There were 2 new TNO discoveries announced since the previous issue of Distant EKOs:
2008 LD18, 2012 HH2
and 5 new Centaur/SDO discoveries:
2004 VM131, 2012 GM12, 2012 GU11, 2012 GX17, 2012 KU50
Reclassified objects:
2012 BX85 (SDOTNO)
2012 FZ78 (SDO
Objects recently assigned numbers:
2010 LJ109 = (328884)
2009 HW77 = (330836)
Deleted/Re-identified objects:
2012 GN12 = 2010 FY28 = 2011 GP61
Current number of TNOs: 1250 (including Pluto)
Current number of Centaurs/SDOs: 354
Current number of Neptune Trojans: 8
Out of a total of 1612 objects:
642 have measurements from only one opposition
624 of those have had no measurements for more than a year
319 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Ever since the very first photometric studies of Centaurs and Kuiper
Belt Objects (KBOs) their visible color distribution has been
controversial. That controversy gave rise to a prolific debate on the
origin of the surface colors of these distant icy objects of the Solar
System. Two different views attempt to interpret and explain the large
variability of colors, hence surface composition. Are the colors mainly
primordial and directly related to the formation region, or are they the
result of surface evolution processes? To date, no mechanism has been
found that successfully explains why Centaurs, which are escapees from
the Kuiper Belt, exhibit two distinct color groups, whereas KBOs do not.
In this letter, we readdress this issue using a carefully compiled set
of B-R colors and 
magnitudes (as proxy for size) for 253
objects, including data for 10 new small objects.
We find that the bimodal behavior seen among Centaurs is a size related
phenomenon, common to both Centaurs and small KBOs, i.e.
independent of dynamical classification. Further, we find that large
KBOs also exhibit a bimodal behavior of surface colors, albeit distinct
from the small objects and strongly dependent on the `Haumea collisional
family' objects. When plotted in B-R, space, the colors
of Centaurs and KBOs display a peculiar 
shape.
To appear in: Astronomy & Astrophysics
For preprints, contact peixinho@mat.uc.pt
or on the web at http://arxiv.org/abs/1206.3153
The transneptunian objects (TNOs) trapped in mean-motion resonances with
Neptune were likely emplaced there during planet migration late in
the giant-planet formation process.
We perform detailed modelling of the resonant objects detected in
the Canada-France Ecliptic Plane Survey (CFEPS) in order to provide
population estimates and, for some resonances, constrain
the complex internal orbital element distribution.
Detection biases play a critical role because phase relationships
with Neptune make object discovery more likely at certain longitudes.
This paper discusses the 3:2, 5:2, 2:1, 3:1, 5:1, 4:3, 5:3, 7:3, 5:4,
and 7:4 mean-motion resonances, all of which had CFEPS detections, along
with our upper limit on 1:1 Neptune Trojans (which is consistent with their
small population estimated elsewhere).
For the plutinos (TNOs in the 3:2 resonance) we refine the orbital
element distribution given in Kavelaars et al. (2009) and show that steep
H-magnitude distributions
(
, with 
0.8-0.9)
are favoured in the range Hg=8-9, and confirm that this resonance does
not share the inclination distribution of the classical Kuiper Belt.
We give the first population estimate for the 5:2 resonance and find
that, to within the uncertainties, the population is equal to that of
the 3:2 (
13,000 TNOs with Hg<9.16),
whereas the 2:1 population is smaller by a factor of 3-4 compared
to the other two resonances.
We also measure significant populations inhabiting the
4:3, 5:3, 7:3, 5:4, 7:4, 3:1, and 5:1 resonances, with
Hg<9.16 (D>100 km) populations in the thousands.
We compare our intrinsic population and orbital-element distributions
with several published models of resonant-TNO production; the most
striking discrepancy is that resonances beyond the 2:1 are in reality
more heavily populated than in published models.
