Thickness and structure of the Martian crust from InSight seismic data

Abstract

A planet's crust bears witness to the history of planetary formation and evolution, but for Mars, no absolute measurement of crustal thickness has been available. Here, we determine the structure of the crust beneath the InSight landing site on Mars using both marsquake recordings and the ambient wavefield. By analyzing seismic phases that are reflected and converted at subsurface interfaces, we find that the observations are consistent with models with at least two and possibly three interfaces. If the second interface is the boundary of the crust, the thickness is 20 +/- 5 kilometers, whereas if the third interface is the boundary, the thickness is 39 +/- 8 kilometers. Global maps of gravity and topography allow extrapolation of this point measurement to the whole planet, showing that the average thickness of the martian crust lies between 24 and 72 kilometers. Independent bulk composition and geodynamic constraints show that the thicker model is consistent with the abundances of crustal heat-producing elements observed for the shallow surface, whereas the thinner model requires greater concentration at depth.M.P.P., S.T., E.B., S.E.S., and W.B.B. were supported by the NASA InSight mission and funds from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. F.B. was supported by research grant ETH-05 17-1. A.K., D.G., M.v.D., and S.S. acknowledge funding by the Swiss National Science Foundation and the Swiss State Secretariat for Education, Research and Innovation, and support from ETHZ through the ETH+ funding scheme (ETH+02 19-1). V.L. and D.K. acknowledge funding from a Packard Foundation Fellowship to V.L. B.T. is supported by the European Union’s Horizon 2020 research and innovation program under Marie Sklodowska-Curie grant agreement 793824. French co-authors acknowledge the support of CNES and ANR (MAGIS, ANR-19-CE31-0008-08). N.S. was supported by NASA grant 80NSSC18K1628. E.B. was funded through NASA Participating Scientist Program grant 80NSSC18K1680. A.-C.P. gratefully acknowledges the financial support and endorsement from the DLR Management Board Young Research Group Leader Program and the Executive Board Member for Space Research and Technology. Geodynamical models used in this work were performed on the supercomputer ForHLR funded by the Ministry of Science, Research and the Arts Baden-Württemberg and by the Federal Ministry of Education and Research. S.M.M. was funded through NASA InSight Participating Scientist Program award no. 80NSSC18K1622. C.M. acknowledges the support of the Institut Universitaire de France (IUF). C.L.J. and A.M. acknowledge support from the InSight Mission, the Canadian Space Agency, and ETH Zurich (ETH fellowship 19-2 FEL-34). N.B. is supported by research grant ETH-06 17-02. The work of A.R. was financially supported by the Belgian PRODEX program managed by the European Space Agency in collaboration with the Belgian Federal Science Policy Offic