There were 2 new TNO discoveries announced since the previous issue of Distant EKOs:
2011 HD103, 2011 HF103
and 3 new Centaur/SDO discoveries:
2011 QF99, 2013 EK73, 2013 EZ27
Deleted object:
2013 CE88
Current number of TNOs: 1260 (including Pluto)
Current number of Centaurs/SDOs: 373
Current number of Neptune Trojans: 9
Out of a total of 1642 objects:
649 have measurements from only one opposition
633 of those have had no measurements for more than a year
325 of those have arcs shorter than 10 days
(for more details, see:
http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg)
Impacts of micrometeoroids on the surfaces of the plutonian small satellites Nix and Hydra can generate dust particles. Even in this region so far from the Sun these tiny ejected particles are under the effects of the solar radiation pressure.
In this work, we investigate the orbital evolution of the escaping ejecta from both the small satellites under the effects of the radiation pressure combined with the gravitational effects of Pluto, Charon, Nix and Hydra. The mass production rate of micron-sized dust particles generated by micrometeoroids hitting the satellites is obtained, and numerical simulations are performed to derive the lifetime of the ejecta. These pieces of information allow us to estimate the optical depth of a putative ring, which extends from the orbits of Nix to Hydra.
The ejected particles, between the orbits of Nix and Hydra, form a wide
ring of about 16,000 km. Collisions with the massive bodies and escape
from the system are mainly determined by the effects of the solar
radiation pressure. This is an important loss mechanism, removing 30 per
cent of the initial set of 1 
m-sized particles in 1 yr. The
surviving particles form a ring too faint to be detectable with the
derived maximum optical depth of
4 x 10-11.
Published in: Monthly Notices of the Royal Astronomical Society, 430, 2761
Since the last Pluto volatile transport models were published in 1996, we have (1) new stellar occultation data from 2002 and 2006-2012 that show roughly twice the pressure as the first definitive occultation from 1988, (2) new information about the surface properties of Pluto, (3) a spacecraft due to arrive at Pluto in 2015, and (4) a new volatile transport model that is rapid enough to allow a large parameter-space search. Such a parameter-space search coarsely constrained by occultation results reveals three broad solutions: a high-thermal inertia, large volatile inventory solution with permanent northern volatiles (PNVs; using the rotational north pole convention); a lower thermal-inertia, smaller volatile inventory solution with exchanges of volatiles between hemispheres and a pressure plateau beyond 2015 (exchange with pressure plateau, EPP); and solutions with still smaller volatile inventories, with exchanges of volatiles between hemispheres and an early collapse of the atmosphere prior to 2015 (exchange with early collapse, EEC). PNV and EPP are favored by stellar occultation data, but EEC cannot yet be definitively ruled out without more atmospheric modeling or additional occultation observations and analysis.
Published in: The Astrophysical Journal Letters, 766, L22 (2013 April 1)
For preprints, contact layoung@boulder.swri.edu
and available online at: http://arxiv.org/abs/1210.7778
We use a statistical-thermodynamic model to investigate the formation
and composition of noble-gas-rich clathrates on Pluto's surface. By
considering an atmospheric composition close to that of today's Pluto
and a broad range of surface pressures, we find that Ar, Kr and Xe can
be efficiently trapped in clathrates if they formed at the surface, in a
way similar to what has been proposed for Titan. The formation on
Pluto of clathrates rich in noble gases could then induce a strong
decrease in their atmospheric abundances relative to their initial
values. A clathrate thickness of order of a few centimeters globally
averaged on the planet is enough to trap all Ar, Kr and Xe if these
noble gases were in protosolar proportions in Pluto's early
atmosphere. Because atmospheric escape over an extended period of time
(millions of years) should lead to a noble gas abundance that either
remains constant or increases with time, we find that a potential
depletion of Ar, Kr and Xe in the atmosphere would best be explained by
their trapping in clathrates. A key observational test is the
measurement of Ar since the Alice UV spectrometer aboard the New
Horizons spacecraft will be sensitive enough to detect its abundance
10 times smaller than in the case considered here.
