Distant EKOs, Issue #104  (June 2016)


News & Announcements
Abstracts of 13 Accepted Papers
Abstracts of 5 Submitted Papers
Abstract of 1 Other Paper of Interest
Job Announcements
Newsletter Information


New Horizons Kuiper Belt Extended Mission Science Planning Opportunity

The centerpiece of the proposed New Horizons Kuiper Belt Extended Mission (NH-KEM) is the very close flyby of the 20-40 km wide KBO 2014 MU69 on 1 January 2019. NH-KEM will also observe 20 other KBOs at phase angles and/or at resolutions not otherwise possible, producing a unique database of KBO phase curves, satellite searches, and ring searches.

If NH-KEM is approved, mission schedules require that both distant KBO observations and MU69 close flyby planning must begin almost immediately.

The New Horizons team plans to use a portion of its Science Team Meeting being held near NASA's Ames Research Center during the week of September 19 to gather community input to NH-KEM observation plans.

Those who are interested in listening to, or potentially presenting, at this activity should complete the indication of interest form at: http://pluto.jhuapl.edu/kem-workshop-1/index.php

There were 39 new TNO discoveries announced since the previous issue of Distant EKOs:

2014 FA72, 2015 GO50, 2016 FA59, 2016 FA60, 2016 FB59, 2016 FB60, 2016 FC59, 2016 FC60, 2016 FD59, 2016 FD60, 2016 FE59, 2016 FE60, 2016 FF59, 2016 FG59, 2016 FH59, 2016 FJ59, 2016 FK59, 2016 FL59, 2016 FM59, 2016 FN59, 2016 FO59, 2016 FP59, 2016 FQ59, 2016 FR59, 2016 FS59, 2016 FT58, 2016 FT59, 2016 FU58, 2016 FU59, 2016 FV58, 2016 FV59, 2016 FW58, 2016 FW59, 2016 FX58, 2016 FX59, 2016 FY58, 2016 FY59, 2016 FZ58, 2016 FZ59

and 14 new Centaur/SDO discoveries:

2012 FH84, 2013 FQ28, 2014 FZ71, 2015 FJ345, 2015 GP50, 2015 RR245, 2016 EB195, 2016 EX, 2016 FD14, 2016 FH13, 2016 GC241, 2016 GR206, 2016 GZ251, 2016 LS

and 5 new Neptune Trojan discoveries:

2010 TS191, 2010 TT191, 2011 SO277, 2011 WG157, 2013 KY18

Reclassified objects:

2016 FL59 (TNO $\rightarrow$ SDO)

Objects recently assigned numbers:

2012 VU85 = (463368)
2014 HY123 = (463663)
2013 LU28 = (468861)
2000 FA8 = (468422)

Deleted/Re-identified objects:

2000 GQ148
2011 GY61 = 2014 GE45
2013 BN45 = 2015 DX155 = 2016 EX

Current number of TNOs: 1491 (including Pluto)
Current number of Centaurs/SDOs: 501
Current number of Neptune Trojans: 17

Out of a total of 2009 objects:
   692 have measurements from only one opposition
     636 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)


Surface Compositions Across Pluto and Charon
W.M. Grundy1, R.P. Binzel2, B.J. Buratti3, J.C. Cook4, D.P. Cruikshank5, C.M. Dalle Ore5,6, A.M. Earle2, K. Ennico5, C.J.A. Howett4, A.W. Lunsford7, C.B. Olkin4, A.H. Parker4, S. Philippe8, S. Protopapa9, E. Quirico8, D.C. Reuter7, B. Schmitt8, K.N. Singer4, A.J. Verbiscer10, R.A. Beyer5, M.W. Buie4, A.F. Cheng11, D.E. Jennings7, I.R. Linscott12, J.Wm. Parker4, P.M. Schenk13, J.R. Spencer4, J.A. Stansberry14, S.A. Stern4, H.B. Throop15, C.C.C. Tsang4, H.A. Weaver11, G.E. Weigle II16, L.A. Young4, and the New Horizons Science Team

1 Lowell Observatory, Flagstaff, AZ 86001, USA
2 Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3 NASA Jet Propulsion Laboratory, La Cañada Flintridge, CA 91011, USA
4 Southwest Research Institute, Boulder, CO 80302, USA
5 NASA Ames Research Center, Space Science Division, Moffett Field, CA 9435, USA
6 Carl Sagan Center at the SETI Institute, Mountain View, CA 94043, USA
7 NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA
8 Université Grenoble Alpes, CNRS, IPAG, F-38000 Grenoble, France
9 Department of Astronomy, University of Maryland, College Park, MD 20742, USA
10 Department of Astronomy, University of Virginia, Charlottesville, VA 22904, USA
11 Johns Hopkins University Applied Physics Laboratory, Laurel, MD, 20723, USA
12 Stanford University, Stanford CA 94305, USA
13 Lunar and Planetary Institute, Houston, TX 77058, USA
14 Space Telescope Science Institute, Baltimore, MD 21218, USA
15 Planetary Science Institute, Mumbai, India
16 Southwest Research Institute, San Antonio, TX 28510, USA

The New Horizons spacecraft mapped colors and infrared spectra across the encounter hemispheres of Pluto and Charon. The volatile methane, carbon monoxide, and nitrogen ices that dominate Pluto's surface have complicated spatial distributions resulting from sublimation, condensation, and glacial flow acting over seasonal and geological time scales. Pluto's water ice ``bedrock" was also mapped, with isolated outcrops occurring in a variety of settings. Pluto's surface exhibits complex regional color diversity associated with its distinct provinces. Charon's color pattern is simpler, dominated by neutral low latitudes and a reddish northern polar region. Charon's near-infrared spectra reveal highly localized areas with strong ammonia absorption tied to small craters with relatively fresh-appearing impact ejecta.

