center, 670 N A'ohoku Place, Hilo, HI 96720 USA
3 Gemini Observatory, Southern Operations Center, c/o AURA, Casilla 603, La Serena, Chile
4 California Institute of Technology, Division of Geological and Planetary Sciences, 1200 E. California Blvd., Pasadena, CA. 91101 USA

Here we present high cadence photometry taken by the Acquisition Camera on Gemini South, of a close passage by the $\sim$540 km radius Kuiper Belt Object, (50000) Quaoar, of a r'=20.2 background star. Observations before and after the event show that the apparent impact parameter of the event was $0.019\pm0.004$", corresponding to a close approach of $580\pm120$ km to the centre of Quaoar. No signatures of occultation by either Quaoar's limb or its potential atmosphere are detectable in the relative photometry of Quaoar and the target star, which were unresolved during closest approach. From this photometry we are able to put constraints on any potential atmosphere Quaoar might have. Using a Markov chain Monte Carlo and likelihood approach, we place pressure upper limits on sublimation supported, isothermal atmospheres of pure N2, CO, and CH4. For N2 and CO, the upper limit surface pressures are 1 and 0.7 $\mu$bar respectively. The surface temperature required for such low sublimation pressures is $\sim$33 K, much lower than Quaoar's mean temperature of $\sim$44 K measured by others. We conclude that Quaoar cannot have an isothermal N2 or CO atmosphere. We cannot eliminate the possibility of a CH4 atmosphere, but place upper surface pressure and mean temperature limits of $\sim$138 nbar and $\sim$44 K respectively.

To appear in: The Astrophysical Journal Letters

For preprints, contact wesley.fraser@nrc.ca
or on the web at http://arxiv.org/abs/1308.2230

The TAOS Project: Results From Seven Years of Survey Data
Z.-W. Zhang1, M. J. Lehner1,2,3, J.-H. Wang1, C.-Y. Wen1, S.-Y. Wang1, S.-K. King1, Á. P. Granados4, C. Alcock3, T. Axelrod5, F. B. Bianco6, Y.-I. Byun7, W. P. Chen8, N. K. Coehlo9, K. H. Cook1, I. de Pater10, D.-W. Kim11, T. Lee1, J. J. Lissauer12, S. L. Marshall13, P. Protopapas14,3, J. A. Rice9, and M. E. Schwamb15,16

1 Institute of Astronomy and Astrophysics, Academia Sinica. 11F of Astronomy-Mathematics Building, National Taiwan University. No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan
2 Department of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
3 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
4 Instituto de Astronomía, Universidad Nacional Autónoma de México, Apdo. Postal 106, Ensenada, Baja California, 22800 México
5 Steward Observatory, 933 North Cherry Avenue, Room N204 Tucson AZ 85721, USA
6 New York University, Center for Cosmology and Particle Physics, 4 Washington Place, New York, NY 10003, USA
7 Department of Astronomy and University Observatory, Yonsei University, 134 Shinchon, Seoul 120-749, Korea
8 Institute of Astronomy, National Central University, No. 300, Jhongda Rd, Jhongli City, Taoyuan County 320, Taiwan
9 Department of Statistics, University of California Berkeley, 367 Evans Hall, Berkeley, CA 94720, USA
10 Department of Astronomy, University of California Berkeley, 601 Campbell Hall, Berkeley CA 94720, USA
11 Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany
12 Space Science and Astrobiology Division 245-3, NASA Ames Research Center, Moffett Field, CA, 94035, USA
13 Kavli Institute for Particle Astrophysics and Cosmology, 2575 Sand Hill Road, MS 29, Menlo Park, CA 94025, USA
14 Initiative in Innovative Computing, Harvard University, 60 Oxford St, Cambridge, MA 02138, USA
15 Department of Physics, Yale University, New Haven, CT 06511, USA
16 Yale Center for Astronomy and Astrophysics, Yale University, P.O. Box 208121, New Haven, CT 06520, USA

The Taiwanese-American Occultation Survey (TAOS) aims to detect serendipitous occultations of stars by small ($\sim$1 km diameter) objects in the Kuiper Belt and beyond. Such events are very rare (<10-3 events per star per year) and short in duration ($\sim$200 ms), so many stars must be monitored at a high readout cadence. TAOS monitors typically $\sim$500 stars simultaneously at a 5 Hz readout cadence with four telescopes located at Lulin Observatory in central Taiwan. In this paper, we report the results of the search for small Kuiper Belt Objects (KBOs) in seven years of data. No occultation events were found, resulting in a 95% c.l. upper limit on the slope of the faint end of the KBO size distribution of q = 3.34 to 3.82, depending on the surface density at the break in the size distribution at a diameter of about 90 km.

