Evidences of the regolith-atmosphere water exchange on Mars from the ISM (Phobos-2) infrared spectrometer observations

The infrared imaging spectrometer (ISM) on board Phobos-2 spacecraft provided the most important and valuable data on the atmospheric water content on Mars in the post-Viking period. Some of the results of this experiment are likely to be the evidence of the existence of the regolith-atmosphere water vapour exchange. Release of the water molecules, stored in the regolith in the adsorbed phase, to the atmosphere, induced by the noon temperature rise can cause up to a factor of 3 increase in the atmospheric water amount above the areas with high adsorbing capabilities such as clay regolith. Much less, about 30%, increase is expected above the terrains, covered with basalt grains. Local time variations of atmospheric water amount, observed by ISM, are within these limits. The dependence of water vapour desorption rate on the regolith properties can result in the spatial variations of atmospheric water content above clay and basalt regions. This is assumed to be the reason of a factor of 5+/-2 increase in the atmospheric water mixing ratio, observed by ISM above the flanks of Martian volcanoes as compared to the surrounding terrains.