There were 5 new TNO discoveries announced since the previous issue of Distant EKOs:
2013 RP98, 2014 QE442, 2014 SQ350, 2015 PL312, 2015 RS245
and 3 new Centaur/SDO discoveries:
2013 SV99, 2013 SY99, 2014 SR350
Reclassified objects:
2014 FA72 (TNOSDO)
2015 UK84 (SDO
Objects recently assigned numbers:
2014 MU69 = (486958) - this is the target of the next New Horizons flyby on Jan 1, 2019
2015 BE519 = (487581)
Current number of TNOs: 1803 (including Pluto)
Current number of Centaurs/SDOs: 695
Current number of Neptune Trojans: 17
Out of a total of 2515 objects:
706 have measurements from only one opposition
704 of those have had no measurements for more than a year
343 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
We report the discovery of the minor planet 2013 SY99, on an
exceptionally distant, highly eccentric orbit. With a perihelion of
50.0 au, 2013 SY99's orbit has a semi-major axis of 
au, the largest known for a high-perihelion trans-Neptunian object
(TNO), well beyond those of (90377) Sedna and 2012 VP113. Yet,
with an aphelion of 
au, 2013 SY99's orbit is
interior to the region influenced by Galactic tides. Such TNOs are not
thought to be produced in the current known planetary architecture of
the Solar System, and they have informed the recent debate on the
existence of a distant giant planet. Photometry from the
Canada-France-Hawaii Telescope, Gemini North and Subaru indicate 2013 SY99
is 
km in diameter and moderately red in colour,
similar to other dynamically excited TNOs. Our dynamical simulations
show that Neptune's weak influence during 2013 SY99's perihelia
encounters drives diffusion in its semi-major axis of hundreds of
astronomical units over 4 Gyr. The overall symmetry of random walks in
semi-major axis allow diffusion to populate 2013 SY99's orbital
parameter space from the 1000-2000 au inner fringe of the Oort cloud.
Diffusion affects other known TNOs on orbits with perihelia of 45 to
49 au and semi-major axes beyond 250 au, providing a formation
mechanism that implies an extended population, gently cycling into and
returning from the inner fringe of the Oort cloud.
To appear in: The Astronomical Journal
on the web at https://arxiv.org/abs/1704.01952
We report the observation and physical characterization of the
possible dwarf planet 2014 UZ224 (``DeeDee''), a dynamically
detached trans-Neptunian object discovered at 92 AU. This object is
currently the second-most distant known trans-Neptunian object with
reported orbital elements, surpassed in distance only by the dwarf
planet Eris. The object was discovered with an r-band magnitude of
23.0 in data collected by the Dark Energy Survey between 2014 and
2016. Its 1140-year orbit has
. It will reach its perihelion distance of 38 AU in the
year 2142. Integrations of its orbit show it to be dynamically stable
on Gyr timescales, with only weak interactions with Neptune. We have
performed followup observations with ALMA, using 3 hours of on-source
integration time to measure the object's thermal emission in the
Rayleigh-Jeans tail. The signal is detected at 7
significance,
from which we determine a V-band albedo of
13.1+3.3-2.4(stat)+2.0-1.4(sys)
percent and a diameter of
635+57-61(stat)+32-39(sys) km,
assuming a spherical body with uniform surface properties.
Published in: The Astrophysical Journal Letters, 839, L15 (2017 Apr 10)
For preprints, contact gerdes@umich.edu
or on the web at https://arxiv.org/abs/1702.00731
2007OR10 is currently the third largest known dwarf planet
(D
1535 km) in the trans-Neptunian region. It has a slow
rotation period of 
45h that was suspected to be caused by
tidal interactions with a satellite undetected at that time. Here we
report on the discovery of a likely moon of 2007OR10, identified on
archival Hubble Space Telescope WFC3/UVIS system images. Although the
satellite is detected at two epochs this does not allow an unambiguous
determination of the orbit and the orbital period. A feasible
1.5-5.8
1021kg estimate for the system mass leads to a
likely 35 to 100d orbital period. The moon is about 4.2mag fainter
than 2007OR10 in HST images that corresponds to a diameter of 237km
assuming equal albedos with the primary. Due to the relatively small
size of the moon the previous size and albedo estimates for the
primary remains unchanged. With this discovery all trans-Neptunian
objects larger than 1000km are now known to harbour satellites, an
important constraint for moon formation theories in the young Solar
system.
