Distant EKOs, Issue #13 (September 2000)

Contents

News & Announcements
Abstracts of 12 Accepted Papers
Titles of 2 Submitted Papers
Title of 1 Other Article
Abstracts of 2 Conference Contributions
Newsletter Information

NEWS & ANNOUNCEMENTS


Bob Marcialis has compiled extensive bibliographies of Pluto and Chiron references. They can be found at: http://www.lpl.arizona.edu/~umpire/science/plubib.html
and http://www.lpl.arizona.edu/~umpire/science/2060bib.html

Links to these and other reference lists are on the Distant EKOs website:

http://www.boulder.swri.edu/ekonews/articles/

At the recent meetings of IAU Commission 20, the Working Group on Comets has been revised to include Centaurs and trans-Neptunian objects. Some of the tasks of the newly named Working Group on Comets and Distant Objects are:

The Working Group consists of 18 members from 10 countries. Input from the Transneptunian research community about the Working Group and its charge is strongly desired. Questions and comments may be addressed to the chair, Brian Marsden, at: bmarsden@cfa.harvard.edu.

Objects with recently assigned numbers and names:
1995 DW2 (10370) Hylonome
1992 QB1 (15760)
1993 SB (15788)
1993 SC (15789)
1994 GV9 (15807)
1994 JS (15809)
1994 JR1 (15810)
1994 TB (15820)
1995 DA2 (15836)
1996 TL66 (15874)
1996 TP66 (15875)
1997 CR29 (15883)

There were 5 new TNO discoveries announced since the previous issue of the Distant EKOs:

1999 DF9, 1999 CL158, 1999 CM158, 1999 RZ253, 2000 GP183

and 3 new Centaur/SDO discoveries:

1996 RX33, 2000 OB51, 2000 OY51

Current number of TNOs: 287 (and Pluto & Charon)
Current number of Centaurs/SDOs: 49

PAPERS ACCEPTED TO JOURNALS


Compositional Surface Diversity in the Trans-Neptunian Objects
M. A. Barucci1, J. Romon1, A. Doressoundiram1, and D. J. Tholen2

1 Observatoire de Paris-Meudon, 5 place Jules Janssen 92195 Meudon Cedex, France
2 Institute for Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA

The knowledge of the physical and chemical properties of Trans-Neptunian Objects (TNOs) is still incomplete and confused. To investigate their physical properties, we are continuing at ESO with the 3.5 m telescope (NTT) the TNO observational programme started in 1997. In February 1999, broad band optical colors were obtained for eight new objects: 1993 FW, 1995 HM5, 1997 CQ29, 1997 CS29, 1997 CT29, 1997 CU29, 1998 FS144, and 1998 WH24. Particular attention has been applied to the observations and data reduction of these faint objects. These new data increase the available statistical sample and will help us to understand the surface properties and the mechanisms of the surface modification of the TNOs. The observed objects present a wide spread of colors. The color distribution does not show any bimodality. Knowledge of the colors of a large number of these objects will be important to understand this population, which represents an important reservoir of primordial material.

Published in: The Astronomical Journal, 120, 496 (2000 July)

For preprints, contact antonella.barucci@obspm.fr
or on the web at http://despa.obspm.fr/~tno/publi_e.htm

Observations of the Trans-Neptunian Objects 1993 SC and 1996 TL66 with the Infrared Space Observatory
Nicolas Thomas1, S. Eggers1, W.-H. Ip1,2, G. Lichtenberg1, A. Fitzsimmons3, L. Jorda1, H. U. Keller1, I. P. Williams4, G. Hahn5, and H. Rauer5

1 Max-Planck-Institut für Aeronomie, Postfach 20, D-37191 Katlenburg-Lindau, Germany
2 Institute of Space Science, National Central University Chung Li, Taiwan
3 Department of Pure and Applied Physics, The Queen's University, Belfast, Northern Ireland
4 Queen Mary and Westfield College University of London, E1 4NS, England, UK
5 DLR Institut für Planetenerkundung, Berlin-Adlershot, Germany