Published in: The Astronomical Journal, 146, 14 (2013 July)

Preprints available on the web at http://arxiv.org/abs/1301.6182

Kuiper Belt Occultation Predictions
Wesley C. Fraser1, Stephen Gwyn1, Chad Trujillo2, Andrew W. Stephens2, JJ Kavelaars1, Michael E. Brown3, Federica B. Bianco4, Richard P. Boyle5, Melissa J. Brucker6, Nathan Hetherington7, Michael Joner8, William C. Keel9, Phil P. Langill10, Tim Lister11, Russet J. McMillan12, and Leslie Young13

1 Herzberg Institute of Astrophysics, 5071 W. Saanich Rd. Victoria, BCV9E 2E7, Canada
2 Gemini Observatory, Northern Operations Center, 670 N A'ohoku Place, Hilo, HI 96720, USA
3 California Institute of Technology, Division of Geological and Planetary Sciences, 1200 E. California Blvd., Pasadena, CA. 91101 USA
4 Center for Cosmology and Particle Physics, Department of Physics, New York University, 4 Washington Place, New York, NY 10003, USA
5 Vatican Observatory Research Group, Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
6 University of Nebraska - Lincoln, Dept. of Physics & Astronomy, Jorgensen Hall, Rm 208, 855 N 16th Street, Lincoln, NE 68588-0299, USA
7 Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H4, Canada
8 Department of Physics and Astronomy, N283 ESC, Brigham Young University, Provo, UT 84602-4360, USA
9 University of Alabama, Tuscaloosa, AL 35487-0324, USA
10 Rothney Astrophysical Observatory, University of Calgary, Calgary AB Canada, T2N 1N4
11 Las Cumbres Observatory Global Telescope Network (LCOGT), 6740 Cortona Drive Suite 102 Goleta, CA 93117, USA
12 Apache Point Observatory, PO Box 59, Sunspot, NM 88349, USA
13 Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA

Here we present observations of 7 large Kuiper Belt Objects. From these observations, we extract a point source catalog with $\sim$0.01" precision, and astrometry of our target Kuiper Belt Objects with 0.04-0.08" precision within that catalog. We have developed a new technique to predict the future occurrence of stellar occultations by Kuiper Belt Objects. The technique makes use of a maximum likelihood approach which determines the best-fit adjustment to cataloged orbital elements of an object. Using simulations of a theoretical object, we discuss the merits and weaknesses of this technique compared to the commonly adopted ephemeris offset approach. We demonstrate that both methods suffer from separate weaknesses, and thus, together provide a fair assessment of the true uncertainty in a particular prediction. We present occultation predictions made by both methods for the 7 tracked objects, with dates as late as 2015. Finally, we discuss observations of three separate close passages of Quaoar to field stars, which reveal the accuracy of the element adjustment approach, and which also demonstrate the necessity of considering the uncertainty in stellar position when assessing potential occultations.

Published in: Publications of the Astronomical Society of the Pacific, 125, 1000

(2013 August)

For preprints, contact wesley.fraser@nrc.ca
or on the web at http://arxiv.org/abs/1306.6626
and http://www.jstor.org/stable/10.1086/672001

TNOs are Cool! : A Survey of the Trans-Neptunian Region.
IX. Thermal Properties of Kuiper Belt Objects and Centaurs from Combined Herschel and Spitzer Observations
E. Lellouch1, P. Santos-Sanz1,2, P. Lacerda3, M. Mommert4, R. Duffard2, J.L. Ortiz2, T.G. Müller5, S. Fornasier1, J. Stansberry6, Cs. Kiss7, E. Vilenius5, M. Mueller8, N. Peixinho9,10, R. Moreno1, O. Groussin11, A. Delsanti1,11, and A.W. Harris4