Published in: Science, 351, 1283 and aad9189 (2016 March 18)

Preprint available at http://science.sciencemag.org/content/351/6279/aad9189

An Atmospheric General Circulation Model for Pluto with Predictions for New Horizons Temperature Profiles
A.M. Zalucha1

1 SETI Institute 189 Bernardo Ave, Mountain View, CA, 94043, USA

Results are presented from a 3-D Pluto general circulation model (GCM) that includes conductive heating and cooling, non-local thermodynamic equilibrium (non-LTE) heating by methane at 2.3 and 3.3 microns, non-LTE cooling by cooling by methane at 7.6 microns, and LTE CO rotational line cooling. The GCM also includes a treatment of the subsurface temperature and surface-atmosphere mass exchange. An initially 1 m thick layer of surface nitrogen frost was assumed such that it was large enough to act as a large heat sink (compared with the solar heating term) but small enough that the water ice subsurface properties were also significant. Structure was found in all three directions of the 3-D wind field (with a maximum magnitude of order 10 m/s in the horizontal directions and 10-5 microbar/s in the vertical direction). Prograde jets were found at several altitudes. The direction of flow over the poles was found to very with altitude. Broad regions of up-welling and down-welling were also found. Predictions of vertical temperature profiles are provided for the Alice and REX instruments on New Horizons, while predictions of light curves are provided for ground-based stellar occultation observations. With this model methane concentrations of 0.2% and 1.0% and 8 and 24 microbar surface pressures are distinguishable. For ground-based stellar occultations, a detectable difference exists between light curves with the different methane concentrations, but not for different initial global mean surface pressures.

To appear in: Monthly Notices of the Royal Astronomical Society, 459, 902

For preprints, contact azalucha@seti.org
or on the web at http://arxiv.org/abs/1501.02848
and http://mnras.oxfordjournals.org/content/459/1/902

Rotational Properties of the Haumea Family Members and Candidates: Short-term Variability
Audrey Thirouin1, Scott S. Sheppard2, Keith S. Noll3, Nicholas A. Moskovitz1, Jose-Luis Ortiz4, and Alain Doressoundiram5

1 Lowell Observatory, 1400 W Mars Hill Rd, Flagstaff, Arizona, 86001, USA
2 Department of Terrestrial Magnetism (DTM), Carnegie Institution for Science, 5241 Broad Branch Rd. NW, Washington, District of Columbia, 20015, USA
3 NASA Goddard Space Flight Center (NASA-GSFC), Greenbelt, Maryland, 20771, USA
4 Instituto de Astrofisica de Andalucia (IAA-CSIC), Apt 3004, 18080, Granada, Spain
5 Observatoire de Paris-LESIA, 5 Place Jules Janssen, Meudon Cedex 92195, France

Haumea is one of the most interesting and intriguing transneptunian objects (TNOs). It is a large, bright, fast rotator, and its spectrum indicates nearly pure water ice on the surface. It has at least two satellites and a dynamically related family of more than ten TNOs with very similar proper orbital parameters and similar surface properties. The Haumean family is the only one currently known in the transneptunian belt. Various models have been proposed but the formation of the family remains poorly understood. In this work, we have investigated the rotational properties of the family members and unconfirmed family candidates with short-term variability studies, and report the most complete review to date. We present results based on five years of observations and report the short-term variability of five family members, and seven candidates. The mean rotational periods, from Maxwellian fits to the frequency distributions, are 6.27$\pm$1.19 h for the confirmed family members, 6.44$\pm$1.16 h for the candidates, and 7.65$\pm$0.54 h for other TNOs (without relation to the family). According to our study, there is a suggestion that Haumea family members rotate faster than other TNOs, however, the sample of family member is still too limited for a secure conclusion. We also highlight the fast rotation of 2002 GH32. This object has a 0.36$\pm$0.02 mag amplitude lightcurve and a rotational period of about 3.98 h. Assuming 2002 GH32 is a triaxial object in hydrostatic equilibrium, we derive a lower limit to the density of 2.56 g cm-3. This density is similar to Haumea's and much more dense than other small TNO densities.

To appear in: The Astronomical Journal

For preprints, contact thirouin@lowell.edu
or on the web at http://arxiv.org/abs/1603.04406

Interpreting the Densities of the Kuiper Belt's Dwarf Planets
A.C. Barr1 and M.E. Schwamb2

1 Planetary Science Institute, 1700 E. Fort Lowell, Suite 106, Tucson, AZ 85719, USA
2 Institute for Astronomy and Astrophysics, Academia Sinica; 11F AS/NTU, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan

Kuiper Belt objects with absolute magnitude less than 3 (radius ${\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$>$}}}$500 km), the dwarf planets, have a range of different ice/rock ratios, and are more rock-rich than their smaller counterparts. Many of these objects have moons, which suggests that collisions may have played a role in modifying their compositions. We show that the dwarf planets fall into two categories when analysed by their mean densities and satellite-to-primary size ratio. Systems with large moons, such as Pluto/Charon and Orcus/Vanth, can form in low-velocity grazing collisions in which both bodies retain their compositions. We propose that these systems retain a primordial composition, with a density of about 1.8 g/cm3. Triton, thought to be a captured KBO, could have lost enough ice during its early orbital evolution to explain its rock-enrichment relative to the primordial material. Systems with small moons, Eris, Haumea, and Quaoar, formed from a different type of collision in which icy material, perhaps a few tens of percent of the total colliding mass, is lost. The fragments would not remain in physical or dynamical proximity to the parent body. The ice loss process has not yet been demonstrated numerically, which could be due to the paucity of KBO origin simulations, or missing physical processes in the impact models. If our hypothesis is correct, we predict that large KBOs with small moons should be denser than the primordial material, and that the mean density of Orcus should be close to the primordial value.