To appear in: Icarus
For preprints, contact olivier.mousis@obs-besancon.fr
or on the web at http://arxiv.org/abs/1303.4595
Because of Pluto's distance from the Sun, the Pluto system has not yet
completed a revolution since its discovery, hence an uncertain
heliocentric distance. In this paper, we present the fitting of our
dynamical model ODIN (Orbite, Dynamique et Intégration Numérique) to
observations. The small satellites P4 and P5 are not taken into account.
We fitted our model to the measured absolute coordinates (RA, DEC) of
Pluto, and to the measured positions of the satellites relative to
Pluto. The masses we found for the bodies of the system are consistent
with those of previous studies. Yet the masses of the small satellites
Nix and Hydra are artificially constrained by the number of observations
of Charon. The best way to improve the determination of their masses
would be to use observations of P4 and P5, but there are still not
enough published observations. Concerning the heliocentric distance of
the system, we compared the value we obtained using ODIN and those of
other models. The difference between the models far exceeds the
uncertainty needed (about 1000 km) for the mission New Horizons. A new
astrometric reduction of old photographic plates may be an efficient way
to constrain this distance. The ephemeris for Pluto's satellites is
available on the web page of the IMCCE at
http://www.imcce.fr/hosted_sites/saimirror/nssreq9hf.htm.
The complete version of the ephemeris is available as a SPICE kernel at
http://www.imcce.fr/~beauvalet.
Published in: Astronomy and Astrophysics, 553, A14 (2013 May)
Context:
The investigation of Centaurs and trans-Neptunian objects (TNOs) provides essential
information about the early conditions and evolution of the outer solar system.
The radiometric technique combines measurements in the visible and thermal infrared;
with these one can estimate the size and albedo of Centaurs and TNOs.
Aims: Our aim is to obtain visible photometry of a sample of Centaurs and TNOs, a subset of the targets of the ``TNOs are cool'' Key Programme at the Herschel Space Observatory.
Methods: We carried out visible photometry of Centaurs and TNOs, making use of the DOLORES instrument at the Telescopio Nazionale Galileo (TNG, La Palma, Spain).
Results: We report photometric observations of 20 objects and present the computed absolute magnitudes. We derive the taxonomy of our targets (nine are classified for the first time, the results for five objects agree with the literature, the other targets are tentatively classified based on incomplete datasets) and combine the results with the literature, searching for correlations between taxonomy and dynamics. We look for comet-like activity in our Centaur sample, including (248835) 2006 SX368, which was previously described as active.
Conclusions: We provide an accurate determination of the absolute magnitude and of the relative error for each of our targets. These values can be readily used in combination with thermal infrared data. The surface of TNO (65489) Ceto seems to be heterogeneous. Our results seem to support an evolutionary origin for the color dichotomy of Centaurs, and the occurrence of a strong mixing after the TNO formation. No evident cometary activity is detected around the five Centaurs in our sample; assuming that an unresolved coma is present around (248835) 2006 SX368, we use the ``photometric model'' to derive the possible dust production rate, finding that Qdust is in the range 1-31 kg/s.
