After many years of ground and space-based KBO searches for a target that the New Horizons spacecraft could reach if it gets an extended mission, NASA, STScI, and the New Horizons team announced the discovery - using the Hubble Space Telescope - of some ``potentially targetable'' candidates for a flyby after next year's encounter with Pluto.
http://hubblesite.org/newscenter/archive/releases/solar-system/2014/47/
http://pluto.jhuapl.edu/overview/piPerspective.php?page=piPerspective_10_23_2014
There were 6 new TNO discoveries announced since the previous issue of Distant EKOs:
2013 RB98, 2014 QL441, 2014 QM441, 2014 QN441, 2014 UH192, 2014 UM33
and 8 new Centaur/SDO discoveries:
2014 ON6, 2014 QF433 2014 RE12, 2014 SR303, 2014 SS303, 2014 SW223, 2014 TZ33, 2014 UT114
Reclassified objects:
2014 QF433 (SDOTNO)
Objects recently assigned numbers:
2001 QJ298 = (408832)
2005 VJ119 = (413666)
Deleted/Re-identified objects:
2006 HH123
Current number of TNOs: 1284 (including Pluto)
Current number of Centaurs/SDOs: 407
Current number of Neptune Trojans: 9
Out of a total of 1700 objects:
656 have measurements from only one opposition
633 of those have had no measurements for more than a year
326 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Asteroids and Kuiper belt objects are remnant planetesimals from the
epoch of planet formation. The first stage of planet formation is the
accumulation of dust and ice grains into mm-cm-sized pebbles. These
pebbles can clump together through the streaming instability and form
gravitationally bound pebble `clouds'. Pebbles inside such a cloud will
undergo mutual collisions, dissipating energy into heat. As the cloud
loses energy, it gradually contracts towards solid density. We model
this process and investigate two important properties of the collapse:
(i) the timescale of the collapse and (ii) the temporal evolution of the
pebble size distribution. Our numerical model of the pebble cloud is
zero-dimensional and treats collisions with a statistical method. We
find that planetesimals with radii larger than 
100 km collapse on
the free-fall timescale of about 25 years. Lower-mass clouds have longer
pebble collision timescales and collapse much more slowly, with collapse
times of a few hundred years for 10-km-scale planetesimals and a few
thousand years for 1-km-scale planetesimals. The mass of the pebble
cloud also determines the interior structure of the resulting
planetesimal. The pebble collision speeds in low-mass clouds are below
the threshold for fragmentation, forming pebble-pile planetesimals
consisting of the primordial pebbles from the protoplanetary disk.
Planetesimals above 100 km in radius, on the other hand, consist of
mixtures of dust (pebble fragments) and pebbles which have undergone
substantial collisions with dust and other pebbles. The Rosetta mission
to the comet 67P/Churyumov-Gerasimenko and the New Horizons mission to
Pluto will both provide valuable information about the structure of
planetesimals in the Solar System. Our model predicts that 67P is a
pebble-pile planetesimal consisting of primordial pebbles from the Solar
Nebula, while the pebbles in the cloud which contracted to form Pluto
must have been ground down substantially during the collapse.
To appear in: Astronomy & Astrophysics
For preprints, contact kalle@astro.lu.se
or on the web at http://arxiv.org/abs/1408.2535
In this work, we investigate the equilibrium figures of a
dumb-bell-shaped sequence with which we are still not well acquainted.
Studies have shown that these elongated and nonconvex figures may
realistically replace the classic ``Roche binary approximation'' for
modeling putative peanut-shaped or contact binary asteroids. The
best-fit dumb-bell shapes, combined with the known rotational period of
the objects, provide estimates of the bulk density of these objects.
This new class of mathematical figures has been successfully tested on
the observed light curves of three noteworthy small bodies: main-belt
Asteroid 216 Kleopatra, Trojan Asteroid 624 Hektor and
Edgeworth-Kuiper-belt object 2001 QG298. Using the direct observations
of Kleopatra and Hektor obtained with high spatial resolution techniques
and fitting the size of the dumb-bell-shaped solutions, we derived new
physical characteristics in terms of equivalent radius, 62.5
5 km
and 925 km, respectively, and bulk density, 4.40.4 g cm-3
and 2.430.35 g cm-3, respectively. In particular, the growing
inadequacy of the radar shape model for interpreting any type of
observations of Kleopatra (light curves, AO images, stellar
occultations) in a satisfactory manner suggests that Kleopatra is more
likely to be a dumb-bell-shaped object than a ``dog-bone.''
Published in: Icarus, 245, 64 (2015 January 1)
For preprints, contact descamps@imcce.fr
or on the web at http://arxiv.org/abs/1410.7962
The present-day orbit distribution of the Neptune Trojans is a powerful
probe of the dynamical environment of the outer solar system during the
late stages of planet migration. In this work, I conservatively debias
the inclination, eccentricity, and libration amplitude distributions of
the Neptune Trojans by reducing a priori unknown discovery and
follow-up survey properties to nuisance parameters and using a
likelihood-free Bayesian rejection sampler for parameter estimation.
