Distant EKOs, Issue #65  (July 2009)


News & Announcements
Abstracts of 16 Accepted Papers
Abstracts of 1 Thesis
Newsletter Information


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

Deleted/Re-identified objects:

2003 UW292 = 2005 UN524

Current number of TNOs: 1093 (including Pluto)
Current number of Centaurs/SDOs: 243
Current number of Neptune Trojans: 6

Out of a total of 1342 objects:
   548 have measurements from only one opposition
     538 of those have had no measurements for more than a year
       288 of those have arcs shorter than 10 days
(for more details, see: http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)


Herschel Open Time Key Programme:
TNOs are Cool: A Survey of the Transneptunian Region
Thomas G. Müller1, Emmanuel Lellouch2, Hermann Böhnhardt3, John Stansberry4, Antonella Barucci2, Jacques Crovisier2, Audrey Delsanti2, Alain Doressoundiram2, Elisabetta Dotto5, René Duffard6, Sonia Fornasier2, Olivier Groussin7, Pedro J. Gutiérrez6, Olivier Hainaut8, Alan W. Harris9, Paul Hartogh3, Daniel Hestroffer10, Jonathan Horner11, Dave Jewitt12, Mark Kidger13, Csaba Kiss14, Pedro Lacerda15, Luisa Lara6, Tanya Lim16, Michael Mueller4, Raphael Moreno2, Jose-Luis Ortiz6, Silvia Protopapa3, Miriam Rengel3, Pablo Santos-Sanz6, Bruce Swinyard16, Nicolas Thomas17, Audrey Thirouin6, and David Trilling18

1MPE Garching, Germany; 2Observatoire de Paris-Meudon, France; 3MPS Katlenburg-Lindau, Germany; 4University of Arizona, USA; 5Osservatorio Astronomico di Roma, Italy; 6IAA-CSIC Granada, Spain; 7Laboratoire d'Astrophysique de Marseille, France; 8ESO, Chile; 9DLR Berlin, Germany; 10Observatoire de Paris, France; 11Open University, Milton Keynes, UK; 12UCLA, USA; 13ESAC, Villafranca del Castillo, Spain; 14Konkoly Observatory, Hungary; 15Queen's University Belfast, Ireland; 16RAL Didcot, UK; 17University of Bern, Switzerland; 18University Northern Arizona, USA

Over one thousand objects have so far been discovered orbiting beyond Neptune. These trans-Neptunian objects (TNOs) represent the primitive remnants of the planetesimal disk from which the planets formed and are perhaps analogous to the unseen dust parent-bodies in debris disks observed around other main-sequence stars. The dynamical and physical properties of these bodies provide unique and important constraints on formation and evolution models of the Solar System. While the dynamical architecture in this region (also known as the Kuiper Belt) is becoming relatively clear, the physical properties of the objects are still largely unexplored. In particular, fundamental parameters such as size, albedo, density and thermal properties are difficult to measure. Measurements of thermal emission, which peaks at far-IR wavelengths, offer the best means available to determine the physical properties. While Spitzer has provided some results, notably revealing a large albedo diversity in this population, the increased sensitivity of Herschel and its superior wavelength coverage should permit profound advances in the field.

Within our accepted project we propose to perform radiometric measurements of 139 objects, including 25 known multiple systems. When combined with measurements of the dust population beyond Neptune (e.g. from the New Horizons mission to Pluto), our results will provide a benchmark for understanding the Solar debris disk, and extra-solar ones as well.

To appear in: Earth, Moon and Planets, Issue 105 (2009 August)

For preprints, contact tmueller@mpe.mpg.de

The History of the Solar System's Debris Disc:
Observable Properties of the Kuiper Belt
Mark Booth1, Mark C. Wyatt1, Alessandro Morbidelli2,
Amaya Moro-Martín3,4, and Harold F. Levison5

1Institute of Astronomy, Madingley Rd, Cambridge CB3 0HA, UK
2Observatoire de la Côte d'Azur, Nice, France
3Centro de Astrobiologia - CSIC/INTA, 28850 Torrejón de Ardoz, Madrid, Spain
4Department of Astrophysical Sciences, Peyton Hall, Ivy Lane, Princeton University, Princeton, NJ 08544, USA
5Department of Space Studies, Southwest Research Institute, Boulder, CO 80302, USA