Published in: Astronomical Journal 144, 23 (2012 July)
Preprints available on the web at http://arxiv.org/abs/1205.7065
Third and fourth order mean motion resonances are studied in the model of the restricted three-body problem by numerical methods for mass parameters corresponding approximately to the Sun-Jupiter and Sun-Neptune systems. In the case of inner resonances, it is shown that there are two regions of libration in the 8:5 and 7:4 resonances, one at low, the other at high eccentricities. In the 9:5 and 7:3 resonances libration can exist only in one region at high eccentricities. The 5:2 and 4:1 resonances are very regular, with one librational zone existing for all eccentricities. There is no visible region of libration at any eccentricities in the 5:1 resonance, the transition between the regions of direct and retrograde circulation is very sharp. In the case of outer resonances, the 8:5 and 7:4 resonances have also two regions of libration, but the 9:5 resonance has three, the 7:3 resonance two librational zones. The 5:2 resonance is again very regular, but it is parted for two regions of libration at high eccentricities. Libration is possible in the 4:1 resonance only at high eccentricities. The 5:1 resonance is very symmetric. In the case of outer resonances, a comparison is made with trans-Neptunian objects (TNO) in higher order mean motion resonances. Several new librating TNOs are identified.
Published in: Celestial Mechanics and Dynamical Astronomy 113, 95 (2012 May)
For preprints, contact B.Erdi@astro.elte.hu
The population of Neptune Trojans is believed to be bigger than that of Jupiter Trojans and that of asteroids in the main belt, although only eight members of this far distant asteroid swarm have been observed up to now. Six leading Neptune Trojans around the Lagrange point L4 discovered earlier have been studied in detail, but two trailing ones found recently around the L5 point, 2004 KV18 and 2008 LC18, have not been investigated yet. In this paper, we report our investigations on the dynamical behaviors of these two new Neptune Trojans. Our calculations show that the asteroid 2004 KV18 is a temporary Neptune Trojan. Most probably, it was captured into the trailing Trojan cloud no earlier than 2.03 x 105yr ago, and it will not keep this identity no later than 1.65 x 105yr in future. Based on the statistics on our orbital simulations, we argue that this object is more like a scattered Kuiper belt object. On the contrary, the orbit of 2008 LC18 is much more stable. Among the clone orbits spreading within the orbital uncertainties, a considerable portion of clones may survive on the L5 tadpole orbits for 4Gyr. The strong dependence of the stability on the semimajor axis and resonant angle suggests that further observations are badly required to confine the orbit in the stable region. We also discuss the implications of the existence and dynamics of these two trailing Trojans on the Solar system history.
To appear in: Research in Astronomy and Astrophysics
For preprints, contact zhouly@nju.edu.cn
or on the web at http://arxiv.org/abs/1205.2206
We report new Hubble Space Telescope and Spitzer
Space Telescope results concerning the physical properties of the
trans-Neptunian Object (TNO) binaries (120347) Salacia-Actaea (formerly 2004 SB60),
and (42355) Typhon-Echidna (formerly 2002 CR46). The mass of the (120347) Salacia-Actaea system
is
kg. The semi-major axis, period, and
eccentricity of the binary orbit are
km,
days, and
, respectively. In terms
of the ratio of the semimajor axis to the radius of the Hill sphere,
a/rH, (120347) Salacia-Actaea is the tightest TNO binary system with a known orbit.
Based on hybrid Standard Thermal Model (hybrid-STM) fits to the data,
the effective diameter and V-band geometric albedo of the system are
km (making it one of the largest known TNOs), and
pV =
3.57+1.03-0.72%. Thermophysical models for (120347) Salacia suggest that
it probably has a thermal inertia 
Jm
-2s-1/2K-1, although we can
not rule out values as high as 30 Jm
-2s-1/2K-1. Based on the magnitude
difference between Salacia and Actaea,
, we
estimate their individual diameters to be
km and
km. The mass density of the components is
g/cm3. Hybrid-STM fits to new Spitzer data for
Typhon-Echidna give an effective diameter and V-band geometric albedo
for the system of
km, and
pV = 6.00+4.10-2.08%.
