There were 9 new TNO discoveries announced since the previous issue of Distant EKOs:
2003 UA414, 2003 UZ413, 2004 NT33, 2004 PF115, 2004 PG115, 2004 XA192, 2005 CA79, 2005 CB79, 2005 UQ513
and 6 new Centaur/SDO discoveries:
2004 LR31, 2005 CC79, 2003 UY413, 2005 QU182, 2007 NC7, 2007 OC10
Reclassified objects:
2007 JG43 (CentaurSDO)
2007 JG43 (SDO
Objects recently assigned numbers:
2000 OL67 = (160091)
2001 KN76 = (160147)
2001 KV76 = (160148)
2002 PD149 = (160256)
2005 RL43 = (160427)
Current number of TNOs: 1063 (including Pluto)
Current number of Centaurs/SDOs: 205
Current number of Neptune Trojans: 5
Out of a total of 1273 objects:
543 have measurements from only one opposition
505 of those have had no measurements for more than a year
268 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.gif)
Aims: The surface composition of the largest TNO, the dwarf planet 136199 Eris, is studied and compared to Pluto's.
Methods: High signal-to-noise visible and near-infrared reflectance spectra were obtained at the TNG and ESO-VLT observatories. The nature and properties of the compounds present on the surface of Eris are investigated by applying Hapke and Shkuratov radiative transfer models to our spectra.
Results: The surface of Eris can be modeled using two areas of distinct composition: about 50% appears to be covered with pure methane ice, while the rest of its surface would be made of an intimate mixture of methane, nitrogen and water ices, and ice tholin. The use of nitrogen in our model is shown to improve significantly the data fit, in particular for high surface albedo values. The icy grains are found to be large, from sub-mm to a few tens of mm in size.
Published in: Astronomy and Astrophysics, 471, 331 (2007 August)
Vis-NIR spectra of some Centaurs and Trans-Neptunian Objects (TNOs)
indicate surfaces rich in H2O, N2, CO2, CH4 and CH3OH.
Cosmic ion irradiation is one of the processes driving the evolution
of TNO surfaces. A main role is played by the chemistry induced by
colliding ions; many molecular bonds are broken along the ion track,
and this may lead to the formation of byproduct molecules. Starting
from laboratory experiments, it is possible to infer the presence
of molecules still undetected on TNOs. For instance, carbonic acid
(H2CO3) is produced after irradiation of H2O:CO2 icy
mixtures, while irradiation of H2O:N2 icy mixtures causes the
production of N2O, NO, and NO2. From H2O:CH4:N2 mixtures,
many species are formed, such as CO, CO2, HCN, HNCO, N2O, and
molecules including CN bonds. Moreover, ion irradiation may modify
the relative intensity of NIR features, as in the case of solid
methanol, whose 2.34 
m band decreases in intensity with respect
to the 2.27 m band, after increasing irradiation doses. We
suggest that this effect may be observed on Centaur Pholus.
Published in: Memorie della Societa Astronomica Italiana Supplement, 11, 185
For preprints, contact gbaratta@oact.inaf.it
or on the web at
http://sait.oat.ts.astro.it/MSAIS/11/PDF/185.pdf
We present here an extensive survey of near infrared spectra of Kuiper belt objects (KBOs) and Centaurs taken with the Keck I Telescope. We find that most spectra in our sample are well characterized by a combination of water ice and a featureless continuum. A comparative analysis reveals that the near Infrared (NIR) spectral properties have little correlation to the visible colors or albedo, with the exception of the fragment KBOs produced from the giant impact on 2003 EL61. The results suggest that the surface composition of KBOs is heterogeneous, though the exposure of water ice may be controlled by geophysical processes. The Centaurs also display diverse spectral properties, but the source of the variability remains unclear. The results for both the KBOs and the Centaurs point to inherent heterogeneity in either the processes acting on these objects or materials from which they formed.
To appear in: The Astronomical Journal
Preprints available at
http://www.gps.caltech.edu/~barkume/publications.html
We present U-band photometry of Kuiper Belt objects taken to further investigate their color-orbit systematics. As at longer optical and near-infrared wavelengths, the U-band colors of Kuiper Belt objects show a wide range and a unimodal distribution. We find no evidence that color systematics in the Kuiper belt are strongly wavelength dependent. This observation is consistent with control of the reflection characteristics by a single (but unidentified) reddening material. No evidence is found for blue/ultraviolet absorption that can arise from charge-transfer transitions in hydrated minerals in some primitive (C-type) asteroids. In the classical KBOs alone the U-B and other color indices are most strongly correlated with the Tisserand parameter measured with respect to Neptune.
To appear in: The Astronomical Journal (2007 December)
The collisional family of Kuiper belt object (KBO) 2003 EL61 opens
the possibility for many interesting new studies of processes
important in the formation and evolution of the outer solar system.
As the first family in the Kuiper belt, it can be studied using
techniques developed for studying asteroid families, although some
modifications are necessary. Applying these modified techniques
allows for a dynamical study of the 2003 EL61 family. The velocity
required to change orbits is used to quantitatively identify objects
near the collision. A method for identifying family members that
have potentially diffused in resonances (like 2003 EL61) is also
developed. Known family members are among the very closest KBOs
to the collision and two new likely family members are identified:
2003 UZ117 and 1999 OY3. We also give tables of candidate family
members which require future observations to confirm membership.