The Nice model of Gomes et al. suggests that the migration of the giant planets caused a planetesimal clearing event which led to the Late Heavy Bombardment (LHB) at 880 Myr. Here we investigate the IR emission from the Kuiper belt during the history of the Solar System as described by the Nice model. We describe a method for easily converting the results of N-body planetesimal simulations into observational properties (assuming black-body grains and a single size distribution) and further modify this method to improve its realism (using realistic grain properties and a three-phase size distribution). We compare our results with observed debris discs and evaluate the plausibility of detecting an LHB-like process in extrasolar systems. Recent surveys have shown that 4% of stars exhibit 24 $\mu$m excess and 16% exhibit 70 $\mu$m excess. We show that the Solar System would have been amongst the brightest of these systems before the LHB at both 24 and 70 $\mu$m. We find a significant increase in 24 $\mu$m emission during the LHB, which rapidly drops off and becomes undetectable within 30 Myr, whereas the 70 $\mu$m emission remains detectable until 360 Myr after the LHB. Comparison with the statistics of debris disc evolution shows that such depletion events must be rare occurring around less than 12% of Sun-like stars and with this level of incidence we would expect approximately one of the 413 Sun-like, field stars so far detected to have a 24 $\mu$m excess to be currently going through an LHB. We also find that collisional processes are important in the Solar System before the LHB and that parameters for weak Kuiper belt objects are inconsistent with the Nice model interpretation of the LHB.

To appear in: Monthly Notices of the Royal Astronomical Society

For preprints, contact mbooth@ast.cam.ac.uk
or on the web at http://uk.arxiv.org/abs/0906.3755

Trans-Neptunian Region Architecture:
Evidence for a Planet Beyond Pluto
Patryk Sofia Lykawka1 and Tadashi Mukai2

1 Kinki University, International Center for Human Sciences (Planetary Sciences), 3-4-1 Kowakae, Higashiosaka, Osaka, 577-8502, Japan
2 Kobe University, Department of Earth and Planetary Sciences, 1-1 rokkodai-cho, nada-ku, Kobe, 657-8501, Japan

Trans-Neptunian objects (TNOs) orbiting in the Edgeworth-Kuiper Belt carry precious information about the origin and evolution of the Solar System. The Kuiper Belt has a very complex orbital structure. Indeed, TNOs exhibit surprisingly large eccentricities, e, and inclinations, i, and are classified in distinct dynamical classes. Here we propose that the Kuiper Belt orbital structure can be explained by a massive scattered planetesimal with tenths of the Earth's mass, which later remained in the system in a distant stable orbit (an outer planet). Near the end of planet formation, the outer planet was firstly scattered by one of the icy giant planets, then it dynamically excited the primordial planetesimal disk over at least tens of Myr, reproducing the levels observed at 40-50 AU and the truncation of the disk at about 48 AU before planet migration. Later, the outer planet was captured by a distant resonance with Neptune of the type r:1 or r:2 (e.g., 6:1, 7:1, ...), acquiring an inclined stable orbit (=100 AU; 20-40$^\circ$), thus preserving the Kuiper Belt over $\sim$4 Gyr. Our model explains the following: 1) Depletion of the inner Kuiper Belt; 2) The entire currently known resonant populations in the Kuiper Belt, including Neptune Trojans and resonant TNOs in distant resonances (>50 AU); 3) Formation of scattered and detached TNOs, including analogues of (136199) Eris, 2004 XR190, (148209) 2000 CR105, and (90377) Sedna; 4) Classical TNOs and their dual nature of cold and hot populations; 5) Orbital excitation of classical TNOs; 6) The Kuiper Belt outer edge at about 48 AU; 7) Loss of $\sim$99% of the initial total mass of the Kuiper Belt through dynamical depletion and enhanced collisional grinding; 8) Neptune's current orbit at 30.1 AU. In summary, our scenario consistently reproduces all main aspects of Kuiper Belt architecture with unprecedented detail. The best constraints obtained from the model for the outer planet are: aP=100-175 AU (currently near or inside an r:1 or r:2 resonance), qP>80 AU, $i_P=20^{\circ}-40^{\circ}$, and apparent magnitude $m_P \sim 15-17$ mag at perihelion (assuming an albedo of 0.1-0.3 and qP=80-90 AU).

