Thermal disturbances caused by lander shadowing and the measurability of the martian planetary heat flow

Abstract

A measurement of the martian planetary heat flow requires the determination of the subsurface temperature gradient, which is affected by surface insolation. I investigate the propagation of thermal disturbances caused by lander shadowing and derive measurement requirements for in situ heat flow experiments. I find that for short term measurements spanning 180 sol, a measurement depth of at least 2m is needed to guarantee a stable thermal environment directly underneath the lander for Moon-like thermal conductivities of 0.02Wm^-1 K^-1. For extremely large conductivities of 0.1Wm^-1 K^-1, this depth needs to be increased to 4m, but if the probe can be deployed outside the lander structure, the respective depths can be decreased by 1m. For long term measurements spanning at least a full martian year heat flow perturbations are smaller than 5% below a depth of 3m directly underneath the lander. Outside the lander structure, essentially unperturbed measurements may be conducted at depths of 0.5 and 1.5m for thermal conductivities of 0.02 and 0.1Wm^-1 K^-1, respectively.