There were 2 new TNO discoveries announced since the previous issue of Distant EKOs:
2004 LV31, 2004 LW31
and 9 new Centaur/SDO discoveries:
2010 VW11, 2011 HO60, 2012 DD86, 2011 HP83, 2012 DR30, 2012 DS85, 2012 GN12, 2012 GV1, 2012 FZ78
Reclassified objects:
2010 RE64 (TNOSDO)
2010 RM45 (TNO
2011 GM27 (TNO
2012 BX85 (TNO
Current number of TNOs: 1247 (including Pluto)
Current number of Centaurs/SDOs: 350
Current number of Neptune Trojans: 8
Out of a total of 1605 objects:
643 have measurements from only one opposition
622 of those have had no measurements for more than a year
318 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Neptune's dynamical history shaped the current orbits of Kuiper belt
objects (KBOs), leaving clues to the planet's orbital evolution. In the
``classical'' region, a population of dynamically ``hot'' high-inclination
KBOs overlies a flat ``cold'' population with distinct physical
properties. Simulations of qualitatively different histories for Neptune
- including smooth migration on a circular orbit or scattering by other
planets to a high eccentricity - have not simultaneously produced both
populations. We explore a general Kuiper belt assembly model that forms
hot classical KBOs interior to Neptune and delivers them to the
classical region, where the cold population forms in situ. First, we
present evidence that the cold population is confined to eccentricities
well below the limit dictated by long-term survival. Therefore Neptune
must deliver hot KBOs into the long-term survival region without
excessively exciting the eccentricities of the cold population. Imposing
this constraint, we explore the parameter space of Neptune's
eccentricity and eccentricity damping, migration, and apsidal
precession. We rule out much of parameter space, except where Neptune is
scattered to a moderately eccentric orbit (e > 0.15) and subsequently
migrates a distance 
= 1-6 AU. Neptune's moderate
eccentricity must either damp quickly or be accompanied by fast apsidal
precession. We find that Neptune's high eccentricity alone does not
generate a chaotic sea in the classical region. Chaos can result from
Neptune's interactions with Uranus, exciting the cold KBOs and placing
additional constraints. Finally, we discuss how to interpret our
constraints in the context of the full, complex dynamical history of the
solar system.
To appear in: The Astrophysical Journal
For preprints, contact rdawson@cfa.harvard.edu
or on the web at http://arxiv.org/abs/1202.6060
The recent discovery of the first Neptune Trojan at the planet's
trailing (L5) Lagrange point, 2008 LC18, offers an opportunity to
confirm the formation mechanism of a member of this important tracer
population for the Solar System's dynamical history. We tested the
stability of 2008 LC18's orbit through a detailed dynamical study, using
test particles spread across the 
range of orbital uncertainties in
a, e, i and 
. This showed that the wide uncertainties of the published
orbit span regions of both extreme dynamical instability, with lifetimes
< 100 Myr, and with significant stability (> 1 Gyr lifetimes). The
stability of 2008 LC18's clones is greatly dependent on their semi-major
axis and only weakly correlated with their orbital eccentricity. Test
particles on orbits with an initial semi-major axis of less than 29.91 AU
have dynamical half-lives shorter than 100 Myr; in contrast,
particles with an initial semi-major axis of greater than 29.91 AU
exhibit such strong dynamical stability that almost all are retained
over the 1 Gyr of our simulations. More observations of this object are
necessary to improve the orbit. If 2008 LC18 is in the unstable region,
then our simulations imply that it is either a temporary Trojan capture,
or a representative of a slowly decaying Trojan population (like its
sibling the L4 Neptunian Trojan 2001 QR322), and that it may not be
primordial. Alternatively, if the orbit falls into the larger, stable
region, then 2008 LC18 is a primordial member of the highly stable and
highly inclined component of the Neptune Trojan population, joining 2005 TN53
and 2007 VL305. We attempted to recover 2008 LC18 using the 2.3m
telescope at Siding Spring Observatory to provide this astrometry, but
were unsuccessful due to the high stellar density of its current sky
location near the galactic centre. The recovery of this object will
require a telescope in the 8m class.
To appear in: Monthly Notices of the Royal Astronomical Society
For preprints, contact j.a.horner@unsw.edu.au
or on the web at http://arxiv.org/abs/1202.3279
Aims. In the framework of a large program, we observed (55638) 2002 VE95
with the ESO-VLT telescope to better constrain its
surface composition and to investigate the possible heterogeneity of the
surface.
Methods. We report new near-infrared observations performed in 2007 and 2008. Using the new constraints of the albedo obtained by Herschel Space Observatory observations, a surface model was computed using the complete set of spectra (from visible to the near-infrared) as well as those of the previous published data to investigate the surface composition properties of (55638) 2002 VE95.