To appear in: Monthly Notices of the Royal Astronomical Society

For preprints, contact amy@psi.edu
or on the web at http://arxiv.org/abs/1603.06224
and http://dx.doi.org/10.1093/mnras/stw1052

The Rings of Chariklo under Close Encounters with the Giant Planets
R.A.N. Araujo1, R. Sfair1, and O.C. Winter1

1 Grupo de Dinâmica Orbital & Planetologia - UNESP - Guaratinguetá, Brazil

The Centaur population is composed by minor bodies wandering between the giant planets and that frequently perform close gravitational encounters with these planets, which leads to a chaotic orbital evolution. Recently, the discovery of two well-defined narrow rings was announced around the Centaur 10199 Chariklo. The rings are assumed to be in the equatorial plane of Chariklo and to have circular orbits. The existence a well-defined system of rings around a body in such perturbed orbital region poses an interesting new problem. Are the rings of Chariklo stable when perturbed by close gravitational encounters with the giant planets? Our approach to address this question consisted of forward and backward numerical simulations of 729 clones of Chariklo, with similar initial orbits, for a period of 100 Myrs. We found, on average, that each clone suffers along its lifetime more than 150 close encounters with the giant planets within one Hill radius of the planet in question. We identified some extreme close encounters able to significantly disrupt or to disturb the rings of Chariklo. About 3% of the clones lose the rings and about 4% of the clones have the ring significantly disturbed. Therefore, our results show that in most of the cases (more than 90%) the close encounters with the giant planets do not affect the stability of the rings in Chariklo-like systems. Thus, if there is an efficient mechanism that creates the rings, then these structures may be common among these kinds of Centaurs.

To appear in: The Astrophysical Journal

For preprints, contact ran.araujo@gmail.com

Photometry of Centaurs and Trans-Neptunian Objects: 2060 Chiron (1977 UB), 10199 Chariklo (1997 CU26), 38628 Huya (2000 EB173), 28978 Ixion (2001 KX76), and 90482 Orcus (2004 DW)
M. Galiazzo1, C. de la Fuente Marcos2, R. de la Fuente Marcos2, G. Carraro3,4, M. Maris5, and M. Montalto6

1 Department of Physics and Astronomy, The University of Western Ontario, London, ON N6A 3K7, Canada
2 Apartado de Correos 3413, E-28080 Madrid, Spain
3 European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago 19, Chile
4 Dipartimento di Fisica e Astronomia, Università degli Studi di Padova, Vicolo dell'Osservatorio 3, I-35122, Padova, Italy
5 INAF, Osservatorio Astronomico di Trieste, via G.B. Tiepolo 11, I-34131, Trieste, Italy
6 Centro de Astrofísica da Universidade do Porto, (CAUP), P-4150-762 Porto, Portugal

Both Centaurs and trans-Neptunian objects (TNOs) are minor bodies found in the outer Solar System. Centaurs are a transient population that moves between the orbits of Jupiter and Neptune, and they probably diffused out of the TNOs. TNOs move mainly beyond Neptune. Some of these objects display episodic cometary behaviour; a few percent of them are known to host binary companions. Here, we study the light-curves of two Centaurs -- 2060 Chiron (1977 UB) and 10199 Chariklo (1997 CU26) -- and three TNOs -- 38628 Huya (2000 EB173), 28978 Ixion (2001 KX76), and 90482 Orcus (2004 DW) -- and the colours of the Centaurs and Huya. Precise, $\sim$1%, R-band absolute CCD photometry of these minor bodies acquired between 2006 and 2011 is presented; the new data are used to investigate the rotation rate of these objects. The colours of the Centaurs and Huya are determined using BVRI photometry. The point spread function of the five minor bodies is analysed, searching for signs of a coma or close companions. Astrometry is also discussed. A periodogram analysis of the light-curves of these objects gives the following rotational periods: 5.5$\pm$0.4 h for Chiron, 7.0$\pm$0.6 h for Chariklo, 4.45$\pm$0.07 h for Huya, 12.4$\pm$0.3 h for Ixion, and 11.9$\pm$0.5 h for Orcus. The colour indices of Chiron are found to be $B-V=0.53\pm0.05$, $V-R=0.37\pm0.08$, and $R-I=0.36\pm0.15$. The values computed for Chariklo are $V-R=0.62\pm0.07$ and $R-I=0.61\pm0.07$. For Huya, we find $V-R=0.58\pm0.09$ and $R-I=0.64\pm0.20$. Our rotation periods are similar to and our colour values are consistent with those already published for these objects. We find very low levels of cometary activity (if any) and no sign of close or wide binary companions for these minor bodies.

Published in: Astrophysics and Space Science, 361, 212 (2016 July)

For preprints, contact gcarraro@eso.org
or on the web at http://arxiv.org/abs/1605.08251

Beyond the Kuiper Belt Edge: New High Perihelion Trans-Neptunian Objects With Moderate Semi-major Axes and Eccentricities
Scott S. Sheppard1, Chadwick Trujillo2, and David J. Tholen3

1 Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Rd. NW, Washington, DC 20015, USA
2 Gemini Observatory, 670 North A`ohoku Place, Hilo, HI 96720, USA
3 Institute for Astronomy, University of Hawai'i, Honolulu, HI 96822, USA

We have been conducting a survey for distant solar system objects beyond the Kuiper Belt edge ($\sim$50 AU) with new wide-field cameras on the Subaru 8 meter and CTIO 4 meter telescopes. We are interested in the orbits of objects that are decoupled from the giant planet region in order to understand the structure of the outer solar system, including whether a massive planet exists beyond a few hundred AU as first reported by Trujillo and Sheppard (2014). In addition to discovering extreme trans-Neptunian objects detailed elsewhere, we have found several objects with high perihelia (q>40 AU) that differ from the extreme and inner Oort cloud objects due to their moderate semi-major axes (50<a<100 AU) and eccentricities ( $e {\hbox{\rlap{\hbox{\lower4pt\hbox{$\sim$}}}\hbox{$<$}}}0.3$). Newly discovered objects 2014 FZ71 and 2015 FJ345 have the third and fourth highest perihelia known after Sedna and 2012 VP113, yet their orbits are not nearly as eccentric or distant. We found several of these high perihelion but moderate orbit objects and observe that they are mostly near Neptune mean motion resonances and have significant inclinations (i>20 degrees). These moderate objects likely obtained their unusual orbits through combined interactions with Neptune's mean motion resonances and the Kozai resonance, similar to the origin scenarios for 2004 XR190. We also find the very distant 2008 ST291 has likely been modified by the MMR+KR mechanism through the 6:1 Neptune MMR. We discuss these moderately eccentric, distant objects along with some other interesting low inclination outer classical belt objects like 2012 FH84 discovered in our ongoing survey.

