“TNOs are Cool”: A survey of the trans-Neptunian region

VII. Size and surface characteristics of (90377) Sedna and 2010 EK₁₃₉

¹ Konkoly Observatory, MTA Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
e-mail: apal@szofi.net
² Department of Astronomy, Loránd Eötvös University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
³ Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, Giessenbachstr., 85741 Garching, Germany
⁴ LESIA-Observatoire de Paris, CNRS, UPMC Univ. Paris 06, Univ. Paris-Diderot, 5 place J. Janssen, 92195 Meudon Cedex, France
⁵ Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Planetenforschung, Rutherfordstrasse 2, 12489 Berlin, Germany
⁶ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Strasse 2, 37191 Katlenburg-Lindau, Germany
⁷ Department of Astronomy, University of Maryland, College Park, MD 20742-2421, USA
⁸ Steward Observatory, University of Arizona, 933 North Cherry Avenue, Tucson, AZ 85721, USA
⁹ Instituto de Astrofísica de Andalucía – CSIC, Apt 3004, 18008 Granada, Spain
¹⁰ Laboratoire d’Astrophysique de Marseille, CNRS & Université de Provence, 38 rue Frédéric Joliot-Curie, 13388 Marseille Cedex 13, France

Received: 23 January 2012
Accepted: 26 March 2012

Abstract

We present estimates of the basic physical properties (size and albedo) of (90377) Sedna, a prominent member of the detached trans-Neptunian object population and the recently discovered scattered disk object 2010 EK₁₃₉, based on the recent observations acquired with the Herschel Space Observatory, within the “TNOs are Cool!” key programme. Our modeling of the thermal measurements shows that both objects have larger albedos and smaller sizes than the previous expectations, thus their surfaces might be covered by ices in a significantly larger fraction. The derived diameter of Sedna and 2010 EK₁₃₉ are 995    ±    80 km and 470⁺³⁵_-10 km, while the respective geometric albedos are p_V = 0.32    ±    0.06 and 0.25^+0.02_-0.05. These estimates are based on thermophysical model techniques.