Dr. Carl Pilcher, Science Director for Exploration of the Solar System in NASA's Office of Space Science, announces the first issue of the new Solar System Exploration newsletter. It is online at http://sse.jpl.nasa.gov/results/newsletter/newslet.html in PDF format. The newsletter will be published several times a year to keep the planetary science community informed about activities and plans at NASA Headquarters, and to facilitate dialog. They invite your feedback; you can e-mail comments and suggestions to cpilcher@hq.nasa.gov or Ronald.S.Saunders@jpl.nasa.gov
In case you missed it, the Scattered Disk Objects (SDOs) were recently moved from the TNO list to the Centaur list at the Minor Planet Center. This shift includes the following objects:
1995 TL8, 1996 TL66, 1998 XY95, 1999 CF119, 1999 CG119, 1999 CV118, 1999 CY118, 1999 CZ118, 1999 DG8, 1999 DP8, 1999 HW11, 1999 RD215, 1999 RE215, 1999 RJ215, 1999 RU214, 1999 RZ214, 1999 RZ215, 1999 TD10
Since then, a number of new probable SDOs have been added to those lists as well. The object lists and plots on the Distant EKOs website (e.g., http://www.boulder.swri.edu/ekonews/objects/) have been modified to reflect this classification change. The orbital characteristics that define SDOs versus TNOs or Centaurs are not unambiguously established (there is clearly a grey area where there is some overlap), so the division used on the Distant EKOs webpages is not definitive.
There were 45 new TNO discoveries announced since the previous issue of the Distant EKOs Newsletter:
1999 RC216, 2000 CL104, 2000 CM104, 2000 CN104, 2000 CP104, 2000 CQ104, 2000 CE105, 2000 CF105, 2000 CG105, 2000 CH105, 2000 CJ105, 2000 CK105, 2000 CL105, 2000 CM105, 2000 CN105, 2000 CO105, 2000 CQ105, 2000 CS105, 2000 CY105, 2000 FA8, 2000 FB8, 2000 FC8, 2000 FD8, 2000 FE8, 2000 FF8, 2000 FG8, 2000 FH8, 2000 FR53, 2000 FS53, 2000 FT53, 2000 GV146, 2000 GW146, 2000 GX146, 2000 GY146, 2000 GZ146, 2000 FU53, 2000 FV53, 2000 FW53, 2000 FX53, 2000 FY53, 2000 GE147, 2000 GF147, 2000 GK147, 2000 GL147, 2000 GM147
and 6 new Centaur/SDO discoveries:
2000 CO104, 2000 CP105, 2000 CR105, 2000 EC98, 2000 GM137, 2000 FZ53
Current number of TNOs: 270 (and Pluto & Charon)
Current number of Centaurs/SDOs: 42
We present V-J colors of 14 Kuiper Belt objects using new infrared (J) data combined, in most cases, with simultaneous visible (V) data. We confirm the V-J vs absolute magnitude relation reported by Jewitt & Luu (1998) for the five objects in their dataset but demonstrate that the relationship does not hold for a larger sample. Kuiper Belt objects exhibit a wide range of V-J colors but there is no correlation with heliocentric distance or orbital class. The bi-modality seen in BVR colors by Tegler & Romanishin (1998) is not present in optical-infrared colors.
To appear in: Icarus
For preprints, contact j.davies@jach.hawaii.edu
or by anonymous ftp to ftp://ftp.jach.hawaii.edu/pub/ukirt/jkd/v-j/v-j.ps
or on the web at http://www.jach.hawaii.edu/JACpublic/UKIRT/public/research.html
Chiron is among the small population of large, outer Solar System objects
called Centaurs. Chiron's unusual, 51-year orbit ranges in distance from 8.5
to just over 19 AU, and exhibits an inclination to the ecliptic plane of
8.5
.
Recent dynamical studies (Levison and Duncan 1994; Dones et al.
1996) show this orbit is unstable to giant-planet perturbations on timescales
of < 106 years, indicating that it is a recent addition to the planetary
region. This, along with its low-inclination orbit, and its size similarity to
the newly-discovered population of 100-400 km diameter Kuiper Disk objects
(Campins et al. 1994; Jewitt and Luu 1995), provides strong circumstantial
evidence that Chiron is an escaped object from the Kuiper Disk. Chiron's
present orbit subjects it to much more intense insolation than objects in the
Kuiper Disk experience. That insolation generates surface activity, as revealed
by a highly variable coma (Hartmann et al. 1989; Meech and Belton 1990; Bus
et al. 1993). The source of Chiron's activity has been speculated on for many
years (Stern 1989) but never observationally identified. We report here the
detection of CO molecules in Chiron's coma, which are probably the sublimation
agent generating Chiron's activity.
Published in: Solar System Research (Astronomicheskii Vestnik), 33, 187 (1999)
For preprints, contact alan@boulder.swri.edu
or on the web at http://www.boulder.swri.edu/~alan/papers/chiron_co.ps
Planets are believed to have formed through the accumulation of a large number of small bodies. In the case of the gas-giant planets Jupiter and Saturn, they accreted a significant amount of gas directly from the protosolar nebula after accumulating solid cores of about 5-15 Earth masses. Such models, however, have been unable to produce the smaller ice giants Uranus and Neptune at their present locations, because in that region of the Solar System the small planetary bodies will have been more widely spaced, and less tightly bound gravitationally to the Sun. When applied to the current Jupiter-Saturn zone, a recent theory predicts that, in addition to the solid cores of Jupiter and Saturn, two or three other solid bodies of comparable mass are likely to have formed. Here we report the results of model calculations that demonstrate that such cores will have been gravitationally scattered outwards as Jupiter, and perhaps Saturn, accreted nebular gas. The orbits of these cores then evolve into orbits that resemble those of Uranus and Neptune, as a result of gravitational interactions with the small bodies in the outer disk of the protosolar nebula.
