Premelting Water and Its Role on Mars

Recent detailed explorations of Mars have revealed various types of landform that are similar to terrestrial periglacial landforms and provided direct and indirect evidence for ground ice. More than 60% of regolith is occupied by ice at high latitudes. Phoenix lander has discovered pure ice by trenching at the landing site, and the volume fraction is up to 90%. Many researchers have investigated formation mechanisms of excess ice, but uncertainties still remain. In addition to acquisition of detailed Martian surface data, a range of water forms such as premelting water and brine water have drawn attention in the Martian environment with the development of premelting dynamics. Premelting water (also called unfrozen water), which is adsorbed to particle surfaces and confined to capillary regions, remains in a liquid state below the nominal melting temperature. Migration and solidification of premelting water causes various periglacial processes such as ice lens formation, frost heave, and soil movement. Although bulk water cannot exist in the recent Martian environment, premelting water can remain in a liquid state due to interaction with regolith and the existence of salt. Electrolytes in water decrease evaporation rate and broaden the stable temperature range of liquid water. Sizemore et al. (2015) investigated the initiation and growth of Martian ice lens by developing an ice lens model and a climate model. Numerical simulations suggest that ice lens initiation is a ubiquitous phenomenon in the high latitudes, but the magnitude of ice lens growth depends highly on soil properties. In particular, deliquescent salts and water vapor are important sources of water. Further development of numerical models and experiments that simulate Martian environments are required.