Published in: Advances in Geosciences, Volume 15 (Planetary Science), 293

For preprints, contact patryksan@gmail.com
or on the web at http://sites.google.com/site/patryksofialykawka/

Kozai Cycles, Tidal Friction, and the Dynamical Evolution of Binary Minor Planets
Hagai B. Perets1 and Smadar Naoz2

1 Weizmann Institute of Science, P.O. Box 26, Rehovot 76100, Israel
2 Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, Tel Aviv 69978, Israel

In recent years, many binary minor planets (BMPs) have been discovered in the solar system. Many models have been suggested for their formation, but these encounter difficulties explaining their observed characteristics. Here, we show that secular perturbations by the Sun (Kozai mechanism) fundamentally change the evolution and the initial distribution of BMPs predicted by such models and lead to unique observational signatures. The Kozai mechanism can lead to a large periodic oscillations in the eccentricity and inclination of highly inclined BMP orbits, where we predict such effects to be observable with current accuracy within a few years (e.g., for the binary asteroid Huenna). In addition, the combined effects of the Kozai mechanism and tidal friction (KCTF) drives BMPs into short-period circular orbits. We predict a specific inclination-dependent distribution of the separation and eccentricity of BMPs, due to these effects, including a zone of avoidance at the highest inclinations. Specifically, the Kozai evolution could explain the recently observed peculiar orbit of the Kuiper Belt binary 2001 QW322. Additionally, the KCTF process could lead to BMPs coalescence and serve as an important route for the formation of irregular shaped single minor planets with large axial tilts.

Published in: The Astrophysical Journal Letters, 699, L17 (2009 July 1)

Preprints available on the web at http://arxiv.org/abs/0809.2095

Formation of the Resonant Populations in the Kuiper Belt: Gas-drag-induced Resonant Capture
Evgeny Griv1 and Ing-Guey Jiang2

1 Department of Physics, Ben-Gurion University of the Negev, PO Box 653, Beer-Sheva 84105, Israel
2 Department of Physics, National Tsing-Hua University, Hsin-Chu City, Taiwan

On the basis of their orbital elements, present-day Kuiper belt objects can be grouped into distinct dynamical classes: classical, resonant and scattered ones. Jiang and Yeh have proposed gas-drag-induced resonant capture in a protostellar disc analogous to the primordial solar nebula as a mechanism able to explain the dominant 3:2 resonant population observed in Kuiper belt objects. de la Fuente Marcos and de la Fuente Marcos further investigated the drag-induced mechanism numerically. Our significant contribution is a hydrodynamic theory derivation of results obtained in the Jiang and Yeh, and de la Fuente Marcos and de la Fuente Marcos numerical simulations.

Published in: Monthly Notices of the Royal Astronomical Society, 396, 1032

For preprints, contact griv@bgu.ac.il or jiang@phys.nthu.edu.tw

Two Dynamical Classes of Centaurs
Brenae L. Bailey1 and Renu Malhotra2

1 Program in Applied Mathematics, 617 N. Santa Rita, The University of Arizona, Tucson, AZ 85721, USA
2 Lunar and Planetary Laboratory, 1629 E. University Blvd., The University of Arizona, Tucson, AZ 85721, USA

The Centaurs are a transient population of small bodies in the outer solar system whose orbits are strongly chaotic. These objects typically suffer significant changes of orbital parameters on timescales of a few thousand years, and their orbital evolution exhibits two types of behaviors described qualitatively as random-walk and resonance-sticking. We have analyzed the chaotic behavior of the known Centaurs. Our analysis has revealed that the two types of chaotic evolution are quantitatively distinguishable: (1) the random walk-type behavior is well described by so-called generalized diffusion in which the rms deviation of the semimajor axis grows with time t as $\sim
t^H$, with Hurst exponent H in the range 0.22-0.95, however (2) orbital evolution dominated by intermittent resonance sticking, with sudden jumps from one mean motion resonance to another, has poorly defined H. We further find that these two types of behavior are correlated with Centaur dynamical lifetime: most Centaurs whose dynamical lifetime is less than $\sim$22 Myr exhibit generalized diffusion, whereas most Centaurs of longer dynamical lifetimes exhibit intermittent resonance sticking. We also find that Centaurs in the diffusing class are likely to evolve into Jupiter-family comets during their dynamical lifetimes, while those in the resonance-hopping class do not.