Published in: Nature, 402, 635 (1999 December 9)
For preprints, contact duncan@astro.queensu.ca
or on the web at http://www.astro.queensu.ca/~thommes/402635A0.pdf
We report on repeated far-infrared photometric observations of the Pluto-Charon
system conducted in 1997 with the Infrared Space Observatory (ISO). These
observations have led to the first detection of the system at 150 and
200 
m and to the first clear detection of its thermal lightcurve at
60 m (and more marginally at 100 m). They definitely prove that
Pluto's surface is not isothermal. The thermal lightcurve is, as expected,
roughly anticorrelated with the visible lightcurve, but not exactly. The data
are fit by physical models including Charon and three separate units on Pluto,
respectively dominated by (1) N2 ice, (2) CH4 ice, and (3) tholins. These
models are constructed in accordance with information from visible imaging and
lightcurve, visible spectroscopy and infrared spectroscopy, considerations on
the thermal balance of N2 and CH4, and include a thermophysical
description of subsurface conduction and infrared beaming. Charon's
contribution, which cannot be separated from Pluto's in the observations, is
assumed to be independent of longitude and equivalent to that of a 
52 K
body. The main implications are that Pluto's surface in units 2 and 3 has a
thermal inertia 
=
(1.5-10)
104 erg cm-2 s-1/2 K-1, comparable to that
of other icy satellites, and relatively high bolometric emissivities (not lower
than 0.5 and most likely 0.8-1). Diurnal temperature variations must be
significant, with maximum dayside temperatures in the range 54-63 K. The
value of thermal inertia may be indicative of porosity in the top centimeters
of Pluto's surface. The observations further confirm that the far-IR brightness
temperatures, though somewhat smaller than indicated by IRAS, are higher than
in the millimeter/submillimeter range. Extending the models to longer
wavelengths suggests that a low radio emissivity, as opposed to a mixing of
temperatures or a subsurface sounding effect, is the correct explanation.
Finally, in spite of large error bars, the 150 m fluxes indicated by ISO
seem unexpectedly high given the spectral properties of ices in the far-IR.
These, and the expected lightcurves of the Pluto-Charon system at
= 15-60 m should be priority measurements for SIRTF.
To appear in: Icarus
For preprints, contact Emmanuel.Lellouch@obspm.fr
We report on 224 photometric measurements of Nereid, a small outer satellite of
Neptune with a 360-day orbit of high eccentricity (0.751). Our photometry
covers 64 nights from 1987 to 1997 and is primarily in the V-band, although
we also have 20 measurements in the U, B, R, and I bands. (1) Nereid
displays large-amplitude brightness variations with a total amplitude of 1.83
magnitude on time scales ranging from a few hours to roughly a year. (2) During
the 12 days of the Voyager encounter with Neptune, Nereid did not display any
short-term variations, however large-amplitude long-term variations could
easily be hidden by the large phase effects and the short duration of
observation. (3) Nereid's variability is caused by high contrast albedo
features, i.e. a dark hemisphere, along with rotational modulation. (4) The
character of the brightness variations changed around 1991 from fast and
large-amplitude to comparatively slow and low-amplitude. This demonstrates that
the direction and magnitude of Nereid's rotational angular momentum vector is
changing on time scales comparable to its orbital period. (5) Large changes in
the magnitude and direction of Nereid's angular momentum vector are predicted
to arise from chaotic rotation during every periapse passage provided that
Nereid is more than 1% nonspherical and is spinning slowly. The match
between prediction and observation could be taken as strong evidence for
chaotic rotation of Nereid. However, the intranight variability cannot be
readily explained by chaotic rotation. (6) The colors of Nereid are
,
,
,
,
and
V-K=1.6, indicating a nearly flat reflectance spectrum from 0.36 to
2.2 m. We identify asteroids, inner satellites, and centaurs with similar
spectra. (7) Nereid is likely either an inner moon of Neptune kicked to its
current orbit or a captured Kuiper Belt object or Centaur, with the latter
possibility being strongly preferred.
To appear in: Icarus
For preprints, contact schaefer@grb2.physics.yale.edu
or on the web at http://xxx.lanl.gov/abs/astro-ph/0005050
Failed Oort Clouds and Planetary Migration
Brad M. S. Hansen1
1 Department of Astrophysical Sciences, Peyton Hall, Princeton University, Princeton, NJ, 08544-1001, USA
Submitted to: The Astrophysical Journal Letters
For preprints, contact hansen@astro.princeton.edu
or on the web at http://xxx.lanl.gov/abs/astro-ph/0004058
Chiron
Joel Wm. Parker1
1 Southwest Research Institute, Boulder, CO 80302 USA
Published in: The Encyclopaedia of Astronomy and Astrophysics
For preprints, contact joel@boulder.swri.edu
or by anonymous ftp to ftp://ftp.boulder.swri.edu/pub/joel/chiron_enc.ps.gz
or on the web at http://www.boulder.swri.edu/~joel/papers.html
Below is the list of the few Kuiper Belt-related papers I gleaned from the program for the 196th Meeting of the American Astronomical Society (2000 June 4-8, Rochester, NY, USA):
We accept submissions for the following sections:
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.