To appear in: The Astrophysical Journal Letters

For preprints, contact sheppard@dtm.ciw.edu
or on the web at http://home.dtm.ciw.edu/users/sheppard/pub/

Finding Planet Nine: A Monte Carlo Approach
C. de la Fuente Marcos1 and R. de la Fuente Marcos1

1 Apartado de Correos 3413, E-28080 Madrid, Spain

Planet Nine is a hypothetical planet located well beyond Pluto that has been proposed in an attempt to explain the observed clustering in physical space of the perihelia of six extreme trans-Neptunian objects or ETNOs. The predicted approximate values of its orbital elements include a semimajor axis of 700 au, an eccentricity of 0.6, an inclination of $30^\circ$, and an argument of perihelion of $150^\circ$. Searching for this putative planet is already under way. Here, we use a Monte Carlo approach to create a synthetic population of Planet Nine orbits and study its visibility statistically in terms of various parameters and focusing on the aphelion configuration. Our analysis shows that, if Planet Nine exists and is at aphelion, it might be found projected against one out of four specific areas in the sky. Each area is linked to a particular value of the longitude of the ascending node and two of them are compatible with an apsidal anti-alignment scenario. In addition and after studying the current statistics of ETNOs, a cautionary note on the robustness of the perihelia clustering is presented.

Published in: Monthly Notices of the Royal Astronomical Society, 459, L66

For preprints, contact carlosdlfmarcos@gmail.com
or on the web at http://adsabs.harvard.edu/abs/2016MNRAS.459L..66D

Dynamical Impact of the Planet Nine Scenario: N-body Experiments
C. de la Fuente Marcos1, R. de la Fuente Marcos1, and Sverre J. Aarseth2

1 Apartado de Correos 3413, E-28080 Madrid, Spain
2Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK

The Planet Nine hypothesis has now enough constraints to deserve further attention in the form of detailed numerical experiments. The results of such studies can help us improve our understanding of the dynamical effects of such a hypothetical object on the extreme trans-Neptunian objects or ETNOs and perhaps provide additional constraints on the orbit of Planet Nine itself. Here, we present the results of direct N-body calculations including the latest data available on the Planet Nine conjecture. The present-day orbits of the six ETNOs originally linked to the hypothesis are evolved backwards in time and into the future under some plausible incarnations of the hypothesis to investigate if the values of several orbital elements, including the argument of perihelion, remain confined to relatively narrow ranges. We find that a nominal Planet Nine can keep the orbits of (90377) Sedna and 2012 VP113 relatively well confined in orbital parameter space for hundreds of Myr, but it may make the orbits of 2004 VN112, 2007 TG422 and 2013 RF98 very unstable on time-scales of dozens of Myr, turning them retrograde and eventually triggering their ejection from the Solar system. Far more stable orbital evolution is found with slightly modified orbits for Planet Nine.

Published in: Monthly Notices of the Royal Astronomical Society, 460, L123

For preprints, contact carlosdlfmarcos@gmail.com
or on the web at http://adsabs.harvard.edu/doi/10.1093/mnrasl/slw078

The Outer Solar System Origins Survey: I. Design and First-Quarter Discoveries
Michele T. Bannister1,2, J. J. Kavelaars1,2, Jean-Marc Petit3, Brett J. Gladman4, Stephen D. J. Gwyn2, Ying-Tung Chen5, Kathryn Volk6, Mike Alexandersen4,5, Susan Benecchi7, Audrey Delsanti8, Wesley Fraser2,9, Mikael Granvik10,11, Will M. Grundy12, Aurélie Guilbert-Lepoutre3, Daniel Hestroffer13, Wing-Huen Ip14,15, Marian Jakubik16, Lynne Jones17, Nathan Kaib18, Catherine F. Kavelaars1, Pedro Lacerda19, Samantha Lawler2, Matthew J. Lehner5,20,21, Hsing Wen Lin14, Tim Lister22, Patryk Sofia Lykawka23, Stephanie Monty1, Michael Marsset8,24, Ruth Murray-Clay25, Keith Noll26, Alex Parker27, Rosemary E. Pike1, Philippe Rousselot3, David Rusk1, Megan E. Schwamb5, Cory Shankman1, Bruno Sicardy28, Pierre Vernazza8, Shiang-Yu Wang5

1 Department of Physics and Astronomy, University of Victoria, Elliott Building, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada
2 NRC-Herzberg Astronomy and Astrophysics, National Research Council of Canada, 5071 West Saanich Rd, Victoria, British Columbia V9E 2E7, Canada
3 Institut UTINAM UMR6213, CNRS, Univ. Bourgogne Franche-Comté, OSU Theta F25000 Besançon, France
4 Department of Physics and Astronomy, University of British Columbia, Vancouver, BC, Canada
5 Institute for Astronomy and Astrophysics, Academia Sinica; 11F AS/NTU, National Taiwan University, 1 Roosevelt Rd., Sec. 4, Taipei 10617, Taiwan
6 Department of Planetary Sciences/Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA
7 Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
8 Aix Marseille Université, CNRS, LAM (Laboratoire d'Astrophysique de Marseille) UMR 7326, 13388, Marseille, France
9 Queen's University Belfast, Astrophysics Research Centre, Belfast, Northern Ireland
10 Department of Physics, P.O. Box 64, 00014 University of Helsinki, Finland
11 Finnish Geospatial Research Institute, P.O. Box 15, 02430 Masala, Finland
12 Lowell Observatory, Flagstaff, Arizona, USA
13 IMCCE, Observatoire de Paris - PSL research univ., UPMC univ. P06, univ. Lille 1, CNRS, F-75014 Paris, France
14 Institute of Astronomy, National Central University, Taiwan
15 Space Science Institute, Macau University of Science and Technology, Macau
16 Astronomical Institute, Slovak Academy of Science, 05960 Tatranska Lomnica, Slovakia
17 University of Washington, Washington, United States
18 HL Dodge Department of Physics & Astronomy, University of Oklahoma, Norman, OK 73019, USA
19 Max Planck Institute for Solar System Research, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
20 Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd St., Philadelphia, PA 19104, USA
21 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA
22 Las Cumbres Observatory Global Telescope Network, Inc., 6740 Cortona Drive Suite 102, Goleta, CA 93117, USA
23 Astronomy Group, School of Interdisciplinary Social and Human Sciences, Kinki University, Japan
24 European Southern Observatory (ESO), Alonso de Córdova 3107, 1900 Casilla Vitacura, Santiago, Chile
25 Department of Physics, University of California, Santa Barbara, CA 93106, USA
26 NASA Goddard Space Flight Center, Code 693, Greenbelt, MD 20771, USA
27 Southwest Research Institute, Boulder, Colorado, USA
28 LESIA, Observatoire de Paris, CNRS UMR 8109, Université Pierre et Marie Curie, Université Paris-Diderot, 5 place Jules Janssen, F-92195 Meudon Cedex, France

