Distribution of the ices exposed near the south pole of Mars using Thermal Emission Imaging System (THEMIS) temperature measurements

Understanding the present and past water cycle on Mars requires an accurate knowledge of the distribution and amount of H₂O available near the surface. In this article, we present a map of the distribution of the surface material exposed between 87°S and 70°S in the summer (e.g., CO₂ and H₂O ices, dust) based on temperature measurements made by Thermal Emission Imaging System (THEMIS). Our compositional map (100 m per pixel) is in good agreement with spectral mapping returned by Observatoire pour la minéralogle, l'Eau, la Glace et l'activité (OMEGA) and Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). Exposed water ice covers a total surface area of approximately 40,000 km². A large fraction of the water ice is exposed at the periphery of the CO₂ cap. An approximately 25,000-km² large patch centered at 83.5°S and 345°E is discovered and represents the largest exposure of water ice in the southern hemisphere. It is not located on the south polar layered deposits but on the surrounding mantled terrains. THEMIS VIS, MOC and HiRISE images indicate that the surface roughness of exposed water ice terrains is typically lower than that of the surrounding dust. Polygonal patterns are observed on the water ice but not exclusively. There is a strong correlation between the surface albedo, the composition of the exposed material, and the timing of the initial seasonal CO₂ frost deposition and final removal. These exposed water ice outcrops are not stable in the present environment and lose a vertical layer of tens to hundreds of micrometer a year to the atmosphere. The spike of water vapor above the south pole during the southern summer occurs while the water ice is still covered by a layer of seasonal CO₂ frost, indicating that the sublimation of the exposed water ice is not the main contributor of vapor for the southern atmosphere. As water ice is not stable, it may indicate the past location of part of the CO₂ perennial cap that has been eroded.