To appear in: Icarus

For preprints, contact renu@lpl.arizona.edu
or on the web at http://arxiv.org/abs/0906.4795

Origin and Dynamical Evolution of Neptune Trojans -
I: Formation and Planetary Migration
Patryk Sofia Lykawka1, Jonathan Horner2, Barrie W. Jones2, and Tadashi Mukai3

1 Kinki University, International Center for Human Sciences (Planetary Sciences), 3-4-1 Kowakae, Higashiosaka, Osaka, 577-8502, Japan
2 The Open University, Department of Physics and Astronomy, Walton Hall, Milton Keynes, MK7 6AA, UK
3 Kobe University, Department of Earth and Planetary Sciences, 1-1 rokkodai-cho, nada-ku, Kobe, 657-8501, Japan

We present the results of detailed dynamical simulations of the effect of the migration of the four giant planets on both the transport of pre-formed Neptune Trojans, and the capture of new Trojans from a trans-Neptunian disk. The cloud of pre-formed Trojans consisted of thousands of massless particles placed on dynamically cold orbits around Neptune's L4 and L5 Lagrange points, while the trans-Neptunian disk contained tens of thousands of such particles spread on dynamically cold orbits between the initial and final locations of Neptune. Through comparison of the results with previous work on the known Neptunian Trojans, we find that scenarios involving the slow migration of Neptune over a large distance (50 Myr to migrate from 18.1 AU to its current location, using an exponential-folding time of t = 10 Myr) provide the best match to the properties of the known Trojans. Scenarios with faster migration (5 Myr, with t = 1 Myr), and those in which Neptune migrates from 23.1 AU to its current location, fail to adequately reproduce the current day Trojan population. Scenarios which avoid disruptive perturbation events between Uranus and Neptune fail to yield any significant excitation of pre-formed Trojans (transported with efficiencies between 30% and 98% whilst maintaining the dynamically cold nature of these objects - e < 0.1, $i < 5^\circ$). Conversely, scenarios with periods of strong Uranus-Neptune perturbation lead to the almost complete loss of such pre-formed objects. In these cases, a small fraction ($\sim$0.15%) of these escaped objects are later recaptured as Trojans prior to the end of migration, with a wide range of eccentricities (<0.35) and inclinations ($<40^\circ$). In all scenarios (including those with such disruptive interaction between Uranus and Neptune) the capture of objects from the trans-Neptunian disk (through which Neptune migrates) is achieved with efficiencies between $\sim$0.1% and $\sim$1%. The captured Trojans display a wide range of inclinations ($<40^\circ$ for slow migration, and $<20\circ$ for rapid migration) and eccentricities (<0.35), and we conclude that, given the vast amount of material which undoubtedly formed beyond the orbit of Neptune, such captured objects may be sufficient to explain the entire Neptune Trojan population.

To appear in: Monthly Notices of the Royal Astronomical Society

For preprints, contact patryksan@gmail.com
or on the web at http://sites.google.com/site/patryksofialykawka/

The Dynamics of Neptune Trojan: I. The Inclined Orbits
Li-Yong Zhou1, Rudolf Dvorak2, and Yi-Sui Sun1

1Department of Astronomy, Nanjing University, Nanjing 210093, China
2Institute for Astronomy, University of Vienna, Türkenschanzstr. 17, A-1180 Wien, Austria

The stability of Trojan type orbits around Neptune is studied. As the first part of our investigation, we present in this paper a global view of the stability of Trojans on inclined orbits. Using the frequency analysis method based on the FFT technique, we construct high resolution dynamical maps on the plane of initial semimajor axis a0 versus inclination i0. These maps show three most stable regions, with i0 in the range of $(0^\circ,12^\circ), (22^\circ,36^\circ)$ and $(51^\circ,59^\circ)$ respectively, where the Trojans are most probably expected to be found. The similarity between the maps for the leading and trailing triangular Lagrange points L4 and L5 confirms the dynamical symmetry between these two points. By computing the power spectrum and the proper frequencies of the Trojan motion, we figure out the mechanisms that trigger chaos in the motion. The Kozai resonance found at high inclination varies the eccentricity and inclination of orbits, while the $\nu_8$ secular resonance around $i_0\sim44^\circ$ pumps up the eccentricity. Both mechanisms lead to eccentric orbits and encounters with Uranus that introduce strong perturbation and drive the objects away from the Trojan like orbits. This explains the clearance of Trojan at high inclination ($>60^\circ$) and an unstable gap around $44^\circ$ on the dynamical map. An empirical theory is derived from the numerical results, with which the main secular resonances are located on the initial plane of (a0,i0). The fine structures in the dynamical maps can be explained by these secular resonances.