We report the discovery, tracking and detection circumstances for 85 trans-Neptunian objects (TNOs) from the first 42 deg2 of the Outer Solar System Origins Survey (OSSOS). This ongoing r-band Solar System survey uses the 0.9 deg2 field-of-view MegaPrime camera on the 3.6 m Canada-France-Hawaii Telescope. Our orbital elements for these TNOs are precise to a fractional semi-major axis uncertainty <0.1%. We achieve this precision in just two oppositions, as compared to the normal 3-5 oppositions, via a dense observing cadence and innovative astrometric technique. These discoveries are free of ephemeris bias, a first for large trans-Neptunian surveys. We also provide the necessary information to enable models of TNO orbital distributions to be tested against our TNO sample. We confirm the existence of a cold ``kernel'' of objects within the main cold classical Kuiper belt, and infer the existence of an extension of the ``stirred'' cold classical Kuiper belt to at least several AU beyond the 2:1 mean motion resonance with Neptune. We find that the population model of Petit et al. (2011) remains a plausible representation of the Kuiper belt. The full survey, to be completed in 2017, will provide an exquisitely characterized sample of important resonant TNO populations, ideal for testing models of giant planet migration during the early history of the Solar System.

To appear in: The Astronomical Journal

Preprints available on the web at http://arxiv.org/abs/1511.02895

OSSOS III - Resonant Trans-Neptunian Populations: Constraints from the First Quarter of the Outer Solar System Origins Survey
Kathryn Volk1, Ruth Murray-Clay2, Brett Gladman3, Samantha Lawler4, Michele T. Bannister4,5, J. J. Kavelaars4,5, Jean-Marc Petit6, Stephen Gwyn4, Mike Alexandersen7, Ying-Tung Chen7, Patryk Sofia Lykawka8, Wing Ip9, Hsing Wen Lin9

1 Department of Planetary Sciences/Lunar and Planetary Laboratory, University of Arizona, 1629 E University Blvd, Tucson, AZ 85721, USA
2 Department of Physics, University of California Santa Barbara, USA
3 Department of Physics and Astronomy, University of British Columbia, 6224 Agricultural Road, Vancouver, BC V6T 1Z1, Canada
4 NRC, National Research Council of Canada, 5071 West Saanich Rd, Victoria, British Columbia V9E 2E7, Canada
5 Department of Physics and Astronomy, University of Victoria, Elliott Building, 3800 Finnerty Rd, Victoria, British Columbia V8P 5C2, Canada
6 Observatoire de Besancon, Universite de Franche Comte - CNRS, Institut UTINAM, 41 bis avenue de l'Observatoire, 25010 Besancon Cedex, France
7 Institute for Astronomy and Astrophysics, Academia Sinica, Taiwan
8 Astronomy Group, School of Interdisciplinary Social and Human Sciences, Kinki University, Japan
9 Institute of Astronomy, National Central University, Taiwan

The first two observational sky ``blocks'' of the Outer Solar System Origins Survey (OSSOS) have significantly increased the number of well-characterized observed trans-Neptunian objects (TNOs) in Neptune's mean motion resonances. We describe the 31 securely resonant TNOs detected by OSSOS so far, and we use them to independently verify the resonant population models from the Canada-France Ecliptic Plane Survey (CFEPS; Gladman et al. 2012), with which we find broad agreement. We confirm that the 5:2 resonance is more populated than models of the outer Solar System's dynamical history predict; our minimum population estimate shows that the high eccentricity (e>0.35) portion of the resonance is at least as populous as the 2:1 and possibly as populated as the 3:2 resonance. One OSSOS block was well-suited to detecting objects trapped at low libration amplitudes in Neptune's 3:2 resonance, a population of interest in testing the origins of resonant TNOs. We detected three 3:2 objects with libration amplitudes below the cutoff modeled by CFEPS; OSSOS thus offers new constraints on this distribution. The OSSOS detections confirm that the 2:1 resonance has a dynamically colder inclination distribution than either the 3:2 or 5:2 resonances. Using the combined OSSOS and CFEPS 2:1 detections, we constrain the fraction of 2:1 objects in the symmetric mode of libration to be 0.2-0.85; we also constrain the ratio of leading to trailing asymmetric librators, which has been theoretically predicted to vary depending on Neptune's migration history, to be 0.05-0.8. Future OSSOS blocks will improve these constraints.

