Rock thermal conductivity and thermal inertia measurements under martian atmospheric pressures

Abstract

The physical properties of rocks on planetary surfaces influence their bulk thermal conductivity (k) and thermal inertia (TI); however, there has been little work done to date to explore quantitative relationships between physical properties (bulk density, porosity, mechanical strength) and thermal properties (k and TI) at Mars-relevant pressures. We present the first k and TI measurements of a comprehensive suite of Mars-relevant igneous and sedimentary rocks under Mars atmospheric pressures. We used modified transient plane source (MTPS) and transient plane source (TPS) methods to measure k and TI values of 40 samples (3 monomineralic, 13 igneous, 24 sedimentary) at pressures between 1 and 10 mbar and at 1 bar, at ∼25 °C. The rock samples were characterized by bulk density, grain density, porosity, uniaxial compressive strength, mineralogy, and major and trace element abundances. We find that bulk density and porosity roughly correlate to k and TI values at Mars pressures by power law relationships. The relationships of the thermal properties with mechanical strength and chemical properties, however, are not straightforward. Many physical and chemical factors play a role in determining k and TI values; thus, it is not possible to relate a single physical or chemical property to k and TI directly based on these measurements. Rock TI values derived from rover surface temperature measurements on Mars agree with our results for similar rock types.