VIRTIS-Rosetta Observations of 67P/Churyumov-Gerasimenko Nucleus and Coma During the Mission Pre-Landing Phase.

Abstract:

The paper will describe the major results obtained during the pre-landing phase, running from July throughout November 2014, of the Rosetta Mission by the instrument VIRTIS (Visible, Infrared and Thermal Imaging Spectrometer), the dual channel spectrometer onboard Rosetta. The nucleus observations were performed in a wide range of conditions with spatial resolution varying from the initial 500m down to 12.5m and have allowed to generate compositional maps of the illuminated areas. Special emphasis was placed on mapping those surface regions considered reachable areas for the Philae Lander descent, and to those area in the “neck” of the nucleus which from the very early Osiris observations did show hints of surface outgassing activity. The surface temperature has been determined since the first distant observations of the nucleus. Already on the mid of july from a distance of 15000km, when the nucleus was filling one VIRTIS-M pixel, the mean surface temperature has been measured as 205+-5K. This pointed to a surface structure largely covered by a porous crust, mainly devoid of water ice. The major results obtained at higher spatial resolution shall be described and discussed. Finally, an extensive campaign of observations at limb to measure abundances of major volatile compounds (H2O, CO2 and CO) as well as dust scattering properties were carried out.

Authors acknowledge the support from national funding agencies.