Thermophysical models for (42355) Typhon suggest somewhat lower albedos
(probably no higher than about 8.2%, as compared to the hybrid-STM
upper limit of 10.1%). Taken together with the previously reported
mass, this diameter indicates a density of
, consistent with the very low densities of most other TNOs
smaller than 500 km diameter. Both objects must have significant amounts
of void space in their interiors, particularly if they contain silicates
as well as water-ice (as is expected). The ensemble of binary-TNO
densities suggests a trend of increasing density with size, with objects
smaller than 400 km diameter all having densities less than 1g/cm3, and
those with diameters greater than 800 km all having densities greater
than 1g/cm3. If the eccentricity of the binary orbit of (42355) Typhon-Echidna is not
due to recent perturbations, considerations of tidal evolution suggest
that (42355) Typhon-Echidna must have a rigidity close to that of solid water ice,
otherwise the orbital eccentricity of the system would have been damped
by now.
Published in: Icarus 219, 676 (2012 June)
For preprints, contact stansber@as.arizona.edu
The Pluto system provides a unique local laboratory for the study of
binaries with multiple low mass companions. In this paper, we study the
orbital stability of P4, the most recently discovered moon in the Pluto
system. This newfound companion orbits near the plane of the
Pluto-Charon binary, roughly halfway between the two minor moons Nix and
Hydra. We use a suite of few body integrations to constrain the masses
of Nix and Hydra, and the orbital parameters of P4. For the system to
remain stable over the age of the Solar System, the masses of Nix and
Hydra likely do not exceed
5 x 1016 kg and
9 x 1016 kg,
respectively. These upper limits assume a fixed mass ratio between Nix
and Hydra at the value implied by their median optical brightness. Our
study finds that stability is more sensitive to their total mass and
that a downward revision of Charon's eccentricity (from our adopted
value of 0.0035) is unlikely to significantly affect our conclusions.
Our upper limits are an order of magnitude below existing astrometric
limits on the masses of Nix and Hydra. For a density at least that of
ice, the albedos of Nix and Hydra would exceed 0.3. This constraint
implies they are icy, as predicted by giant impact models. Even with
these low masses, P4 only remains stable if its eccentricity
.
The 5:1 commensurability with Charon is particularly unstable, Combining
stability constraints with the observed mean motion places the preferred
orbit for P4 just exterior to the 5:1 resonance. These predictions will
be tested when the New Horizons satellite visits Pluto. Based on the
results for the Pluto-Charon system, we expect that circumbinary,
multi-planet systems will be more widely spaced than their singleton
counterparts. Further, circumbinary exoplanets close to the three-body
stability boundary, such as those found by Kepler, are less likely to
have other companions nearby.
To appear in: The Astrophysical Journal
Preprints available on the web at http://arxiv.org/abs/1205.5273
An analytic expression for the variation in surface and sub-surface
temperature is developed for worlds whose surface pressures are nearly
constant with latitude and longitude and whose atmospheres are in
vapor-pressure equilibrium with the dominant surface volatiles. Such
worlds include the current Pluto and Triton, and other volatile-covered
Kuiper Belt Objects during some portion of their heliocentric orbit. The
expressions also apply on airless worlds with negligible horizontal heat
flow, such as asteroids. Temperature variations in volatile-covered or
bare areas as a function of time is derived in terms of three thermal
parameters relating to (1) the thermal wave within the substrate, (2)
the energy needed to heat an isothermal volatile slab, and (3) the
buffering by the latent heat needed to change the atmospheric surface
pressure. For Pluto's current surface pressure (
17 
bar), atmospheric
buffering dominates over subsurface effects on diurnal timescales, and
should keep the surface pressure over a Pluto day constant to within
0.2%.