To appear in: The Astronomical Journal

For preprints, contact kat.volk@gmail.com
or on the web at https://arxiv.org/abs/1604.08177

Commensurabilities between ETNOs: a Monte Carlo Survey
C. de la Fuente Marcos1 and R. de la Fuente Marcos1

1 Apartado de Correos 3413, E-28080 Madrid, Spain

Many asteroids in the main and trans-Neptunian belts are trapped in mean motion resonances with Jupiter and Neptune, respectively. As a side effect, they experience accidental commensurabilities among themselves. These commensurabilities define characteristic patterns that can be used to trace the source of the observed resonant behaviour. Here, we explore systematically the existence of commensurabilities between the known ETNOs using their heliocentric and barycentric semimajor axes, their uncertainties, and Monte Carlo techniques. We find that the commensurability patterns present in the known ETNO population resemble those found in the main and trans-Neptunian belts. Although based on small number statistics, such patterns can only be properly explained if most, if not all, of the known ETNOs are subjected to the resonant gravitational perturbations of yet undetected trans-Plutonian planets. We show explicitly that some of the statistically significant commensurabilities are compatible with the Planet Nine hypothesis; in particular, a number of objects may be trapped in the 5:3 and 3:1 mean motion resonances with a putative Planet Nine with semimajor axis $\sim$700 au.

Published in: Monthly Notices of the Royal Astronomical Society, 460, L64

For preprints, contact carlosdlfmarcos@gmail.com
or on the web at http://adsabs.harvard.edu/doi/10.1093/mnrasl/slw077

The Research and Education Collaborative Occultation Network: A System for Coordinated TNO Occultation Observations
Marc W. Buie1 and John M. Keller2

1 Southwest Research Institute, 1050 Walnut St., Suite 300, Boulder, CO 80302, USA
2 California Polytechnic State University, 1 Grand Avenue, San Luis Obispo, CA 93407, USA

We describe a new system and method for collecting coordinated occultation observations of trans-Neptunian objects (TNOs). Occultations by objects in the outer solar system are more difficult to predict due to their large distance and limited span of the astrometric data used to determine their orbits and positions. This project brings together the research and educational community into a unique citizen-science partnership to overcome the difficulties of observing these distant objects. The goal of the project is to get sizes and shapes for TNOs with diameters larger than 100 km. As a result of the system design it will also serve as a probe for binary systems with spatial separations as small as contact systems. Traditional occultation efforts strive to get a prediction sufficiently good to place mobile ground stations in the shadow track. Our system takes a new approach of setting up a large number of fixed observing stations and letting the shadows come to the network. The nominal spacing of the stations is 50 km so that we ensure two chords at our limiting size. The spread of the network is roughly 2000 km along a roughly north-south line in the western United States. The network contains 56 stations that are committed to the project and we get additional ad hoc support from International Occultation Timing Association members. At our minimum size, two stations will record an event while the other stations will be probing the inner regions for secondary events. Larger objects will get more chords and will allow determination of shape profiles. The stations are almost exclusively sited and associated with schools, usually at the 9-12 grade level. We present a full description of the system we have developed for the continued exploration of the Kuiper Belt.

Published in: The Astronomical Journal, 151, 73 (2016 March)

For preprints, contact buie@boulder.swri.edu
or available on the web at http://www.boulder.swri.edu/~buie/biblio/pub101.html


Past Epochs of Significantly Higher Pressure Atmospheres on Pluto
S.A. Stern1, R.P. Binzel2, A.M. Earle2, K.N. Singer1, L.A. Young1, H.A. Weaver3, C.B. Olkin1, K. Ennico4, J. Moore4, W. McKinnon5, J. Spencer1, and the New Horizons Geology and Geophysics Investigation Team

1 Southwest Research Institute, Boulder, CO, USA
2 Massachusetts Institute of Technology, Cambridge, MA 02139, USA
3 Johns Hopkins University Applied Physics Laboratory, Laurel, MD 20723, USA
4 NASA Ames Research Center, Moffett Field, CA, USA
5 Department of Earth and Planetary Sciences, Washington University in St. Louis, St. Louis, MO 63130, USA

Pluto is known to have undergone thousands of cycles of obliquity change and polar precession. These variations have a large and corresponding impact on the total average solar insolation reaching various places on Pluto's surface as a function of time. We show here that such changes produce changes in Pluto's atmospheric pressure, in many cases exceeding 1 millibar, and in some cases reaching 10s to 100s of millibars. Such past epochs of high pressure may help explain certain features observed by New Horizons on Pluto's surface.

Submitted to: Icarus

New Horizons Constraints on Charon's Present Day Atmosphere
S.A. Stern1, J. Kammer1, G.R. Gladstone2, A. Steffl1, A. Cheng3, L.A. Young1, H.A. Weaver3, C.B. Olkin1, K. Ennico4, J.Wm. Parker1, A.H. Parker1, T.R. Lauer5, A. Zangari1, M. Summers6, and the New Horizons Atmospheres Team

1 Southwest Research Institute, Boulder, CO, USA 2 Southwest Research Institute, San Antonio, TX, USA
3 Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
4 NASA Ames Research Center, Moffett Field, CA, USA
5 National Optical Astronomy Observatory, Tucson, AZ, USA
6 George Mason University, Fairfax, VA 22030, USA

New Horizons used a variety of standard techniques including a solar ultraviolet occultation, ultraviolet airglow searches, and high phase look back particulate search imaging to search for an atmosphere around Pluto's large moon Charon during its flyby in July 2015. Data from these observations have been sent to Earth and are examined here. No evidence for a present day atmosphere has been found for 14 potential atomic and molecular species, all of which are now constrained to have pressures below 0.3 nanobar, much more stringent upper limits than the previously available 15-100 nanobar constraints; for example, the 3$\sigma$ upper limit for an N2 atmosphere on Charon is 4.2 picobars and the 3$\sigma$ upper limit for the brightness of any atmospheric haze layer on Charon is I/F=9 x 10-5

Submitted to: Icarus

First Direct Size Measurement of a Detached Object:
Results from a Triple Chord Occultation and
Far-infrared Photometry of (229762) 2007 UK126
K. Schindler1,2, J. Wolf1,2, J. Bardecker3, A. Olsen3, T. Müller4, C. Kiss5, J.L. Ortiz6, F. Braga-Ribas7, J.I.B. Camargo7,8, D. Herald3, and A. Krabbe1