To appear in: Astronomy & Astrophysics
For preprints, contact davide.perna@obspm.fr
m
Transneptunian Objects (TNOs) are bodies populating the Kuiper Belt and
they are believed to retain the most pristine and least altered material
of the Solar System. The Herschel Open Time Key Program entitled ``TNOs
are Cool: A survey of the Transneptunian Region'' has been awarded
373 hours to investigate the albedo, size distribution and thermal
properties of TNOs and Centaurs. Here we focus on the brightest targets
observed by both the PACS and SPIRE multiband photometers: the dwarf
planet Haumea, 6 TNOs (Huya, Orcus, Quaoar, Salacia, 2002 UX25, and 2002 TC302),
and two Centaurs (Chiron and Chariklo). Flux densities are
derived from PACS and SPIRE instruments using optimised data reduction
methods. The spectral energy distribution obtained with the Herschel
PACS and SPIRE instruments over 6 bands (centered at 70, 100, 160, 250,
350 and 500 m), with Spitzer-MIPS at 23.7 and 71.4 m, and with
WISE at 11.6 and 22.1 m in the case of 10199 Chariklo, has been
modeled with the NEATM thermal model in order to derive the albedo,
diameter and beaming factor. For the Centaurs Chiron and Chariklo, and
for the 1000 km sized Orcus and Quaoar, a thermophysical model was also
run to better constrain their thermal properties. We derive the size,
albedo, and thermal properties, including thermal inertia and surface
emissivity, for the 9 TNOs and Centaurs. Several targets show a
significant decrease of their spectral emissivity longward of 300
m and especially at 500 m. Using our size estimations and the
mass values available in the literature, we also derive the bulk
densities for the binaries Quaoar/Weywot (2.18
+0.43-0.36 g/cm3),
Orcus/Vanth (1.53
+0.15-0.13 g/cm3), and
Salacia/Actea (1.29
+0.29-0.23 g/cm3). Quaoar's density is
similar to that of the other dwarf planets Pluto and Haumea, and its
value implies high contents of refractory materials mixed with ices.
To appear in: Astronomy and Astrophysics
For preprints, contact sonia.fornasier@obspm.fr
A recent stellar occultation by dwarf planet Makemake
provided an excellent opportunity
to measure the size and shape of one of the largest
objects in the Kuiper belt. The analysis of these results
provided what were reported to be precise measurements of the
lengths of the projected axes, the albedo, and even the density
of Makemake, but these results were, in part, derived from
qualitative arguments.
We reanalyzed the occultation timing data
using a quantitative
statistical description, and, in general,
find the previously reported results on the shape of Makemake
to be unjustified.
In our solution, in which we use our inference
from photometric data that Makemake is being viewed
nearly pole-on, we find a 1
upper limit to the projected
elongation of Makemake of 1.02, with measured equatorial diameter
of 1434
14 km and a projected polar diameter of 142214 km, yielding
an albedo of 0.81
+0.01-0.02. If we remove the external
constraint on the pole position of Makemake, we find instead a 1
upper limit to the elongation of 1.06, with a measured equatorial diameter of
1434+48-18 km and a projected polar diameter of 1420+18-24 km,
yielding an albedo of 0.81
+0.03-0.05.
Critically, we find that
the reported measurement of the density of Makemake was
based on the misapplication of the volatile retention models.
A corrected analysis shows that the
occultation measurements provide no meaningful constraint on the density
of Makemake.
Published in: The Astrophysical Journal Letters, 767, L7 (2013 Apr 10)
Preprints available on the web at
http://www.gps.caltech.edu/~mbrown/papers/pubs.html
The Centaurs are a population of small, planet-crossing objects in the
outer solar system. They are dynamically short-lived and represent the
transition population between the Kuiper belt and the Jupiter family
short-period comets. Dynamical models and observations of the physical
properties of the Centaurs indicate that they may have multiple source
populations in the trans-Neptunian region. It has been suggested that
the inclination distribution of the Centaurs may be useful in
distinguishing amongst these source regions. The Centaurs, however,
undergo many close encounters with the giant planets during their
orbital evolution; here we show that these encounters can substantially
determine the inclination distribution of the Centaurs. Almost any
plausible initial inclination distribution of a Kuiper belt source
results in Centaurs having inclinations peaked near 
.
Our studies also find that the Kuiper belt is an extremely unlikely
source of the retrograde Centaur that has been observed.
