North polar deposits of Mars: Extreme purity of the water ice

Abstract : The polar layered deposits are the largest reservoir of water on the surface of Mars. The physical properties of the ice and their spatial distribution are largely unknown. 140,000 data points from the sounding radar SHARAD on the Mars Reconnaissance Orbiter were analyzed over the Gemina Lingula region, one-fourth of the north polar layered deposits area. Maps of the dielectric properties of the bulk ice were drawn up. There is no basal melting signature. A drop of the dielectric constant in north-west of Gemina Lingula could be explained by an abrupt 250-meter uplift of the base. The bulk ice of the studied region has an average dielectric constant of 3.10 (σ = 0.12) and a loss tangent <0.0026 (σ = 0.0005). Analytic interpretations shown the volume of ice is pure at ≥95%. The impurities have a radial distribution, with higher concentrations at margins.