Near Surface Properties of Martian Regolith Derived From InSight HP3-RAD Temperature Observations During Phobos Transits

We use the Martian surface temperature response to Phobos transits observed next to the InSight lander in Elysium Planitia to constrain the thermal properties of the uppermost layer of regolith. Modeled transit lightcurves validated by solar panel current measurements are used to modify the boundary conditions of a 1D heat conduction model. We test several model parameter sets, varying the thickness and thermal conductivity of the top layer to explore the range of parameters that match the observed temperature response within its uncertainty both during the eclipse as well as the full diurnal cycle. The measurements indicate a thermal inertia (TI) of 103-16+22Jm-2K-1s-1/2 in the uppermost layer of 0.2-4 mm, significantly smaller than the TI of 200Jm-2K-1s-1/2 derived from the diurnal temperature curve. This could be explained by larger particles, higher density, or some or slightly higher amount of cementation in the lower layers.

Automated summary

The study utilized Martian surface temperature response to Phobos transits to constrain the thermal properties of the uppermost layer of regolith. By modeling and varying parameters, a thermal inertia of 103-16+22Jm-2K-1s-1/2 in the top layer of 0.2-4 mm was derived, indicating smaller thermal properties compared to the diurnal temperature curve.