Published in: Icarus, 224, 66 (2013 May)
For preprints, contact kvolk@lpl.arizona.edu
or on the web at http://arxiv.org/abs/1211.2774
and http://www.sciencedirect.com/science/article/pii/S0019103513000766
The Saturnian satellite system has been observed in detail by the Cassini-Huygens mission. These satellites present different surface features, including impact craters caused by small objects probably coming from the trans-Neptunian region. In this paper we calculate the production of craters on the mid-sized Saturnian satellites produced by Centaurs from the scattered disk (SD) and plutinos in order to determine this contribution, and we compare our estimations with the Cassini observations. We used a method developed in a previous paper that uses a numerical investigation of the dynamical evolution of Centaur objects to calculate the production of craters. We used a size-frequency distribution (SFD) of scattered disk objects (SDOs) as a power law with a break at diameters d = 60 km considering two cases for the differential power-law index: s2 = 2.5 and s2=3.5 for d < 60 km. We calculated the number of craters, the greatest crater produced by Centaurs from the SD and plutinos, and the present cratering rate on each of the mid-sized satellites, for both cases of the SFD of SDOs considered. The contribution of plutinos is negligible compared to SDOs. From our calculations and the comparison with observations we note that the calculated number of craters for s2=3.5 is in general nearer the observed number. However, in general for smaller craters, the observed number is less than the calculated one. This trend can be explained by at least two mechanisms. One the one hand, this could be caused by an erasing process that gradually buries the craters, which does not affect large craters. On the other hand, the comparison of the calculated and observed crater size-frequency distribution for different size ranges implies that for d < 60 km, the SFD of SDOs is consistent with the assumed index s2 = 3.5, for d > 0.2 - 1.4 km and for d < 0.2 - 1.4 km, it is consistent with s2 = 2.5. Then in the range d < 0.2 - 1.4 km, the SFD of SDOs could have a new break. This change of slope could explain the reduction of small craters, at least for some cases. We found a good agreement when comparing our results with observations. However, independent determination of surface ages and geological processes are needed to determine if there is a new break on the SFD of SDOs, if there is a planetocentric source of craters in the Saturnian system, and which craters are primordial.
To appear in: Astronomy and Astrophysics
For preprints, contact romina@fcaglp.unlp.edu.ar
The current solar system architecture is a heritage of the protoplanetary disk that surrounded the young sun, 4.56 Gy ago. Primitive extraterrestrial objects provide means to trace back the primordial composition and radial distribution of matter in this disk. Here, we present a combined micro-IR, Raman, chemical and isotopic study of two ultra-carbonaceous micrometeorites recovered from Antarctica (UCAMMs). This study reveals particles containing an unusually high nitrogen- and deuterium- rich organic matter analogous to a polyaromatic hydrogenated carbon nitride, characterised by nitrogen concentration with bulk atomic N/C ratios of 0.05 and 0.12 (locally exceeding 0.15). We propose that such nitrogen-rich carbonaceous material can be formed by energetic irradiations of nitrogen-rich ices in very low temperature regions of the solar system. Such conditions are encountered at the surface of small objects beyond the trans-Neptunian region. UCAMMs provide unique insights on physico-chemical processes that occurred beyond the nitrogen snow-line, revealing organic material from the extreme outer regions of the solar system that cannot be investigated by remote sensing methods.
Published in: Icarus 224, 243 (2013 May)
For preprints, contact emmanuel.dartois@ias.u-psud.fr , cecile.engrand@csnsm.in2p3.fr
The infrared (IR) and ultraviolet (UV) absorption spectra of pure solid
N2 and CH4 diluted in solid N2 (1/100) irradiated with
energetic electrons at 10 K were obtained. The IR absorption
measurements of the electron-bombarded pure N2 solid reveal the
formation of N3 and N3+ , which was confirmed by the observed
electronic transitions 
of N3
and
- of N3+ . In the case of
N2 ice containing a small proportion of CH4, we have identified
the products of irradiated CH4/N2 ice, including N3, CnN (n
= 1-3), CN2, (CN)2, CH3N, HCN2, HC2N, C(NH)2, HNC,
HCN, CH3, C2H, C2H2, CN-, NH3+ , and HC3N+.
