Seasonal Variations of Soil Thermal Conductivity at the InSight Landing Site

The heat flow and physical properties package measured soil thermal conductivity at the landing site in the 0.03-0.37 m depth range. Six measurements spanning solar longitudes from 8.0 degrees to 210.0 degrees were made and atmospheric pressure at the site was simultaneously measured using InSight's Pressure Sensor. We find that soil thermal conductivity strongly correlates with atmospheric pressure. This trend is compatible with predictions of the pressure dependence of thermal conductivity for unconsolidated soils under martian atmospheric conditions, indicating that heat transport through the pore filling gas is a major contributor to the total heat transport. Therefore, any cementation or induration of the soil sampled by the experiments must be minimal and soil surrounding the mole at depths below the duricrust is likely unconsolidated. Thermal conductivity data presented here are the first direct evidence that the atmosphere interacts with the top most meter of material on Mars.