An Analysis of Regional H2O and CH3OH Production rates of Comet 67P from the MIRO Measurements

The coma structure and gas production rates of H₂O, CO, CH₃OH, and NH₃ of comet 67P/Churyumov-Gerasimenko were investigated in detail by different instruments onboard the Rosetta spacecraft between August 2014 and September 2016. We analyzed the nadir-pointing microwave spectroscopic data from the MIRO experiment before and during the perihelion passage in June, July, and August 2015 in order to examine the solar zenith angle dependence of the gas production rates (Q) of H₂O and CH₃OH, respectively. From a detailed analysis of the spectral shapes of H_2¹⁸O at a frequency of 547.676 GHz and those of CH₃OH at 553.146 GHz, the surface distributions of H₂O and CH₃OH can be mapped. We found that the Q-values generally increased with solar insolation. However, there also existed large variations that might be related to chemical heterogeneity of the cometary nucleus surface (or subsurface in individual geomorphological areas and at different spatial scales). A comparison of the CH₃OH/H₂O mixing ratio in the two lobes will also be attempted.