1 Deutsches SOFIA Institut, Universität Stuttgart, Pfaffenwaldring 29, 70569 Stuttgart, Germany
2 SOFIA Science Center, NASA Ames Research Center, Mail Stop N211-1, Moffett Field, CA 94035, USA
3 International Occultation Timing Association (IOTA)
4 Max Planck Institute for Extraterrestrial Physics, Giessenbachstrasse 1, 85748 Garching, Germany
5 Konkoly Observatory, Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences,
Konkoly Thege 15-17, 1121 Budapest, Hungary
6 Instituto de Astrofisica de Andalucia-CSIC, Glorieta de la Astronomia, 3, 18080 Granada, Spain
7 Observatório Nacional/MCTI, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil
8 Laboratório Interinstitucional de e-Astronomia - LIneA, Rua Gal. José Cristino 77, Rio de Janeiro, RJ 20921-400, Brazil

Context. A passage of a trans-Neptunian object (TNO) in front of a star provides an opportunity to probe the size and shape of these distant, pristine objects in our Solar System. In the past six years, several occultations by TNOs could be observed. However, most events have been observed from a single location. Not counting the Pluto system, only five objects have been sampled simultaneously from multiple locations, and sufficient data for a fully determined ellipse fit could be obtained for only two objects.

Aims. Here we present the first observation of an occultation by the TNO 2007 UK126 on 15 November 2014, measured by three observers located almost symmetrically to and nearly on the shadow's center line (176.8 km north, 7.1 km north and 199.6 km south). Our work presents the first observation of an occultation of a so-called ``detached object'', a subgroup with perihelion distances so large that Neptune and the other giant planets have likely not perturbed their orbits. We comprehensively characterize 2007 UK126 by combining the results from the occultation with a radiometric analysis.

Methods. We use freely available software to reduce data from two commercial video camera systems and an EMCCD camera. While shadow sizes are typically estimated by direct ellipse fitting, we use an error-in-variable regression approach that allows us to solve the non-linear problem to propagate timing errors into uncertainties of the geometric ellipse parameters. We have revisited existing Herschel/PACS far-infrared data for this object and applied a new reduction method to improve the accuracy of the measured fluxes compared to previously published values. A thermo-physical model (TPM) code is used to predict model fluxes based on thermal and geometrical properties.

Results. The fortunate geographical locations, combined with zero dead-time imaging and precise GPS time measurements, allow for an accurate determination of the projected shadow size ( $686.03 \pm
60.23~\textnormal{km} \times 593.63 \pm 61.91~\textnormal{km}$). We estimate a geometric albedo of $p_{V} = 14.3 \pm 2.5$%. From the shadow geometry, we derive plausible shapes and sizes of 2007 UK126, and use these estimates as an additional constraint for a subsequent radiometric analysis. Via a parametric study, we can discard a pole-on viewing geometry at the time of the occultation and find that 2007 UK126 must have been observed rather near the equator. Matching modeled with observed fluxes while using physically plausible values for thermal inertia and surface roughness constrains the effective diameter of 2007 UK126 to $d_{\rm eff} = 536 - 656$ km. We conclude that subsolar surface temperatures are on the order of $\approx~50 - 55~\textnormal{K}$.

Submitted to: Astronomy & Astrophysics

Results from the 2014 November 15th Multi-chord Stellar Occultation by the TNO (229762) 2007 UK126
G. Benedetti-Rossi1, B. Sicardy2, M.W. Buie3, J.L. Ortiz4, R. Vieira-Martins1,5, J.M. Keller6, F. Braga-Ribas7, J.I.B. Camargo1,8, M. Assafin5, N. Morales4, R. Duffard4, A. Dias-Oliveira1, P. Santos-Sanz4, J. Desmars9, A.R. Gomes-Júnior5, R. Leiva2,10, J. Bardecker11,16, J.K. Jr. Bean16, A.M. Olsen11, D.W. Ruby12,16, R. Sumner16, A. Thirouin13, M.A. Gómez-Muñoz14, L. Gutierrez14, L. Wassermann13, D. Charbonneau15, J. Irwin15, S. Levine13, and B. Skiff13

1 Observatório Nacional - ON/MCT&I, Brazil
2 LESIA, Observatoire de Paris, CNRS UMR 8109, Université Pierre et Marie Curie, Université Paris-Diderot, Meudon, France
3 Southwest Research Institute, Boulder, CO, USA
4 Instituto de Astrofísica de Andalucía, IAA-CSIC, Spain
5 Observatório do Valongo - OV/UFRJ, Brazil
6 California Polytechnic State University, San Luis Obispo, CA, USA
7 Universidade Tecnológica Federal do Paraná - UTFPR, Brazil
8 Laboratório Interinstitucional de e-Astronomia - LIneA, Rio de Janeiro, Brazil
9 Institut de Mécanique Céleste et de Calcul des Éphémérides - Observatoire de Paris, UMR 8028 CNRS, France
10 Instituto de Astrofísica, Facultad de Física, Pontificia Universidad Católica de Chile, Santiago 7820436, Chile
11 IOTA, International Occultation Timing Association, USA
12 University of Nevada, Reno, NV, USA
13 Lowell Observatory, Flagstaff, AZ, USA
14 Instituto de Astronomía - Universidad Nacional Autónoma de México - UNAM, Mexico
15 Harvard-Smithsonian Center for Astrophysics, MA, USA
16 RECON, Research and Education Collaborative Occultation Network

We present results derived from the first multi-chord stellar occultation by the trans-Neptunian object (229762) 2007 UK126, observed on 2014 November 15. The event was observed by the RECON project and IOTA collaborators throughout the United States. Use of two different data analysis methods obtain a satisfactory fit to seven chords, yielding an elliptical fit to the chords with an equatorial radius of R=338-10+15 km and equivalent radius of Req=319-7+14 m. A circular fit also gives a radius of R=324-23+30 km. Assuming that the object is a Maclaurin spheroid with indeterminate aspect angle, and using two published absolute magnitudes for the body, we derive possible ranges for geometric albedo between pV=0.159-0.013+0.007 and pR=0,189-0,015+0,009, and for the body oblateness between $\epsilon=0.105_{-0.040}^{+0.050}$ and $\epsilon=0.118 _{-0.048}^{+0.055}$. For a nominal rotational period of 11.05 h, an upper limit for density of $\rho=1740$ kg m-3 is estimated for the body.

