Issue No. 119 April 2019 r ✤✜ s ✓✏ DISTANT EKO ❞✐ ✒✑ The Kuiper Belt Electronic Newsletter ✣✢ Edited by: Joel Wm. Parker [email protected] www.boulder.swri.edu/ekonews CONTENTS News & Announcements ................................. 2 Abstracts of 11 Accepted Papers ........................ 3 Newsletter Information .............................. 11 1 NEWS & ANNOUNCEMENTS Icarus is sponsoring a special issue on results related to the exploration of the Pluto system, the Kuiper Belt, and Kuiper Belt Objects by New Horizons. Papers are solicited from authors inside and outside the New Horizons team. The deadline for this special issue is 15 September 2019. Alan Stern Principal Investigator, New Horizons Rosaly Lopes Editor, Icarus ................................................... ............................................... EPSC-DPS Session SB5: Trans-Neptunian objects and their dust environment, Pluto, 2014 MU69, and Centaurs This session welcomes papers about the trans-Neptunian objects and their environment, including investigations of space weathering. We encourage scientific investigations based on both space and Earth-based observations as well as theoretical and laboratory investigations. Papers based on observations and measurements obtained from within the Kuiper Belt are particularly encouraged including those focusing on 2014 MU69 (a target of the New Horizons mission). We also welcome papers about the Pluto system including investigations of the geology, composition, atmosphere, climate and environment. Papers on processes that may be active in the Pluto system are particularly encouraged and include topics such as formation of organics in Pluto’s atmosphere and surface, or seasonal/climatic models of volatile transports. This session will also welcome abstracts devoted to studies of the Centaurs, in particular on their structure, composition, dynamics and activity patterns. We invite studies that describe observations, theory, experimental work, and future spacecraft encounters related to: (i) the onset and provenance of activity beyond Jupiter’s orbit, and (ii) the nature of surface modification at these heliocentric distances (including, but not limited to, solar radiation, space weathering and impacts). The abstract submission deadline is May 8, 2019, 13:00 CEST. https://meetingorganizer.copernicus.org/EPSC-DPS2019/session/34462 Please join us in Geneva, Sept. 15-20 2019, for what is sure to be a great meeting. Conveners: Kelsi Singer, Maria Teresa Capria, Heather Elliott, Sonia Fornasier, Walter Harris, Rodrigo Leiva, Catherine Olkin, Davide Perna, Simon Porter, Silvia Protopappa, Gal Sarid, Bernard Schmitt, Anne Verbiscer, Laura Woodney ................................................... ............................................... There were 56 new TNO discoveries announced since the previous issue of Distant EKOs: 2009 XM26, 2009 YR26, 2009 YS26, 2009 YT26, 2010 AV153, 2010 DF106, 2010 JF210, 2010 JH210, 2010 JJ210, 2010 NF146, 2010 RJ190, 2010 RK190, 2010 TR195, 2010 TS195, 2010 TT195, 2010 WN75, 2011 BO170, 2011 BQ170, 2011 EY90, 2011 EZ90, 2011 GZ61, 2011 HN104, 2011 LJ29, 2011 OC61, 2011 SW281, 2012 BZ159, 2012 DQ106, 2012 FN87, 2012 JD68, 2012 PU45, 2012 UE185, 2012 VB116, 2012 WD37, 2012 XW159, 2012 YF12, 2012 YG12, 2013 CF229, 2013 PE84, 2014 AF61, 2014 BD70, 2014 GK65, 2014 JQ92, 2014 JR92, 2014 KF113, 2014 OX415, 2014 SA365, 2014 WC536, 2014 WW535, 2014 WZ535, 2015 AQ293, 2015 DZ250, 2015 KG178, 2015 KK178, 2016 AN278, 2016 NZ90, 2017 FD163 2 and 55 new Centaur/SDO discoveries: 2010 AW153, 2010 BP153, 2010 CD270, 2010 JG210, 2010 NG146, 2010 OE153, 2010 PC88, 2010 QQ7, 2010 UU110, 2010 WM75, 2011 BM170, 2011 BN170, 2011 BP170, 2011 MV11, 2011 QY100, 2011 VZ24, 2012 AZ25, 2012 FM87, 2012 GT41, 2012 HW87, 2012 HX87, 2012 LB27, 2012 PV45, 2013 GW141, 2013 LZ36, 2013 ME14, 2013 NT33, 2013 NU33, 2013 PD84, 2014 BE70, 2014 BF70, 2014 GJ65, 2014 HO211, 2014 KE113, 2014 PM82, 2014 WA536, 2014 WB536, 2014 WV535, 2014 WX535, 2014 WY535, 2015 AR293, 2015 BE568, 2015 BF568, 2015 BG568, 2015 FG415, 2015 RQ281, 2015 XW379, 2016 CN323, 2016 SE56, 2017 OK69, 2017 VO34, 2018 AZ18, 2018 GT12, 2018 JT6, 2018 JU6 Current number of TNOs: 2499 (including Pluto) Current number of Centaurs/SDOs: 921 Current number of Neptune Trojans: 22 Out of a total of 3442 objects: 693 have measurements from only one opposition 686 of those have had no measurements for more than a year 368 of those have arcs shorter than 10 days (for more details, see: http://www.boulder.swri.edu/ekonews/objects/recov_stats.jpg) PAPERS ACCEPTED TO JOURNALS Impact Craters on Pluto and Charon Indicate a Deficit of Small Kuiper Belt Objects K.N. Singer1, W.B. McKinnon2, B. Gladman3, S. Greenstreet4, et al. 1 Southwest Research Institute, Boulder, CO, USA 