To appear in: Monthly Notices of the Royal Astronomical Society

For preprints, contact zhouly@nju.edu.cn
or on the web at http://arxiv.org/abs/0906.5075

The Creation of Haumea's Collisional Family
Hilke E. Schlichting1 and Re'em Sari1,2

   1 California Institute of Technology, MC 130-33, Pasadena, CA 91125, USA
2 Racah Institute of Physics, Hebrew University, Jerusalem 91904, Israel

Recently, the first collisional family was discovered in the Kuiper belt. The parent body of this family, Haumea, is one of the largest objects in the Kuiper belt and is orbited by two satellites. It has been proposed that the Haumea family was created from dispersed fragments that resulted from a giant impact. This proposed origin of the Haumea family is however in conflict with the observed velocity dispersion between the family members ($\sim$140 m/s) which is significantly less than the escape velocity from Haumea's surface ($\sim$900 m/s). In this paper we propose a different formation scenario for Haumea's collisional family. In our scenario the family members are ejected while in orbit around Haumea. This scenario, therefore, gives naturally rise to a lower velocity dispersion among the family members than expected from direct ejection from Haumea's surface. In our scenario Haumea's giant impact forms a single moon that tidally evolves outward until it suffers a destructive collision from which the family is created. We show that this formation scenario yields a velocity dispersion of $\sim$190 m/s among the family members which is in good agreement with the observations. We discuss an alternative scenario that consists of the formation and tidal evolution of several satellites that are ejected by collisions with unbound Kuiper belt objects. However, the formation of the Haumea family in this latter way is difficult to reconcile with the large abundance of Kuiper belt binaries. We therefore favor forming the family by a destructive collision of a single moon of Haumea. The probability for Haumea's initial giant impact in todays Kuiper belt is less than 10-3. In our scenario, however, Haumea's giant impact can occur before the excitation of the Kuiper belt and the ejection of the family members afterwards. This has the advantage that one can preserve the dynamical coherence of the family and explain Haumea's original giant impact, which is several orders of magnitude more likely to have occurred in the primordial dynamically cold Kuiper belt compared to the dynamically excited Kuiper belt today.

Published in: The Astrophysical Journal, 700, 1242 (2009 August)

For preprints, contact hes@astro.caltech.edu

Can Collisional Activity Produce a Crystallization of Edgeworth-Kuiper Belt Comets?
U. Marboeuf1, J-M. Petit1, and O. Mousis2,1

1Institut UTINAM, CNRS-UMR 6213, Observatoire de Besançon, Université de Franche-Comté, France
2Lunar and Planetary Laboratory, University of Arizona, Tucson, AZ, USA

Kuiper Belt Objects and cometary nuclei are considered among the most pristine bodies of the outer solar system. However, the composition of these objects might not reflect that of the planetesimals from which they accreted. They have experienced some collisional activity since the formation of the Edgeworth-Kuiper Belt, leading to a possible alteration of their structure and composition. Here, we examine the possible alteration of icy bodies (10 to 100 km radii) located in the primitive Edgeworth-Kuiper Belt due to the heat generated by collisions of planetesimals with sizes not exceeding 10% of the target body. We use a cometary nucleus model initially made of a mixture of amorphous ice and dust to investigate the influence of the target's intrinsic properties on its post-impact thermodynamical evolution. We show that multiple collisions must be considered over long periods to trigger a continuous crystallization within a target owning a typical cometary composition. However, the collision rates we have determined are approximately 1000 times greater than those predicted for the current collisional environment in the Edgeworth-Kuiper Belt. This implies that the collisional processes that occurred over the age of the Solar System did not produce any phase transition of H2O ice from amorphous to crystalline form in cometary size bodies located in the primitive Edgeworth-Kuiper Belt.