Using this survey-agnostic approach, I confirm that the Neptune
Trojans are a dynamically excited population: at >95% confidence, the
Neptune Trojans' inclination width must be
. For
comparison and motivation purposes, I also model the Jupiter Trojan
orbit distributions in the same basis and produce new estimates of their
parameters (Jupiter Trojan
,
, and
). The debiased inclination, libration amplitude, and eccentricity
distributions of the Neptune Trojans are nominally very similar to those
of the Jupiter Trojans. I use these new constraints to inform a suite of
simulations of Neptune Trojan capture by an eccentric, rapidly-migrating
Neptune from an initially dynamically-hot disk. These simulations
demonstrate that if migration and eccentricity-damping timescales were
short (
Myr,
Myr), the disk that
Neptune migrated into must have been pre-heated (prior to
Neptune's appearance) to a width comparable to the Neptune Trojans'
extant width to produce a captured population with an inclination
distribution width consistent with that of the observed population.
To appear in: Icarus, 247, 112 (2015 February)
For preprints, contact alexharrisonparker@gmail.com
or on the web at http://arxiv.org/abs/1409.6735
The Jupiter Trojan asteroids and the Plutinos are two peculiar populations. They are dynamically resonant, therefore with heliocentric distances relatively bounded for long timescales, as a fairly general rule. As a consequence, some correlation with the surface color properties of their respective members is expected. Indeed, there are apparent differences in the B-V vs. V-R color-color diagram of the two populations. Using a simple model based on the surface color due to the contribution of two components, one pristine and one altered, we find as plausible that the difference is due to the interplay of space weathering by energetic cosmic-radiation and collisional effects.
To appear in: Icarus
For preprints, contact melita@iafe.uba.ar
Infrared spectroscopic observations have established the presence of
hydrocarbon ices on Pluto and other TNOs, but the abundances of such
molecules cannot be deduced without accurate optical constants (n, k)
and reference spectra. In this paper we present our recent measurements of
near- and mid-infrared optical constants for ethane (C2H6) and
ethylene (C2H4) in multiple ice phases and at multiple temperatures.
As in our recent work on acetylene (C2H2), we also report new
measurements of the index of refraction of each ice at 670
nm.
Comparisons are made to earlier work where possible, and electronic
versions of our new results are made available.
Published in: Icarus 243, 148 (2014 November 15)
For preprints, contact reggie.hudson@nasa.gov
Download data and preprints on the web at http://science.gsfc.nasa.gov/691/cosmicice
http://www.nrc-cnrc.gc.ca/eng/careers/index.html
Desired starting date: 1 September 2015
The National Research Council (NRC) is pleased to announce the 2014 competition for two Plaskett Postdoctoral Research Associate (RA) positions tenable at DAO in Victoria, BC, Canada. The successful candidates will be outstanding recent doctoral graduates in astrophysics who are highly motivated to exploit facilities administered by NRC for Canadian astronomers and contribute to projects led by NRC Herzberg staff members. We are particularly seeking candidates who will contribute to one or more of the following research areas:
3500
square degrees of deep u-band imaging of the Milky Way halo; the
Pan-Andromeda Archaeological Survey (PAndAS) and associated datasets;
and optical and near IR observations of Galactic globular clusters
(including high spatial resolution Gemini/GeMS MCAO studies) [NRC staff
members: Pat Côté, Stéphanie Côté, Tim Davidge, Alan McConnachie, Peter
Stetson]
The successful candidates are expected to work independently and perform original research in collaboration with NRC Herzberg staff members associated with projects most relevant to his or her area of expertise. Additionally, candidates are expected to keep an active engagement with the community to advance NRC Herzberg's mandate. In particular, NRC Herzberg is involved in several ground- and space-based telescopes of the present (e.g., ALMA, CFHT, Gemini, JCMT) and future (e.g., JWST, CASTOR, Astrosat, WFIRST, Astro-H, SKA, MSE, TMT), as well as in scientific data preservation, distribution, and analysis techniques. The Canadian Astronomy Data Centre, home to the Canadian Virtual Observatory, the CANFAR cloud computing network, and data archives including, e.g., CFHT, Canadian Galactic Plane Survey, Gemini, HST, and JCMT, are also located at NRC Herzberg. Candidates with interests in developing studies of next-generation instrumentation and facilities will be given highest consideration.
The successful candidates will share with other Plaskett RAs the organization of the weekly seminar series that runs September-April, and have access via Canada's TAC process to the astronomical facilities operated by NRC, as well as other facilities with open competition. The positions will constitute initial appointments of two years, which may be extended for one further year (subject to performance and availability of funds). In addition to highly competitive benefits and salary, Plaskett RAs will receive support for observing and conference travel, page charges, and access to professionally managed computers.
Applicants must have acquired their Ph.D. within the last five years or expect to obtain their degree before taking up the position. Applications should be made by 12 December 2014 via the process described at the URL provided.
NRC is an equal opportunity employer.
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.