Water vapour and carbon dioxide IR emissions in 67P/CG coma: first detection by Rosetta/VIRTIS-M

Taking advantage of Rosetta’s terminator orbits around 67P/CG nucleus in December 2014, VIRTIS-M, the mapping channel of the Visible and Infrared Thermal Imaging Spectrometer has carried out systematic observations of the comet limb in the 0.25-5 μm spectral range with the aim to detect fluorescence emissions of gas species like water vapour and carbon dioxide. We report about the first detections of these molecules by VIRTIS-M and correlate them with respect to the nucleus orientation at the time of the observation. These features appear variable in time, depending on numerous parameters like comet’s activity state, relative position of the spacecraft with respect to the nucleus, tangent altitude of the line of sight above the limb, heliocentric distance and solar phase. Water vapour emission at 2.7 μm appears considerably more intense in correspondence of the jets emitted by the active regions in the neck while carbon dioxide emission at 4.25 μm increases in limb observations taken above the head and body regions