Having completed its successful flyby of the Pluto system, the New Horizons spacecraft is on a trajectory to encounter Kuiper Belt Object 2014 MU69. Pending NASA approval for an extended mission, New Horizons will also take advantage of being an observing platform in the outer solar system to observe a select number of other KBOs having favorable geometries for resolved or high signal-to-noise measurements.
Earth-based observations can support these pending New Horizons measurements through calibrated photometry at low phase angle (Earth), which will be complementary to the higher phase angle data from the spacecraft. In particular for objects having the potential for resolved imaging from the spacecraft, knowledge of the rotational phase at the time of the New Horizons observations can help constrain the overall shape of these distant objects.
An Earth-based campaign website in support of the pending science from
the New Horizons extended mission is under construction
http://www.boulder.swri.edu/nh-support-obs/kbo. Available there now
is a table listing the pending targets having the highest priority for
supporting observations. Register on that page to indicate interest.
There were 4 new TNO discoveries announced since the previous issue of Distant EKOs:
2012 HE85, 2015 BZ517, 2015 QT11, 2015 SP21
and 4 new Centaur/SDO discoveries:
2015 KH162, 2015 PK312, 2015 SO21, 2016 AE193
Reclassified objects:
2016 AE193 (SDOCentaur)
2001 OO108 (TNO
2002 PR170 (TNO
Objects recently assigned numbers:
2013 XZ8 = (459865)
2014 AT28 = (459870)
2014 ON6 = (459971)
1999 OM4 = (455171)
2001 FE193 = (455206)
2001 KT76 = (455209)
2003 UZ413 = (455502)
2007 TH422 = (456826)
Objects recently assigned names:
2012 BX85 = Praamzius
Current number of TNOs: 1453 (including Pluto)
Current number of Centaurs/SDOs: 489
Current number of Neptune Trojans: 12
Out of a total of 1954 objects:
659 have measurements from only one opposition
639 of those have had no measurements for more than a year
328 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Thermal observations of the Pluto-Charon system acquired by the Herschel Space Observatory in February 2012 are presented. They consist
of photometric measurements with the PACS and SPIRE instruments (nine
visits to the Pluto system each), covering six wavelengths from 70 to
500 
m altogether. The thermal light curve of Pluto-Charon is
observed in all filters, albeit more marginally at 160 and especially
500 m. Putting these data into the context of older ISO, Spitzer and ground-based observations indicates that the brightness
temperature (TB) of the system (rescaled to a common heliocentric
distance) drastically decreases with increasing wavelength, from
53 K at 20 m to 35 K at 500 m, and perhaps even
less at longer wavelengths. Considering a variety of diurnal and/or
seasonal thermophysical models, we show that TB values of 35 K are
lower than any expected temperature for the dayside surface or
subsurface of Pluto and Charon, implying a low surface emissivity. Based
on multiterrain modeling, we infer a spectral emissivity that decreases
steadily from 1 at 20-25 m to 0.7 at 500 m. This kind of
behavior is usually not observed in asteroids (when proper allowance is
made for subsurface sounding), but is found in several icy surfaces of
the solar system. We tentatively identify that a combination of a strong
dielectric constant and a considerable surface material transparency
(typical penetration depth 1 cm) is responsible for the effect.
Our results have implications for the interpretation of the temperature
measurements by REX/New Horizons at 4.2 cm wavelength.
To appear in: Astronomy & Astrophysics
Preprints available on the web at http://arxiv.org/abs/1601.05606
To confirm the previous observational results of Pluto's atmospheric CO in the J = 2-1 rotational transition, we conducted a new observation of CO (J = 3-2) in Pluto's atmosphere in 2014 August with the Atacama Submillimeter Telescope Experiment 10 m single-dish telescope. In contrast to the previous observational result obtained with the James Clerk Maxwell Telescope in 2009 and 2010 by using the J = 2-1 transition, no emission structure was observed near the rest frequency in our attempt. Possible explanations for the nondetection result of the J = 3-2 transition are discussed.
Published in: Publications of the Astronomical Society of Japan, 68, L1
We present numerical simulations of the evolution of synthetic Trans-Neptunian Binaries (TNBs) under the influence of the solar perturbation, tidal friction, and collisions with the population of Classical Kuiper Belt Object (KBOs).
We show that these effects,
acting together, have strongly sculpted the primordial population of TNBs.
If the population of Classical KBOs have a power law size distribution
as the ones that are inferred from recent observational surveys (Petit et al. 2011,
Adams et al. 2014, Fraser at al. 2014), the fraction of
surviving binaries at present would be 70% of the
primordial population. The orbits of the surviving synthetic systems
match reasonably well the observed sample.
The collisional process excites the mutual orbital eccentricity of the
binaries, acting against the effect of tides. Therefore only 10%
of the objects reach total orbital circularization (
).
In addition, our results predict that the population of
contact binaries in the Trans Neptunian region should be small.
Ultra wide binaries are naturally obtained by the combined action of Kozai Cycles and Tidal Friction (KCTF) and collisional evolution, being the number and orbital distribution of them very similar to the ones of the observed population.
