The interior of Comet 67P/C-G; revisiting CONSERT results with the exact position of the Philae lander

Abstract : CONSERT, a bistatic radar onboard the Rosetta spacecraft and its Philae lander, was designed to probe the nucleus of comet 67P/Churyumov-Gerasimenko with radio waves at 90 MHz frequency. In September 2016 the exact position of Philae was retrieved, within the region previously identified by CONSERT. This allowed us to revisit the measurements and improve our analysis of the properties of the interior, the results of which we present here. The relative permittivity of the materials is found to range from about 1.7 to 1.95 in the shallow subsurface (<25 m) and about 1.2 to 1.32 in the interior. These differences indicate different average densities between the shallow subsurface and the interior of comet. They can be explained by various physical phenomena such as different porosities, the possible compaction of surface materials or even perhaps different proportions of the same materials. This strongly suggests that the less dense interior has kept its pristine nature.