The Kuiper Belt Electronic Newsletter, Issue #7, September 1999


News & Announcements
Abstracts of 4 Accepted Papers
Titles of 2 Submitted Papers
Titles of 24 Conference Contributions
Conference Information
Job Announcements
Newsletter Information


Ethane ice has been detected on Pluto using the Cooled Infrared Spectrograph/Camera (CISCO) instrument on the Subaru Telescope. The ethane appears to be individual grains but is dissolved in the nitogen ice. Details at:

With this issue, Distant EKOs celebrates its first birthday with 289 subscribers in at least 23 countries. Thanks to all the readers and contributors for your support and feedback to make this a valuable communication tool for Kuiper Belt research.

There were 17 new EKO discoveries announced since the previous issue of the Distant EKOs Newsletter:

1999 DH8, 1999 HG12, 1999 HH12, 1999 HJ12, 1998 SN165, 1999 GS46, 1999 JH132, 1999 JJ132, 1999 JK132, 1999 KR16, 1999 KS16, 1999 KT16, 1999 KK17, 1999 KL17, 1999 OA4, 1999 OY3, 1999 OZ3,

It is possible that 1999 KS16 is a rediscovery of the ``lost'' object 1995 GA7 (see M.P.E.C. 1999-O36).

Also, a new Centaur was discovered: 1999 OX3

Current number of EKOs: 191 (and Pluto & Charon)
Current number of Centaurs: 15


Evidence for Early Stellar Encounters in the Orbital Distribution of Edgeworth-Kuiper Belt Objects

Shigeru Ida1,2, John Larwood1,3, and Andreas Burkert1

1 Max-Planck-Institut für Astronomie, Königstuhl 17, D-69117 Heidelberg, Germany
2 Dept. of Earth and Planetary Science, Tokyo Institute of Technology, Tokyo 152-8551, Japan
3 Astronomy Unit, Queen Mary & Westfield College, London E1 4NS, United Kingdom

We show that early stellar encounters can explain the high eccentricities and inclinations observed in the outer part (>42AU) of the Edgeworth-Kuiper Belt (EKB). We consider the proto-sun as a member of a stellar aggregation that undergoes dissolution on a timescale $\sim 10^8$ yrs, such that the solar nebula experiences a flyby encounter at pericenter distance (q) on the order of 100AU. Using numerical simulations we show that a stellar encounter pumps the velocity dispersion in the young solar nebula in the outer parts. In the case of a nearly parabolic encounter with a solar-mass companion the velocity dispersion at $a \ \lower 3pt\hbox{${\buildrel > \over \sim}$ }\0.25q$ is pumped up to such an extent that collisions between planetesimals would be expected to become highly disruptive, halting further growth of planetesimals. This has the consequence that planet formation is forestalled in that region. We also find that a stellar encounter with pericenter distance $q \sim 100$-200AU could have pumped up the velocity dispersion of EKB objects outside 42AU to the observed magnitude while preserving that inside Neptune's 3:2 mean-motion resonance (located at 39.5AU). This allows for the efficient capture of objects by the resonance during a phase of orbital migration by proto-Neptune, which we also test with simulations. We point out that such a stellar encounter generally affects the dynamical and material structure of a protoplanetary disk and the planetesimal distribution can remain imprinted with this signature over much of the main sequence lifetime of the star. In particular, our results support the notion that an analogous process has operated in some recently observed extrasolar dust disks.

To appear in: The Astrophysical Journal

For preprints, contact
or on the web at

Emissivity and the Fate of Pluto's Atmosphere

J.A. Stansberry1 and R.V. Yelle2

1 Steward Observatory, University of Arizona, Tucson 85721
2 Physics and Astronomy, Northern Arizona University, Flagstaff 86011

We present a simplified model for seasonal changes in Pluto's surface-atmosphere system. The model demonstrates the potential importance of the solid-state phase transition between $\alpha$-N2 and $\beta$-N2, and the accompanying change in emissivity, for predicting the seasonal bulk of Pluto's (and Triton's) atmosphere. Specifically, the model shows that under simplified but not unreasonable assumptions Pluto may have nearly the same atmospheric pressure at aphelion as it does now, near perihelion. The emissivity change which accompanies the $\alpha$ -$\beta$ phase change should be included in the next generation of Pluto and Triton seasonal models for the purposes of understanding the evolution of their atmospheres over seasonal and climatic time-scales.

