The CONSERT bistatic radar onboard the Rosetta spacecraft and the Philae lander has begun to reveal the internal structure of Comet 67P/Churyumov-Gerasimenko, through radio tomographic mapping between the lander and main spacecraft. The small lobe was found to be structurally homogeneous, at the spatial scale of ten meters, corresponding to a few wavelengths of CONSERT instrument . The real part of the relative permittivity has been derived from the travel time of the strongest signals obtained on 12-13 November 2014, from Philae final landing site. Since the final position of the lander was not accurately defined, numerous ray-tracing simulations were performed to constrain the ambiguities on Philae position using the known position of Rosetta and the propagation time and paths inside and outside the nucleus. A least square statistical analysis between measurements and simulations lead to deduce a bulk relative permittivity about (1.27 ± 0.1); meanwhile, the uncertainty in the lander location was reduced to an area of about 21 by 34 square meters .Ongoing theoretical and experimental simulations are providing more insights on the nucleus properties. Numerical ray-tracing simulations of the propagation at grazing angles have been performed for various subsurface permittivity models. They establish that a permittivity gradient in the shallow sub-surface would have a strong effect on the wave propagation. The permittivity probably decreases with depth, suggesting that a significant increase of dust/ice ratio with depth is unlikely . Laboratory simulations of the permittivity of subsurface cometary analog materials , and of surface porous analog samples  have taken place. Results suggest 67P dielectric properties to be mainly controlled by porosity, the dust/ice volumetric ratio to range from 0.4 to 2.6 and the porosity to range from 75 to 85% . Further on-going laboratory measurements will be discussed.Supports from CNES and NASA are acknowledged. Kofman et al. Science 349, 6247 aab0639, 2015. Ciarletti et al. A&A (Rosetta issue), in press, 2015. E. Heggy et al. Icarus 221, 925, 2012. Brouet et al. A&A (Rosetta issue), in press, 2015.
AAS/Division for Planetary Sciences Meeting Abstracts #47
- Pub Date:
- November 2015