HR: 0830h
AN: P11B-1031    [PDF]
TI: Basal Melting of Snow on Early Mars: Possible Origin of Valley Networks.
AU: * Carr, M H
EM: carr@usgs.gov
AF: U.S. Geological Survey, 345 Middlefield Rd., Menlo Park, CA 94025 United States
AB: Simulations suggest that early Mars could not have been warmed enough by a CO2-H20 greenhouse to permit rainfall. The vulnerability of an early atmosphere to impact erosion, the likely rapid scavenging of CO2 from the atmosphere by weathering if warm conditions did occur, and the lack of detection of weathering products from orbit all support the supposition of a cold early Mars. Yet valley networks appear to be cut by liquid water. One possibility is that the valley networks formed as a result of basal melting of thick snow and ice deposits that formed at low latitudes during periods of high obliquity, when ice would have sublimated from the polar regions. Basal melting on early Mars is facilitated by the high heat flows expected at that time. The depths to melting of a snow pack on early Mars were estimated by scaling pressure-density relations for terrestrial dry snow packs to Mars, using empirically derived thermal conductivities for different density ices, and taking estimates of the heat flow from various modeling studies. The results suggest that a snow pack a few to several hundred meters thick would undergo basal melting on early Mars, depending on the heat flow. Such basal melting could provide runoff to cut the valley networks directly or to recharge the groundwater system and so enable groundwater sapping. That basal melting did occur is supported by the emergence of large channels from under the Dorsa Argentea Formation near the south pole.
DE: 6225 Mars
SC: Planetary Sciences [P]
MN: 2003 Fall Meeting