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June 21, 2013: Thermophysical Modeling and Measurements of Martian-Like Particulated Materials: Effect of Temperature and Cementing Phases

Posted on Jun 12, 2013 in Seminars

Sylvain Piqueux (JPL)

Remote temperature measurements have increased our understanding of the physical properties of the Martian surface layer. Typical grain sizes, rock abundances, subsurface layering, soil cementation, bedrock exposures, and ice presence/compositions have been derived and mapped using temperature data in conjunction with subsurface models of heat conduction, and have helped to constrain numerous global-scale processes. However, the simplicity of these models precludes more significant advances in the characterization of the physical nature of the Martian surface. For this seminar, I will present a new model of heat conduction for planetary soils derived from a combination of finite element modeling and laboratory measurements for homogeneous particulated media accounting for the grain size, porosity, gas pressure and composition, temperature, and the effect of any cementing phase. I will show that incorporating the temperature dependence of bulk conductivity alters the predicted diurnal and seasonal temperatures as compared to temperatures predicted with a temperature-independent conductivity model. Inconsistencies between observed temperatures and those predicted using temperature-independent conductivity models have been interpreted to result from subsurface heterogeneities, but they may partially be explained by a temperature-dependency of the thermal inertia, with additional implications on the derived grain sizes. Cements are shown to significantly increase the bulk conductivity of a particulated medium, and bond fractions <5% per volume are consistent with Martian thermal inertia observations previously hypothesized to correspond to a global duricrust. I will conclude with general thoughts on the predicted thermophysical properties of particulated materials on other planetary bodies with atmospheres.