Volume 548, December 2012
|Number of page(s)||9|
|Section||Planets and planetary systems|
|Published online||15 November 2012|
Physical properties of OSIRIS-REx target asteroid (101955) 1999 RQ36
Max-Planck-Institut für extraterrestrische Physik (MPE),
2 European Space Astronomy Centre (ESAC), European Space Agency, Apartado de Correos 78, 28691 Villanueva de la Cañada, Madrid, Spain
3 Observatoire de Paris, Laboratoire d’Études Spatiales et d’Instrumentation en Astrophysique (LESIA), 5 place Jules Janssen, 92195 Meudon Cedex, France
4 Konkoly Observatory, Research Center for Astronomy and Earth Sciences, Hungarian Academy of Sciences; Konkoly Thege 15–17, 1121 Budapest, Hungary
5 Ludwig-Maximilians-Universität München, Fakultät für Physik, Schellingstraße 4, 80799 München, Germany
6 INSA at European Space Astronomy Centre (ESAC), European Space Agency, Apartado de Correos 78, 28691 Villanueva de la Cañada, Madrid, Spain
Received: 20 July 2012
Accepted: 8 October 2012
In September 2011, the Herschel Space Observatory performed an observation campaign with the PACS photometer observing the asteroid (101955) 1999 RQ36 in the far infrared. The Herschel observations were analysed, together with ESO VLT/VISIR and Spitzer/IRS data, by means of a thermophysical model in order to derive the physical properties of 1999 RQ36. We find the asteroid has an effective diameter in the range 480 to 511 m, a slightly elongated shape with a semi-major axis ratio of a/b = 1.04, a geometric albedo of 0.045+0.015-0.012, and a retrograde rotation with a spin vector between –70 and –90° ecliptic latitude. The thermal emission at wavelengths below 12 μm-originating in the hot sub-solar region- shows that there may be large variations in roughness on the surface along the equatorial zone of 1999 RQ36, but further measurements are required for final proof. We determine that the asteroid has a disk-averaged thermal inertia of Γ = 650 Jm-2 s-0.5 K-1 with a 3-σ confidence range of 350 to 950 Jm-2 s-0.5 K-1, equivalent to what is observed for 25143 Itokawa and suggestive that 1999 RQ36 has a similar surface texture and may also be a rubble-pile in nature. The low albedo indicates that 1999 RQ36 very likely contains primitive volatile-rich material, consistent with its spectral type, and that it is an ideal target for the OSIRIS-REx sample return mission.
Key words: minor planets, asteroids: individual: (10955) 1999 RQ36 / radiation mechanisms: thermal / techniques: photometric / infrared: planetary systems
© ESO, 2012
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