Seepages and the astrobiological potential of polar dunes on Mars

At the polar dunes of Mars branching dark slope streaks emanate from Dark Dune Spots were observed in local springtime on MOC and HiRISE image. They seep downward with speed of 1.4 meter/sol when the temperature of the terrain on 3 km spatial resolution is between 180 and 250 K. Theoretical considerations and calculations suggest interfacial liquid-like water have to be present on the Mars, and probably cause the observed seepage features. The thin water lubricated grains may slide over each other, and/or the stress caused by the refreezing of this interfacial wate could also produce such markings, as well as the moving front of solid ice/liquid water phase changes. Such ephemerally wet environment between the dune grains may have astrobiological significance.