Mars Soil Temperature and Thermal Properties From InSight HP3 HP³ Data

Diurnal and seasonal variations in soil and surface temperature measured with the thermal probe and radiometer of NASA's InSight Mars mission are reported. At a representative depth of 10–20 cm, an average temperature of 217.5 K was found, varying by 5.3–6.7 K during a sol and by 13.3 K during the seasons. From the damping of the temperature variation with depth and the phase shift, a thermal diffusivity of (3.93 0.39) × /s was derived for the upper 10 cm from the diurnal temperature variation and of (3.63 0.53) × /s for the 40 cm depth range of the mole from the annual temperature variation. Using published thermal conductivity and inertia values together with the diffusivities, soil densities of 1,470 and 1,730 kg/ were derived for these depths. The temperatures allow the deliquescence of thin films of brine, the efflorescence of which may explain the cemented duricrust observed.