Published in: Monthly Notices of the Royal Astronomical Society, 397, L74

For preprints, contact marboeuf@obs-besancon.fr

Thermal Evolution of Kuiper Belt Objects, With Implications For Cryovolcanism
S.J. Desch1, J.C. Cook2, T.C. Doggett1, and S.B. Porter1

1 School of Earth and Space Exploration, Arizona State University, Tempe, AZ 85287, USA
2 Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA

We investigate the internal thermal evolution of Kuiper belt objects (KBOs), small (radii < 1000 km), icy (mean densities < 2500 kg m-3) bodies orbiting beyond Neptune, focusing on Pluto's moon Charon in particular. Our calculations are time-dependent and account for differentiation. We review evidence for ammonia hydrates in the ices of KBOs, and include their effects on the thermal evolution. A key finding is that the production of the first melt, at the melting point of ammonia dihydrate, $\approx$176 K, triggers differentiation of rock and ice. The resulting structure comprises a rocky core surrounded by liquids and ice, enclosed within a > 100 km thick undifferentiated crust of rock and ice. This structure is especially conducive to the retention of subsurface liquid, and bodies the size of Charon or larger (radii > 600 km) are predicted to retain some subsurface liquid to the present day. We discuss the possibility that this liquid can be brought to the surface rapidly via self-propagating cracks. We conclude that cryovolcanism is a viable process expected to affect the surfaces of large KBOs including Charon.

Published in: Icarus, 202, 694 (2009 August)

ESO Large Program about TNOs:
Surface variations on (47171) 1999 TC$_{\bf 36}$
S. Protopapa1, A. Alvarez-Candal2, M.A. Barucci2, G.P. Tozzi3, S. Fornasier2, A. Delsanti2, and F. Merlin2

1 Max-Planck-Institute for Solar System Research, Max-Planck-Str. 2, 37191 Katlenburg-Lindau, Germany
2 LESIA, Observatoire de Paris, 92195 Meudon Principal Cedex, France
3 INAF, Osservatorio Astrofisico di Arcetri, Largo E. Fermi 5, I-50125 Firenze, Italy

Aims. We investigate the surface composition of the Plutino (47171) 1999 TC36.

Methods. We completed near-infrared photometric and spectroscopic observations of (47171) 1999 TC36 with the adaptive optics instrument NACO at the ESO VLT during 12 October 2006, and present these data with ISAAC and SINFONI spectroscopic observations carried out about one month later on 9 November 2006 and 8 November 2006, respectively. The ISAAC and SINFONI spectroscopic observations were combined with a visible spectrum obtained by FORS1 on 9 November 2006. Composition and properties of the compounds present on the surface of the target are investigated by applying a Hapke radiative transfer model to the measured spectra and to previously published observations.

Results. We present the relative reflectance spectrum of (47171) 1999 TC36 in the wavelength range (0.37-2.33) $\mu m$. An intimate mixture of Triton tholin, Titan tholin, serpentine, and Triton tholin diluted in water ice represents the best-fit model description of the measured spectrum. Any significant differences from the published spectra of (47171) 1999 TC36 taken on 2001 and 2003 could be due to surface heterogeneity.

Published in: Astronomy & Astrophysics, 501, 375 (2009 July)

Composition of KBO (50000) Quaoar
C. Morea Dalle Ore1,2, M.A. Barucci3, J.P. Emery4, D.P. Cruikshank1, L.V. Dalle Ore1, F. Merlin5, A. Alvarez-Candal3, C. de Bergh3, D.E. Trilling6, D. Perna3,7,8, S. Fornasier3, R.M.E. Mastrapa1,2, and E. Dotto7

1 NASA Ames Research Center, Mail Stop 245-6, Moffett Field, CA 94035, USA
2 SETI Institute, 515 N. Whisman Rd., Mountain View, CA 94043 CA, USA
3 LESIA, Observatoire de Paris, 92195 Meudon Pricipal Cedex, France
4 Earth and Planetary Sciences Dept, University of Tennessee, Knoxville, TN 37996, USA
5 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
6 Department of Physics and Astronomy, Northern Arizona University, Flagstaff, AZ 86011, USA
7 INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
8 Università di Roma Tor Vergata, via della Ricerca Scientifica 1, 00133 Roma, Italy

Aims. The objective of this work is to investigate the physical properties of objects beyond Neptune -- the new frontiers of the Solar System -- and in particular to study the surface composition of (50000) Quaoar, a classical Transneptunian (or Kuiper Belt) object. Because of its distance from the Sun, Quaoar is expected to have preserved, to a degree, its original composition. Our goals are to determine to what degree this is true and to shed light on the chemical evolution of this icy body.

