Mars Soil Temperature and Thermal Properties from InSight HP3 Data

Diurnal and seasonal soil (and surface) temperature variations are reported, measured with the NASA InSight Mars mission’s HP3 thermal probe (and radiometer). 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. The damping of the surface temperature variation in the soil and the phase shift were used to derive a thermal diffusivity of 3.92 ± 0.39 × 10−8 m2/s for the top ∼10 cm from the diurnal variation and 3.63 ± 0.53 × 10−8 m2/s for the depth range of the mole of ∼40 cm from the annual temperature variation. The temperatures are conducive to the deliquescence of thin films of brine, which may explain the observed cemented duricrust. The thermal diffusivity suggests that published estimates of the depth to the cryosphere may need downward revision by around 5 %.