Published in: The Astrophysical Journal Letters, 2017, 838, L1 (2017 March 20)
For preprints, contact kiss.csaba@csfk.mta.hu
or on the web at https://arxiv.org/abs/1703.01407
Milgromian dynamics (MD or MOND) uniquely predicts motion in a galaxy
from the distribution of its stars and gas in a remarkable agreement
with observations so far. In the solar system, MD predicts the
existence of some possibly non-negligible dynamical effects, which can
be used to constrain the freedom in MD theories. Known extreme
trans-Neptunian objects (ETNOs) have their argument of perihelion,
longitude of ascending node, and inclination distributed in highly
non-uniform fashion; ETNOs are bodies with perihelion distances
greater than the orbit of Neptune and with semimajor axes greater than
150 au and less than 
au. It is as if these bodies have been
systematically perturbed by some external force. We investigated a
hypothesis that the puzzling orbital characteristics of ETNOs are a
consequence of MD. We set up a dynamical model of the solar system
incorporating the external field effect (EFE), which is anticipated to
be the dominant effect of MD in the ETNOs region. We used constraints
available on the strength of EFE coming from radio tracking of the
Cassini spacecraft. We performed several numerical experiments,
concentrating on the long-term orbital evolution of primordial
(randomised) ETNOs in MD. The EFE could produce distinct non-uniform
distributions of the orbital elements of ETNOs that are related to the
orientation of an orbit in space. If we demand that EFE is solely
responsible for the detachment of Sedna and 2012 VP113, then
these distributions are at odds with the currently observed statistics
on ETNOs unless the EFE quadrupole strength parameter Q2 has
values that are unlikely (with probability 
) in light of the
Cassini data.
To appear in: Astronomy & Astrophysics
For preprints, contact pauco@fmph.uniba.sk
or on the web at https://arxiv.org/abs/1703.06682
Aims. Numerous trans-Neptunian objects are known to be in
mean-motion resonance with Neptune. We aim to describe their long-term
orbital evolution (both past and future) by means of a
one-degree-of-freedom secular model. In this paper, we focus only on
objects with a semi-major axis larger than 50 astronomical units (au).
Methods. For each resonant object considered, a 500,000-year numerical integration is performed. The output is digitally filtered to get the parameters of the resonant secular model. Their long-term (Giga-year) orbital evolution is then represented by the level curves of the secular Hamiltonian.
Results. For the majority of objects considered, the mean-motion resonance has little impact on the long-term trajectories (the secular dynamics is similar to a non-resonant one). However, a subset of objects is strongly affected by the resonance, producing moderately-high-amplitude oscillations of the perihelion distance and/or libration of the argument of perihelion around a fixed centre. Moreover, the high perihelion distance of the object 2015FJ345 is plainly explained by long-term resonant dynamics, allowing us to also deduce its orbital elements at the time of capture in resonance (at least 15 million years ago). The same type of past evolution is expected for 2014FZ71.
To appear in: Astronomy & Astrophysics
For preprints, contact melaine.saillenfest@obspm.fr
or on the web at https://arxiv.org/abs/1704.05881
(60558) 174P/Echeclus is an unusual object that belongs to a class of
minor planets called Centaurs, which may be intermediate between
Kuiper Belt Objects and Jupiter Family comets. It is sporadically
active throughout its orbit at distances too far for water ice to
sublimate, the source of activity for most comets. Thus, its coma must
be triggered by another mechanism. In 2005, Echeclus had a strong
outburst with peculiar behavior that raised questions about the
nucleus' homogeneity. In order to test nucleus models, we performed
the most sensitive search to date for the highly volatile CO molecule
via its J=2-1 emission toward Echeclus during 2016 May-June (at 6.1
astronomical units from the Sun) using the Arizona Radio Observatory
10-m Submillimeter Telescope. We obtained a 3.6- detection
with a slightly blue-shifted (
v = -0.55 
0.10 km
s-1) and narrow (
vFWHM = 0.53 0.23 km
s-1) line. The data are consistent with emission from a cold gas
from the sunward side of the nucleus, as seen in two other comets at 6
au. We derive a production rate of Q(CO) =
mol s-1,
which is capable of driving the estimated dust production
rates. Echeclus' CO outgassing rate is 40 times lower than what
is typically seen for another Centaur at this distance,
29P/Schwassmann-Wachmann 1. We also used the IRAM 30-m telescope to
search for the CO J=2-1 line, and derive an upper limit that is above
the SMT detection. Compared to the relatively unprocessed comet C/1995
O1 (Hale-Bopp), Echeclus produces significantly less CO, as do Chiron
and four other Centaurs.
