There was 1 new TNO discovery announced since the previous issue of Distant EKOs:
2012 BX85
and 4 new Centaur/SDO discoveries:
2000 GQ148, 2012 BR61, 2012 CE17, 2012 CG
Objects recently assigned numbers:
2010 EP65 = (312645)
2008 QD4 = (315898)
2010 EN65 = (316179)
2008 AP129 = (315530)
Objects recently assigned names:
1997 CS29 = Sila-Nunam
Current number of TNOs: 1249 (including Pluto)
Current number of Centaurs/SDOs: 337
Current number of Neptune Trojans: 8
Out of a total of 1594 objects:
644 have measurements from only one opposition
624 of those have had no measurements for more than a year
316 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Recently, the first collisional family was identified in the
trans-Neptunian belt (otherwise known as the Edgeworth-Kuiper belt),
providing direct evidence of the importance of collisions between
trans-Neptunian objects (TNOs). The family consists of the dwarf planet
(136108) Haumea (formerly 2003 EL61), located at a semi-major axis, a,
of 
43 AU, and at least ten other 100 km-sized TNOs located
in the region a = 42-44.5 AU. In this work, we model the long-term
orbital evolution (4 Gyr) of an ensemble of fragments (particles)
representing hypothetical post-collision distributions at the time of
the family's birth based on our limited current understanding of the
family's creation and of asteroidal collision physics. We consider three
distinct scenarios, in which the kinetic energy of dispersed particles
were varied such that their mean ejection velocities (veje) were of
order 200 m/s, 300 m/s and 400 m/s, respectively. Each simulation
considered resulted in collisional families that reproduced that
currently observed, despite the variation in the initial conditions
modeled. The results suggest that 60-75% of the fragments created in
the collision will remain in the trans-Neptunian belt, even after 4 Gyr
of dynamical evolution. The surviving particles were typically
concentrated in wide regions of orbital element space centred on the
initial impact location, with their orbits spread across a region
spanning
AU,
and
, with the exact range covered being proportional to
the veje used in the model. Most of the survivors populated the
so-called Classical and Detached regions of the trans-Neptunian belt,
whilst a minor fraction entered the Scattered Disk reservoir (<1%), or
were captured in Neptunian mean motion resonances (<10%). In addition,
except for those fragments located near strong resonances (such as the
5:3 and 7:4), the great majority displayed negligible long-term orbital
variation. This implies that the orbital distribution of the intrinsic
Haumean family can be used to constrain the orbital conditions and
physical nature of the collision that created the family, billions of
years ago. Indeed, our results suggest that the formation of the Haumean
collisional family most likely occurred after the bulk of Neptune's
migration was complete, or even some time after the migration had
completely ceased, although future work is needed to confirm this result.
To appear in: Monthly Notices of the Royal Astronomical Society
For preprints, contact patryksan@gmail.com
or on the web at http://sites.google.com/site/patryksofialykawka/
We present the first results of the Hubble Wide Field Camera 3 Test of
Surfaces in the Outer Solar System (H/WTSOSS). The purpose of this
survey was to measure the surface properties of a large number of Kuiper
belt objects and attempt to infer compositional and dynamical
correlations. We find that the Centaurs and the low-perihelion scattered
disk and resonant objects exhibit virtually identical bifurcated optical
colour distributions and make up two well defined groups of object. Both
groups have highly correlated optical and NIR colours which are well
described by a pair of two component mixture models that have different
red components, but share a common neutral component. The small,
high-perihelion excited objects are entirely
consistent with being drawn from the two branches of the mixing model
suggesting that the colour bifurcation of the Centaurs is apparent in
all small excited objects. On the other hand, objects larger than
are not consistent with the mixing model, suggesting
some evolutionary process avoided by the smaller objects. The existence
of a bifurcation amongst all excited populations argues that the two
separate classes of object existed in the primordial disk before the
excited Kuiper belt was populated. The cold classical objects exhibit a
different type of surface which has colours that are consistent with
being drawn from the red branch of the mixing model, but with much
higher albedos.
