There was 1 new TNO discovery announced since the previous issue of Distant EKOs:
2013 TH159
and 1 new Centaur/SDO discovery:
2015 PJ311
Current number of TNOs: 1373 (including Pluto)
Current number of Centaurs/SDOs: 457
Current number of Neptune Trojans: 12
Out of a total of 1842 objects:
660 have measurements from only one opposition
635 of those have had no measurements for more than a year
327 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
We present estimates of the basic physical properties
- including size and albedo - of the extreme Centaur
2013AZ60. These properties have been derived from optical and thermal infrared
measurements. Our optical measurements revealed a likely full period
of 
h with a shallow amplitude of 4.5%. By combining
optical brightness information and thermal emission data, we are able
to derive a diameter of 
km and a
geometric albedo of 2.9% - corresponding to an extremely dark
surface. Additionally, our finding of
50 Jm-2K-1s-1/2 for
the thermal inertia is also noticeably for objects in such a distance.
The results of dynamical simulations yield an unstable orbit,
with a 50% probability that the target will be ejected from the Solar System
within 700,000 years. The current orbit of this object as well as its
instability could imply a pristine cometary surface.
This possibility is in agreement with the observed low geometric albedo
and red photometric colour indices for the object, which are a good
match for the surface of a dormant comet - as would be expected for a
long-period cometary body approaching perihelion. Despite the fact it
was approaching ever closer to the Sun, however, the object exhibited
star-like profiles in each of our observations, lacking any sign of
cometary activity. By the albedo,
2013AZ60 is a candidate for the darkest body among the known TNOs.
To appear in: Astronomy & Astrophysics
For preprints, contact apal@szofi.net
or on the web at http://arxiv.org/abs/1507.05468 and http://www.aanda.org/
We present an analysis of the colors available for seven trans-neptunian objects (TNOs) and three Centaurs among the reddest known, aimed at characterizing their surface chemical properties. In particular we seek to obtain evidence in support of the proposed correlation between the visible coloration of the surface of TNOs and their surface compositions (Brown et al. 2011).
The analysis focuses on nine available colors in the visible-near IR
(0.3-4.5 
m) spectral range scaled to the V albedo to provide a proxy
for the spectral shape of the objects. The colors include Spitzer IRAC
data never published before, key in providing an effective constraint in
the discrimination of ices contributing to the surface composition of
the objects.
Compositions are obtained by comparing the data to a grid of radiative transfer models convolved by the filter response functions of the colors adopted in the spectrum-proxies to match the resolution of the observations. We find evidence suggesting the presence of hydrocarbons and/or methanol on the surfaces of most objects in our sample, supporting the hypothesis by Brown et al. (2011) that the coloration of red TNOs could be linked to their methanol content.
From our finding of methanol/hydrocarbon ices on the surfaces of the objects in our sample of very red TNOs and Centaurs we infer that ultra-red objects in general might contain these ices and therefore might have formed in the outer part of the Solar System. We also deduce that the surfaces of most of the very red TNOs in our dataset are probably still quite pristine, and that their organic materials could have been produced by irradiation of the volatile ices whose traces are still present on their surface. Although our sample is small, we infer that the irradiation process is still in progress, as hinted by the Centaurs' slightly elevated organic amounts at smaller perihelion distances. However, considering the relatively similar amounts of organics found in our data at a wide variety of perihelion distances, we also infer that it could have started before Neptune's migration.
The technique used to constrain the composition described as part of this study introduces a new approach at investigating the surface chemistry of the very small and numerous objects that constitute the bulk of the TNO and Centaur populations. This innovative method has the potential to provide constraints for irradiation theories and for models of dynamical and chemical evolution of the Solar System.
Published in: Icarus, 252, 311 (2015 May)
For preprints, contact Cristina.M.DalleOre@nasa.gov
Minor bodies trapped in 1:1 co-orbital resonances with a host planet could be relevant to explain
the origin of captured satellites. Among the giant planets, Uranus has one of the smallest known
populations of co-orbitals, three objects, and all of them are short-lived. Asteroid 2015 DB216
has an orbital period that matches well that of Uranus, and here we investigate its dynamical
state. Direct N-body calculations are used to assess the current status of this object, reconstruct
its immediate dynamical past, and explore its future orbital evolution. A covariance matrix-based
Monte Carlo scheme is presented and applied to study its short-term stability. We find
that 2015 DB216 is trapped in a temporary co-orbital resonance with Uranus, the fourth known
minor body to do so. A detailed analysis of its dynamical evolution shows that it is an unstable
but recurring co-orbital companion to Uranus. It currently follows an asymmetric horseshoe
trajectory that will last for at least 10 kyr, but it may remain inside Uranus' co-orbital zone
for millions of years. As in the case of other transient Uranian co-orbitals, complex multibody
ephemeral mean motion resonances trigger the switching between the various resonant co-orbital
states. The new Uranian co-orbital exhibits a secular behaviour markedly different from
that of the other known Uranian co-orbitals because of its higher inclination, nearly 38
. Given
its rather unusual discovery circumstances, the presence of 2015 DB216 hints at the existence
of a relatively large population of objects moving in similar orbits.