Methods. We present new near-infrared (3.6 and 4.5 $\mu$m) photometric data obtained with the Spitzer Space Telescope. These data complement high resolution, low signal-to-noise spectroscopic and photometric data obtained in the visible and near-infrared (0.4-2.3 $\mu$m) at VLT-ESO and provide an excellent set of constraints in the model calculation process. We perform spectral modeling of the entire wavelength range -- from 0.3 to 4.5 $\mu$m by means of a code based on the Shkuratov radiative transfer formulation of the slab model. We also attempt to determine the temperature of H2O ice making use of the crystalline feature at 1.65 $\mu$m.

Results. We present a model confirming previous results regarding the presence of crystalline H2O and CH4 ice, as well as C2H6 and organic materials, on the surface of this distant icy body. We attempt a measurement of the temperature and find that stronger constraints on the composition are needed to obtain a precise determination.

Conclusions. Model fits indicate that N2 may be a significant component, along with a component that is bright at $\lambda > 3.3~\mu$m, which we suggest at this time could be amorphous H2O ice in tiny grains or thin grain coatings. Irradiated crystalline H2O could be the source of small-grained amorphous H2O ice. The albedo and composition of Quaoar, in particular the presence of N2, if confirmed, make this TNO quite similar to Triton and Pluto.

Published in: Astronomy & Astrophysics, 501, 349 (2009 July)

The Rotation Period and Light-Curve Amplitude of Kuiper Belt Dwarf Planet 136472 Makemake (2005 FY9)
A.N. Heinze1 and D. deLahunta2

1 Swarthmore College, 500 College Avenue, Swarthmore, PA 19081, USA
2 University of Rochester, 500 Joseph C. Wilson Blvd., Rochester, NY 14627, USA

Kuiper Belt dwarf planet 136472 Makemake, formerly known as 2005 FY9, is currently the third-largest known object in the Kuiper Belt, after the dwarf planets Pluto and Eris. It is currently second only to Pluto in apparent brightness, due to Eris' much larger heliocentric distance. Makemake shows very little photometric variability, which has prevented confident determination of its rotation period until now. Using extremely precise time-series photometry, we find that the rotation period of Makemake is $7.7710 \pm 0.0030$ hr, where the uncertainty is a 90% confidence interval. An alias period is detected at 11.41 hr, but is determined with approximately 95% confidence not to be the true period. Makemake's 7.77 hr rotation period is in the typical range for Kuiper Belt objects, consistent with Makemake's apparent lack of a substantial satellite to alter its rotation through tides. The amplitude of Makemake's photometric light curve is $0.0286 \pm 0.0016$ mag in V. This amplitude is about 10 times less than Pluto's, which is surprising given the two objects' similar sizes and spectral characteristics. Makemake's photometric variability is instead similar to that of Eris, which is so small that no confident rotation period has yet been determined. It has been suggested that dwarf planets such as Makemake and Eris, both farther from the Sun and colder than Pluto, exhibit lower photometric variability because they are covered with a uniform layer of frost. Such a frost is probably the correct explanation for Eris. However, it may be inconsistent with the spectrum of Makemake, which resembles reddish Pluto more than neutrally colored Eris. Makemake may instead be a more Pluto-like object that we observe at present with a nearly pole-on viewing geometry -- a possibility that can be tested with continuing observations over the coming decades.

Published in: The Astronomical Journal, 138, 428 (2009 August)

A Search for Occultations of Bright Stars by Small Kuiper Belt Objects Using Megacam on the MMT
F.B. Bianco1,2, P. Protopapas2,3, B. McLeod2, C.R. Alcock2, M.J. Holman2, and M.J. Lehner4,1

1 Dept. of Physics and Astronomy, University of Pennsylvania, 209 South 33rd Street, Philadelphia, PA 19104, USA
2 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
3 Initiative in Innovative Computing at Harvard, 60 Oxford Street, Cambridge, MA 02138, USA
4 Institute of Astronomy and Astrophysics, Academia Sinica, P.O. Box 23-141, Taipei 106, Taiwan

