Studies on atmosphere-surface interaction phenomena occurring at the surface of Mars are carried out in the frame of the ESA's Mars Express mission.
The Martian surface comprises sulfates and ferric oxides at significant levels. Intensive interaction has taken place between the atmosphere and surface during the geological evolution of Mars, as it has been shown by mass balance considerations and statistical analysis of chemical surface compositions. The formation of sulfates is considered to be related to volcanic emanation of sulfur-bearing steams into the atmosphere and subsequent weathering of surface materials (acid-sulfate weathering). In the course of weathering, the initially ferrous soil and reducing sulfur-bearing vapors were obviously oxidized by photo-chemically liberated oxygen.