UV absorption measurement of the ice sample was carried out and the
possible carriers associated with the observed absorption bands were
assigned and discussed.
Published in: The Astrophysical Journal, 768, 83 (2013 May 1)
Size, Shape, Albedo, Density and Atmospheric Limit of Transneptunian Object (50000) Quaoar from Multi-chord Stellar Occultations
F. Braga-Ribas 1,2, B. Sicardy2,3, J.L. Ortiz 4, E. Lellouch 2, G. Tancredi5, J. Lecacheux2, R. Vieira-Martins1,6,7, J.I.B. Camargo1, M. Assafin7, R. Behrend8, F. Vachier6, N. Morales4, A. Maury9, M. Emilio10, A. Amorim11, E. Unda-Sanzana12, S. Roland5, S. Bruzzone5, L.A. Almeida13, C.V. Rodrigues13, C. Jacques14, R. Gil-Hutton15, L. Vanzi16, A.C. Milone13, W. Schoenell11,4, R. Salvo5, L. Almenares5, E. Jehin17, J. Manfroid17, S. Sposetti18, P. Tanga19, A. Klotz20, E. Frappa21, P. Cacella22, J.P. Colque12, C. Neves10, E. M. Alvarez23, M. Gillon17, E. Pimentel14, B. Giacchini14, F. Colas6, F. Roques2, T. Widemann2, V.S. Magalhães13, A. Thirouin4, R. Duffard4, R. Leiva16, I. Toledo24, J. Capeche5, W. Beisker25, J. Pollock26, C. E. Cedeño Montaña13, K. Ivarsen27, D. Reichart27, J. Haislip27, and A. Lacluyze27
1 Observatório Nacional, Rio de Janeiro, Brazil
2 Observatoire de Paris, LESIA, Meudon, France
3 Université Pierre et Marie Curie, Paris, France
4 Instituto de Astrofísica de Andalucía - CSIC, Granada, Spain
5 Observatorio Astronomico Los Molinos, Uruguay
6 Observatoire de Paris, IMCCE, Paris, France
7 Observatório do Valongo / UFRJ, Rio de Janeiro, Brazil
8 Observatoire de Genève, Switzerland
9 San Pedro de Atacama Celestial Explorations, San Pedro de Atacama, Chile
10 Universidade Estadual de Ponta Grossa, Ponta Grossa, Brazil
11 Universidade Federal de Santa Catarina, Florianópolis, Brazil
12Unidad de Astronomía, Universidad de Antofagasta, Antofagasta, Chile
13 Instituto Nacional de Pesquisas Espaciais, DAS, São José dos Campos, Brazil
14 Centro de Estudos Astronômicos de Minas Gerais (CEAMIG), Belo Horizonte, Brazil
15 Complejo Astronómico El Leoncito & San Juan National University, Argentina
16 Department of Electrical Engineering and Center of Astro-Engineering, Pontificia Universidad Católica de Chile, Santiago, Chile
17 Institut d'Astrophysique de l'Université de Liége, Belgium
18 Gnosca Observatory, Switzerland
19 Laboratoire Lagrange, Université de Sophia Antipolis, Observatoire de la Côte d'Azur, CNRS UMS7293
20 Université de Toulouse, UPS-OMP, IRAP, France
21 Euraster, 1B cours J. Bouchard, St-Etienne, France
22 Rede de Astronomia Observacional, Brasilia, Brazil
23 Observatorio Los Algarrobos, Salto, Uruguay
24 Joint ALMA Observatory, Alonso de Córdova 3107, Vitacura, Santiago, Chile
25 International Occultation Timing Association - European Section, Munich, Germany
26 Department of Physics and Astronomy, Appalachian State Univ.,
Boone, NC 28608, USA
27 Physics and Astronomy Department, University of North Carolina, Chapel Hill, USA
Submitted to: The Astrophysical Journal
For preprints, contact ribas@on.br
Transneptunian objects (TNOs) are fossils of the Solar System beyond Neptune. Over 1200 TNOs have been found since 1992, and among them we find dwarf-planets such as Pluto, Makemake and Eris. The dynamics, internal and surface composition, size and mass distribution may have information about the early ages and evolution of the Solar System.