To appear in: The Astrophysical Journal
For preprints, contact fraserw@gps.caltech.edu
or on the web at http://arxiv.org/abs/1202.0827
We have observed the mid-UV spectra of both Pluto and its large satellite, Charon, at two rotational epochs using the Hubble Space Telescope (HST) Cosmic Origins Spectrograph (COS) in 2010. These are the first HST/COS measurements of Pluto and Charon. Here we describe the observations and our reduction of them, and present the albedo spectra, average mid-UV albedos, and albedo slopes we derive from these data. These data reveal evidence for a strong absorption feature in the mid-UV spectrum of Pluto; evidence for temporal change in Pluto's spectrum since the 1990s is reported, and indirect evidence for a near-UV spectral absorption on Charon is also reported.
Published in: The Astronomical Journal, 143, 22 (2012 January)
Physical characterization of Trans-Neptunian objects, a primitive
population of the outer solar system, may provide constraints on their
formation and evolution. The goal of this work is to characterize a set
of 15 scattered disk (SDOs) and detached objects, in terms of their
size, albedo, and thermal properties. Thermal flux measurements obtained
with the Herschel-PACS instrument at 70, 100 and 160 
m,
and whenever applicable, with Spitzer-MIPS at 24 and 70 m,
are modeled with radiometric techniques, in order to derive the objects'
individual size, albedo and when possible beaming factor. Error bars are
obtained from a Monte-Carlo approach. We look for correlations between
these and other physical and orbital parameters. Diameters obtained for
our sample range from 100 to 2400 km, and the geometric albedos (in V
band) vary from 3.8% to 84.5%. The unweighted mean V geometric
albedo for the whole sample is 11.2% (excluding Eris); 6.9% for the
SDOs, and 17.0
for the detached objects (excluding Eris). We obtain
new bulk densities for three binary systems: Ceto/Phorcys,
Typhon/Echidna and Eris/Dysnomia. Apart from correlations clearly due to
observational bias, we find significant correlations between albedo and
diameter (more reflective objects being bigger), and between albedo,
diameter and perihelion distance (brighter and bigger objects having
larger perihelia). We discuss possible explanations for these
correlations.
To appear in: Astronomy & Astrophysics
For preprints, contact pablo.santos@obspm.fr
or on the web at http://arxiv.org/abs/1202.1481
The Herschel Open Time Key Programme TNOs are Cool: A Survey of the
Trans-Neptunian Region aims to derive physical and thermal properties for a
set of 140 Centaurs and Trans-Neptunian Objects (TNOs), including
resonant, classical, detached and scattered disk objects. One goal of the
project is to determine albedo and size distributions for specific classes and
the overall population of TNOs.
We present Herschel PACS photometry of 18 Plutinos and determine sizes and albedos for these objects using thermal modeling. We analyze our results for correlations, draw conclusions on the Plutino size distribution, and compare to earlier results.
Flux densities are derived from PACS mini scan-maps using specialized data reduction and photometry methods. In order to improve the quality of our results, we combine our PACS data with existing Spitzer MIPS data where possible, and refine existing absolute magnitudes for the targets. The physical characterization of our sample is done using a thermal model. Uncertainties of the physical parameters are derived using customized Monte Carlo methods. The correlation analysis is performed using a bootstrap Spearman rank analysis.
We find the sizes of our Plutinos to range from 150 to 730 km and
geometric albedos to vary between 0.04 and 0.28. The average albedo of the
sample is 
, which is comparable to the mean albedo of Centaurs,
Jupiter Family comets and other Trans-Neptunian Objects. We were able to
calibrate the Plutino size scale for the first time and find the cumulative
Plutino size distribution to be best fit using a cumulative power law with
q=2 at sizes ranging from 120-400 km and q=3 at larger sizes. We revise
the bulk density of 1999 TC36 and find
g cm-3.
On the basis of a modified Spearman rank analysis technique our
Plutino sample appears to be biased with respect to object size but unbiased
with respect to albedo. Furthermore, we find biases based on geometrical
aspects and color in our sample. There is qualitative evidence that icy
Plutinos have higher albedos than the average of the sample.
To appear in: Astronomy & Astrophysics.
For preprints, contact michael.mommert@dlr.de
or on the web at http://arXiv.org/abs/1202.3657
Colors of Trans-Neptunian Objects (TNOs) are used to study the evolutionary
processes of bodies in the outskirts of the
Solar System, and to test theories regarding their origin.