We estimate that a minimum of 
1 GYr is needed for resonance
diffusion to produce the current position of 2003 EL61, implying
that the family is likely primordial. Future refinement of the age
estimate is possible once (many) more resonant objects are identified.
The ancient nature of the collision contrasts with the seemingly
fresh surfaces of known family members, suggesting that our
understanding of outer solar system surfaces is incomplete.
To appear in: The Astronomical Journal
For preprints, contact darin@gps.caltech.edu
or on the web at http://arxiv.org/abs/0709.0328
We analyze the Centaur population as a group of objects with
perihelion distances (q) of less than 30 AU and heliocentric
distances outside the orbit of Jupiter, formed by objects entering
this region from the Scattered Disk (SD). We perform a numerical
integration of 95 real scattered disk objects (SDOs) extracted from
the Minor Planet Center database and of 905 synthetic SDOs compensating
for observational biases. SDOs have in the Centaur zone a mean
lifetime of 72 My, though this number falls with a decrease of q.
After this incursion, 30% of them enter the zone interior to
Jupiter's orbit. We find that the contribution to the Centaur
population from the SD gives a total of
Centaurs with a radius R > 1 km. We also propose a model for the
intrinsic distribution of orbital elements of Centaurs and their
distance and apparent magnitude distribution.
Published in: Icarus, 190, 224 (2007 September)
For preprints, contact romina@fcaglp.unlp.edu.ar
The inverse square law of gravity is poorly probed by experimental
tests at distances of 10 AUs. Recent analysis of the trajectory
of the Pioneer 10 and 11 spacecraft have shown an unmodeled
acceleration directed toward the Sun which was not explained by any
obvious spacecraft systematics, and occurred when at distances
greater than 20 AUs from the Sun. If this acceleration represents
a departure from Newtonian gravity or is indicative of an additional
mass distribution in the outer solar system, it should be detectable
in the orbits of Trans-Neptunian Objects (TNOs). To place limits
on deviations from Newtonian gravity, we have selected a well
observed sample of TNOs found orbiting between 20 and 100 AU from
the Sun. By examining their orbits with modified orbital fitting
software, we place tight limits on the perturbations of gravity
that could exist in this region of the solar system.
Published in: The Astrophysical Journal, 666, 1296 (2007 Sep 10)
For preprints, contact jwallin@gmu.edu
or on the web at http://arxiv.org/abs/0705.3408
A model of the Oort cloud has been developed by accounting for
planetary, stellar and Galactic perturbations using numerical
symplectic integrations covering 4.5 Gyr. The model is consistent
with the broad dynamical characteristics of the observed cometary
populations injected from the Oort cloud into different regions of
the Solar system. We show that the majority of observed high-eccentricity
trans-Neptunian objects, Centaurs and short-period comets have
visited the Oort cloud (
AU) during their dynamical
history. Assuming from observations that the near-parabolic flux
from the Oort cloud with absolute magnitudes 
,
perihelion distances 
AU and 
AU is approximately
1 comet per year, our calculations imply a present Oort cloud
population of
comets with
. Roughly half this number has AU. The number
of comets reaching the planetary region from the Oort cloud
( AU) is more than an order of magnitude higher per
unit perihelion distance immediately beyond Neptune than in the
observable zone AU. Similarly, the new-comet flux from
the Oort cloud per unit perihelion distance is a few tens of times
higher in the near-Neptune region than in the observable zone. The
present number of high-eccentricity trans-Neptunian objects
(
AU and
AU) originating from the Oort
cloud is in the approximate range 1-3
x 1010, depending
on details of the initial model. A substantial fraction of these
have 
AU and/or 
AU, and they are found mostly
to originate from initial orbits with
AU. Similarly,
the number of Centaurs produced from the Oort cloud, where we define
Centaurs to have 
AU and 
AU, is smaller
by a factor of 20-30. About 90 per cent of these Centaurs have
AU. Objects that have visited the Oort cloud represent
a substantial fraction of the Jupiter-family comet population,
achieving short-period orbits by a process of gradual dynamical
transfer, including a Centaur stage, from the outer Solar system
to near-Earth space. A similar mechanism produces Halley-type
comets, in addition to the well-known diffusion process operating
at small perihelion distances.
To appear in: Monthly Notices of the Royal Astronomical Society
Preprint on the web at
http://star.arm.ac.uk/preprints/2007/501.pdf
Below is one more chapter that will appear in the ``Kuiper Belt'' book (M.A. Barucci, H. Boehnhardt,D. Cruikshank, and A. Morbidelli, eds.; U. Arizona Press, Tucson, 2007). Abstracts of other chapters were published in issues #51, #52, and #53 of this newsletter.
We review the history of the prediction of, and searches for, a population of comets and trans-Neptunian planetesimals. Starting with initial speculations before and after the discovery of Pluto we examine various predictions by Edgeworth, Kuiper and others on the existence of such a population and review the increasingly sophisticated theoretical efforts which eventually showed that the number of short-period comets requires that an ecliptic trans-Neptunian population exists. We then recount various search programmes which culminated in the discovery of the first few trans-Neptunian objects and led to the realization that this region is dynamically much more complicated than at first suspected and has important links both to Centaurs and the dense inner core of the Oort cloud.
For preprints, contact jkd@roe.ac.uk
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.