1 LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 6, Univ. Paris-Diderot, 5 Place J. Janssen, 92195 Meudon Cedex, France
2 Instituto de Astrofísica de Andalucía (CSIC), Glorieta de la Astronomía s/n, Granada, Spain.
3 Queen's University, University Rd, Belfast BT7 1NN, United Kingdom
4 Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institute of Planetary Research, Rutherfordstrasse 2, 12489 Berlin, Germany
5 Max-Planck-Institut für extraterrestrische Physik (MPE), Postfach 1312, Giessenbachstr., 85741 Garching, Germany
6 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore MD 21218, USA
7 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences, Konkoly Thege 15-17, H-1121 Budapest, Hungary
8 SRON, Postbus 800, 9700 AV Groningen, The Netherlands
9 Center for Astrophysics of the University of Coimbra, Geophysical and Astronomical Observatory, Almas de Freire, 3040-004 Coimbra, Portugal
10 Unidad de Astronomía de la Universidad de Antofagasta, Avda. Angamos 601, Antofagasta 1270300, Chile
11Aix-Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France

The goal of this work is to characterize the ensemble thermal properties of the Centaurs / trans-Neptunian population.

Thermal flux measurements obtained with Herschel/PACS and Spitzer/MIPS provide size, albedo, and beaming factors for 85 objects (13 of which are presented here for the first time) by means of standard radiometric techniques. The measured beaming factors are influenced by the combination of surface roughness and thermal inertia effects. They are interpreted within a thermophysical model to constrain, in a statistical sense, the thermal inertia in the population and to study its dependence on several parameters. We use in particular a Monte-Carlo modeling approach to the data whereby synthetic datasets of beaming factors are created using random distributions of spin orientation and surface roughness.

Beaming factors $\eta$ range from values <1 to $\sim$2.5, but high $\eta$ values (>2) are lacking at low heliocentric distances (rh < 30 AU). Beaming factors lower than 1 occur frequently (39% of the objects), indicating that surface roughness effects are important. We determine a mean thermal inertia for Centaurs/TNO of $\Gamma =
(2.5 \pm 0.5)$ J m-2 s-1/2 K-1, with evidence of a trend toward decreasing $\Gamma$ with increasing heliocentric (by a factor $\sim$2.5 from 8-25 AU to 41-53 AU). These thermal inertias are 2-3 orders of magnitude lower than expected for compact ices, and generally lower than on Saturn's satellites or in the Pluto/Charon system. Most high-albedo objects are found to have unusually low thermal inertias. Our results suggest highly porous surfaces, in which the heat transfer is affected by radiative conductivity within pores and increases with depth in the sub-surface.

To appear in: Astronomy and Astrophysics

For preprints, contact emmanuel.lellouch@obspm.fr

On a Possible Size/Color Relationship in the Kuiper Belt
R.E. Pike1,2 and J.J. Kavelaars2,1

1 Department of Physics and Astronomy, University of Victoria, Victoria, BC, V8W 3P6l, Canada
2 National Research Council of Canada, 5071 West Saanich Road, Victoria, BC, V9E 2E7, Canada

Color measurements and albedo distributions introduce non-intuitive observational biases in size-color relationships among Kuiper Belt Objects (KBOs) that cannot be disentangled without a well characterized sample population with systematic photometry. Peixinho et al. report that the form of the KBO color distribution varies with absolute magnitude, H. However, Tegler et al. find that KBO color distributions are a property of object classification. We construct synthetic models of observed KBO colors based on two B-R color distribution scenarios: color distribution dependent on H magnitude (H-Model) and color distribution based on object classification (Class-Model). These synthetic B-R color distributions were modified to account for observational flux biases. We compare our synthetic B-R distributions to the observed `Hot' and `Cold' detected objects from the Canada-France Ecliptic Plane Survey and the Meudon Multicolor Survey. For both surveys, the Hot population color distribution rejects the H-Model, but is well described by the Class-Model. The Cold objects reject the H-Model, but the Class-Model (while not statistically rejected) also does not provide a compelling match for data. Although we formally reject models where the structure of the color distribution is a strong function of H magnitude, we also do not find that a simple dependence of color distribution on orbit classification is sufficient to describe the color distribution of classical KBOs.

