Water ice at low to midlatitudes on Mars

In this paper, we analyze water ice occurrences at the surface of Mars using near-infrared observations, and we study their distribution with a climate model. Latitudes between 45 degrees S and 50 degrees N are considered. Data from the Observatoire pour la Mineralogie, l'Eau, les Glaces et l'Actitite and the Compact Reconnaissance Imaging Spectrometer for Mars are used to assess the presence of surface water ice as a function of location and season. A modeling approach combining the 1-D and 3-D versions of the General Circulation Model of the Laboratoire de Meteorologie Dynamique de Jussieu is developed and successfully compared to observations. Ice deposits 2-200 mu m thick are observed during the day on pole facing slopes in local fall, winter, and early spring. Ice extends down to 13 degrees latitude in the Southern Hemisphere but is restricted to latitudes higher than 32 degrees in the north. On a given slope, the pattern of ice observations at the surface is mainly controlled by the global variability of atmospheric water (precipitation and vapor), with local ground properties playing a lower role. Only seasonal surface ice is observed: no exposed patches of perennial ground ice have been detected. Surface seasonal ice is however sensitive to subsurface properties: the results presented in this study are consistent with the recent discovery of low-latitude subsurface ice obtained through the analysis of CO2 frost.