Photometry, spectroscopic, thermal (far infra-red) give information about their rotational period, surface composition, size and albedo estimations.
Nevertheless, due to their distance (greater than 30 Astronomical Units) and their sizes, we do not have the necessary technology to directly measure their size and detect possible atmospheres, as their angular sizes are smaller than a 50 miliarcseconds (mas).
The stellar occultation technique consists of observing the transit of a TNO in front of a star. The precise duration of the event, observed from several different sites, allows to deduce their size and shape with kilometre accuracy. So, precise determination of their albedo can be derived, and for those bodies that have their mass deduced from its satellite orbit, precise determination of their densities is allowed. Besides, tenuous atmospheres at the nanobar level, can be detected as they promote an attenuation of the star light right before and after the occultation.
In this work it is described (1) the prediction method applied to more then fifty TNOs, with accuracy of about 30 mas, (2) the world-wide campaigns with tens of professional and amateurs observatories, (3) the observation, analysis, and interpretation of the observed occultation by Quaoar and other large transneptunian objects.
Since 2009, fourteen occultations by TNOs were already observed, twelve by the Paris/Rio consortium. In addition to the detailed discussion about the Quaoar events, a compilation of all the other results comprising as size, shape, albedo, density and atmosphere, obtained from TNO stellar occultations is presented. In particular occultations by Eris, Makemake, 2003 AZ84, Varuna and Sedna, all of which are new.
We present constraints over size, shape, albedo of these bodies, and also upper limits on possible atmospheres up to the nanobar level.
Dissertation directed by R. Vieira-Martins and B. Sicardy.
Ph.D. awarded February, 2013 from Observaório Nacional and Observatoire de Paris-Meudon.
Address as of May, 2013: Observatório Nacional / MCTI, Rua General José Cristino, 77, Rio de Janeiro, RJ, Brazil, CEP: 20921-400.
For preprints, contact ribas@on.br
or on the web at
http://www.on.br/conteudo/dppg_e_iniciacao/dppg/neweb_astro/conteudo/teses.html
http://plutoscience.jhuapl.edu
The planning for the Pluto-2013 Conference is proceeding on schedule.
Given the importance of this meeting for optimizing the scientific return from NASA's New Horizons mission, we expect NASA to allow participation by its civil servants, at least those already involved in KBO research. And, as usual for scientific conferences, researchers can use their grant money to fund their participation in this conference.
The deadline for oral abstract submissions passed on April 15th (111 abstracts were received), but poster abstracts can still be submitted through June 15th. We encourage you to consider submitting an abstract, and to register for the meeting.
Both registration and abstract submission are available for the Pluto
2013 conference at: http://plutoscience.jhuapl.edu
Abstract submission information:
Abstracts are solicited on all facets of the Pluto system including
origins, interiors, surfaces, compositions, atmospheres, satellites,
plasma, and context in the Kuiper Belt. Abstracts should be in PDF
Format. Abstracts are limited to two pages but any shorter length is
also welcome. Abstracts must be uploaded to the conference website;
please create a user account using the "Request an Account" form.
Deadlines:
Early Bird Registration Deadline: May 31, 2013
Late Abstract Deadline (posters): June 15, 2013
Reception: July 21, 2013
Meeting Dates: July 22-26, 2013
The meeting will be held at The Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland, USA. A special issue of Icarus is planned to publish new results and prediction papers in advance of the New Horizons flyby.
Alan Stern (Program Committee Chair)
Hal Weaver (Local Organizing Committee Chair)
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.