The Nucleus and Coma of Comet 67P/C-G at Millimeter and Submillimeter Wavelengths as seen by MIRO

Abstract:

The Microwave Instrument on the Rosetta Orbiter (MIRO) makes submillimeter- and millimeter-wavelength observations of Comet 67P/Churyumov-Gerasimenko. Broadband continuum measurements at wavelengths of 0.5 and 1.6 mm probe the thermal and dielectric properties of the nucleus subsurface. High-resolution spectroscopic measurements of 8 molecular lines in the submillimeter (H₂O, H₂¹⁷O, H₂¹⁸O, CO, NH₃, and three lines of CH₃OH) constrain the abundance, velocity, and temperature of gases in the coma. These measurements allow MIRO to study the nucleus and coma as a coupled system.

Using its two continuum channels, MIRO has mapped the thermal properties of the nucleus subsurface (depths from millimeters to tens of centimeters), and generally finds its properties to be consistent with very porous, dusty material. We see temperature variations due to diurnal and seasonal changes in insolation, and also see evidence for subsurface ice in some regions. This talk will provide an update on our observations of variations over time, variations with temperature, and variations in composition. We also will report on our attempts to detect the continuum thermal emission of dust in the coma. MIRO's spectroscopic observations have shown the abundance and velocity of gas as it comes off the nucleus to vary with time and location. The regions MIRO sees as particularly active are generally consistent with activity reported by other instruments. Moving away from the nucleus, MIRO is sensitive to the three-dimensional structure of the coma. We will present an update on our understanding of that structure, which is influenced by the shape of the nucleus, nucleus rotation, and processes acting within and on the coma. Our ultimate goal is to develop a coupled model of the nucleus and coma, tracing the processes by which solar heating of the surface drives sublimation of subsurface ice and generation of dust, and how gases and dust evolve in the coma.

Part of this work was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract to NASA. Part of the research was conducted at the Max-Planck Institute (Göttingen), Obs. de Paris, National Central Univ. (Taiwan), and Univ. of Mass. (Amherst). Government, DLR, CNES, and CNRS sponsorship is acknowledged.