The role of soils and soil heterogeneities in the dynamics and stability of Martian ground ice

The dynamical state and equilibrium location of shallow ground ice on Mars have relevance to a variety of science questions, as well as future human and robotic exploration. I investigate the role of soils in the dynamical transport of ground ice and the role of soil heterogeneities in the equilibrium depth of the ice table.;First, assuming ice to be in equilibrium with atmospheric water vapor, I develop a multi-dimensional model of ground-ice stability and use it to place quantitative constraints on the response of the ice table to meter-scale rocks, dust lenses, and albedo variations in the current climate. I find that rocks create localized areas of deep ice, producing depressions of a few to 60 cm over a horizontal range of 1-2 rock radii. Patches of dust produce locally shallow ice; however, the magnitude of this effect is small (1-4 cm). I employ these results to investigate the role played by heterogeneities in orbital estimates of ice table depth. I find that surface rocks can account for more than half of the discrepancy between ice table depths inferred from leakage neutron flux and those predicted by ice-stability simulations that utilize thermophysical observations.;Turning to considerations of ground-ice dynamics, I present laboratory measurements of the structural properties most relevant to gas transport in five groups of Mars-analog soils. These measurements indicate that diffusive loss of ground ice on Mars can likely proceed up to four times faster than predicted by theoretical studies and that the pore volume in some Mars-analog soils is sufficiently large to explain high volumetric ice abundances inferred from Mars Odyssey Gamma Ray Spectrometer data as simple pore ice.;The upcoming Mars Scout Mission Phoenix may provide links between the dynamical and equilibrium views of ground-ice. I combine simulations of ground-ice stability with statistical estimates of the abundance of rocks at the Phoenix landing site to predict the degree of ice table depth variability that may be observed at the landing site if the assumption of current diffusive equilibrium is appropriate. I also discuss in situ tests for determining the dynamical state of ground ice.