To appear in: Icarus

For preprints, contact

Near-infrared Spectra of Icy Outer Solar System Surfaces: Remote Determination of H2O Ice Temperatures

W.M. Grundy1, M.W. Buie1, J.A. Stansberry2, J.R. Spencer1, and B. Schmitt3

1 Lowell Observatory, 1400 W. Mars Hill Rd., Flagstaff AZ 86001
2 Steward Observatory, University of Arizona, 933 N. Cherry Ave., Tucson AZ 85721
3 Laboratoire de Planetologie de Grenoble, Batiment D de Physique, B.P. 53, 38041 Grenoble Cedex 9, France

We present new 1.20 to 2.35 $\mu$m spectra of satellites of Jupiter, Saturn, and Uranus, and the rings of Saturn, obtained in 1995 and 1998 at Lowell Observatory. For most of the target objects, our data provide considerable improvement in spectral resolution and signal-to-noise over previously published data. Absorption bands with shapes characteristic of low-temperature, hexagonal crystalline H2O ice dominate the spectra of most of our targets in this wavelength range. We make use of newly published temperature-dependent wavelengths and relative strengths of H2O absorption bands to infer ice temperatures from our spectra. These ice temperatures are distinct from temperatures determined from thermal emission measurements or simulations of radiative balances. Unlike those methods, which average over all terrains including ice-free regions, our temperature-sensing method is only sensitive to the ice component. Our method offers a new constraint which, combined with other observations, can lead to better understanding of thermal properties and textures of remote, icy surfaces. Ice temperatures are generally lower than thermal emission brightness temperatures, indicative of the effects of thermal inertia and segregation between ice and warmer, darker materials. We also present the results of experiments to investigate possible changes of water ice temperature over time, including observations of Titania at two epochs, and of Ganymede and saturnian ring particles following emergence from the eclipse shadows of their primary planets. Finally, we discuss limitations of our temperature measurement method which can result from the presence of H2O in phases other than hexagonal ice-I$_{\rm h}$, such as amorphous ice, hydrated mineral phases, or radiation-damaged crystalline ice. Our spectra of Europa and Enceladus exhibit peculiar spectral features which may result from effects such as these.

To appear in: Icarus

For preprints, contact
or on the web at

Forming the Dusty Ring in HR 4796A
Scott J. Kenyon1, Kenneth Wood1, Barbara A. Whitney2, and Michael J. Wolff2

1 Harvard-Smithsonian Center for Astrophysics, 60 Garden St, Cambridge, MA 02138 USA
2 Space Science Institute, Suite 23, 1540 30th Street, Boulder, CO 80303-1012 USA

We describe planetesimal accretion calculations for the dusty ring observed in the nearby A0 star HR 4796A. Models with initial masses of 10-20 times the minimum mass solar nebula produce a ring of width 7-15 AU and height 0.3-0.6 AU at 70 AU in $\sim$ 10 Myr. The ring has a radial optical depth $\sim$ 1. These results agree with limits derived from infrared images and from the excess infrared luminosity.

To appear in: The Astrophysical Journal

For preprints, contact
or on the web at


Triton's Surface Age and Impactor Flux Revisited

S.A. Stern1, & W.B. McKinnon2

1 Department of Space Studies, Southwest Research Institute, #426, 1050 Walnut Street, Boulder, CO 80302, USA
2 Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, Missouri, USA

Submitted to: The Astronomical Journal

For preprints, contact

Collision Rates in the Present-day Kuiper Belt and Centaur Regions: Applications to Surface Activation and Modification on Comets, Kuiper Belt Objects, Centaurs, and Pluto-Charon

D. D. Durda1 & S. A. Stern1

1 Department of Space Studies, Southwest Research Institute, #426, 1050 Walnut Street, Boulder, CO 80302, USA

Submitted to: Icarus

For preprints, contact


The American Astronimical Society's 31st Annual Meeting of the Division of Planetary Science (DPS) meeting will be held October 10-15 in Padova, Italy. The full list of sessions can be found at:
Below I list some Kuiper Belt-related papers to be presented at the meeting:

Modeling Resonant Structure in the Kuiper Belt

E. K. Holmes, S. F. Dermott, K. Grogan

Close Approaches of the trans-Neptunian Objects to Pluto Left Observable Signatures on Their Orbital Distribution

F. Roig, D. Nesvorny, S. Ferraz-Mello

The Physical Nature of Centaur Asteroids; Rotation and Colors

N. Peixinho, J.L. Ortiz, P.J. Gutierrez), A. Doressoundiram, M. Roos-Serote

1-2.5 Micron Spectra of Centaurs and Trans-Neptunian Objects

S. Kern, D. McCarthy, H. Campins, R.H. Brown, M. Rieke, S. Stolovy

Detection of the Kuiper Belt by Stellar Occultation: II

M. Moncuquet, F. Roques

Evidence for Early Stellar Encounters in the Orbital Distribution of Edgeworth-Kuiper Belt Objects

S. Ida, J.D. Larwood, A. Burkert

Pluto's Family: Might Some Plutinos Be Debris from the Pluto-Charon Binary Formation Event?