Here I describe a search for serendipitous Sloan Digital Sky Survey (SDSS)
observations of known TNOs and Centaurs.
I present a catalog of SDSS photometry, colors and astrometry of
388 measurements of 42 outer Solar-System objects.
I find a weak evidence, at the
level (per trial),
for a correlation
between the g-r color and inclination of
scattered disk objects and hot classical KBOs.
I find a correlation
between the g-r color and the angular momentum in the z direction
of all the objects in this sample.
These findings should be verified using
larger samples of TNOs.
Light curves as a function of phase angle are constructed for 13 objects.
The steepness of the slopes of these light curves
suggests that the coherent backscatter mechanism plays a major role
in the reflectivity of outer Solar-System small objects
at small phase angles.
I find a weak evidence for an anti-correlation,
significant at the 
confidence level (per trial),
between the
g-band phase angle slope parameter
and the semi-major axis, as well as the aphelion distance, of these objects
(i.e., they show a more prominent ``opposition effect'' at smaller
distances from the Sun).
However, this plausible correlation should be verified using larger sample.
I discuss the origin of this possible correlation and argue that if this
correlation is real it probably indicates that ``Sedna''-like objects
have a different origin than other classes of TNOs.
Finally, I identify several objects with large variability amplitudes.
To appear in: The Astrophysical Journal
Preprints available on the web at http://arxiv.org/abs/1202.1538
We investigate whether coagulation models of planet formation can explain the observed size distributions of transneptunian objects (TNOs). Analyzing published and new calculations, we demonstrate robust relations between the size of the largest object and the slope of the size distribution for sizes 0.1 km and larger. These relations yield clear, testable predictions for TNOs and other icy objects throughout the solar system. Applying our results to existing observations, we show that a broad range of initial disk masses, planetesimal sizes, and fragmentation parameters can explain the data. Adding dynamical constraints on the initial semimajor axis of `hot' KBOs along with probable TNO formation times of 10-700 Myr restricts the viable models to those with a massive disk composed of relatively small (1-10 km) planetesimals.
To appear in: The Astronomical Journal
For preprints, contact skenyon@cfa.harvard.edu
or on the web at http://arxiv.org/abs/1201.4395
In contrast to all other debris disks, where the dust can be seen via an
infrared excess over the stellar photosphere, the dust emission of the
Edgeworth-Kuiper belt (EKB) eludes remote detection due to the strong
foreground emission of the zodiacal cloud. In this paper, we access the
expected EKB dust disk properties by modeling. We treat the debiased
population of the known transneptunian objects (TNOs) as parent bodies
and generate the dust with our collisional code. The resulting dust
distributions are modified to take into account the influence of
gravitational scattering and resonance trapping by planets on migrating
dust grains as well as the effect of sublimation. A difficulty with the
modeling is that the amount and distribution of dust are largely
determined by sub-kilometer-sized bodies. These are directly
unobservable, and their properties cannot be accessed by collisional
modeling, because objects larger than 
m in the present-day
EKB are not in a collisional equilibrium. To place additional
constraints, we use in-situ measurements of the New Horizons spacecraft
within 20 AU. We show that, to sustain a dust disk consistent with these
measurements, the TNO population has to have a break in the size
distribution at 
km. However, even this still leaves us with
several models that all correctly reproduce a nearly constant dust
impact rates in the region of giant planet orbits and do not violate the
constraints from the non-detection of the EKB dust thermal emission by
the COBE spacecraft. The modeled EKB dust disks, which conform to the
observational constraints, can either be transport-dominated or
intermediate between the transport-dominated and collision-dominated
regime. The in-plane optical depth of such disks is
and their fractional
luminosity is
. Planets and sublimation are found to
have little effect on dust impact fluxes and dust thermal emission. The
spectral energy distribution of an EKB analog, as would be seen from
10 pc distance, peaks at wavelengths of
m at 
mJy, which is less than 
of the photospheric flux at those
wavelengths. Therefore, EKB analogs cannot be detected with present-day
instruments such as Herschel/PACS.
To appear in: Astronomy and Astrophysics
For preprints, contact vitense@astro.uni-jena.de
or on the web at http://arxiv.org/abs/1202.2257
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.
