Determining the volatile surface activity of comet 67P/CG from Rosetta remote sensing measurements

The activity regions of volatiles on surfaces of comets may provide clues to the mechanism and the environment conditions of comet formation. Abundant data obtained by various instruments from the Rosetta mission, which made both in situ and remote measurements of comet 67P/CG at a close distance over two years, offers us an unprecedented opportunity to study the cometary surface activity. Fougere et al., 2016a&b have developed a spherical harmonics inversion method applied it to ROSINA DFMS mass spectrometer measurements to obtain potential surface activity maps of H2O, CO2, CO and O2 averaged over a time period of more than one year. In this work, we will demonstrate that by applying a similar inversion method to column density maps derived from VIRTIS imaging data, we are able to derive potential surface activity maps as well. The one advantage of VIRTIS remote sensing maps over DFMS densities is that remote sensing measures the distribution of gas in coma very close to the nucleus at kilometer scales, whereas the mass spectrometer measures the distribution of gas far from the nucleus (10-400 km) where detailed information of the distribution of the source region at the nucleus has been smeared out. In addition, one VIRTIS image can supply thousands of data points necessary to constrain the inversion method, and allows us to identify temporary or short-lived activity regions. Results and temporal evolution of activity regions of H2O and CO2 will be discussed. This work is supported by the grant 80NSSC18K1280 from the NASA Rosetta Data Analysis Program.