Inferring the Properties of Ices on Comet 67P/Churyumov-Gerasimenko from the Microwave Instrument on the Rosetta Orbiter (MIRO) Measurements

Wednesday, 17 December 2014: 11:40 AM
Mathieu Choukroun1, Samuel Gulkis1, Mark D Hofstadter1, Paul Von Allmen1, Mark Allen1, Gerard Beaudin2, Nicolas Biver3, Dominique Bockelée-Morvan3, Jacques Crovisier3, Pierre Encrenaz2, Therese Encrenaz3, Margaret A. Frerking1, Paul Hartogh4, Wing-Huen Ip5, Michael A Janssen1, Christopher Jarchow4, Stephen Joseph Keihm1, Emmanuel Lellouch2, Seungwon Lee1, Cedric Leyrat3, Ladislav Rezac4, F. Peter Schloerb6 and Thomas R Spilker7, (1)Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Observatoire de Paris, LERMA, Paris, France, (3)LESIA Observatoire de Paris, Meudon, France, (4)Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, (5)NCU National Central University of Taiwan, Jhongli, Taiwan, (6)University of Massachusetts Amherst, Amherst, MA, United States, (7)Retired, Monrovia, CA, United States
ESA’s Rosetta spacecraft just arrived at comet 67P/Churyumov-Gerasimenko. Since the approach in June 2014, the MIRO instrument has been acquiring two types of data: continuum emission thermal data from the nucleus at the two operating wavelengths of 190 and 562 GHz, and spectroscopic data at 562 GHz on the gas present in the coma. The two continuum channels allow for probing the temperature in the shallow subsurface over two effective depths on the order of a few millimeters to a few centimeters. The submillimeter spectrometer is sensitive to the gas molecules (H2O including oxygen isotopologues, CO, NH3, and CH3OH) emitted by the nucleus.

The location of the ices that are at the source of the gases found in the coma is still poorly constrained, as well as their state: pure condensate ices, hydrates or clathrate hydrates, or gas entrapped in an amorphous ice matrix. Icy grains emitting water vapor have been observed in the inner coma of comet 103P/ Hartley 2 by the EPOXI mission. Although a similar behavior might occur on 67P/ Churyumov-Gerasimenko as well, such icy grains need to be lifted off the nucleus by pre-existing gas, and thus may only represent a secondary source of the gas present in the coma. We will focus here on the potential reservoir(s) of ices within the nucleus, which is most likely the primary source of the activity.

We will compare the results obtained on the thermal emission of the nucleus and on the composition of the inner coma, particularly at the local/regional scale, with the phase diagrams and sublimation/dissociation rates of the various types of ices, in order to assess the location and composition of the ices in the source region(s) within the 67P/Churyumov-Gerasimenko nucleus.

Acknowledgments: Part of this work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Copyright 2014. All rights reserved. Government sponsorship acknowledged.