Published in: Monthly Notices of the Royal Astronomical Society, 453, 1288
For preprints, contact carlosdlfmarcos@gmail.com
or on the web at http://arxiv.org/abs/1507.07449
Several objects whose perihelion lies between Jupiter and Neptune have large semi-major axes a > 100 au, two of them having semi-major axis above 1000 au. Since these objects' perihelia share the same region as the classical Centaurs, a coherent nomenclature for them could be large semi-major axis Centaurs (Laces). It has been argued that the classical Centaurs, with semi-major axes below 50 au, originate from the Scattered Disk. However, the Laces most likely originate from the Oort Cloud. We determine the brightest object in the Laces, classical Centaurs (with semi-major axis >20 au) and Scattered Disk populations using a procedure that introduces observational bias to a set of objects in orbits obtained from numerical simulations of the evolution of the Oort cloud and Scattered Disk in the framework of the Nice model. The application of the procedure consistently determines that the brightest distant Lace (semi-major axis above 500 au) is fainter than the brightest classical Centaur by about one magnitude, no matter what parameters were used for the procedure. However, reality shows a reversed situation: there is an excess of Laces with lower visual magnitudes. It is not clear why this is the case. We test whether a planetary-mass solar companion could produce an excess of bright Laces in comparison with classical Centaurs. We find that with the companion there is an excess of luminous Laces compared to when there is no companion. However, the companion model also produces many classical Centaurs with lower visual magnitudes than the observed ones. Thus we conclude that the companion does not solve this visual magnitude inconsistency, although the results are in general more coherent under the model with the companion than without.
Published in: Icarus, 258, 37
For preprints, contact rodney@on.br
We adapted a multi-species escape model, developed for close-in extrasolar planets, to calculate the escape rates of CH4 and N2 from Pluto. In the absence of escape, CH4 should overtake N2 as the dominant species below the exobase. The CH4 profile depends strongly on the escape rate, however, and the typical escape rates predicted for Pluto lead to a nearly constant mixing ratio of less than 1% below the exobase. In this case the CH4 escape rate is only 5-10% of the N2 escape rate. Observations of the CH4 profile by the New Horizons/ALICE spectrograph can constrain the CH4 escape rate and provide a unique test for escape models.
To appear in: Geophysical Research Letters
For preprints, contact tommi@lpl.arizona.edu
on the web at http://arxiv.org/abs/1508.02672
We report the discovery of the eighth and ninth known Trojans in stable
orbits around Neptune's leading Lagrange point, L4. The objects
2014 QO441 and 2014 QP441 were detected in data obtained
during the 2013-14 and 2014-15 observing seasons by the Dark Energy
Survey, using the Dark Energy Camera (DECam) on the 4-meter Blanco
telescope at Cerro Tololo Inter-American Observatory. Both are in
high-inclination orbits (18.8
and 19.4
respectively). With an eccentricity of 0.104, 2014 QO441 has the
most eccentric orbit of the eleven known stable Neptune Trojans. Here
we describe the search procedure and investigate the objects' long-term
dynamical stability and physical properties.
Submitted to: The Astronomical Journal
For preprints, contact gerdes@umich.edu
or on the web at http://arxiv.org/abs/1507.05177
Haumea is a dwarf planet with two known satellites, an unusually high
spin rate, and a large collisional family, making it one of the most
interesting objects in the outer solar system. A fully self-consistent
formation scenario responsible for the satellite and family formation is
still elusive, but some processes predict the initial formation of many
small moons, similar to the small moons recently discovered around
Pluto. Deep searches for regular satellites around KBOs are difficult
due to observational limitations, but Haumea is one of the few for which
sufficient data exist. We analyze Hubble Space Telescope (HST)
observations, focusing on a ten-consecutive-orbit sequence obtained in
July 2010, to search for new very small satellites. To maximize the
search depth, we develop, implement, and validate a non-linear
shift-and-stack method. No additional satellites of Haumea are found,
but by implanting and recovering artificial sources, we characterize our
sensitivity. At distances between 
10,000 km and 150,000 km
from Haumea, satellites with radii as small as 10 km are ruled
out, assuming an albedo (
) similar to Haumea. This search
method rules out objects similar in size to the small moons of Pluto. By
developing clear criteria for determining the number of non-linear rates
to use, we find that far fewer shift rates are required (35) than
might be expected, suggesting that this method is more tractable than
commonly assumed, particularly as applied to satellite searches.
Submitted to: The Astronomical Journal
For preprints, contact dragozzine@fit.edu
During the planet formation process, billions of comets are created and
ejected into interstellar space. The detection and characterization of
such interstellar comets (also known as extra-solar planetesimals or
extra-solar comets) would give us in situ information about the
efficiency and properties of planet formation throughout the galaxy.
However, no interstellar comets have ever been detected, despite the
fact that their hyperbolic orbits would make them readily identifiable
as unrelated to the solar system. Moro-Martín et al. 2009 have
made a detailed and reasonable estimate of the properties of the
interstellar comet population. We extend their estimates of
detectability with a numerical model that allows us to consider
``close'' interstellar comets, e.g., those that come within the orbit of
Jupiter. We include several constraints on a ``detectable'' object that
allow for realistic estimates of the frequency of detections expected
from the Large Synoptic Survey Telescope (LSST) and other surveys. The
influence of several of the assumed model parameters on the frequency of
detections is explored in detail. Based on the expectation from
Moro-Martín et al. 2009, we expect that LSST will detect 0.01-100
interstellar comets during its lifetime, with most of the uncertainty
from the unknown number density of small (0.1-1 km) interstellar
comets. Both asteroid and comet cases are considered, where the latter
includes various empirical prescriptions of brightening. Using simulated
LSST-like astrometric data, we study the problem of orbit determination
for these bodies, finding that LSST could identify their orbits as
hyperbolic and determine an ephemeris sufficiently accurate for
follow-up in about 4-7 days. We give the hyperbolic orbital parameters
of the most detectable interstellar comets. Taking the results into
consideration, we give recommendations to future searches for
interstellar comets.
Submitted to The Astrophysical Journal
For preprints, contact dragozzine@fit.edu
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.