S.A. Stern, R.M. Canup, E. Asphaug, D.D. Durda

Cratering Rates in the Outer Solar System

K. Zahnle, H. Levison, L. Dones, P. Schenk

Separate Spectra of Charon and Pluto from HST/NICMOS

M.W. Buie, W.M. Grundy, S.D. Kern

Near-infrared spectral observations of Pluto and Charon

W.M. Grundy, M.W. Buie, S.D. Kern

Kuiper Belt Objects

S.C. Tegler, W. Romanishin

Stability of Volatiles in the Kuiper Belt and in Extra-Solar Dust Disks

J. Stansberry, R.H. Brown, J. Lunine, D. Trilling, W. Grundy

Observations of EKOs and Centaurs: Recoveries, Lightcurves, and Visible-IR Colors

J. Wm. Parker, W. D. Vacca

Broad Band Optical Colors of Trans-Neptunian Objects

M.A. Barucci, J. Romon, A. Le Bras, M. Fulchignoni, D. Tholen

A Deep Ecliptic Survey with MOSAIC at Kitt Peak National Observatory

R. L. Millis, M. W. Buie, L. H. Wasserman, J. L. Elliot, R. M. Wagner

The Scattered Kuiper Belt Objects

C. A. Trujillo, D. C. Jewitt, J. X. Luu

Distant TNOs: first results of the ESO survey

A.C. Delsanti, O.R. Hainaut, H. Boehnhardt, C.E. Delahodde, T. Sekiguchi, R.M. West

Pioneer 10 Encounter with a Trans-Neptunian Object at 56 AU?

G. Giampieri, J.D. Anderson, E.K. Lau

Detection of the Kuiper Belt by Stellar Occultation: I

F. Roques, M. Moncuquet

Cometary Activity in TNOs: A Status Report

O.R. Hainaut, C.E. Delahodde, H. Boehnhardt, E. Dotto, M.A. Barucci, K.J. Meech, J. Bauer, R.M West, A. Doressoundiram, G.P. Tozzi

Exploration at the Edge of the Solar System: The Pluto-Kuiper Express Mission

R. J. Terrile

Pluto, The Edgeworth-Kuiper Belt, and the Pluto-Kuiper Express Flyby Mission

S.A. Stern

Uranus and Neptune: Refugees from the Jupiter-Saturn zone?

E. W. Thommes, M. J. Duncan, H. F. Levison

The Effects of Gap Formation and Orbital Migration on Planetary Systems

G. Bryden, D. N. C. Lin


Pluto and Triton: Comparison and Evolution Over Time
23-25 September 1999
Lowell Observatory, Flagstaff, Arizona, USA

A decade after the Voyager flyby of Triton and the end of the Pluto/Charon mutual event season, this meeting will provide an opportunity to synthesize recent investigations of this fascinating class of worlds and to explore and compare processes affecting them over time scales ranging from diurnal to cosmological. Themes to be addressed include recent data, interpretations, and models, as well as consideration of what are the most pressing unanswered questions and how they can be resolved through future work.

For more information, visit:

There will not be a proceedings volume published from this conference (although abstracts will be available at the website). However, there will be a special Pluto/Triton issue of Icarus. Papers can be submitted by any authors, regardless of whether the attended this workshop or not. Submission deadline is November 15, 1999.

The New Era of Wide-Field Astronomy
2000 August 21-24
Centre for Astrophysics, University Of Central Lancashire, Preston, UK

The conference is prompted by the success of the UK Joint Infrastructure Fund bid for VISTA -- the Visible and Infrared Survey Telescope for Astronomy -- a 4-m survey telescope to be constructed in Chile by late 2003.

We are at the beginning of a new era in wide-field astronomy, with major new surveys now in production, and with new telescopes and instruments, both ground- and space-based, scheduled to be in production in the next few years. This conference aims to review the present and future of this exciting new era of wide-field astronomy, and to discuss the optimum exploitation of the remarkable range of new facilities.

The conference will cover all aspects of the new era -- cosmology and both extragalactic and galactic astronomy, from X-ray to radio. Themes include the following:

For more information and preliminary registration visit the conference web site at

Centre for Astrophysics
Attn: Dr R.G. Clowes
University of Central Lancashire
United Kingdom

Phone: +44 (0) 1772 893540
Fax: +44 (0) 1772 892996


The AAS Job Register ( has the most complete and up-to-date listing of astronomy jobs. Here are a selected few jobs I gleaned from the list that may be of interest to Kuiper belt scientists. For brevity, I have omitted the job descriptions, but you can follow the links given below, or from the Distant EKOs job page at

Lowell Postdoctoral Fellowship

Lowell Observatory, Flagstaff, Arizona, USA

Planetary Science Faculty Position

Massachusettes Institute of Technology, Cambridge, Massachusettes, USA

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:
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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.

Moving ... ??

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Joel Parker