Distant EKOs Issue #8 (November 1999)


News & Announcements
Abstracts of 5 Accepted Papers
Conference Information
Job Announcements
Newsletter Information


Two more Centaurs have been named:
1995 GO (8405) = Asbolus
1997 CU26 (10199) = Chariklo

Did the Pioneer 10 spacecraft have a close encounter with an EKO?

Pioneer page: http://spaceprojects.arc.nasa.gov/Space_Projects/pioneer/PNhome.html
BBC story: http://news.bbc.co.uk/hi/english/sci/tech/newsid_460000/460095.stm

There were 6 (or 7...?) new EKO discoveries announced since the previous issue of the Distant EKOs Newsletter:
1999 KR18, 1999 OC4, 1999 OD4, 1999 OE4, 1999 OF4, 1999 TR11

Then, there is the question of 1999 TD10, which with a current heliocentric distance of 13 AU was assumed to be a Centaur (MPEC 1999-T46). However, followup observations now give a nominal solution of a semi-major axis of 155 AU, although ``The semimajor axis could be as small as 75 AU. A parabolic orbit also fits the data.'' (MPEC 1999-V07). At the moment, 1999 TD10 is not listed by the Minor Planet Center as either a Centaur or an EKO, though it apparently is a related scattered disk-type object. This unusual object clearly warrants further observations.
MPEC 1999-T46 -- http://cfa-www.harvard.edu/mpec/J99/J99T46.html
MPEC 1999-V07 -- http://cfa-www.harvard.edu/mpec/J99/J99V07.html

One Centaur discovery was reported minutes before this issue was sent out:
1999 UG5

Current number of EKOs: 197 (and Pluto & Charon)
Current number of Centaurs: 16


Light curves of the Trans-Neptunian Objects
1996 TP66 and 1994 VK8

S.J. Collander-Brown1, A. Fitzsimmons1, E. Fletcher1, M.J. Irwin2 and I.P. Williams3

1Dept. of Pure and Applied Physics, Queens University, Belfast, UK
2Institute of Astronomy, Cambridge University, Cambridge, UK
3Astronomy Unit, Queen Mary and Westfield College, London, UK

We have obtained a number of CCD images of two Trans-Neptunian Objects, 1994 VK8 and 1996 TP66, over two nights. The changes in magnitude of these objects were then examined, in a search for periodic variation. In the case of 1996 TP66 nothing other than random noise could be found to within the errors of $\sim0.04$ magnitudes. Though a periodic signal was found for 1994 VK8 it appears to be an artifact, as the same frequency appears in the variation of sky brightness and is probably due to the sampling of the data. However 1994 VK8 did exhibit a variation of $\sim0.5$ magnitudes. This would suggest either significant non-sphericity or a change in surface composition over a large area. In either case 1994 VK8 warrants further investigation.

Published in: Monthly Notices of the Royal Astronomical Society (vol 308, p 588)

For preprints, contact S.C.Brown@qub.ac.uk

Spectrophotometry of Four Kuiper Belt Objects with NICMOS

K. S. Noll1, J. Luu2, and D. Gilmore1

1 Space Telescope Science Institute, 3700 San Martin Dr., Baltimore MD 21218, USA
2 Leiden University, Postbus 9504, 2300 RA Leiden, The Netherlands

We have obtained spectrophotometric observations of four Kuiper Belt objects using the Hubble Space Telescope's Near Infrared Camera and Multi-Object Spectrometer, NICMOS, in broad and medium bandwidth filters selected to search for the presence of strong solid state spectral features in the 1.6-2.2 m$\mu$m range. We find distinct differences in the spectra of the four objects. The spectra of 1996 TQ66, 1996 TP66, and 1996 TS66 are broadly similar; red optical colors and red-neutral colors from 1.0-2.5 m$\mu$m. 1996 TS66 and 1996 TQ66 show evidence of an absorption feature near 1.9 m$\mu$m. This feature is unidentified, but is inconsistent with water ice. In sharp contrast, the reflectance of 1996 TO66 drops by more than a factor of two from 1 - 2 m$\mu$m and displays discrete features consistent with absorption by water ice as reported by others. The surface composition of Kuiper Belt objects as revealed by infrared observations is considerably more complex than the suggested by the possible bimodal distribution of optical colors in these objects.

