Inferring the Properties of Ices on Comet 67P/Churyumov-Gerasimenko from the Microwave Instrument on the Rosetta Orbiter (MIRO) Measurements
Mathieu Choukroun1, Samuel Gulkis2, Mark D Hofstadter3, Paul Von Allmen2, Mark Allen2, Gerard Beaudin4, Nicolas Biver5, Dominique Bockelée-Morvan5, Jacques Crovisier5, Pierre Encrenaz4, Therese Encrenaz6, Margaret A. Frerking2, Paul Hartogh7, Wing-Huen Ip8, Michael A Janssen2, Christopher Jarchow9, Stephen Joseph Keihm2, Emmanuel Lellouch10, Seungwon Lee2, Cedric Leyrat5, Ladislav Rezac9, F. Peter Schloerb11 and Thomas R Spilker12, (1)Jet Propulsion Laboratory, Pasadena, United States, (2)Jet Propulsion Laboratory, Pasadena, CA, United States, (3)Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, United States, (4)Observatoire de Paris, LERMA, Paris, France, (5)LESIA Observatoire de Paris, Meudon, France, (6)Paris Observatory-PSL, LIRA, Meudon, France, (7)Max Planck Institute for Solar System Research, Göttingen, Germany, (8)National Central University, Institute of Astronomy, Taoyuan City, Taiwan, (9)Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, (10)LESIA, Observatoire de Paris, Paris, France, (11)University of Massachusetts Amherst, Amherst, MA, United States, (12)Independent Consultant, Pasadena, CA, United States
Abstract:
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 (H
2O including oxygen isotopologues, CO, NH
3, and CH
3OH) 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.
