Publication Date:
2016-12-29
Description:
Infrared observations of the coma of 67P/Churyumov–Gerasimenko were carried out from 2015 July to September, i.e. around perihelion (2015 August 13), with the high-resolution channel of the Visible and Infrared Thermal Imaging Spectrometer instrument onboard Rosetta . We present the analysis of fluorescence emission lines of H 2 O, CO 2 , 13 CO 2 , OCS, and CH 4 detected in limb sounding with the field of view at 2.7–5 km from the comet centre. Measurements are sampling outgassing from the illuminated Southern hemisphere, as revealed by H 2 O and CO 2 raster maps, which show anisotropic distributions, aligned along the projected rotation axis. An abrupt increase of water production is observed 6 d after perihelion. In the meantime, CO 2 , CH 4 , and OCS abundances relative to water increased by a factor of 2 to reach mean values of 32, 0.47, and 0.18 per cent, respectively, averaging post-perihelion data. We interpret these changes as resulting from the erosion of volatile-poor surface layers. Sustained dust ablation due to the sublimation of water ice maintained volatile-rich layers near the surface until at least the end of the considered period, as expected for low thermal inertia surface layers. The large abundance measured for CO 2 should be representative of the 67P nucleus original composition, and indicates that 67P is a CO 2 -rich comet. Comparison with abundance ratios measured in the Northern hemisphere shows that seasons play an important role in comet outgassing. The low CO 2 /H 2 O values measured above the illuminated Northern hemisphere are not original, but the result of the devolatilization of the uppermost layers.
Print ISSN:
0035-8711
Electronic ISSN:
1365-2966
Topics:
Physics
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