Results. The surface is heterogeneous. This red object is covered by different icy compounds, such as water (4-19%) and methanol (10-12%). Different organic compounds, such as titan and triton tholins seem also to be present in the surface. The amount of the components is different depending on the observed area. That methanol ice seems to be present mainly on very red surface favors the hypothesis that surfaces of very red objects are more primordial.
Published in: Astronomy and Astrophysics, 539, 152 (2012 March)
For preprints, contact antonella.barucci@obspm.fr
The Centaurs are a transitional population of minor bodies of the solar system and the evolutionary link between the trans-Neptunian objects and the short period comets. The surface properties of these objects are very peculiar, because currently available data suggest that their visual surface colors divide the population into two distinctive groups, those with reddish slopes of the visual reflection spectra and those with neutral spectra. Moreover, some of them are known to posses comas produced by cometary activity.
We aim to investigate possible links between the orbital dynamical history and the surface physical properties of the bodies of this population.
By means of numerical integrations of the equations of motion we calculated the orbital evolution of three groups of Centaurs: the Red group, the Gray group and the Active group. We looked for statistical differences in the timescales spent by the objects of each group at heliocentric distances below certain values that are associated with locations where certain particular physical processes occur at the surfaces.
We find remarkable differences when we compare the fraction of objects that penetrate below typical heliocentric distances for each group.
Our results suggest that the observed bimodality in the distribution of surface colors of the Centaurs is caused by the different thermal reprocessing on the surface of bodies of the Red group on one side and the Active and Gray groups on the other. Centaurs of the Gray group likely had cometary activity, therefore their color distribution is similar to that of comet nuclei.
Published in: Astronomy and Astrophysics, 539, 144 (2012 March)
For preprints, contact melita@iafe.uba.ar
We examine a large collection of low resolution near-infrared spectra of
Kuiper belt objects and centaurs in an attempt to understand the
presence of water ice in the Kuiper belt. We find that water ice on the
surface of these objects occurs in three separate manners: (1) Haumea
family members uniquely show surfaces of nearly pure water ice,
presumably a consequence of the fragmentation of the icy mantle of a
larger differentiated proto-Haumea; (2) large objects with absolute
magnitudes of H<3 (and a limited number to H=4.5) have surface
coverings of water ice - perhaps mixed with ammonia - that appears to
be related to possibly ancient cryovolcanism on these large objects; and
(3) smaller KBOs and centaurs which are neither Haumea family members
nor cold-classical KBOs appear to divide into two families (which we
refer to as ``neutral'' and ``red''), each of which is a mixture of a
common nearly-neutral component and either a slightly red or very red
component that also includes water ice. A model suggesting that the
difference between neutral and red objects s due to formation in an
early compact solar system either inside or outside, respectively, of
the 
20 AU methanol evaporation line is supported by the
observation that methanol is only detected on the reddest objects, which
are those which would be expected to have the most of the methanol
containing mixture.
To appear in: The Astronomical Journal
For preprints, contact mbrown@caltech.edu
or on the web at http://arxiv.org/abs/1204.3638
We present three near-infrared spectra of Pluto taken with the IRTF and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model, and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf planets with two methane phases - one highly-diluted by nitrogen and the other rich in methane.
For Pluto, we find bulk, hemisphere-averaged, methane abundances of
%, 
%, and 
% for sub-Earth
longitudes of 
, 
, and 
. Application of
the Wilcoxon rank sum test to our measurements finds these small
differences are statistically significant. For Triton, we find bulk,
hemisphere-averaged, methane abundances of 
% and 
%
for sub-Earth longitudes of 
and 
.
Application of the Wilcoxon rank sum test to our measurements finds the
differences are not statistically significant. For Eris, we find a bulk,
hemisphere-averaged, methane abundance of 
%.
Pluto, Triton, and Eris do not exhibit a trend in methane-nitrogen mixing ratio with depth into their surfaces over the few cm range probed by these observations. This result is contrary to the expectation that since visible light penetrates deeper into a nitrogen-rich surface than the depths from which thermal emission emerges, net radiative heating at depth would drive preferential sublimation of nitrogen leading to an increase in the methane abundance with depth.
To appear in: The Astrophysical Journal
For preprints, contact Stephen.Tegler@nau.edu
or on the web at http://arxiv.org/abs/1203.6888
Trans-Neptunian objects (TNO) represent the leftovers of the formation of the Solar System. Their physical properties provide constraints to the models of formation and evolution of the various dynamical classes of objects in the outer Solar System.
