Infrared detection of exposed Carbon Dioxide ice on 67P/CG nucleus surface by Rosetta-VIRTIS

In the period August 2014 - early May 2015 the heliocentric distance of the nucleus of 67P/CG decreased from 3.62 to 1.71 AU and the subsolar point moved towards the southern hemisphere. We investigated the IR spectra obtained by the Rosetta/VIRTIS instrument close to the newly illuminated regions, where colder conditions were present and consequently higher chances to observe highly volatility ices than water. We report about the discovery of CO2 ice identified in a region of the nucleus that recently passed through terminator. The quantitative abundance has been determined by means of spectral modeling of H2O-CO2 icy grains mixed to dark terrains as done in Filacchione et al., Nature, 10.1038/nature16190. The CO2 ice has been identified in an area in Anhur with abundance reaching up to 1.6% mixed with dark terrain. It is interesting to note that CO2 ice has been observed only for a short transient period of time, possibly demonstrating the seasonal nature of the presence of CO2 at the surface. A parallel study on the water and carbon dioxide gaseous emissions in the coma above this volatile-rich area is reported by Migliorini et al., this conference.