Distribution of water around the nucleus of comet 67P/Churyumov-Gerasimenko at 3.4 AU from the Sun as seen by the MIRO instrument on Rosetta

¹ LESIA, Observatoire de Paris, CNRS, UPMC, Université Paris-Diderot, 5 place Jules Janssen, 92195 Meudon, France
e-mail: nicolas.biver@obspm.fr
² JPL/California Institute of Technology, 4800 Oak Grove Dr., Pasadena, CA 91109, USA
³ University of Massachusetts, 619 Lederle Graduate Research Tower, Amherst, MA, USA
⁴ Max Planck Institut für Sonnensystemforschung, Justus-von-Liebig-Weg 3, 37077 Göttingen, Germany
⁵ National Central University, Jhongli, 32001 Taoyuan City, Taiwan
⁶ LERMA, Observatoire de Paris, PSL Research University, UPMC, CNRS, 61 avenue de l’Observatoire, 75014 Paris, France

Received: 13 March 2015
Accepted: 2 May 2015

Abstract

The Microwave Instrument on the Rosetta Orbiter (MIRO) has been observing the coma of comet 67P/Churyumov-Gerasimenko almost continuously since June 2014 at wavelengths near 0.53 mm. We present here a map of the water column density in the inner coma (within 3 km from nucleus center) when the comet was at 3.4 AU from the Sun. Based on the analysis of the H₂¹⁶O and H₂¹⁸O (110-101) lines, we find that the column density can vary by two orders of magnitude in this region. The highest column density is observed in a narrow region on the dayside, close to the neck and north pole rotation axis of the nucleus, while the lowest column density is seen against the nightside of the nucleus where outgassing seems to be very low. We estimate that the outgassing pattern can be represented by a Gaussian distribution in a solid angle with FWHM ≈ 80°.