Volume 583, November 2015
Rosetta mission results pre-perihelion
|Number of page(s)||11|
|Section||Planets and planetary systems|
|Published online||30 October 2015|
MIRO observations of subsurface temperatures of the nucleus of 67P/Churyumov-Gerasimenko
University of Massachusetts,
619 Lederle Graduate Research Tower,
2 JPL, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
3 LESIA-Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
4 LERMA, Observatoire de Paris, PSL Research University, CNRS, UMR 8112, UPMC, 75014 Paris, France
5 Max-Planck-Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
6 Planetary Science Institute, Tucson, AZ 85719, USA
7 National Central University, Jhongli, 32001 Taoyuan City, Taiwan
8 Aix Marseille Université, CNRS, Laboratoire d’Astrophysique de Marseille, UMR 7326, 13388 Marseille, France
9 Institut für Geophysik und extraterrestrische Physik, Technische Universität Braunschweig, 38106 Braunschweig, Germany
10 Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, 12489 Berlin, Germany
Received: 21 March 2015
Accepted: 7 July 2015
Observations of the nucleus of 67P/Churyumov-Gerasimenko in the millimeter-wave continuum have been obtained by the Microwave Instrument for the Rosetta Orbiter (MIRO). We present data obtained at wavelengths of 0.5 mm and 1.6 mm during September 2014 when the nucleus was at heliocentric distances between 3.45 and 3.27 AU. The data are fit to simple models of the nucleus thermal emission in order to characterize the observed behavior and make quantitative estimates of important physical parameters, including thermal inertia and absorption properties at the MIRO wavelengths. MIRO brightness temperatures on the irregular surface of 67P are strongly affected by the local solar illumination conditions, and there is a strong latitudinal dependence of the mean brightness temperature as a result of the seasonal orientation of the comet’s rotation axis with respect to the Sun. The MIRO emission exhibits strong diurnal variations, which indicate that it arises from within the thermally varying layer in the upper centimeters of the surface. The data are quantitatively consistent with very low thermal inertia values, between 10–30 J K-1 m-2 s-1/2, with the 0.5 mm emission arising from 1 cm beneath the surface and the 1.6 mm emission from a depth of 4 cm. Although the data are generally consistent with simple, homogeneous models, it is difficult to match all of its features, suggesting that there may be some vertical structure within the upper few centimeters of the surface. The MIRO brightness temperatures at high northern latitudes are consistent with sublimation of ice playing an important role in setting the temperatures of these regions where, based on observations of gas and dust production, ice is known to be sublimating.
Key words: comets: general / comets: individual: 67P/Churyumov-Gerasimenko / radio continuum: planetary systems
© ESO, 2015
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