Observations at 90 $\mu$m of the trans-Neptunian objects (TNOs), 1993 SC and 1996 TL66, using the Infrared Space Observatory (ISO) are reported. Five individual observations of 1993 SC were acquired giving a $2.7 \sigma$detection (a confidence level of 99.6%). The signal level of $11.46 \pm 4.24$ mJy has been modeled using a standard thermal model (STM) and gives an effective radius of 164+29-33 km and a geometric albedo of 0.022+0.013-0.006. Estimated radii and albedos using the fast rotator approximation and the thermophysical model are also presented. Two individual observations of 1996 TL66 are also reported. A clear signal of $39.77 \pm 11.62$ mJy at 90 $\mu$m was recorded. However, the position of the signal on the detector does not correspond to the position expected. A detailed investigation has not revealed a satisfactory explanation. Assuming that ISO was mispointed and that the origin of the signal is 1996 TL66, application of the STM gives an effective radius of 316+42-49 km and a geometric albedo of 0.030+0.012-0.007. This is in good agreement with expectations based on the assumption that the surfaces of TNOs are similar to those of cometary nuclei. The results for 1996 TL66 and 1993 SC indicate that TNOs are large, spherical, and very dark objects. A main-belt asteroid, 1997 SU15, was also detected giving an effective radius of $1.13 \pm 0.04$ km and a geometric albedo of $0.25 \pm 0.02$. An estimate of the relative dependence of the zodiacal light background in the ecliptic on elongation angle at 90 m was also determined.

Published in: The Astrophysical Journal, 534, 446 (2000 May 1)

Available on the web at
http://www.journals.uchicago.edu/ApJ/journal/issues/ApJ/v534n1/40276/40276.html

Infrared Spectroscopy of the Centaur 8405 Asbolus: First Observations at ESO-VLT
M. A. Barucci1, C. De Bergh1, J. G. Cuby2, A. Le Bras1,3, B. Schmitt4, and J. Romon1

1 Observatoire de Paris-Meudon, 5 place Jules Janssen 92195 Meudon Cedex, France
2 ESO, Santiago, Chile
3 IAS, Orsay, France
4 Lab. Planétologie de Grenoble, St Martin d'Hères, France

Centaurs constitute a separate population of Solar System objects, with orbits crossing one or more of the giant planets' orbits. They are located on unstable orbits with short lifetimes, and are probably transition objects between Trans-Neptunians and short-period comets. We present near-infrared spectroscopic observations of one of the Centaurs, 1995 GO, now named 8405 Asbolus, carried out at the ESO-Very Large Telescope (Mount Paranal, Chile) in May 1999. Spectra obtained in the J, H, and K bands show a rather featureless behavior with, in particular, no detection of H2O ice.

Published in: Astronomy & Astrophysics, 357, L53 (2000 May)

For preprints, contact antonella.barucci@obspm.fr
or on the web at http://despa.obspm.fr/~tno/publi_e.htm

Near-infrared Spectroscopy of the Bright Kuiper Belt Object 2000 EB173
Michael E. Brown1, Geoffrey A. Blake1, and Jacqueline E. Kessler1

1 Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125, USA

We have obtained a near-infrared spectrum of the bright Kuiper belt object 2000 EB173; the spectrum appears featureless. The spectrum has sufficient signal-to-noise to rule out 1.5 and 2.0 $\mu$m absorption from water ice even at the low level seen in the Centaur Chariklo. In addition we can rule out 2.3 $\mu$m absorption at the level seen in the Centaur Pholus.

To appear in: Astrophysical Journal Letters

For preprints, contact mbrown@gps.caltech.edu
or on the web at http://www.gps.caltech.edu/~mbrown/papers

The Distribution and Physical State of H2O on Charon
M. W. Buie1 and W. M. Grundy1

1 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff AZ 86001, USA

We present new 1.4-2.5 $\mu$m geometric albedo spectra of Charon taken with HST/NICMOS in 1998. These new data provide global coverage of the surface with four spectra at evenly spaced longitudes. The surface of Charon is seen to be globally dominated by H2O ice. The data indicate the ice is in the crystalline phase at a temperature consistent with its heliocentric distance. The spectrum of Charon has only weak variations with longitude. There is an indication of a slightly stronger H2O ice absorption on the leading hemisphere. No variations in the spectrum are seen in response to differing solar phase angle. From model fits there is no indication of any of the volatile species that are seen on Pluto, i.e., CO, CH4, or N2. There is spectroscopic evidence for a contaminant with an absorption coefficient which increases with wavelength past $\sim$2 $\mu$m. This contaminant is unidentified but is similar to what is seen on other icy satellites in the outer solar system. We also present a standard spectrophotometric model for Charon that can be used to subtract Charon light from ground based spectra of the combined Pluto-Charon system.