To appear in: Icarus
For preprints, contact layoung@boulder.swri.edu
or on the web at
http://www.boulder.swri.edu/~layoung/eprint/LYoung2012_VolXferI_rev2full.pdf
We use a simple Pluto general circulation model (sPGCM) to predict for the first time the wind on Pluto and its global, large-scale structure, as well as the temperature and surface pressure. Wind is a fundamental atmospheric variable that has previously been neither measured nor explicitly modeled on Pluto. We ran the sPGCM in 2D mode (latitude, height, and time varying) using the Massachusetts Institute of Technology general circulation model dynamical core, a simple radiative-convective scheme, and no frost cycle. We found that Pluto's atmosphere is dynamically active in the zonal direction with high-speed, high-latitude jets that encircle the poles in gradient wind balance and prograde with Pluto's rotation. The meridional and vertical winds do not show evidence for a Hadley cell (or other large-scale structure), due to the low altitude temperature inversion. The horizontal variation in surface pressure is a small fraction of the previously derived inter-annual variation in surface pressure. The sGCM output was validated with stellar occultation light curve data from the years 1988, 2002, 2006, and 2007. For 2006 and 2007, the best-fit global mean surface pressure was 24 microbar, in 2002 it was 22 microbar, while in 1988 it was 12 microbar (1 microbar error bars). For all years the methane mixing ratio was 1% (0.2% error bars). This work is a first step for future Pluto, Triton, and KBO atmosphere general circulation models that will also include longitudinal variations and a volatile cycle.
Published in: Journal of Geophysical Research, 117, E05002 (2012 May)
For preprints, contact angela@boulder.swri.edu
or on the web at http://www.boulder.swri.edu/~angela/zalucha2012JGR.117.E05002.pdf
The discovery of the largest trans-neptunian object 2003 UB313 (dwarf planet Eris) was made more than 5 years ago, but the question on the true relation of the sizes of Pluto and Eris (and according to of their densities) remains debatable in view of a sizable scatter of their size's estimates obtained by the various methods. Here, we first used a semi-empirical approach to deduce the expression linking the orbital parameter eccentricity to the physical properties of the trans-neptunian dwarf planets and have applied it to determining the mean size of these planets. In doing so is proved that the mean Eris' size should be about 9% larger than of Pluto's. Based on the published photometric data and the derived mean diameter the possible estimates of the minimum and maximum diameters of Pluto and Eris on the assumption of a deviation their form from spherical are provided. The probable reason for an occurrence of such an aspherical form of these dwarf planets is briefly discussed.
Preprint available on the web at http://arxiv.org/abs/1203.0524
http://www.chem.hawaii.edu/Bil301/Ice2013.html
During the last decade, significant new experimental techniques have been developed to investigate the interaction of ionizing radiation (UV, VUV, gamma rays, charged particles) and of neutrals (atoms, radicals, molecules, grains) with surfaces of solids (ices, minerals, carbonaceous compounds) in the Solar System and in the Interstellar Medium (ISM). These processes provide new fundamental insights - sometimes on the molecular level - into the processes that are critical to the chemistry in the ISM, star and planet forming regions, and on/in icy objects in the Solar System from the formation of the simplest molecule (molecular hydrogen) to astrobiologically important species such as amino acids and sugars. There is an increasing convergence of interests of these fields, so a 'united', bi-annual workshop is highly desired.
The first workshop features invited (senior and junior researchers) as well as contributed talks focusing on the interaction of ionizing radiation (UV, VUV, gamma rays, charged particles) and neutrals (atoms, radicals, molecules, grains) with low temperature solids (ices, minerals, organics). The talks can be extended to observations, modeling, and electronic structure calculations, but only if these topics can be directly linked - as evident from the abstract - to laboratory experiments. Poster submissions are highly encouraged; this will allow a broad participation of newcomers to the field (Ph.D. students, postdocs).
Accommodation: The workshop will take place in the Sheraton Kauai Resort in Poipu, Kauai, Hawaii, starting with a reception and registration on February 24, 2013, at 6 pm. The hotel will allocate a block of rooms for workshop participants. Reservations must be made by December 1, 2012. Group rates are available three days pre and post group arrival and departure dates. Additional information will be posted soon.
Transportation: Sheraton Kauai Resort is a short drive (20 minutes) from the airport (LIH). LIH can be reached from LAX, SFO, or HNL.
Registration: The registration deadline is November 1, 2012. The registration fee of $250 includes the reception, snacks, and a book-of-abstracts.
Additional information available at:
http://www.chem.hawaii.edu/Bil301/Ice2013.html If you have
additional questions, please email Ralf Kaiser (ralfk@hawaii.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.