We conducted a search for occultations of bright stars by Kuiper Belt Objects (KBOs) to estimate the density of sub-km KBOs in the sky. We report here the first results of this occultation survey of the outer solar system conducted in 2007 June and 2008 June/July at the MMT Observatory using Megacam, the large MMT optical imager. We used Megacam in a novel shutterless continuous-readout mode to achieve high precision photometry at 200 Hz, which with point-spread function convolution results in an effective sampling of $\sim30~\mathrm{Hz}$. We present an analysis of 220 star hours at signal-to-noise ratio of 25 or greater, taken from images of fields within $3^\circ$ of the ecliptic plane. The survey efficiency is greater than 10% for occultations by KBOs of diameter $d \geq 0.7$ km, and we report no detections in our data set. We set a new 95% confidence level upper limit for the surface density $\Sigma_N(d)$ of KBOs larger than 1 km: $\Sigma_N(d\geq
1~\mathrm{km}) \leq 2.0 \times 10^8~\mathrm{deg}^{-2}$, and for KBOs larger than $0.7~\mathrm{km}~\Sigma_N(d\geq 0.7~km) \leq 4.8 \times

Published in: The Astronomical Journal, 138, 568 (2009 August)

For preprints, contact fbianco@cfa.harvard.edu

Buoyancy Waves in Pluto's High Atmosphere:
Implications for Stellar Occultations
W.B. Hubbard1, D.W. McCarthy2, C.A. Kulesa2, S.D. Benecchi3, M.J. Person4, J.L. Elliot4,5, and A.A.S. Gulbis4,6

1 Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson AZ 85721, USA
2 Steward Observatory, The University of Arizona, 933 N. Cherry Ave, Tucson, AZ 85721, USA
3 Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA
4 Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Ave., Cambridge, MA 02139, USA
5 Physics, MIT, 77 Massachusetts Ave., Cambridge, MA 02139, USA
6 Southern African Astronomical Observatory, P.O. Box 9, Observatory, 7935, Cape Town, South Africa

We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto’s high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation.

To appear in: Icarus

For preprints, contact hubbard@lpl.arizona.edu
or on the web at http://arxiv.org/abs/0906.4141


Orbital Dynamics of Kuiper Belt Object Satellites, A Kuiper Belt Family, and Extra-Solar Planet Interiors
Darin Ragozzine1

1 California Institute of Technology, Pasadena, CA 91125, USA

This thesis discusses research into four different orbital dynamics problems, where the main goal of each chapter is to characterize the strongest non-Keplerian effect. These problems are introduced and discussed in Chapter 1, to help provide context for the subsequent chapters. In Chapter 2, I discuss a new technique for probing the interior density distributions of extra-solar planets by observing apsidal precession. Using a detailed theoretical and observational model of this precession, I conclude that NASA's Kepler mission will be able to detect the presence or absence of a massive core in very hot Jupiters with eccentricities greater than 0.003. The remaining chapters discuss the orbital dynamics of Kuiper belt objects (KBOs) orbiting the Sun beyond Neptune. The family of dwarf planet Haumea (2003 EL61) is characterized in Chapter 3, including a list of candidate family members sorted by dynamical proximity. Using a numerical integration of resonance diffusion, I also show that the Haumea family is at least 1 Gyr old and is probably primordial. In Chapter 4, I analyze and fit astrometric data for the two satellites of Haumea (Hi'iaka and Namaka) to determine their orbital properties and the masses of Haumea and Hi'iaka. The implications of the new orbital solution are discussed, including the exciting conclusion that Haumea and Namaka are currently starting a season of mutual events. A more general investigation of the orbital and tidal evolution of KBO binaries is given in Chapter 5. A new orbital evolution model is described that accounts for perturbations from the Sun, self-consistent tidal evolution, and non-hydrostatic quadrupoles of solid KBOs. Using this model, I find that the orbital parameters of KBO binaries may have been modified significantly over the age of the solar system. Applied to the Orcus-Vanth binary, this model shows that a short-period circular orbit does not necessarily imply a collisional formation. In all, the work in this thesis has sought to analyze observational data by using the theoretical tools of orbital dynamics.

Dissertation advised by Michael E. Brown
Ph.D. awarded June, 2009 from California Institute of Technology

Now working as a postdoctoral researcher with Matthew Holman. New address as of July 2009:
Darin Ragozzine
Harvard-Smithsonian Center for Astrophysics
60 Garden Street, MS-51
Cambridge, MA 02138

Entire thesis available on the web at

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Joel Parker 2009-08-02