Published in: The Astronomical Journal, 153, 5 (2017 May)
For preprints, contact kacperwierzchos@gmail.com
or on the web at https://arxiv.org/abs/1703.07660
The activity of most comets near the Sun is dominated by the
sublimation of frozen water, the most abundant ice in comets. Some
comets, however, are active well beyond the water-ice sublimation
limit of 3 au. Three bodies dominate the observational record
and modeling efforts for distantly active comets: the long-period
comet C/1995 O1 (Hale-Bopp), and the short-period comets (with Centaur
orbits) 29P/Schwassmann-Wachmann 1 and 2060 Chiron. We summarize what
is known about these three objects with an emphasis on their gaseous
comae. We calculate their CN/CO and CO2/CO production rate ratios
from the literature and discuss implications, such as HCN and CO2
outgassing are not significant contributors to their comae. Using our
own data we derive CO production rates, Q(CO), for all three objects
to examine whether there is a correlation between gas production and
different orbital histories and/or size. The CO measurements of
Hale-Bopp (4-11 AU) and 29P are consistent with a nominal production
rate of Q(CO)
= 3.5 x 1029 r2 superimposed with sporadic outbursts.
The similarity of Hale-Bopp CO production rates for pre- and
post-perihelion suggests that thermal inertia was not very important
and therefore most of the activity is at or near the surface of the
comet. We further examine the applicability of existing models in
explaining the systematic behavior of our small sample. We find that
orbital history does not appear to play a significant role in
explaining 29P's CO production rates. 29P outproduces Hale-Bopp at the
same heliocentric distance, even though it has been subjected to much
more solar heating. Previous modeling work on such objects predicts
that 29P should have been devolatilized over a fresher comet like
Hale-Bopp. This may point to 29P having a different orbital history
than current models predict, with its current orbit acquired more
recently. On the other hand, Chiron's CO measurements are consistent
with it being significantly depleted over its original state, perhaps
due to increased radiogenic heating made possible by its much larger
size or its higher processing due to orbital history. Observed
spectral line profiles for several volatiles are consistent with the
development and sublimation of icy grains in the coma at about 5-6 au
for 29P and Hale-Bopp, and this is probably a common feature in
distantly active comets, and an important source of volatiles for all
comets within 5 au. In contrast, the narrow CO line profiles indicate
a nuclear, and not extended, origin for CO beyond 4 au.
Published in: Publications of the Astronomical Society of the Pacific, 129, 973
(2017 March)
For preprints, contact mariawomack@gmail.com
or on the web at http://adsabs.harvard.edu/abs/2017PASP..129c1001W
The surprising discovery by the Rosetta spacecraft of molecular oxygen
(O2) in the coma of comet 67P/Churyumov-Gerasimenko (Bieler et al.
2015) challenged our understanding of the inventory of this volatile
species on and inside bodies from the Kuiper Belt. That discovery
motivated our search for oxygen in the atmosphere of Kuiper Belt
planet Pluto, because O2 is volatile even at Pluto's surface
temperatures. During the New Horizons flyby of Pluto in July 2015, the
spacecraft probed the composition of Pluto's atmosphere using a
variety of observations, including an ultraviolet solar occultation
observed by the Alice UV spectrograph (Stern et al. 2015; Gladstone et
al. 2016; Young et al. 2017). As described in these reports,
absorption by molecular species in Pluto's atmosphere yielded
detections of N2, as well as hydrocarbon species such as CH4,
C2H2, C2H4, and C2H6. Our work here further examines
this data to search for UV absorption from molecular oxygen (O2),
which has a significant cross section in the Alice spectrograph
bandpass. We find no evidence for O2 absorption, and place an upper
limit on the total amount of O2 in Pluto's atmosphere as a function
of tangent height up to 700 km. In most of the atmosphere this upper
limit in line of sight abundance units is
cm-2, which depending on tangent height corresponds to a
mixing ratio of 10-6 to 10-4, far lower than in comet 67P.
Submitted to: The Astronomical Journal
Several trace constituents of Pluto's present day atmosphere can reach saturation vapor pressure in Pluto's present day atmosphere. We describe a search for discrete cloud features in Pluto's atmosphere using New Horizons data obtained on 14-15 July 2015, during the Pluto flyby closest approach. We report that Pluto's present day atmosphere is at least largely (>99% by surface area) free of discrete clouds. We also report a handful of features that may plausibly be clouds, all of which were detected near the terminator and at high phase angle observing geometry. No cloud candidates were identified elsewhere, such as at high altitudes, away from the terminators, or in low phase (backscattering geometry) images.
Submitted to: The Astronomical Journal
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