Surface Water Ice and Aerosols Evolution of 77°n, 90°e Mars Crater during Early Summer by Omega/mex

Introduction: Observations of Mars North Pole surface temperatures by Viking/IRTM lead to the discovery of the main permanent cap component: water ice. The lack of H2O ice absorption features in the visible wavelengths makes water ice properties diagnosis ambiguous when using visible data, as has been previously notified by some authors [1, 2, 3]. An increase in visible albedo can be due to a deposition of water frost on ice-free or icy surfaces, a modification of ice grain size or a decrease in dust abundance inside the ice or above it (aerosols). Repeated seasonal visible albedo increases of 77°N, 90°E crater during early 1970s summers (in particular between Ls=97° and Ls=117°) have been interpreted in [4] by water frost deposition on icy and ice-free surfaces. The same team has noticed in [5, 6] that recent MOC images of the crater do not show systematically the same visible albedo evolution during a similar period. The visible and near IR imaging spectrometer OMEGA, on board Mars Express Mission, has provided the coverage of this crater during early 2004 summer. The strong absorption features of water ice in the near IR make it possible for OMEGA to unambiguously map surface water ice, and to investigate its properties. This study examines the [1 μm 2.5 μm] spectral evolution of surface water ice in terms of aerosols, dust content and ice grains size evolution during early 2004 summer (Ls=96°-118°).