The Distant EKOs Newsletter just broke the 500 subscriber mark, with readers from at least 35 countries. It has been running for 13 years with 78 issues (coincidentally the 100th issue should come out when New Horizons flies past Pluto). Thanks to all of you for your interest and submissions.
There were 21 new TNO discoveries announced since the previous issue of Distant EKOs:
2009 DK143, 2009 DL143, 2009 DN143, 2009 DO143, 2009 DP143, 2009 DQ143, 2009 DR143, 2009 DS143, 2009 DT143, 2009 JA19, 2009 JB19, 2009 JD19, 2009 JE19, 2009 JF19, 2009 JT18, 2009 JV18, 2009 JW18, 2009 KT36, 2009 KU36, 2009 KV36, 2009 KW36
and 14 new Centaur/SDO discoveries:
2009 DJ143, 2009 DM143, 2009 JC19, 2009 JU18, 2009 JX18, 2009 JY18, 2009 JZ18, 2009 KA37, 2009 KX36, 2009 KY36, 2009 KZ36, 2011 SR250, 2011 UD63, 2011 WR74
Objects recently assigned numbers:
2005 QU182 = (303775)
2008 QY40 = (305543)
2005 PR21 = (303712)
2006 XQ51 = (309139)
2007 RW10 = (309239)
2008 SJ236 = (309737)
2008 UZ6 = (309741)
2010 KR59 = (310071)
2004 PG115 = (307982)
2006 SQ372 = (308933)
2001 KQ77 = (306792)
2002 KW14 = (307251)
2002 MS4 = (307261)
2002 VU130 = (307463)
2003 QW90 = (307616)
2005 CB79 = (308193)
2005 RS43 = (308379)
2005 SC278 = (308460)
2005 XU100 = (308634)
Deleted/Re-identified objects:
1999 TZ1
2008 HG67
2000 SN331
Current number of TNOs: 1248 (including Pluto)
Current number of Centaurs/SDOs: 333
Current number of Neptune Trojans: 8
Out of a total of 1589 objects:
641 have measurements from only one opposition
619 of those have had no measurements for more than a year
315 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
We seek to constrain the surface composition of the Trans-Neptunian Object (90482) Orcus and its small satellite Vanth, as well as their mass and density.
We acquired near-infrared spectra (1.4-2.4
m) of (90482) Orcus
and its companion Vanth using the adaptive-optics-fed integral-field
spectrograph SINFONI mounted on Yepun/UT4 at the European Southern
Observatory Very Large Telescope. We took advantage of a very
favorable appulse (separation of only 4'') between Orcus and the
UCAC2 29643541 star (mR = 11.6) to use the adaptive optics mode of
SINFONI, allowing both components to be spatially resolved and Vanth
colors to be extracted independently from Orcus.
The spectrum of Orcus we obtain has the highest signal-to-noise ratio
to date, and we confirm the presence of H2O ice in crystalline
form, together with the presence of an absorption band at 2.2m.
We set an upper limit of about 2% for the presence of methane, and
5% for ethane. Because the methane alone cannot account for the
2.2m band, the presence of ammonia is suggested to the level of
a couple of percent. The colors of Vanth are found slightly redder
than those of Orcus, but the large measurement uncertainties forbid us
from drawing conclusions on the origin of the pair (capture or
co-formation). Finally, we reset the orbital phase of Vanth around
Orcus, and confirm the orbital parameters derived by Brown et al.
(2010, AJ 139).
Published in: Astronomy & Astrophysics, 534, A115 (2011 October)
For preprints, contact benoit.carry@esa.int
or on the web at http://benoit.carry.free.fr/science/article/2011-AA-534-Carry.pdf
Kuiper Belt object 2007 TY430 is the first wide, equal-sized, binary
known in the 3:2 mean motion resonance with Neptune. The two
components have a maximum separation of about 1 arcsecond and are on
average less than 0.1 magnitudes different in apparent magnitude with
identical ultra-red colors (
mags). Using nearly
monthly observations of 2007 TY430 from 2007-2011, the orbit of the
mutual components was found to have a period of 
days
with a semi-major axis of 
km and eccentricity of
. The inclination with respect to the ecliptic is
degrees and extensive observations have allowed the
mirror orbit to be eliminated as a possibility. The total mass for
the binary system was found to be
kg.
