Near surface properties derived from Phobos transits with HP RAD³ on
InSight, Mars
Abstract
We use the surface temperature response to Phobos transits as observed
by a radiometer on board of the InSight lander 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 of
103+48-24
Jm-2K-1s-1/2 in
the uppermost layer of 0.2 to 4 mm, significantly smaller than the
thermal inertia of 200
Jm-2K-1s-1/2
derived from the diurnal temperature curve. This could be explained by
larger particles, higher density, or a very small amount of cementation
in the lower layers.