Thin films of liquid brines may be forming in soils on equatorial Mars and evaporating overnight, according to a study published online in Nature Geoscience. The findings suggest an active exchange of water between the Martian atmosphere and surface.
The Curiosity rover, which is traversing Gale crater on equatorial Mars, has detected a type of salt called perchlorate. Perchlorate salts lower the freezing temperature of water and can absorb water vapour from the atmosphere to form corrosive brines.
Javier Martin-Torres and colleagues analysed atmospheric humidity and temperature data for a full Martian year, from an instrument on the Curiosity rover that is monitoring environmental conditions near the surface. They find that the measurements are compatible with the formation of liquid brines in the uppermost soils of Gale crater during the Martian night. These brines would then evaporate after sunrise as the ground and air warm. Estimates of subsurface water content derived from Curiosity data are consistent with the existence of water molecules absorbed by perchlorates in soils.
Perchlorates are thought to be widespread on the Martian surface, suggesting that liquid brines may be more abundant beyond the equatorial regions where environmental conditions are even more favourable to brine formation. However, the authors found that the ground temperature in Gale crater is too low to support microbial life as we know it, even if brines are present.