To appear in: Icarus

For preprints, contact buie@lowell.edu

Search for Variations in Pluto's Millimeter-Wave Emission
E. Lellouch1, G. Paubert2, R. Moreno3, and B. Schmitt4

1 DESPA, Observatoire de Paris, F-92195 Meudon, France
2 IRAM, Avenida Divina Pastora, E-18012 Granada, Spain
3 IRAM, Domaine Universitaire, F-38400 St-Martin d'Hères, France
4 LPG, Domaine Universitaire, F-38400 St-Martin d'Hères, France

We report on repeated bolometric observations of the Pluto-Charon system at 1.2 mm with the IRAM 30-m telescope. These observations indicate at most little ($\sim$1-2 mJy) variations of the millimeter-wave emission of Pluto with orbital longitude, suggesting that the dark regions of Pluto have a millimeter emissivity of $\sim$0.6-0.7.

To appear in: Icarus

For preprints, contact Emmanuel.Lellouch@obspm.fr

Evolution of Porosity in Small Icy Bodies
J. Leliwa-Kopystynski1 and K. J. Kossacki1

1 Institute of Geophysics, University of Warsaw, ul. Pasteura 7, 02-093 Warszawa, Poland

In this paper we consider self-compaction of icy bodies with radii from 60 to 200 km. They could be some of the icy satellites of the giant planets and some of the Kuiper belt objects. It is assumed that the considered globes were formed as porous bodies by the process of homogeneous accretion. They are not products of disruptive collisions. The evolution is considered from an early stage of formation (the embryo stage), through the stage when accretion is completed (present-day mass is settled), until the time when the present state (present-day radius, as well as the moment of inertia, if available) is reached.

The model we use to calculate the evolution of the distributions of density (or porosity) and of temperature is based on that presented by Kossacki and Leliwa-Kopystynski (1993. Planet. Space Sci. 41(10), 729-741). The model can be applied with various rheological formulae for pressure- and temperature-dependent compaction of granular, initially porous, icy-mineral medium. The bodies under consideration are assumed to be composed of water ice with an admixture of ammonia and of silicates. The components are uniformly distributed with a mass ratio C of silicates to total being fixed. An abundance x of ammonia relative to water is one of the crucial parameters of the model. The internal sources of energy leading to the evolution are: (i) the gravitational energy of initially porous globes; and (ii) the energy of radioactive decay of radionuclides dispersed within the mineral component. The amount of long lived isotopes is that corresponding to chondritic meteorites. Moreover, an initial presence of short lived Al26 is not excluded a priori. Its initial abundance is another parameter of the model.

The particular examples of calculations concern bodies with the sizes and densities of Mimas, Janus and Epimetheus. The three-dimensional (3-D) presentation of the results has allowed us to estimate physically reasonable ranges for ammonia and Al26 contents.

Published in: Planetary and Space Science, 48, 727 (2000 June)

Orbit Fitting and Uncertainties for Kuiper Belt Objects
Gary Bernstein1 and Bharat Khushalani2

1 Department of Astronomy, University of Michigan, Ann Arbor, MI 48109-1090, USA
2 Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI 48109-2140, USA

We present a procedure for determination of positions and orbital elements, and associated uncertainties, of outer Solar System planets. The orbit-fitting procedure is greatly streamlined compared to traditional methods because acceleration can be treated as a perturbation to the inertial motion of the body. These techniques are immediately applicable to Kuiper Belt Objects, for which recovery observations are costly. Our methods produce positional estimates and uncertainty ellipses even in the face of the substantial degeneracies of short-arc orbit fits; the sole a priori assumption is that the orbit should be bound or nearly so. We use these orbit-fitting techniques to derive a strategy for determining Kuiper Belt orbits with a minimal number of observations.

Orbit-fitting software is available via: http://www.astro.lsa.umich.edu/users/garyb

To appear in: The Astronomical Journal

Preprints available on the web at http://arXiv.org/abs/astro-ph/0008348

Comparative Study of Mean-Motion Resonances in the Trans-Neptunian Region
M. D. Melita1 and A. Brunini1

1 Facultad de Ciencias Astronómicas y Geofísicas, Universidad Nacional de La Plata, La Plata, Argentina

In this work we are interested in the present dynamical structure of the trans-neptunian region. It is known that at moderate to high eccentricities, stable orbits lie close to an exterior-mean-motion resonance with Neptune (NMMR). We study some NMMRs under different points of view. Intrinsic probabilities of collision and dynamical diffusion time-scales using frequency-map analysis have been computed. We have found that collisions and gravitational encounters by themselves would not produce remarkable differences between the number of objects orbiting in each resonance at present. However, frequency-map analysis reveals a much more robust region at the 2:3 NMMR than at the other NMMRs. Naturally the net orbital effect of the encounters can be enhanced differently in each individual NMMR due to differences in size of the stable niches, allowing the populations in the more unstable regions to evaporate sooner. We also study how certain evolutionary models, related with the orbital expansion of the outer planets during their formation stage, could result in resonant populations with a noticeably different primordial number of members. Finally, our results are discussed with reference to the present observational evidence and to our current understanding of the formation of the outer Solar System.

