Mars is today a cold, dry and sterile world, but in the past it had a thicker atmosphere and liquid water flowing on its surface. MARSIS is a synthetic-aperture, orbital sounding radar carried by the European Space Agency spacecraft Mars Express searching for subsurface water and ice. Recently, MARSIS found anomalously bright subsurface reflections within a well-defined, 20 km wide zone in the Southern polar cap. Quantitative analysis of the radar signals produced estimates of relative dielectric permittivity matching that of water-bearing materials. The search for subsurface water is far from being complete, however, but MARSIS is approaching the end of its operative life and SHARAD, a higher-frequency radar sounder also operating at Mars, cannot penetrate at the depth at which MARSIS detected liquid water. The only possibility to extend the search for subglacial water in the Martian poles lays with the Mars Global Remote Sensing Orbiter, the first Chinese mission to Mars.

The goal of this proposal is the search of subglacial water in the Martian polar caps using radar sounding data, both past and future. This will be achieved through several coordinated activities, i.e. analysis of all available radar sounding data acquired over the Martian polar caps; acquisition of raw data mode MARSIS observations over selected locations; electromagnetic modelling of the radar response of the polar caps; electromagnetic simulations of radar propagation in the Martian polar deposits at the frequencies of MARSIS, SHARAD and Mars Global Remote Sensing Orbiter radar sounder. We envision that these activities will produce a global map of potential and confirmed locations of basal liquid water; a range of hypotheses on the nature of scattering within the Martian polar terrains; an interpretation of the effect of such scattering based on numerical experiments and its effect on the future Chinese radar at Mars; a set of recommendations for an effective science strategy in the future search for liquid water beneath the Martian polar caps by the Mars Global Remote Sensing Orbiter radar sounder.