To appear in: The Astronomical Journal

Preprints are on the web at http://arxiv.org/abs/1308.0014

A Portrait of the Extreme Solar System Object 2012 DR30
Cs. Kiss1, Gy. Szabó1,2,3, J. Horner4, B.C. Conn5, Th.G. Müller6, E. Vilenius6, K. Sárneczky1,2, L.L. Kiss1,2,7, M. Bannister8, D. Bayliss8, A. Pál1,9, S. Góbi1, E. Verebélyi1, E. Lellouch10, P. Santos-Sanz11, J.L. Ortiz11, R. Duffard11, and N. Morales11

1 Konkoly Observatory, MTA CSFK, H-1121 Budapest, Konkoly Th.M. út 15-17., Hungary
2 ELTE Gothard-Lendület Research Group, H-9700 Szombathely, Szent Imre herceg út 112, Hungary
3 Dept. of Exp. Physics & Astronomical Observatory, University of Szeged, H-6720 Szeged, Hungary
4 Department of Astrophysics, School of Physics, University of New South Wales, Sydney, NSW 2052, Australia
5 Max-Planck-Institut für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
6 Max-Planck-Institut für extraterrestrische Physik, Giessenbachstrasse, 85748 Garching, Germany
7 Sydney Institute for Astronomy, School of Physics, A28, The University of Sydney, NSW 2006, Australia
8 Research School of Astronomy and Astrophysics, the Australian National University, ACT 2612, Australia
9 Department of Astronomy, Loránd Eötvös University, Pázmány Péter sétány 1/A, H-1119 Budapest, Hungary
10 Observatoire de Paris, Laboratoire d'Études Spatiales et d'Instrumentation en Astrophysique (LESIA), 5 Place Jules Janssen, 92195 Meudon Cedex, France
11 Instituto de Astrofísica de Andalucía (IAA-CSIC) Glorieta de la Astronomía, s/n 18008 Granada, Spain

2012 DR30 is a recently discovered Solar System object on a unique orbit, with a high eccentricity of 0.9867, a perihelion distance of 14.54 AU and a semi-major axis of 1109 AU, in this respect outscoring the vast majority of trans-Neptunian objects. We performed Herschel/PACS and optical photometry to uncover the size and albedo of 2012 DR30, together with its thermal and surface properties. The body is 185 km in diameter and has a relatively low V-band geometric albedo of $\sim$8%. Although the colours of the object indicate that 2012 DR30 is an RI taxonomy class TNO or Centaur, we detected an absorption feature in the Z-band that is uncommon among these bodies. A dynamical analysis of the target's orbit shows that 2012 DR30 moves on a relatively unstable orbit and was most likely only recently placed on its current orbit from the most distant and still highly unexplored regions of the Solar System. If categorised on dynamical grounds 2012 DR30 is the largest Damocloid and/or high inclination Centaur observed so far.

Published in: Astronomy and Astrophysics, 555, A3 (2013 July)

For preprints, contact pkisscs@konkoly.hu
or on the web at http://arxiv.org/abs/1304.7112

Perspectives on Effectively Constraining the Location of a Massive Trans-Plutonian Object with the New Horizons Spacecraft: A Sensitivity Analysis
L. Iorio1

1 Ministry of Education, University and Research (M.I.U.R.), Viale Unità di Italia 68, 70125, Bari (BA), Italy

The radio tracking apparatus of the New Horizons spacecraft, currently traveling to the Pluto system where its arrival is scheduled for July 2015, should be able to reach an accuracy of 10 m (range) and 0.1 mm/s (range-rate) over distances up to 50 au. This should allow to effectively constrain the location of a putative trans-Plutonian massive object, dubbed Planet X (PX) hereafter, whose existence has recently been postulated for a variety of reasons connected with, e.g., the architecture of the Kuiper belt and the cometary flux from the Oort cloud. Traditional scenarios involve a rock- ice planetoid with $m_X \approx 0.7 m_\oplus$ at some 100-200 au, or a Jovian body with $m_X {\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$<$}}}5~m_J$ at about 10,000-20,000 au; as a result of our preliminary sensitivity analysis, they should be detectable by New Horizons since they would impact its range at a km level or so over a time span 6 years long. Conversely, range residuals statistically compatible with zero having an amplitude of 10 m would imply that PX, if it exists, could not be located at less than about 4,500 au ( $m_X = 0.7~m_\oplus$) or 60,000 au (mX = 5 mJ), thus making a direct detection quite demanding with the present-day technologies. As a consequence, it would be appropriate to rename such a remote body as Thelisto. Also fundamental physics would benefit from this analysis since certain subtle effects predicted by MOND for the deep Newtonian regions of our Solar System are just equivalent to those of a distant pointlike mass.

