Constraints on Thermal History of Mars from Depth of Pore Closure Below InSight

Planetary crusts undergo viscous closure of pores at depth; if the thickness of this porous layer can be measured, constraints on crustal thermal evolution can be derived. We apply a pore closure model developed for the Moon to Mars and take into account the geological processes that may alter the depth of this transition region. If the 8-11 km deep discontinuity in seismic wave speed detected by the InSight lander marks the base of the porous layer, the heat flux at the time the porosity was created must have exceed 60 mW m(-2), probably indicating a time prior to 4 Ga. Plain Language Summary On long timescales, and with enough heat or pressure, rocks in the crust of a planet can flow. This viscous deformation allows the empty pore spaces in a rock to close up. The history of the temperature at depth plays an important role in how deep one may expect porosity to exist. One can use a computational model to calculate the thickness of this porous layer as a function of the crust's thermal history. If the InSight Mars lander detects the thickness of such a porous layer, we can estimate the necessary temperature structure of the Martian crust and when porosity in the crust was generated. From a potential measurement of this porous layer at around 10 km thick, we predict the last significant pore formation event to have occurred at least 4 Gyr before present.