Equal-sized, wide binaries and ultra-red colors are common in the low
inclination ``cold'' classical part of the Kuiper Belt and likely
formed through some sort of three body interactions within a much
denser Kuiper Belt. To date 2007 TY430 is the only ultra-red,
equal-sized binary known outside of the classical Kuiper belt
population. Numerical simulations suggest 2007 TY430 is moderately
unstable in the outer part of the 3:2 resonance and thus 2007 TY430 is
likely an escaped ``cold'' classical object that later got trapped in
the 3:2 resonance. Similar to the known equal-sized, wide binaries in
the cold classical population, the binary 2007 TY430 requires a high
albedo and very low density structure to obtain the total mass found
for the pair. For a realistic minimum density of 0.5 g/cm3 the
albedo of 2007 TY430 would be greater than 0.17. For reasonable
densities, the radii of either component should be less than 60 km,
and thus the relatively low eccentricity of the binary is interesting
since no tides should be operating on the bodies at their large
distances from each other. The low prograde inclination of the binary
also makes it unlikely the Kozai mechanism could have altered the
orbit, making the 2007 TY430 binary orbit likely one of the few
relatively unaltered primordial binary orbits known. Under some
binary formation models, the low inclination prograde orbit of the
2007 TY430 binary indicates formation within a relatively high
velocity regime in the Kuiper Belt.
To appear in: The Astronomical Journal
The widely-separated, near-equal mass binaries hosted by the cold
Classical Kuiper Belt are delicately bound and subject to disruption by
many perturbing processes. We use analytical arguments and numerical
simulations to determine their collisional lifetimes given various
impactor size distributions, and include the effects of mass-loss and
multiple impacts over the lifetime of each system. These collisional
lifetimes constrain the population of small (
km) objects
currently residing in the Kuiper Belt, and confirm that the size
distribution slope at small size cannot be excessively steep -- likely
. We track mutual semi-major axis, inclination, and
eccentricity evolution through our simulations, and show that it is
unlikely that the wide binary population represents an evolved tail of
the primordially-tight binary population. We find that if the wide
binaries are a collisionally-eroded population, their primordial mutual
orbit planes must have preferred to lie in the plane of the solar
system. Finally, we find that current limits on the size distribution at
small radii remain high enough that the prospect of detecting
dust-producing collisions in real-time in the Kuiper Belt with future
optical surveys is feasible.
To appear in: The Astrophysical Journal
For preprints, contact alexhp@uvic.ca
or on the web at http://arxiv.org/abs/1111.2046
Numerical integrations of the equations of motion of the giant planets and scattering particles show that there is a possible orbital itinerary that a particle may follow from a scattering mode up to a stable position near the orbit of 2004 XR190. This orbital evolution requires that the particle gets trapped in a mean motion resonance with Neptune coupled with the Kozai resonance. Imposing migration on Neptune while a particle is experiencing both resonances can entail an escape from resonance at a low particle's eccentricity. This eccentricity and the associated inclination are always similar to those of 2004 XR190. I conclude that 2004 XR190 was most likely a scattered object that went through those resonance processes and was eventually deposited at its current position. By the same argument, it is expected that there must exist several other objects with similar semimajor axis, eccentricity and inclination as those of 2004 XR190.
Published in: Icarus 215, 661 (2011 October)
For preprints, contact rodney@on.br
We present the faintest mid ecliptic latitude survey in the second
part of HST archival search for outer Solar System bodies. We report
the discovery of 28 new trans-Neptunian objects and 1 small centaur
(
km) in the band
off the ecliptic. The
inclination distribution of these excited objects is consistent with
the distribution derived from brighter ecliptic surveys. We suggest
that the size and inclination distribution should be estimated
consistently using suitable surveys with calibrated search algorithms
and reliable orbital information.
Published in: The Astrophysical Journal, 742, 118 (2011 December 1)
For preprints, contact cesar.i.fuentes@nau.edu
or on the web at http://arxiv.org/abs/1108.5213
saka-shi, 
saka, Japan
We analyse the origin of three Centaurs with perihelia in the range
15 AU to 30 AU, inclinations above 70
and semi-major axes
shorter than 100 AU. Based on long-term numerical simulations we
conclude that these objects most likely originate from the Oort cloud
rather than the Kuiper Belt or Scattered Disc. We estimate that there
are currently between 1 and 200 of these high-inclination,
high-perihelion Centaurs with absolute magnitude H<8.
To appear in: Monthly Notices of the Royal Astronomical Society
For preprints, contact brasser_astro@yahoo.com
or on the web at http://arxiv.org/abs/1111.7037
The current dynamical structure of the Kuiper belt was shaped by the
orbital evolution of the giant planets, especially Neptune, during the
era following planet formation, when the giant planets may have
undergone planet-planet scattering and/or planetesimal-driven migration.
