Martian Gullies: An Ecological Niche?

Heat transfer calculations support the following proposed explanation of the formation of martian gullies: (1) Sheltered geometry and high-latitude, pole-facing locations, cause gullies to accumulate a disproportionate amount of CO2 frost in winter, which persists into the spring. (2) In spring, sunlight drives water into warmer air, the CO2 frost sublimates, and water ice condenses on the cold surfaces, exchanging latent heat of condensation of H2O for latent heat of sublimation of CO2. (3) When the CO2 is gone, sunlight warms the ice to melting, wetting the surface soil under a crust of ice. (4) Liquid water and solid CO2 cause seasonal erosion of the gullies, which initially form in natural alcoves and depressions. Regular resurfacing explains the absence of old, degraded gullies. The astonishing implication of this simple model is that wet soil may have been present seasonally in these select locations for billions of years, dating from the time that Mars is argued to have been warm and wet. Moreover, microbial systems could easily enhance this environment through control of geometry, albedo, conductivity, and evaporation.