There were 2 new TNO discoveries announced since the previous issue of Distant EKOs:
2010 VK201, 2010 VL201
and 1 new Centaur/SDO discovery:
2011 AC72
Reclassified objects:
2010 VZ98 (TNOSDO)
Deleted objects:
2010 VS11
Current number of TNOs: 1164 (including Pluto)
Current number of Centaurs/SDOs: 291
Current number of Neptune Trojans: 7
Out of a total of 1427 objects:
635 have measurements from only one opposition
577 of those have had no measurements for more than a year
323 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Another measure of the astrometric ``secure vs. lost'' status for TNOs is from
Marc Buie's web page http://www.boulder.swri.edu/~buie/kbo/kbofollowup.html
Out of 1427 objects:
159 have secure positions
376 have decent positions
382 are at risk (uncertainty < 0.5 deg and ``need ratio'' > 1)
510 are lost (uncertainty > 0.5 deg)
Centaur 10199 Chariklo appears to have a varying spectral behavior. While three different spectral studies detect the presence of water ice at the surface, two more recent studies do not detect any absorption bands. In this article we consider the possibility that Chariklo undergoes cometary activity that could be responsible for the observed spectral variations. We simulate its thermal evolution, finding that crystalline water ice should be present in the object core, and amorphous water ice should be found at the surface. Upon entering the inner solar system, Chariklo might experience some cometary activity due to water ice crystallization if the obliquity is high, due to the adjustment of the internal structure to a new thermal equilibrium. No other activity is expected from this source, unless an external source like an impact provides the heat needed. In the case of such an event, we find that dust emitted in a coma is unlikely to be responsible for the observed spectral variations. On the contrary, water ice grains in the coma would reproduce this pattern, meaning that the water ice detected after Chariklo's discovery was present in these grains and not on the object surface. Nonetheless, any activity would require an external additional heat source to be triggered, through an outburst, which might favor the spatial variations hypothesis.
To appear in: The Astronomical Journal
It is generally believed that Charon formed as a result of a large, grazing collision with Pluto that supplied the Pluto-Charon system with its high angular momentum. It has also been proposed that Pluto's small outer moons, Nix and Hydra, formed from debris from the Charon-forming impact (Stern et al. 2006; Ward & Canup 2006), although the viability of this scenario remains unclear. Here I use SPH impact simulations to show that it is possible to simultaneously form an intact Charon and an accompanying debris disk from a single impact. The successful cases involve colliding objects that are partially differentiated prior to impact, having thin outer ice mantles overlying a uniform composition rock-ice core. The composition of the resulting debris disks varies from a mixture of rock and ice (similar to the bulk composition of Pluto and Charon) to a pure ice disk. If Nix and Hydra formed from such an impact-generated disk, their densities should be less than or similar to that of Charon and Pluto, and the small moons could be composed entirely of ice. If they were instead formed from captured material (e.g., Lithwick & Wu 2008), a mixed rock-ice composition and densities similar to that of Charon and Pluto would be expected. Improved constraints on the properties of Nix and Hydra through occultations and/or the New Horizons encounter may thus help to distinguish between these two modes of origin, particularly if the small moons are found to have ice-like densities.
Published in: The Astronomical Journal, 141, 35 (2011 February)
Approximately 10-20% of all Kuiper belt objects (KBOs) occupy
mean-motion resonances with Neptune. This dynamical configuration likely
resulted from resonance capture as Neptune migrated outward during the
late stages of planet formation. The details of Neptune's
planetesimal-driven migration, including its radial extent and the
concurrent eccentricity evolution of the planet, are the subject of
considerable debate. Two qualitatively different proposals for
resonance capture have been proposed--migration-induced capture driven
by smooth outward evolution of Neptune's orbit and chaotic capture
driven by damping of the planet's eccentricity near its current
semi-major axis. We demonstrate that the distribution of
comparable-mass, wide-separation binaries occupying resonant orbits can
differentiate between these two scenarios. If migration-induced capture
occurred, this fraction records information about the formation
locations of different populations of KBOs. Chaotic capture, in
contrast, randomizes the orbits of bodies as they are placed in
resonance. In particular, if KBO binaries formed by dynamical capture
in a protoplanetary disk with a surface mass density typical of observed
extrasolar disks, then migration-induced capture produces the following
signatures. The 2:1 resonance should contain a dynamically cold
component, with inclinations less than 5-10
, having a binary
fraction comparable to that among cold classical KBOs. If the 3:2
resonance also hosts a cold component, its binary fraction should be
20-30% lower than in the cold classical belt. Among cold 2:1 (and if
present 3:2) KBOs, objects with eccentricities e < 0.2 should have a
binary fraction 
20% larger than those with e > 0.2. Other
binary formation scenarios and disk surface density profiles can
generate analogous signatures but produce quantitatively different
results. Searches for cold components in the binary fractions of
resonant KBOs are currently practical. The additional
migration-generated trends described here may be distinguished with
objects discovered by LSST.