Published in: Monthly Notices of the Royal Astronomical Society, 455, 4487
(2016 February 1)
For preprints, contact abrunini@yahoo.com.ar
Observations in 2013 and 2014 of the Centaur 10199 Chariklo and its
ring system consistently indicated that the radial width of the inner,
more massive ring varies with longitude. That strongly suggests that
this ring has a finite eccentricity despite the fast differential
precession that Chariklo's large quadrupole moment should induce. If
the inferred apse alignment is maintained by the ring's self-gravity,
as it is for the Uranian rings, we estimate a ring mass of a few times
1016 g and a typical particle size of a few meters. These imply a
short collisional spreading time of 
years, somewhat shorter than
the typical Centaur dynamical lifetime of a few Myrs and much shorter
than the age of the solar system. In light of this time constraint, we
evaluate previously suggested ring formation pathways including
collisional ejection and satellite disruption. We also investigate in
detail a contrasting formation mechanism, the lofting of dust
particles off Chariklo's surface into orbit via outflows of
sublimating CO and/or N2 triggered after Chariklo was scattered
inward by giant planets. This latter scenario predicts that rings
should be common among 100-km class Centaurs but rare among Kuiper
belt objects and smaller Centaurs. It also predicts that Centaurs
should show seasonal variations in cometary activity with activity
maxima occurring shortly after equinox.
To appear in: The Astrophysical Journal
For preprints, contact http://pan at astro dot utoronto dot ca
or on the web at http://arxiv.org/abs/1602.01769
We present results from a multi-chord Pluto stellar occultation observed
on 29 June 2015 from New Zealand and Australia. This occurred only two
weeks before the NASA New Horizons flyby of the Pluto system and serves
as a useful comparison between ground-based and space results. We find
that Pluto's atmosphere is still expanding, with a significant pressure
increase of 5
2% since 2013 and a factor of almost three since
1988. This trend rules out, as of today, an atmospheric collapse
associated with Pluto's recession from the Sun. A central flash, a rare
occurrence, was observed from several sites in New Zealand. The flash
shape and amplitude are compatible with a spherical and transparent
atmospheric layer of roughly 3 km in thickness whose base lies at about
4 km above Pluto's surface, and where an average thermal gradient of
about 5 K km-1 prevails. We discuss the possibility that small
departures between the observed and modeled flash are caused by local
topographic features (mountains) along Pluto's limb that block the
stellar light. Finally, using two possible temperature profiles, and
extrapolating our pressure profile from our deepest accessible level
down to the surface, we estimate a range of 12.4-13.2 bar for the
surface pressure.
Submitted to: Astrophysical Journal Letters
For preprints, contact bruno.sicardy@obspm.fr
or on the web at http://arxiv.org/abs/1601.05672
Comets are remnants of the icy planetesimals that formed beyond the ice
line in the Solar Nebula. Growing from m-sized dust and
ice particles to km-sized objects is, however, difficult
because of growth barriers and time scale constraints. The gravitational
collapse of pebble clouds that formed through the streaming instability
may provide a suitable mechanism for comet formation. We study the
collisional compression of silica, ice, and silica/ice-mixed pebbles
during gravitational collapse of pebble clouds. Using the initial
volume-filling factor and the dust-to-ice ratio of the pebbles as free
parameters, we constrain the dust-to-ice mass ratio of the formed comet
and the resulting volume-filling factor of the pebbles, depending on the
cloud mass. We use the representative particle approach, which is a
Monte Carlo method, to follow cloud collapse and collisional evolution
of an ensemble of ice, silica, and silica/ice-mixed pebbles. Therefore,
we developed a collision model which takes the various collision
properties of dust and ice into account. We study pebbles with a compact
size of 1 cm and vary the initial volume-filling factors,
, ranging from 0.001 to 0.4. We consider mixed pebbles as
having dust-to-ice ratios between 0.5 and 10. We investigate four
typical cloud masses, M, between
2.6 x 1014 g (very low) and
2.6 x 1023 g (high). Except for the very low-mass
cloud (
M=2.6 x 1014 g), silica pebbles are always
compressed during the collapse and attain volume-filling factors in the
range from
to 0.43, regardless of
. Ice pebbles experience no significant compression in very
low-mass clouds. They are compressed to values in the range
to 0.17 in low- and
intermediate-mass clouds
(
M=2.6 x 1017 - 2.6 x 1020 g); in high-mass clouds
(
M=2.6 x 1023 g), ice pebbles end up with
. Mixed pebbles obtain filling factors
in between the values for pure ice and pure silica. We find that the
observed cometary density of 0.5 g cm-3 can
only be explained by either intermediate- or high-mass clouds,
regardless of , and also by either very low- or low-mass clouds
for initially compact pebbles. In any case, the dust-to-ice ratio must
be in the range of between
to match the observed
bulk properties of comet nuclei.
To appear in: Astronomy & Astrophysics
For preprints, contact lorek@mps.mpg.de
or on the web at http://arxiv.org/abs/1601.05726
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.