Numerical simulations of this process, while reproducing many properties
of the belt, fail to generate the high inclinations and eccentricities
observed for some objects while maintaining the observed dynamically
``cold" population. We present the first of a three-part parameter study
of how different dynamical histories of Neptune sculpt the planetesimal
disk. Here we identify which dynamical histories allow an in situ
planetesimal disk to remain dynamically cold, becoming today's cold
Kuiper belt population. We find that if Neptune undergoes a period of
elevated eccentricity and/or inclination, it secularly excites the
eccentricities and inclinations of the planetesimal disk. We demonstrate
that there are several well-defined regimes for this secular excitation,
depending on the relative timescales of Neptune's migration, the damping
of Neptune's orbital inclination and/or eccentricity, and the secular
evolution of the planetesimals. We model this secular excitation
analytically in each regime, allowing for a thorough exploration of
parameter space. Neptune's eccentricity and inclination can remain high
for a limited amount of time without disrupting the cold classical belt.
In the regime of slow damping and slow migration, if Neptune is located
(for example) at 20 AU, then its eccentricity must stay below 0.18 and
its inclination below 6.
To appear in: The Astrophysical Journal
For preprints, contact rdawson@cfa.harvard.edu
or on the web at http://arxiv.org/abs/1112.1954
We revisit the issue of the cause of the dynamical instability
during the so-called Nice model, which describes the early
dynamical evolution of the giant planets (Tsiganis et al. 2005,
Gomes et al. 2005). In particular, we address the problem of the
interaction of planets with a distant planetesimal disk in the time
interval between the dispersal of the proto-solar nebula and the
instability. In contrast to previous works, we assume that the
inner edge of the planetesimal disk is several AUs beyond the orbit
of the outermost planet, so that no close encounters between planets
and planetesimals occur. Moreover, we model the disk's viscous
stirring, induced by the presence of embedded Pluto-sized objects.
The four outer planets are assumed to be initially locked in a
multi-resonant state that most likely resulted from a preceding
phase of gas-driven migration (Morbidelli et al. 2007). We show
that viscous stirring leads to an irreversible exchange of energy
between a planet and a planetesimal disk even in absence of close
encounters between the planet and disk particles. The process is
mainly driven by the most eccentric planet, which is the inner ice
giant in the case studied here. If in isolation, this would cause
this ice giant to migrate inward. However, because it is locked in
resonance with Saturn, its eccentricity increases due to adiabatic
invariance. During this process, the system crosses many weak
secular resonances -- many of which can disrupt the mean motion
resonance and make the planetary system unstable. We argue that
this basic dynamical process would work in many generic
multi-resonant systems -- forcing a good fraction of them to become
unstable. Because the energy exchange proceeds at a very slow pace,
the instability manifests itself late, on a time scale consistent
with the epoch of the Late Heavy Bombardment (LHB, 
My).
In the migration mechanism presented here, the instability time is
much less sensitive to the properties of the planetesimal disk
(particularly the location of its inner edge) than in the classic
Nice-model mechanism.
Published in: The Astronomical Journal, 142, 152 (2011 November)
For preprints, contact hal@boulder.swri.edu
Modelling the formation of super-km-sized planetesimals by gravitational collapse of regions overdense in small particles requires numerical algorithms capable of handling simultaneously hydrodynamics, particle dynamics and particle collisions. While the initial phases of radial contraction are dictated by drag forces and gravity, particle collisions become gradually more significant as filaments contract beyond Roche density. Here we present a new numerical algorithm for treating momentum and energy exchange in collisions between numerical superparticles representing a high number of physical particles. We adopt a Monte Carlo approach where superparticle pairs in a grid cell collide statistically on the physical collision time-scale. Collisions occur by enlarging particles until they touch and solving for the collision outcome, accounting for energy dissipation in inelastic collisions. We demonstrate that superparticle collisions can be consistently implemented at a modest computational cost. In protoplanetary disc turbulence driven by the streaming instability, we argue that the relative Keplerian shear velocity should be subtracted during the collision calculation. If it is not subtracted, density inhomogeneities are too rapidly diffused away, as bloated particles exaggerate collision speeds. Local particle densities reach several thousand times the mid-plane gas density. We find efficient formation of gravitationally bound clumps, with a range of masses corresponding to contracted radii from 100 to 400 km when applied to the asteroid belt and 150 to 730 km when applied to the Kuiper belt, extrapolated using a constant self-gravity parameter. The smaller planetesimals are not observed at low resolution, but the masses of the largest planetesimals are relatively independent of resolution and treatment of collisions.
