Analog experiments on thermal creep gas flow through Martian soil

Abstract

At the low atmospheric pressure on Mars, thermal creep within its soil is unavoidable. Soil is a complex mixture of particles and pores and it is not clear a priori how to quantify such subsoil thermal creep gas flow. A capillary model of flow through granular beds was set up recently based on laboratory experiments. Here, we extend the earlier experiment to probe different parameter ranges of the model. For a different granular bed we directly traced the resulting gas flow in a pressure regime of 2–300 Pa. We specifically analyze the dependence of thermal creep on different gas species - we used He, CO2, N2 and air. These data agree well to the model calculations. This latest evidence strongly supports the simple but analytical model of granular thermal creep. Including CO2 in the measurements the model now allows quantitative calculations of gas circulation and pressure distribution within Martian soil as a network of Knudsen pumps.