Temporal evolution of comet 67P/Churyumov-Gerasimenko surface properties as observed by VIRTIS-M from pre-perihelion to post-perihelion

Abstract

The Visible and Infrared Thermal Imaging Spectrometer on board the Rosetta spacecraft acquired disk-resolved images of the nucleus of comet 67P/Churyumov-Gerasimenko for more than two years from August 2014 to September 2016. The observation campaigns have been carried out using both the visible (VIS) and infrared (IR) channels of the instrument covering the 0.25-5.1 μm spectral range up to May 2015 and by means of the sole VIS channel (0.25-1 μm) for the remaining part of the mission. This allowed monitoring the spectral properties of the comet surface as a function of the heliocentric distance for the inbound part of the orbit from 3.6 AU to perihelion (1.3 AU) and the outbound part up to 3.3 AU. Throughout this period the surface evolution was further complicated by the combination of the relatively large orbital eccentricity, of the irregular shape of 67P/CG's nucleus and of the inclination of its rotational axis (52°) which amplify the seasonal effects.