2 Department of Earth and Planetary Sciences and McDonnell Center for the Space Sciences, Washington University, St. Louis, MO, USA 3 University of British Columbia, Department of Physics and Astronomy, Vancouver, BC, Canada 4 Las Cumbres Observatory, Goleta, CA and the University of California, Santa Barbara, CA, USA The flyby of Pluto and Charon by the New Horizons spacecraft provided high-resolution images of cratered surfaces embedded in the Kuiper belt, an extensive region of bodies orbiting beyond Neptune. Impact craters on Pluto and Charon were formed by collisions with other Kuiper belt objects (KBOs) with diameters from ∼40 kilometers to ∼300 meters, smaller than most KBOs observed directly by telescopes. We find a relative paucity of small craters less than approximately 13 kilometers in diameter, which cannot be explained solely by geological resurfacing. This implies a deficit of small KBOs (less than 1 to 2 kilometers in diameter). Some surfaces on Pluto and Charon are likely greater than 4 billion years old, thus their crater records provide information on the size-frequency distribution of KBOs in the early Solar System. Published in: Science, 363, 955 (2019 March 1) Available online at http://adsabs.harvard.edu/abs/2019Sci...363..955N ................................................... ............................................... 3 Col-OSSOS: Color and Inclination are Correlated Throughout the Kuiper Belt Micha¨el Marsset1,2, Wesley C. Fraser1, Rosemary E. Pike3, Michele T. Bannister1,4,5, Megan E. Schwamb6, Kathryn Volk7, J.J. Kavelaars5,4, Mike Alexandersen3, Ying-Tung Chen3, Brett J. Gladman8, Stephen D.J. Gwyn5, Matthew J. Lehner3,9,10, Nuno Peixinho11, Jean-Marc Petit12, and Shiang-Yu Wang3 1 Astrophysics Research Centre, Queen’s University Belfast, Belfast BT7 1NN, United Kingdom 2 Department of Earth, Atmospheric and Planetary Sciences, MIT, 77 Massachusetts Avenue, Cambridge, MA 02139, USA 3 Institute of Astronomy and Astrophysics, Academia Sinica; 11F of AS/NTUAstronomy-Mathematics Building, No.1, Sec. 4, Roosevelt Rd, Taipei 10617, Taiwan, R.O.C. 4 Department of Physics and Astronomy, University of Victoria, Elliott Building, 3800 Finnerty Rd, Victoria, BC V8P 5C2, Canada 5 NRC-Herzberg Astronomy and Astrophysics, National Research Council of Canada, 5071 West Saanich Rd, Victoria, BC V9E 2E7, Canada 6 Gemini Observatory, Northern Operations Center, 670 North A’ohoku Place, Hilo, HI 96720, USA 7 Lunar and Planetary Laboratory, The University of Arizona, 1629 E. University Blvd., Tucson, AZ 85721, USA 8 Department of Physics and Astronomy, University of British Columbia, Vancouver, BC V6T 1Z1, Canada 9 Department of Physics and Astronomy, University of Pennsylvania, 209 S. 33rd St., Philadelphia, PA 19104, USA 10 Harvard-Smithsonian Center for Astrophysics, 60 Garden St., Cambridge, MA 02138, USA 11 CITEUC – Centre for Earth and Space Science Research of the University of Coimbra, Geophysical and Astronomical Observatory of the University of Coimbra, 3040-004 Coimbra, Portugal 12 Institut UTINAM UMR6213, CNRS, Univ. Bourgogne Franche-Comt´e, OSU Theta F25000 Besan¸con, France Both physical and dynamical properties must be considered to constrain the origins of the dy- namically excited distant Solar System populations. We present high-precision (g-r) colors for 25 small (Hr>5) dynamically excited Trans-Neptunian Objects (TNOs) and centaurs acquired as part of the Colours of the Outer Solar System Origins Survey (Col-OSSOS). We combine our dataset with previously published measurements and consider a set of 229 colors of outer Solar System objects on dynamically excited orbits. The overall color distribution is bimodal and can be decomposed into two distinct classes, termed ‘gray’ and ‘red’, that each has a normal color distribution. The two color classes have different inclination distributions: red objects have lower inclinations than the gray ones. This trend holds for all dynamically excited TNO populations. Even in the worst-case scenario, biases in the discovery surveys cannot account for this trend: it is intrinsic to the TNO population. Considering that TNOs are the precursors of centaurs, and that their inclinations are roughly preserved as they become centaurs, our finding solves the conundrum of centaurs being the only outer Solar System population identified so far to exhibit this property (Tegler et al. 2016). The different orbital distributions of the gray and red dynamically excited TNOs provide strong evidence that their colors are due to different formation locations in a disk of planetesimals with a compositional gradient. Published in: The Astronomical Journal, 157, 94 (2019 March) For preprints, contact [email protected] or on the web at http://adsabs.harvard.edu/abs/2019AJ....157...94M