Submitted to: The Astrophysical Journal

For preprints, contact gugabrossi@gmail.com

Red, Rough, Fast, and Perturbed: New Horizons Observations of KBO (15810) 1994 JR1 from the Kuiper Belt
Simon B. Porter1, John R. Spencer1, Susan Benecchi2, Anne Verbiscer3, Amanda M. Zangari1, H. A. Weaver4, Tod R. Lauer5, Alex H. Parker1, Marc W. Buie1, Andrew F. Cheng4, Leslie A. Young1, Cathy B. Olkin1, Kimberly Ennico6, S. Alan Stern1, and the New Horizons Science Team

1 Southwest Research Institute, Boulder, CO, USA
2 Planetary Science Institute, Tucson, AZ, USA
3 University of Virginia, Charlottesville, VA, USA
4 Johns Hopkins Applied Physics Laboratory, Laurel, MD, USA
5 National Optical Astronomy Observatory, Tucson, AZ, USA
6 NASA Ames Research Center, Moffett Field, CA, USA

The 3:2 resonant KBO (15810) 1994 JR1 was observed by NASA's New Horizons spacecraft on November 2, 2015 from a distance of 1.85 AU, and again on April 7, 2016 from a distance of 0.71 AU. Acquired using the LOng Range Reconnaissance Imager (LORRI), these were the first close observations of any KBO other than Pluto, and the first ever of a small KBO. Combining ground-based and HST observations at small phase angles and the LORRI observations at higher phase angles, we produced the first disk-integrated solar phase curve of a typical KBO from $\alpha$=0.6-58$^\circ$. Observations at these geometries, attainable only from a spacecraft in the outer Solar System, constrain surface properties such as macroscopic roughness and the single particle phase function. 1994 JR1 has a rough surface with a 37$\pm$5$^\circ$ mean topographic slope angle and has a relatively rapid rotation period of 5.47$\pm$0.33 hours. 1994 JR1 is currently 2.7 AU from Pluto; our astrometric points enable high-precision orbit determination and integrations which show that it comes this close to Pluto every 2.4 million years, causing Pluto to perturb 1994 JR1. During the November spacecraft observation, the KBO was simultaneously observed using the Hubble Space Telescope in two colors, confirming its very red spectral slope. These observations have laid the groundwork for numerous potential future distant KBO observations in the proposed New Horizons-Kuiper Belt Extended Mission.

Submitted to: The Astrophysical Journal Letters

Preprints on the web at http://arxiv.org/abs/1605.05376


TRIPPy: Trailed Image Photometry in Python
W. Fraser1, M. Alexandersen2, M. Schwamb2, M. Marsset3, R. Pike4, JJ Kavelaars5, M. Bannister4, S. Benecchi6, and A. Delsanti7

1 Queen's University Belfast, Astrophysics Research Center, David Bates Building, Belfast, BT7 1NN, United Kingdom
2 Institute for Astronomy and Astrophysics, Academia Sinica, Taiwan
3 European Southern Observatory, Aix Marseille University, CNRS, LAM, France
4 University of Victoria, Canada
5 NRC Herzberg, National Research Council, Canada
6 Planetary Science Institute, USA
7 Aix Marseille University, CNRS, LAM, France

Photometry of moving sources typically suffers from reduced signal-to-noise (SNR) or flux measurements biased to incorrect low values through the use of circular apertures. To address this issue we present the software package, TRIPPy: TRailed Image Photometry in Python. TRIPPy introduces the pill aperture, which is the natural extension of the circular aperture appropriate for linearly trailed sources. The pill shape is a rectangle with two semicircular end-caps, and is described by three parameters, the trail length and angle, and the radius. The TRIPPy software package also includes a new technique to generate accurate model point-spread functions (PSF) and trailed point-spread functions (TSF) from stationary background sources in sidereally tracked images. The TSF is merely the convolution of the model PSF, which consists of a moffat profile, and super sampled lookup table. From the TSF, accurate pill aperture corrections can be estimated as a function of pill radius with a accuracy of 10 millimags for highly trailed sources. Analogous to the use of small circular apertures and associated aperture corrections, small radius pill apertures can be used to preserve signal-to-noise of low flux sources, with appropriate aperture correction applied to provide an accurate, unbiased flux measurement at all SNR.

To appear in: The Astronomical Journal

For preprints, contact wes.fraser@qub.ac.uk
or on the web at http://arxiv.org/abs/1604.00031


Research Fellow in Solar System Astrophysics
School of Mathematics and Physics
Queen's University Belfast

This post is available for 1.5 years from 1 October 2016 to work as part of the Solar System Group within the Astrophysics Research Centre. Faculty members of the QUB Solar System Group are current leaders of large telescope surveys, including an ESO large program on Kuiper Belt Object lightcurves (PI: Pedro Lacerda), the Colours of the Outer Solar System Origins Survey using the Gemini-North and Canada-France-Hawaii Telescopes (PI Wesley Fraser), and the Pan-STARRS Solar System Survey (Co-lead Alan Fitzsimmons).

The successful candidate will exploit these three datasets to study outer Solar System targets. Analysis of these data will focus on the following projects: searches for activity, photometric variability, and colour studies.

Informal enquiries may be directed to Dr. Wesley Fraser (telephone: +44 02890976354; email: wes.fraser@qub.ac.uk). More information at:
(Ref. 16/104687)

Application closing date: 11 July 2016

Anticipated interview date: 27 July 2016

Salary: £31,656 - £41,255 per annum

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The Distant EKOs Newsletter is dedicated to provide researchers with easy and rapid access to current work regarding the Kuiper belt (observational and theoretical studies), directly related objects (e.g., Pluto, Centaurs), and other areas of study when explicitly applied to the Kuiper belt.

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Joel Parker 2016-06-23