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

Abstract

At last year’s AGU, the first author presented his and his co-authors' work as narrated by an animated cartoon representation of himself. Since rocks in the crust of a planet can flow on long timescales with enough heat or pressure, empty pore spaces and fractures in rock can close deep into the crust. The thickness of the porous upper layer of the Martian crust is dependent on the history of temperature at depth. The InSight Mars lander has discovered a transition in crustal properties at about 10 km under the surface. If this transition is due to pore closure, then the last significant pore formation events, likely large impacts, would have occurred at least 4 Gyr ago, which is consistent with the end of large impacts on Mars. Following that presentation, newer work has shown that the change in seismic wave speeds deeper than 10 km depth is not consistent with full pore closure, but instead simply a transition from an upper porous crust to a deeper less-porous crust at 10 km depth. This can be explained by an aquifer at depth, but we investigate if it is possible to close pores at depth and then re-open them. We preliminarily find that even small 0.3 km radius projectiles at 15 km/s can fracture rock below some previous 10 km pore closure depth.