To appear in: Astronomical Journal, February 2000

For preprints, contact noll@stsci.edu

Spectrophotometric Observations of
Edgeworth-Kuiper Belt Objects

M.A. Barucci1, A. Doressoundiram1, D. Tholen2, M. Fulchignoni1,3and M. Lazzarin4

1 Observatoire de Paris,92195 Meudon, France
2 IfA, Univ. of Hawaii, Honolulu, Hawaii 96822, USA
3 Univ. Paris VII, Paris, Italy
4 Dipartimento di Astronomia, Univ. di Padova, 35122 Padua, Italy

The Edgeworth-Kuiper Belt (EKB) objects are fossil remnants of the formation of the Solar System and they represent an important reservoir of primordial, thermally unprocessed material. The study of these objects has rapidly evolved in the last few years. The new observational works allowed the planetary scientists to investigate evolutionary and dynamical processes in the outer solar system, putting some constraints on, for example, the origin of comets and the accretion of planetesimals. The chemical and physical information on this population is still very poor: intensive observational studies are needed. For this reason we started in 1997 a spectrophotometric observation programme at ESO with the NTT telescope to investigate the EKB. We present the obtained results for six objects (1994 JR1, 1994 TB, 1995 QY9, 1996 TL66, 1996 TO66, and 1996 TP66). We analysed all the B, V, R, and I data available in the literature to investigate some bulk properties. We found an indication of a complex and inhomogeneous population.

To appear in: Icarus, vol. 142

For preprints, contact barucci@obspm.fr

Triton's Surface Age and Impactor Population Revisited in Light of Kuiper Belt Fluxes: Evidence for Small Kuiper Belt Objects and Recent Geological Activity

S.A. Stern1, and 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

Neptune's largest satellite, Triton, is one of the most fascinating and enigmatic bodies in the solar system. Among its numerous interesting traits, Triton appears to have far fewer craters than would be expected if its surface was primordial. Here we combine the best available crater count data for Triton with improved estimates of impact rates by including the Kuiper Belt as a source of impactors. We find that the population of impactors creating the smallest observed craters on Triton must be sub-km in scale, and that this small-impactor population can be best fit by a differential power-law size index near -3. Such results provide interesting, indirect probes of the unseen small body population of the Kuiper Belt. Based on the modern, Kuiper Belt and Oort Cloud impactor flux estimates, we also recalculate estimated ages for several regions of Triton's surface imaged by Voyager 2, and find that Triton was probably active on a time scale no greater than 0.1-0.3 Gyr ago (indicating Triton was still active after some 90% to 98% of the age of the solar system), and perhaps even more recently. The time-averaged volumetric resurfacing rate on Triton implied by these results, 0.01 km3 yr-1 or more, is likely second only to Io and Europa in the outer solar system, and is within an order of magnitude of estimates for Venus and for the Earth's intraplate zones. This finding indicates that Triton likely remains a highly geologically active world at present, some 4.5 Gyr after its formation. We briefly speculate on how such a situation might obtain.

To appear in: The Astronomical Journal

For preprints, contact alan@boulder.swri.edu

Disappearance of Stellar Debris Disks around Main-sequence Stars after 400 Million Years

H.J. Habing1, C. Dominik1, M. Jourdain de Muizon2, M.F. Kessler3, R.J. Laureijs3, K. Leech3, L. Metcalfe3, A. Salama3, R. Siebenmorgen3, and N. Trams4

1 Leiden Observatory, The Netherlands
2 Observatoire de Paris and LAEFF, VILSPA, Spain
3 European Space Agency, ISO operations, VILSPA, Spain
4 Space Science Division, European Space Agency, ESTEC, Noordwijk, The Netherlands

Almost 5 billion years ago, the Sun formed in a local contraction of a cloud of molecular gas. A rotating disk of gas and dust is believed to have fed material onto the proto-Sun for the first few million years of its life, and to have formed the planets, comets and other Solar System objects. Similar disks, but with less mass, have been observed around a few main-sequence stars such as Vega. The dust particles orbiting stars like Vega will be removed on timescales of the order of 1 Myr (Vega is about 350 Myr old), and therefore must be resupplied, at least for a time. But earlier surveys lacked the sensitivity to determine how many nearby stars have dust disks, and which ones truly do not have a disk. Here we report infrared observations on a sample of 84 stars indicating that most stars younger than 300 Myr have dust disks, while most older than 400 Myr do not: ninety per cent of the disks disappear when the star is between 300 and 400 Myr old. Several events that are related to the ``clean up'' of debris in the early history of our Solar System have a similar timescale.

