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A. Zent (NASA Ames Research Center)
The martian high-latitude, volatile-rich mantle deposit, at least locally, contains more ice than can be accounted for in undisturbed pore volume. Excess ice cannot be cold-trapped from the atmosphere; hypotheses for how excess ice might occur include burying surface ice, or post-depositional in situ processing that causes the formation segregated ice. The terrestrial record indicates that segregated ground ice occurs in a limited number of ways: outright melting and flow, or temperature-dependent suction that develops in a porous freezing soil. Implicit in the post-depositional formation of segregated ice is significant H2O mobility, and consequently, the periodic presence of substantial unfrozen water in the mantle deposit. It is possible that the mantle represents the remnants of a dusty snowbank, or frozen body of surface water. Post-depositional processing would be limited to vapor-phase dessication of the upper tens of centimeters. The correspondence between vapor-phase transport models and the observed GRS distribution of ice suggests that vapor phase transport has operated to redistribute H2O in the deposit. Wedge ice would satisfy the GRS observations, but requires relatively saturated conditions to form in the same manner terrestrial wedges form. In unsaturated soils, water responds to potentials resulting from osmotic and interfacial (matric) forces. Only in near-saturated soils are gravitational potentials strong enough to drive flow. Cryosuction is a response to negative pressure potential in wet soils, and is the dominant redistribution mechanism in unsaturated soil. Cryosuction requires unfrozen water, and effective hydraulic conductivity that allows water to be transported to the freezing front. Numerical estimates of the times, locations, and quantities of unfrozen water in the near-surface regolith will be presented. These quantitative estimates will be essential for assessing future hypotheses of mantle development, geochemical weathering, and climate history and regolith habitability.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.