Calibrations of ROSINA-COPS and Observations at Comet 67P/Churyumov-Gerasimenko

Abstract

Comets are thought to be the most pristine objects in the Solar System. Investigating comets will therefore shed light on the origin and formation of the Solar System. For this purpose the European Space Agency selected the Rosetta mission to carry out a study of the Jupiter family comet 67P/Churyumov-Gerasimenko at a close distance continuously for a period of more than two years around its closest approach to the Sun. This work presents laboratory calibration and neutral gas coma measurements of the COmet Pressure Sensor (COPS) of the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA). Following a brief introduction to the mission and the instrument, the data treatment principles are illustrated. Next, the laboratory calibrations to characterize COPS long term stability and to verify the data analysis methods are demonstrated. Finally, the results of COPS observations in the coma of comet 67P are shown and discussed in detail. A few highlights are as follows: the peak total neutral gas production rate is slightly shifted from perihelion passage and estimated to be approximately 4·1028 molecules/s; neutral gas expansion velocities in October 2014 have been derived to be around 300 to 1200 m/s depending on illumination conditions on the surface and Rosetta’s location above the comet; though built to measure neutral gas, COPS surprisingly observed as well dust and plasma signatures. All in all, COPS was working well throughout the Rosetta mission and has assisted to unravel a small section of the extensive puzzle about the formation of our Solar System.