To appear in: Astronomy & Astrophysics
For preprints, contact anders@astro.lu.se
or on the web at http://arxiv.org/abs/1111.0221
A combined fluid/kinetic model is developed to calculate thermally driven escape of N2 from Pluto's atmosphere for two solar heating conditions: no heating above 1450 km and solar minimum heating conditions. In the combined model, one-dimensional fluid equations are applied for the dense part of the atmosphere, while the exobase region is described by a kinetic model and calculated by the direct simulation Monte Carlo method. Fluid and kinetic parts of the model are iteratively solved in order to maintain constant total mass and energy fluxes through the simulation region. Although the atmosphere was found to be highly extended, with an exobase altitude at 6000 km at solar minimum, the outflow remained subsonic and the escape rate was within a factor of two of the Jeans rate for the exobase temperatures determined. This picture is drastically different from recent predictions obtained solely using a fluid model which, in itself, requires assumptions about atmospheric density, flow velocity and energy flux carried away by escaping molecules at infinity. Gas temperature, density, velocity and heat flux versus radial distance are consistent between the hydrodynamic and kinetic model up to the exobase, only when the energy flux across the lower boundary and escape rate used to solve the hydrodynamic equations is obtained from the kinetic model. This limits the applicability of fluid models to atmospheric escape problems. Finally, the recent discovery of CO at high altitudes, the effect of Charon and the conditions at the New Horizon encounter are briefly considered.
To appear in: Icarus
For preprints, contact ojt9j@virginia.edu
or on the web at http://arxiv.org/abs/1111.2808
The dwarf planet Eris is a Trans-Neptunian Object (TNO) with an
elongated orbit (eccentricity 0.44), a large inclination (44 degrees)
relative to the ecliptic plane, and a surface composition very similar
to Pluto. It presently resides at 95.7 astronomical units (1 AU is the
Earth-Sun distance) from Earth, near its aphelion and more than three
times farther than Pluto. Owing to this great distance, measuring its
size or detecting a putative atmosphere is difficult. Here we report the
observation of a multi-chord stellar occultation by Eris on November 6,
2010 UT. The event is consistent with a spherical shape for Eris, with
radius
6 km, density
g cm-3
and a high visible geometric albedo
.
No nitrogen, argon or methane
atmospheres are detected with surface pressure larger than 
1 nbar,
about 10,000 times more tenuous than Pluto's present atmosphere. As
Pluto's radius is estimated between 1,150 and 1,200 km, Eris appears as
a Pluto-twin, with a bright surface possibly caused by a collapsed
atmosphere, owing to its cold environment. We anticipate that this
atmosphere may periodically sublimate as Eris approaches its perihelion,
at 37.8 AU from the Sun.
Published in: Nature 478, 493 (2011 October 27)
For preprints, contact Bruno.Sicardy@obspm.fr
Neptune's Wild Days: Constraints from the Eccentricity Distribution of the Classical Kuiper Belt
Rebekah I. Dawson1 and Ruth A. Murray-Clay1
1 Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 USA
Submitted to:
For preprints, contact rdawson@cfa.harvard.edu
Ultra-wide Trans-Neptunian Binaries (TNBs) are extremely sensitive to
perturbation, and therefore make excellent probes of the past and
present dynamical environment of the outer Solar System. Using data
gathered from a host of facilities we have determined the mutual orbits
for a sample of seven wide TNBs whose periods exceed one year. This
characterized sample provides us with new information about the probable
formation scenarios of TNBs, and has significant implications for the
early dynamical and collisional history of the Kuiper Belt. We show that
these wide binaries have short collisional lifetimes, and use them to
produce a new estimate of the number of small (1 km) objects in
the Kuiper Belt. Additionally, these systems are susceptible to tidal
disruption, and we show that it is unlikely that they were ever
subjected to a period of close encounters with the giant planets. We
find that the current properties of these ultra-wide Trans-Neptunian
Binaries suggest that planetesimal growth in the Cold Classical Kuiper
Belt did not occur through slow hierarchical accretion, but rather
through rapid gravitational collapse.
Dissertation directed by JJ Kavelaars
Ph.D. awarded October 2011 from the University of Victoria
For preprints, contact alexhp@uvic.ca
or on the web at http://hdl.handle.net/1828/3400
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.
