Study of the coma of comet 67P/Churyumov-Gerasimenko based on the ROSINA/RTOF instrument onboard Rosetta
Abstract:The ROSETTA spacecraft of ESA is in the environment of comet 67P/Churyumov-Gerasimenko since August 2014. Among the experiments onboard the spacecraft, the ROSINA experiment (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) includes two mass spectrometers (DFMS and RTOF) to analyze the composition of neutrals and ions, and a pressure sensor (COPS) to monitor the density and velocity of neutrals in the coma .
We will here analyze and discuss the data of the ROSINA/RTOF instrument during the comet escort phase. The Reflectron-type Time-Of-Flight (RTOF) mass spectrometer possesses a wide mass range and a high temporal resolution [1,2]. It was designed to measure cometary neutral gas as well as cometary ions.
A detailed description of the main volatiles (H2O, CO2, CO) dynamics and of the heterogeneities of the coma will then be provided. The influence of various parameters on the coma measurements is investigated on a statistical basis, with the parameters being distance to the comet, heliocentric distance, longitude and latitude of nadir point. Our analysis of the northern hemisphere summer season shows the presence of water vapor mostly in the illuminated northern hemisphere near the neck region with cyclic diurnal variations whereas CO2 was confined to the cold southern hemisphere with a more spatially homogeneous composition, in agreement with previous observations of 67P  or Hartley 2 . A comparison will also be provided with the COPS total density and DFMS abundance measurements.
 Balsiger et al., "ROSINA - Rosetta Orbiter Spectrometer for Ion and Neutral Analysis", Space Sci. Rev., 2007.
 Scherer et al., "A novel principle for an ion mirror design in time-of-flight mass spectrometry," Int. Jou. Mass Spectr., 2006.
 Hässig et al., "Time variability and heterogeneity in the coma of 67P/Churyumov-Gerasimenko", Science, 2015.
 A’Hearn et al., "EPOXI at comet Hartley 2", Science, 2011.