Three types of liquid water in icy surfaces of celestial bodies

It is shown that, at temperatures far below the triple point and under appropriate conditions, liquid water can stably or temporarily exist in upper ice-covered surfaces of planetary bodies (like Mars) in three different types: (i) undercooled interfacial water (due to freezing point depression by van der Waals forces and “premelting”), (ii) water in brines (due to freezing point depression in solutions), and (iii) sub-surface melt water (due to a solid-state greenhouse effect driven heating). The physics behind and the related conditions for these liquid waters to evolve and to exist, and possibly related consequences, are discussed. These calculations are mainly made in view of the possible presence of these sub-surface liquids in the upper surface of the present Mars