One of the long-standing questions of the martian climate involves the history of water. Current martian surface conditions allow water to be stable only in a frozen state at the polar surface or as subsurface ground ice within the regolith at mid and high latitudes. Water in the equatorial regions of Mars would rapidly freeze, then sublimate (evaporate) into the dry atmosphere. Research is being carried out by Michael Mellon to investigate the behavior of ground ice and the relationship between subsurface ice, subsurface water, and small-scale geologic features.
Of particular interest are features now being observed in high resolution Mars Global Surveyor images, namely small polygonal networks and young, apparently water-carved, gullies. Polygonal networks of fractures that are ubiquitous in terrestrial ice-rich permafrost and are now observed on Mars in relative abundance. Fractures form in ice rich soils when seasonal cooling causes contraction. The presence of these features on Mars indicates the presence of subsurface ice, which previously has been only theoretically predicted to be there.
Images: Gullies on Mars. These small scale features are thought to be carved by liquid water based on morphological evidence and Earth analogs. Yet they occur in regions on Mars where the ground temperatures are continuously well below freezing. Researchers at LASP are investigating the origin of these features.
Small geologically young gullies have also been discovered, that indicate surface water erosion in regions of Mars where surface water is unstable, and should rapidly freeze. These features raise questions about where liquid water could originate in the current martian climate. In collaboration with Roger Phillips (visiting from the Washington University), Michael Mellon has developed a possible solution to this paradox. Shallow aquifers may exist as a result of global average geothermal heating and thermal insulation from unusually dry loose surface soil.
Additional research includes the study of analogous geologic features in the Antarctic Dry Valleys these valleys are among the coldest and driest places on Earth and are therefore similar in condition to the martian climate. The study of these terrestrial geologic features, may help us to better understand the processes that possibly form similar structures on Mars. A combination of field work in the Antarctic Dry Valleys, laboratory analysis of permafrost samples, and theoretical study of ice stability and polygon formation are being employed.
