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Friday 10/03/2023 @ 11:30, Sala riunioni quarto piano e on-line (

Roberto Orosei (INAF-IRA Bologna), "The search for liquid water beneath the Martian South Polar Layered Deposits"

The Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) was built to probe the Martian subsurface down to depths of kilometers by transmitting electromagnetic pulses in the MHz frequency range. Echoes coming from a depth of about 1.5 km, stronger than surface reflections, were repeatedly detected in a 20 km wide area centered at 193°E, 81°S. Quantitative analysis of such echoes yielded values of the relative dielectric permittivity at the base of the South Polar Layered Deposits (SPLD) greater than 15, matching that of water-bearing materials. Reanalysis of observations, using signal processing procedures previously applied to terrestrial polar ice sheets, confirmed that the properties of MARSIS echoes match those of reflections from subglacial lakes, while the analysis of subsequent observations revealed the presence of other wet areas nearby. Because of the very low temperatures expected beneath the SPLD, it was proposed that the waters are hypersaline perchlorate brines, known to form at Martian polar regions and thought to survive for an extended period of time on a geological scale at below-eutectic temperatures. Because of its significance in the study of the biologic potential of Mars, the identification of liquid water has been closely scrutinized by the scientific community at large, and several counter-arguments and alternative interpretations of MARSIS measurements have been proposed over last four years. Here we aim at providing a summary of the existing literature on the topic, and at assessing the current status of the debate.