Analysis of Methanol Spectral Lines Obtained with the Microwave Instrument on the Rosetta Orbiter (MIRO) for Comet 67P/Churuymov-Gerasimenko.

Paul Von Allmen1, Seungwon Lee2, Samuel Gulkis3, Mark D Hofstadter4, F. Peter Schloerb5, Nicolas Biver6, Dominique Bockelée-Morvan7, Mathieu Choukroun8, Paul Hartogh9, Michael A Janssen1, Christopher Jarchow10, Stephen Joseph Keihm1, Emmanuel Lellouch11, Cedric Leyrat12, Ladislav Rezac13, Jacques Crovisier6, Pierre Encrenaz14, Therese Encrenaz15 and Wing-Huen Ip16, (1)NASA Jet Propulsion Laboratory, Pasadena, CA, United States, (2)Jet Propulsion Laboratory, Pasadena, CA, United States, (3)California Institute of Technology, Pasadena, CA, United States, (4)Jet Propulsion Laboratory/California Institute of Technology, Pasadena, CA, United States, (5)University of Massachusetts Amherst, Amherst, MA, United States, (6)LESIA Observatoire de Paris, Meudon, France, (7)Paris Observatory, Paris, France, (8)Jet Propulsion Laboratory, Pasadena, United States, (9)Max Planck Institute for Solar System Research, Göttingen, Germany, (10)Max Planck Institute for Solar System Research, Katlenburg-Lindau, Germany, (11)LESIA, Observatoire de Paris, Paris, France, (12)Paris Observatory Meudon, Meudon, France, (13)Max Planck Institute for Solar System Research, Planetary, Katlenburg-Lindau, Germany, (14)Observatoire de Paris, LERMA, Paris, France, (15)Paris Observatory-PSL, LIRA, Meudon, France, (16)National Central University, Institute of Astronomy, Kanagawa, Japan

Contact First Author: Paul Von Allmen; pva@jpl.nasa.gov

Abstract ID#: 36693

 

English Abstract:
Since the early summer 2014, the Microwave Instrument on the Rosetta Orbiter (MIRO) has been measuring emission from the coma of 67P/Churyumov-Gerasimenko in the sub-millimeter channel at 562 GHz and the millimeter channel at 190 GHz. The high-resolution spectrometer in the sub-millimeter channel is tuned to molecular lines of H2O, CO, CH3OH and NH3. We will discuss the analysis of the three methanol lines at 553.146 GHz, 568.566 GHz and 579.151 GHz and present estimates of the gas abundance in the coma relative to water. The line shape analysis relies on our non-local thermal equilibrium radiative transfer software. Some of the key parameters needed to determine the population of the rotational levels, which enter the radiative transfer calculation, are the state-to-state collision coefficients between the methanol and water molecules. We have calculated theses collision coefficients using a dipole-dipole interaction Hamiltonian and first order perturbation theory for the collision process. Collisional cross-sections between rotational levels in the vibrational ground state will be given in ranges of gas temperature and density present in the coma.
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