Published in: Nature, 401, 456 (1999 September 30)

Preprints can be obtained via ftp at: ftp://strw.leidenuniv.nl/pub/habing/nature.ps.gz


IAU Colloquium 180: Towards Models and Constants for Sub-microarcsecond Astrometry

27-31 March 2000
U.S. Naval Observatory, Washington, DC, USA


The adoption of the International Celestial Reference System (ICRS) by the XXIII General Assembly of the IAU has provided an improved reference system for positional astronomy. The major purpose of this colloquium is to prepare resolutions for consideration by the XXIV IAU General Assembly that will complete the specification of the ICRS. These resolutions will, in effect, specify definitions, standard algorithms, and parameters that link observable quantities with reference coordinates within the ICRS system. Specifically to be recommended are definitions of the celestial ephemeris pole and celestial ephemeris origin, an improved precession/nutation theory, and a new set of standard values for astronomical constants.

This colloquium will also discuss future requirements of the celestial reference system that are necessary to support present and planned high-precision astrometric programs. The microarcsecond-level of precision anticipated for future observational systems demands improved models at all levels of analysis. These improved models are likely to require increased attention to the definitions of the various reference frames involved and the transformations between them, within a well defined relativistic framework.

US - European Celestial Mechanics Workshop
3-7 July 2000
Adam Mickiewicz University, Poznan, Poland

The primary purpose of the Workshop is to develop collaborative research activities in Celestial Mechanics between young scientists in the US and the former Eastern Block countries. However, this goal cannot be accomplished without the recognition and assessment of current research activities in Celestial Mechanics worldwide. To that end, various aspects of theoretical and applied Celestial Mechanics will be discussed to establish the current status and prospects for future research in this branch of astronomy.

The expectation is that out of this workshop will come proposals for collaborative research grants in Celestial Mechanics. The Workshop is to present review papers on selected subjects along with contributed papers and poster papers. Each Workshop session will be followed by a discussion about the prospects of future research on the session topic.

The Workshop will comprise approximately 12 sessions each with a preliminary review paper for each topic followed by a limited number of contributed papers. Workshop sessions are to be divided among the broad categories listed below:

Chaos, Resonances & Stability
Kuiper Belt Objects
Satellites, Minor Planets, Comets, and Meteors
Orbit Uncertainty and Error Analysis for NEO and Artificial Satellites
Stellar and Galactic Dynamics
Drag and Atmospheric Modeling & Theory (Non-gravitational Force Modeling)
Numerical Methods, Parallel Processing, Ephemeris Generation
Satellite Constellation Dynamics and Control
Orbit and Attitude Dynamics
NEO and Debris Observations and Motions
Reference Systems for Astronomy and Astrodynamics
Exo-planetary systems

For further information, visit the website: http://www.astro.amu.edu.pl/Science/Conference
or contact:

Prof. Edwin Wnuk
Astronomical Observatory
Adam Mickiewicz University
Sloneczna 36
PL 60286 Poznan

Fax: +48 (0)618686511
E-mail: wnuk@juno.astro.amu.edu.pl or wnuk@amu.edu.pl

IAU Symposium 202: Planetary Systems in the Universe - Observation, Formation and Evolution
7-10 August 2000
Manchester, UK


The main topics of the symposium will be:

The aim of the symposium is to join the new extra-solar planet discoveries, the observations of dust disks round stars and other planetary system and Solar System observations into the context of our theories of the formation and evolution of planetary systems. A goal will be to consider how future observations and searches and theoretical studies can best work together. It is hoped to bring together planetary system and Solar System observers and theoreticians.

For further information, visit the website: http://astro1.bnsc.rl.ac.uk/symp202/
or send e-mail to: symp202@ast.star.rl.ac.uk


It is the time of year when job announcements are more plentiful. The AAS Job Register is an excellent centralized source for astronomy jobs: postdoctoral, tenure-track, education/public outreach, research, teaching, etc. 82 new positions were announced in October and 86 in November. Though none explicitly mentioned Kuiper Belt research, quite a few were interested in applicants with related skills (observation, dynamics, numerical modeling, solar system formation, planetary science, instruction), so rather than list the jobs here, I recommend perusing the Job Register at the following address link:


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:

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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