To appear in: The Astrophysical Journal
For preprints, contact rmurray-clay@cfa.harvard.edu
or on the web at http://arxiv.org/abs/1102.1430
We consider the application of interferometry to measuring the sizes and
shapes of small bodies in the solar system that cannot be spatially
resolved by today's single-dish telescopes. Assuming ellipsoidal
shapes, we provide a formalism to derive the shape parameters from
visibility measurements along three different baseline orientations.
Our results indicate that interferometers can measure the size of an
object to better than 15% uncertainty if the limb-darkening is unknown.
Assuming a Minnaert scattering model, one can theoretically derive the
limb-darkening parameters from simultaneous measurements of visibilities
at several different projected baseline lengths to improve the size and
shape determination to an accuracy of a few percent. The best size
measurement can be reached when one axis of the object's projected disk
is aligned with one baseline orientation, and the measurement of
cross-sectional area is independent of baseline orientation. We
construct a 3-D shape model for the dwarf planet Haumea and use it to
synthesize interferometric data sets. Using the Haumea model, we
demonstrate that when photometric light curve, visibility light curve,
and visibility phase center displacement are combined, the rotational
period and sense of rotation can all be derived, and the rotational pole
can be estimated. Because of its elongated shape and the dark red spot,
the rotation of Haumea causes its optical photocenter to move in a loop
on the sky. Our simulations show that this loop has an extend of about
80 
as without the dark red spot, and about 200 as with it.
Such movements are easily detectable by space-based astrometric
interferometer designed e.g. for planet detection. As an example, we
consider the possible contributions to the study of small bodies in the
solar system by the Space Interferometry Mission. We show that such a
mission could make substantial contributions in characterizing the
fundamental physical properties of the brightest Kuiper Belt Objects and
Centaurs as well as a large number of main belt asteroids. We compile a
list of Kuiper Belt Objects and Centaurs that are potentially
scientifically interesting and observable by such missions.
Published in: Icarus 211, 1007 (2011 February)
For preprints, contact jyli@astro.umd.edu
We present a new near-infrared photometric system for detection of
water ice and methane ice in the solar system. The system consists of
two medium-band filters in the K-band region of the near-infrared,
which are sensitive to water ice and methane ice, plus continuum
observations in the J-band and Y-band. The primary purpose of
this system is to distinguish between three basic types of Kuiper Belt
Objects (KBOs) -- those rich in water ice, those rich in methane ice,
and those with little absorbance. In this work, we present
proof-of-concept observations of 51 KBOs using our filter system, 21
of which have never been observed in the near-IR spectroscopically.
We show that our custom photometric system is consistent with previous
spectroscopic observations while reducing telescope observing time by
a factor of 
. We use our filters to identify Haumea
collisional family members, which are thought to be collisional
remnants of a much larger body and are characterized by large
fractions of water ice on their surfaces. We add 2009 YE7
to the Haumea collisional family based on our water ice band
observations (
) which indicate a high
amount of water ice absorption, our calculated proper orbital
elements, and the neutral optical colors we measured,
, which are all consistent with the rest of the Haumea
family. We identify several objects dynamically similar to Haumea as
being distinct from the Haumea family as they do not have water ice on
their surfaces. In addition, we find that only the largest KBOs have
methane ice, and we find that Haumea itself has significantly less
water ice absorption than the smaller Haumea family members. We find
no evidence for other families in the Kuiper Belt.