Published in: Icarus, 147, 205 (2000 September)

For preprints, contact melita@fcaglp.unlp.edu.ar

Planetary Migration and Plutinos Orbital Inclinations
R. S. Gomes1

1 Observatório Nacional, Rua General José Cristino, 77, 20921-400, Rio de Janeiro, RJ, Brazil

I investigate which mechanisms could have acted during Neptune's past radial migration to excite plutinos orbital inclinations to their present values. These processes include Kozai resonance and the $\nu_{18}$ secular resonance, both prior to and after the plutino's capture into the 2:3 mean motion resonance with Neptune. In the case $\nu_{18}$ acted before the 2:3 resonance encounter, the plutino would have been originally formed near 34 AU. If the plutino was captured near the beginning of the migration process at around 30.5 AU then the secular resonance must have acted inside the 2:3 resonance with high amplitude libration. In this case, the libration amplitude must damp either during the migration by some dynamical process or after migration through dynamical scattering by other Kuiper Belt objects, thus making the final orbit stable. All plutinos with well determined orbits and inclination above $10^{\circ}$ seem to have suffered secular resonance.

To appear in: The Astronomical Journal

For preprints, contact rodney@on.br

A Wide-Field CCD Survey For Centaurs and Kuiper Belt Objects
Scott S. Sheppard1, David C. Jewitt1, Chadwick A. Trujillo1, Michael J. I. Brown2, and Michael C. B. Ashley3

1 Institute for Astronomy, University of Hawaii, 2680 Woodlawn Drive, Honolulu, HI 96822, USA
2 School of Physics, University of Melbourne, Parkville, Vic. 3010, Australia
3 School of Physics, University of New South Wales, NSW 2052, Australia

A modified Baker-Nunn camera was used to conduct a wide-field survey of 1428 deg2 of sky near the ecliptic in search of bright Kuiper Belt objects and Centaurs. This area is an order of magnitude larger than any previously published CCD survey for Centaurs and Kuiper Belt Objects. No new objects brighter than red magnitude mR=18.8 and moving at a rate 1'' hr-1 to 20'' hr-1 were discovered, although one previously discovered Centaur 1997 CU26 Chariklo was serendipitously detected. The parameters of the survey were characterized using both visual and automated techniques. From this survey the empirical projected surface density of Centaurs was found to be $\Sigma_{C}(m_{R}\leq 18.8)=7.8(^{+16.0}_{-6.6})\times 10^{-4} \mbox { deg}^{-2}$ and we found a projected surface density $3\sigma$ upper confidence limit for Kuiper Belt objects of $\Sigma_{K}(m_{R}\leq 18.8)<4.1\times 10^{-3} \mbox{ deg}^{-2}$. We discuss the current state of the cumulative luminosity functions of both Centaurs and Kuiper Belt objects. Through a Monte Carlo simulation we show that the size distribution of Centaurs is consistent with a $q\sim 4$ differential power law, similar to the size distribution of the parent Kuiper Belt Objects. The Centaur population is of order $1\times 10^{7}$ (radius $\geq$1 km) assuming a geometric albedo of 0.04. About 100 Centaurs are larger than 50 km in radius, of which only 4 are presently known. The current total mass of the Centaurs is 10-4  $M_{\oplus}$. No dust clouds were detected resulting from Kuiper Belt object collisions, placing a $3\sigma$ upper limit <600 collisionally produced clouds of mR<18.8 per year.

To appear in: The Astronomical Journal (2000 November)

For preprints, contact sheppard@ifa.hawaii.edu
or on the web at http://arXiv.org/abs/astro-ph/0008445

Signatures of Exo-solar Planets in Dust Debris Disks
Leonid M. Ozernoy1,2, Nick N. Gorkavyi2,3, John C. Mather2, and Tanya A. Taidakova4

1School of Computational Sciences and Department of Physics & Astronomy, 5C3, George Mason U., Fairfax, VA 22030-4444, USA
2Code 685, Laboratory for Astronomy and Solar Physics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
3NRC/NAS
4 Computational Consulting Services, College Park, MD 20740, USA

