Characterizing the interior of 67P in the vicinity of Abydos
Résumé
Since the arrival of Rosetta at comet 67P, numerous pictures have been delivered by the cameras onboard both the main spacecraft and the Philae lander. They revealed, at the nucleus' surface and inside the walls of the deep pits, few-meters scale repeating structures, thus providing hints about the internal structure of the nucleus, and suggesting that primordial 'cometesimals' may be objects around 3m in size.
The CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission) experiment is a radar that has been designed to specifically sound the interior of the nucleus and to provide information on the nucleus internal structure. The work presented here is based on the CONSERT data collected during the First Science Sequence (FSS) and marginally during Philae’s Separation Descent and Landing (SDL) for comparison.
During FFS, the smaller lobe of the nucleus in the vicinity of Abydos has been actually sounded by CONSERT’s electromagnetic waves at 90 MHz with a spatial resolution around 10 m. The propagation delays measured during FSS are consistent with a very low bulk permittivity value for the investigated cometary material, which confirms the high porosity of the nucleus. The sharp shape of the received pulses indicates that the electromagnetic waves suffered weak scattering when propagating through the nucleus. This suggests that the sounded part nucleus is thus fairly homogeneous on a spatial scale of tens of meters.
We will present further results on the variation of the CONSERT’s pulse shape transmitted through the small lobe of the nucleus. For a more accurate analysis and interpretation of the data, we split the FSS data into two distinct sets corresponding to soundings performed West and East of Philae in order to investigate potential differences. Tentative interpretation in terms of nucleus internal structure based on propagation simulations performed in non-homogeneous nucleus numerical models will be presented.