To appear in: Astrophysical Journal, vol. 730 (2011 March 20)
For preprints, contact trujillo@gemini.edu
or on the web at http://arxiv.org/abs/1102.1971
The existence of strong absorption bands of singly deuterated methane
(CH3D) at wavelengths where normal methane (CH4) absorbs
comparatively weakly could enable remote measurement of D/H ratios in
methane ice on outer solar system bodies. We performed laboratory
transmission spectroscopy experiments, recording spectra at wavelengths
from 1 to 6 m to study CH3D bands at 2.47, 2.87, and 4.56 m,
wavelengths where ordinary methane absorption is weak. We
report temperature-dependent absorption coefficients of these bands when
the CH3D is diluted in CH4 ice and also when it is dissolved in
N2 ice, and describe how these absorption coefficients can be
combined with data from the literature to simulate arbitrary D/H ratio
absorption coefficients for CH4 ice and for CH4 in N2 ice. We
anticipate these results motivating new telescopic observations to
measure D/H ratios in CH4 ice on Triton, Pluto, Eris, and Makemake.
To appear in: Icarus
Preprint available on the web at
http://www.lowell.edu/~grundy/abstracts/2011.CH3D.html
Triton, the large satellite of Neptune, was imaged by the Voyager 2
spacecraft in 1989 with dark plumes originating in its volatile-rich
south polar region. Southern summer solstice, a time when seasonal
volatile transport should be at a maximum, occurred in 2001.
Ground-based observations of Triton's rotational light curve obtained
from Table Mountain Observatory in 2000-2004 reveal volatile transport
on its surface. When compared with a static frost model constructed from
Voyager images, the light curve shows an increase in total amplitude. An
earlier light curve obtained in 1992 from Mauna Kea Observatory is
consistent with the static frost model. This movement of volatiles on
the surface agrees with recent imaging results from the Hubble Space
Telescope (Bauer et al. 2010). The changes in the light curve can be
explained by the transport of nitrogen frost on the surface or by the
uncovering of bedrock of less volatile methane. We also find that Triton
exhibits a large opposition surge at solar phase angles less than 0.1.
This surge cannot be entirely explained by the effects of coherent
backscatter.
To appear in: Icarus
Serendipitous stellar occultation search is so far the only way to detect the existence of very small, very dim, remote objects in the Solar system. To date, however, there are only very few reported detections for trans-Neptunian objects (TNOs) in optical bands. In the X-ray band, with the RXTE/PCA data of Sco X-1 taken from 2007 June to 2009 October, we found one possible X-ray occultation event. We discuss the veracity and properties of this event, and suggest upper limits to the size distribution of TNOs at hectometre size and of main-belt asteroids at decametre size.
Published in: Monthly Notices of the Royal Astronomical Society, 411, 427 (2011 Feb.)
Preprints available on the web at
http://arxiv.org/abs/1009.2547
Interplanetary Dust Particles (IDPs) are potentially of cometary origin.
They may therefore provide important clues to a better understanding of
the early Solar System physical and chemical conditions. A chondritic
porous aggregate IDP (named L2021C5) was analyzed using mid to far FTIR
(2-60 m) micro-spectroscopy, Raman micro-spectroscopy,
field-emission scanning electron microscopy (FESEM) and energy
dispersive X-ray (EDX) analyses. The IDP was pressed between diamond
windows to increase the quality of the spectral data by overcoming the
diffraction limitation and minimizing light scattering effects from
particles of a global size similar to the wavelength of the observation.
This combination of techniques has enabled a mineralogical, organic and
compositional description of the compressed particle. The IR spectra
show that in L2021C5 amorphous silicates are more abundant than
crystalline ones, and that the crystalline component is richer in
olivine than in pyroxene. The composition and distribution of these
inorganic components match very well the small silicate grains emission
observed for comet Hale-Bopp from ISO-SWS spectra. Raman spectroscopy
has allowed the detection of carbonaceous structures displaying
different degrees of order, covering almost the whole range observed so
far for IDPs. The combination of the three analytical techniques
indicates that L2021C5 is a low-Ca, chondritic porous aggregate that
experienced only mild flash heating on atmospheric entry, as indicated
by the disordered carbon properties, the Fe/S atomic ratio of sulfides,
the absence of Na depletion, and the small depletion of S. Based on a
plausible cometary origin and on the estimated low entry velocity, we
suggest that this IDP came from the Zodiacal cloud that is dominated by
dust from Jupiter-Family comets.
To appear in: Icarus
For preprints, contact rosario.brunetto@ias.u-psud.fr
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.
