Theoretical prediction of the thermal conductivity and temperature variation inside mars soil analogues

Mars soil analogues, in dry and frozen conditions, are investigated, as far as the thermal conductivity prediction and the temperature variation, along its depth, are concerned. The thermal conductivity is theoretically predicted with the cubic cell model, which requires the knowledge of the thermal conductivity of the solid particle and of the materials present, i.e. atmospheric gas and/or frozen ice, and the porosity of the soil analogue. The soil mineral composition allows to evaluate the thermal conductivity of the solid particle. The heat capacity of the soil analogue is evaluated with the knowledge of its physical properties, the porosity and the specific heats of the materials present. The thermal diffusivity is calculated as the ratio of the thermal conductivity and heat capacity and results to be a function of the porosity and the ice mass content of the soil analogue. The temperature variations, in dry and partially frozen soil analogues, are predicted during a Martian day. The temperature variation, at different depth, is attenuated, as compared to the surface variation and a phase delay is present, depending on the soil thermal properties. The temperature variation, as well as the derivative of the temperature variation with the depth, is dependent on the thermal diffusivity of the soil analogue. In conclusion, the temperature measurement, along the depth of a Martian soil analogue, can be used to verify its physical status, i.e. dry or partially frozen.