Published in: Celestial Mechanics and Dynamical Astronomy, 116, 357 (2013 August)

For preprints, contact lorenzo.iorio@libero.it
or online at http://arxiv.org/abs/1301.3831


Study of Trans-Neptunian Objects using Photometric Techniques and Numerical Simulations
Audrey Thirouin1

1 Instituto de Astrofísica de Andalucía - CSIC, Apt 3004, 18008 Granada, Spain

More than 1,400 Trans-Neptunian Objects (TNOs) have been detected since the discovery of 1992 QB1 (Jewitt and Luu 1992). The Trans-Neptunian belt is the largest and relatively stable reservoir of small bodies in the Solar System. Due to their distances from the Sun, the TNOs are considered the least evolved bodies of the Solar System and therefore, their studies provide us with information about the composition and properties of the primitive solar nebula. The study of these bodies provide us clues about the origin and the evolution of the early Solar System. In addition, the Trans-Neptunian belt provides a natural connection to the study of the protoplanetary disks observed around some stars.

The main objective of this thesis was to determine and analyze, for a large sample of objects, the ranges of variability, their rotational periods, as well as other physical parameters that can be derived from short-term variability. The aim was to derive physical parameters such as axis ratios, phase coefficients, albedos, density, porosity, etc., for a good sample of TNOs and centaurs because only few studies were published prior to this thesis. Short-term variability studies allow us to determine the rotational, dynamical and physical evolution of these objects. But a lot of observing time is required to provide reliable short-term variability studies. In addition, it is thought that large objects are less collisionally evolved, so they probably retain the distribution of the primitive angular momentum of the early stages of the Solar System (Davis and Farinella 1997).

At the beginning of this PhD, the sample of objects with measured rotational periods and lightcurve amplitudes was very limited. Only $\sim$50 objects with short-term variability were reported and many published rotational periods were uncertain or erroneous. In addition, Sheppard et al. (2008) noticed an observational bias towards large amplitudes and short rotational periods. Increasing the sample size, improving rotational periods, lightcurves, and trying to overcome some observational biases were some of the objectives of this study. On the other hand, binary objects required a special treatment, with the objective to derive relevant physical parameters, some of them from the tidal effects in such systems.

Another motivation to carry out photometry observations was the support to the Herschel Space Observatory (HSO) key project "TNOs are cool!". HSO is a mission of the European Space Agency (ESA) and of the National Aeronautics and Space Administration (NASA). "TNOs are cool!" is a key-project of HSO dedicated to the observations of thermal emission from 130 TNOs and centaurs in $\sim$400 h of observing time (Müller et al. 2009). This key project was the largest key-project of HSO and required a large international effort with more than 40 team members. For the analysis and interpretation of the thermal data from HSO, thermal models or thermophysical models (Müller et al. 2009, Vilenius et al. 2012, Mommert et al. 2012) are required. To derive diameters and albedos, all these models require input parameters such as absolute magnitudes and spin periods or constraints on them, all of which require ground based photometry.

As a result of early findings during the project, a new model from a numerical point of view to explain the formation of the Haumea system is developed. By extension, this model is also able to explain the formation of some binary/multiple systems, and even the formation of unbound pairs of TNOs that was not considered as a possibility in the Trans-Neptunian belt. Haumea is a large object with very peculiar characteristics. Several models have been proposed by different authors to explain the formation of this object and its "family" as well as the peculiar characteristics of Haumea, but all of them have some inconsistencies.

Dissertation directed by A. Campo-Bagatin and J. Ortiz-Moreno.
Ph.D. awarded July 9, 2013 from the University of Granada, Spain.

For preprints, contact A. Thirouin thirouin@iaa.es

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