Based on a sample of 19 classical TNOs we determine radiometric sizes,
geometric albedos and beaming parameters. Our sample is composed of both
dynamically hot and cold classicals. We study the correlations of
diameter and albedo of these two subsamples with each other and with
orbital parameters, spectral slopes and colors. We have done three-band
photometric observations with Herschel/PACS and we use a
consistent method for data reduction and aperture photometry of this
sample to obtain monochromatic flux densities at 70.0, 100.0 and
160.0 
m. Additionally, we use Spitzer/MIPS flux densities at
23.68 and 71.42 m when available, and we present new Spitzer
flux densities of eight targets. We derive diameters and albedos with
the near-Earth asteroid thermal model (NEATM). As auxiliary data we use
reexamined absolute visual magnitudes from the literature and data
bases, part of which have been obtained by ground based programs in
support of our Herschel key program.
We have determined for the first time radiometric sizes and albedos of
eight classical TNOs, and refined previous size and albedo estimates or
limits of 11 other classicals. The new size estimates of 2002 MS4 and
120347 Salacia indicate that they are among the 10 largest TNOs known.
Our new results confirm the recent findings that there are very diverse
albedos among the classical TNOs and that cold classicals possess a high
average albedo (
). Diameters of classical TNOs strongly
correlate with orbital inclination in our sample. We also determine the
bulk densities of six binary TNOs.
To appear in: Astronomy and Astrophysics
For preprints, contact vilenius@mpe.mpg.de
or on the web at http://arxiv.org/abs/1204.0697
We present estimates of the basic physical properties
(size and albedo) of (90377) Sedna, a prominent member of the detached
trans-Neptunian object population and
the recently discovered scattered disk object 2010 EK139, based
on the recent observations acquired with the
Herschel Space Observatory,
within the ``TNOs are Cool!'' key programme.
Our modeling of the thermal measurements shows that both objects
have larger albedos and smaller sizes than the previous expectations,
thus their surfaces might be covered by ices in a significantly
larger fraction. The derived diameter of Sedna and
2010 EK139 are 
km and
470+35-10km, while the
respective geometric albedos are
and
0.25+0.02-0.05. These estimates are
based on thermophysical model techniques.
To appear in: Astronomy & Astrophysics Letters
For preprints, contact apal@szofi.net
or on the web at http://arxiv.org/abs/1204.0899
Pluto is the multiple system that has been observed the longest. Yet, the masses of its smallest satellites, Nix and Hydra, which were discovered in 2005, are still imprecisely known, because of the short time span and number of available observations. We present a numerical model that takes into account the second order gravity fields and Pluto's orbital motion in the solar system. We investigated the dynamical parameters that may be reliably determined today. We also assessed the possible improvements on the parameter uncertainties with the future increase of observations, including the New Horizons mission. Fitting our model to simulated data, we show that the precision of observations prevents the quantification of the polar oblateness J2 and equatorial bulge c22 of Pluto and Charon. Similarly, we show that the masses are on the detection limit. In particular, unless 25 observations are made every year, the mass of Nix may be constrained with confidence only with New Horizons data. Hydra's mass will only be constrained by the probe. The recent discovery of P4 might change this situation, but our knowledge of this object is still too vague to draw any conclusion.
Published in: Astronomy and Astrophysics, 540, 65 (2012 April)
For preprints, contact beauvalet@imcce.fr
We study large trans-neptunian objects (TNOs) using stellar
occultations. We derive precise astrometric predictions for stellar
occultations by Eris, Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna,
Varuna, 2002 TX300, and 2003 AZ84 for 2011-2015. We construct
local astrometric catalogs of stars complete to magnitudes as faint as R
= 18-19 in the UCAC2 (Second US Naval Observatory CCD Astrograph
Catalog) frame covering the sky path of these objects. During 2007-2009,
we carried out an observational program at the ESO2p2/WFI (2.2 m
Max-Planck ESO telescope with the Wide Field Imager) instrument. The
observations covered the sky path of the selected targets from 2008 to
2015. We performed the astrometry of 316 GB images using the Platform
for Reduction of Astronomical Images Automatically (PRAIA). With the
help of field distortion patterns derived for the WFI mosaic of CCDs, we
reduced the overlapping mosaics of CCDs. We derive positions in the
UCAC2 frame with 40 mas precision for stars up to the catalog magnitude
completeness limit (about R = 19). New stellar proper motions are also
determined with 2MASS (Two Micron All Sky Survey) and the USNO B1.0
(United States Naval Observatory B 1.0) catalog positions as a first
epoch. Astrometric catalogs with proper motions were produced for each
TNO, containing more than 5.35 million stars covering the sky paths with
30
width in declination. The magnitude completeness is about R
= 19 with a limit of about R = 21. We predicted 2717 stellar occultation
candidates for all targets. Ephemeris offsets with about from 50 mas to
100 mas precision were applied to each TNO orbit to improve the
predictions. They were obtained during 2007-2010 from a parallel
observational campaign carried out with from 0.6 m to 2.2 m in size
telescopes. This extends our previous work for the Pluto system to large
TNOs, using the same observational and astrometric procedures. The
obtained astrometric catalogs are useful for follow-up programs at small
to large telescopes used to improve the candidate star positions and TNO
ephemeris. They also furnish valuable photometric information for the
field stars. For each TNO, updates on the ephemeris offsets and
candidate star positions (geometric conditions of predictions and
finding charts) are made available in the web by the group:
http://www.lesia.obspm.fr/perso/bruno-sicardy/
To appear in: Astronomy & Astrophysics
Preprints on the web at http://arxiv.org/abs/1204.4234
and http://www.aanda.org/articles/aa/pdf/forth/aa18349-11.pdf
Observations indicate that the gaseous circumstellar disks around young
stars vary significantly in size, ranging from tens to thousands of AU.
