Characterization of rocks buried in the subsurface by the GPR WISDOM/ExoMars 2020
Résumé
The search for evidence of past life on Mars is the main objective of the ESA-Roscosmos ExoMars Rover mission. Given the hostile environment at the surface, if such evidence is to be found anywhere, it will most likely be in the subsurface. This is why the ExoMars rover mission has been optimized to investigate the subsurface. Among the instruments accommodated onboard the Rover, the polarimetric ground penetrating radar WISDOM (Water Ice Subsurface Deposits Observation On Mars, Ciarletti et al., 2011) has been designed to investigate the shallow subsurface and search for the most favorable locations where to drill and collect samples for analysis. WISDOM is able to probe down to a depth of few meters with a vertical resolution of a few centimeters, and will provide key information on the geological context of the environment.In particular, insights into density, size and shape of the rocks buried beneath the rover would be clues for a better understanding of the geological and hydrological history of the Rover site. In addition, the density and size of the buried rocks will have to be taken into account for the safety of the drilling operations.In this paper, we will focus on the ability of WISDOM to detect, localize and characterize (in terms of size and shape), rocks in the shallow subsurface of Mars. More specifically, we use a 3D numerical code based on the Finite Difference in Time Domain method to model the antenna system of WISDOM and simulate the instrument operations on realistic environments with buried rocks. In this approach, size-frequency distribution of rocks in agreement with observations from orbit and by cameras operated from the Martian surface will be considered. We will present results of simulations for different density and shape of buried rocks, including critical configurations where the density of rocks is too high to allow individual detection of rocks. In addition, we will present experimental data for comparison with the simulated data.References:V. Ciarletti, C. Corbel, D. Plettemeier, P. Caïs, S. M. Clifford, and S. E. Hamran, "WISDOM GPR Designed for Shallow and High-Resolution Sounding of the Martian Subsurface " Proceedings of the IEEE, vol. 99, no. 99, pp. 1-13, 2011.