We apply our recently elaborated, powerful numerical approach to the high-resolution modeling of the structure and emission of circumstellar dust disks, incorporating all relevant physical processes. Specifically, we examine the resonant structure of a dusty disk induced by the presence of one planet. It is shown that the planet, via resonances and gravitational scattering, produces (1) an asymmetric resonant dust belt with one or more clumps intermittent with one or a few off-center cavities; and (2) a central cavity void of dust. These features can serve as indicators of a planet embedded in the circumstellar dust disk and, moreover, can be used to determine its major orbital parameters and even the mass of the planet. The results of our study reveal a remarkable similarity with various types of highly asymmetric circumstellar disks observed with the James Clerk Maxwell Telescope around Epsilon Eridani and Vega. The proposed interpretation of the clumps in those disks as being resonant patterns is testable - it predicts the asymmetric design around the star to revolve, viz., by $1.2^\circ$-$1.6^\circ$ yr-1about Vega and $0.6^\circ$-$0.8^\circ$ yr-1 about $\epsilon$ Eri.

Published in: The Astrophysical Journal Letters, 537, L147 (2000 July 10)

For preprints, contact ozernoy@science.gmu.edu
or on the web at http://arXiv.org/abs/astro-ph/0007014

PAPERS RECENTLY SUBMITTED TO JOURNALS


The Size Distribution of the Kuiper Belt Objects

Cheng-Pin Chen and Ing-Guey Jiang

Academia Sinica, Institute of Astronomy and Astrophysics, Taipei, Taiwan

Submitted to: The Astrophysical Journal Letters

For preprints, contact jiang@asiaa.sinica.edu.tw
or on the web at http://arXiv.org/abs/astro-ph/0008171

Distribution of Dust from Kuiper Belt Objects

Nick N. Gorkavyi1,2, Leonid M. Ozernoy3,2, Tanya Taidakova4, and John C. Mather2

1 NRC/NAS Senior Research Associate
2 Code 685, Laboratory for Astronomy and Solar Physics, NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA
3 5C3, School of Computational Sciences and Department of Physics & Astronomy, George Mason U., Fairfax, VA 22030-4444, USA
4 Computational Consulting Service, College Park, MD 20740, USA

Submitted to: Planetary and Space Science

For preprints, contact gorkavyi@stars.gsfc.nasa.gov or ozernoy@stars.gsfc.nasa.gov
or the web at http://arXiv.org/abs/astro-ph/0006435

OTHER ARTICLES


Into the Outer Limits

S. Alan Stern1

1 Southwest Research Institute, Suite 426, 1050 Walnut Street, Boulder, CO 80302, USA

Published in: Astronomy, 28, 52 (2000 September 1)

For reprints, contact astern@boulder.swri.edu

CONFERENCE PAPERS


Constraints on Collisional Evolution in the Edgeworth-Kuiper Belt: Exploiting The ``Vesta Crust'' Paradigm

D. D. Durda1, S. A. Stern1, J. I. Lunine2, and A. Morbidelli3

1 Southwest Research Institute, 1050 Walnut Street, Boulder, CO 80302, USA
2 Lunar and Planetary Laboratory, University of Arizona, Tucson AZ 85721
3 Institute l'Observatoire de Nice, Nice, F-06304

To appear in: 32nd Annual DPS meeting (2000 October)

Collisional Evolution of Proto-Comets in the Solar Nebula During Ejection to the Oort Cloud: A Key Process

S. A. Stern1, P. R. Weissman2, and D. D. Durda1

1 Southwest Research Institute, Suite 426, 1050 Walnut Street, Boulder, CO 80302, USA
2 Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109, USA

To appear in: 32nd Annual DPS meeting (2000 October)





Newsletter Information

The Distant EKOs Newsletter is dedicated to provide researchers with easy and rapid access to current work regarding the Kuiper belt (observational and theoretical studies), directly related objects (e.g., Pluto, Centaurs), and other areas of study when explicitly applied to the Kuiper belt.

We accept submissions for the following sections:

A LaTeX template for submissions is appended to each issue of the newsletter, and is sent out regularly to the e-mail distribution list. Please use that template, and send your submission to:
ekonews@boulder.swri.edu
The Distant EKOs Newsletter is available on the World Wide Web at:
http://www.boulder.swri.edu/ekonews
Recent and back issues of the Newsletter are archived there in various formats. The web pages also contain other related information and links.

Distant EKOs is not a refereed publication, but is a tool for furthering communication among people interested in Kuiper belt research. Publication or listing of an article in the Newsletter or the web page does not constitute an endorsement of the article's results or imply validity of its contents. When referencing an article, please reference the original source; Distant EKOs is not a substitute for peer-reviewed journals.



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If you move or your e-mail address changes, please send the editor your new address. If the Newsletter bounces back from an address for three consecutive issues, the address will be deleted from the mailing list. All address changes, submissions, and other correspondence should be sent to:
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Joel Parker
2000-09-01