Models of planet formation depend critically upon the properties of
these primordial disks, yet in general it is impossible to connect an
existing planetary system with an observed disk. We present a method by
which we can constrain the size of our own protosolar nebula using the
properties of the small body reservoirs in the solar system. In standard
planet formation theory, after Jupiter and Saturn formed they scattered
a significant number of remnant planetesimals into highly eccentric
orbits. In this paper, we show that if there had been a massive,
extended protoplanetary disk at that time, then the disk would have
excited Kozai oscillations in some of the scattered objects, driving
them into high-inclination (
), low-eccentricity
orbits (
AU). The dissipation of the gaseous disk would
strand a subset of objects in these high-inclination orbits; orbits that
are stable on Gyr timescales. To date, surveys have not detected any
Kuiper-belt objects with orbits consistent with this dynamical
mechanism. Using these non-detections by the Deep Ecliptic Survey and
the Palomar Distant Solar System Survey we are able to rule out an
extended gaseous protoplanetary disk (
AU) in our solar
system at the time of Jupiter's formation. Future deep all sky surveys
such as the Large Synoptic Survey Telescope will allow us to further
constrain the size of the protoplanetary disk.
Published in: The Astronomical Journal, 143, 91 (2012 April)
For preprints, contact kretke@boulder.swri.edu
or on the web at http://arxiv.org/abs/1202.2343
We have performed detailed thermophysical and dynamical modelling of the
Jovian Trojan (1173) Anchises. Our results show that this is a most
unusual object. By examining observational data taken of Anchises by
IRAS, Akari and WISE at wavelengths between 11.5 and 60 microns,
together with the variations in its optical lightcurve, we find that
Anchises is most likely an elongated body, with an axes-ratio, a/b, of
around 1.4. This results in calculated best-fit dimensions for Anchises
of 170x121x121 km (or an equivalent diameter of 136 +18/-11 km). We find
that the observations of Anchises are best fit by the object having a
retrograde sense of rotation, and an unusually high thermal inertia in
the range 25 to 100 Jm-2s-0.5K-1 (3-
confidence
level). The geometric albedo of Anchises is found to be 0.027 (+0.006/-0.007).
Anchises therefore has one of the highest published
thermal inertias of any object larger than 100 km in diameter, at such
large heliocentric distances, as well as being one of the lowest albedo
objects ever observed. More observations (visual and thermal) are needed
to see whether there is a link between the very shallow phase curve,
with almost no opposition effect, and the derived thermal properties for
this large Trojan asteroid. Our dynamical investigation of Anchises'
orbit has revealed it to be dynamically unstable on timescales of
hundreds of millions of years, similar to the unstable Neptunian Trojans
2001 QR322 and 2008 LC18. Unlike those objects, however, we find
that the dynamical stability of Anchises is not a function of its
initial orbital elements, the result of the exceptional precision with
which its orbit is known. Our results are the first time that a Jovian
Trojan has been shown to be dynamically unstable, and add further weight
to the idea that the planetary Trojans likely represent a significant
ongoing contribution to the dynamically unstable Centaur population, the
parents of the short-period comets. The observed instability (fully half
of all clones of Anchises escape the Solar system within 350 Myr) does
not rule out a primordial origin for Anchises, but when taken in concert
with the result of our thermophysical analysis, suggest that it would be
a fascinating target for future study.
To appear in: Monthly Notices of the Royal Astronomical Society
For preprints, contact j.a.horner@unsw.edu.au
or on the web at http://arxiv.org/abs/1204.1388
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.
