First observations of core-Transiting seismic phases on Mars

We present the first observations of seismic waves propagating through the core of Mars. These observations, made using seismic data collected by the InSight geophysical mission, have allowed us to construct the first seismically constrained models for the elastic properties of Mars core. We observe core-Transiting seismic phase SKS from two farside seismic events detected on Mars and measure the travel times of SKS relative to mantle traversing body waves. SKS travels through the core as a compressional wave, providing information about bulk modulus and density. We perform probabilistic inversions using the core-sensitive relative travel times together with gross geophysical data and travel times from other, more proximal, seismic events to seek the equation of state parameters that best describe the liquid iron-Alloy core. Our inversions provide constraints on the velocities in Mars core and are used to develop the first seismically based estimates of its composition. We show that models informed by our SKS data favor a somewhat smaller (median core radius = 1,780 to 1,810 km) and denser (core density = 6.2 to 6.3 g/cm3) core compared to previous estimates, with a P-wave velocity of 4.9 to 5.0 km/s at the core mantle boundary, with the composition and structure of the mantle as a dominant source of uncertainty. We infer from our models that Mars core contains a median of 20 to 22 wt% light alloying elements when we consider sulfur, oxygen, carbon, and hydrogen. These data can be used to inform models of planetary accretion, composition, and evolution.W.B.B., K.J.H, and M.P.P. were supported by the NASA InSight mission and funds from the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the NASA (80NM0018D0004). V.L. and N.C.S. were supported by funding from NASA grant 80NSSC18K1628 and NASA SSERVI Cooperative Agreement 80NSSC19M0216. C.D., A.K., D.G., S.C., J.C., D.K., and S.C.S. acknowledge support from ETH through the ETH+ funding scheme (ETH+02 19-1: “Planet Mars”). The Marsquake Service (MQS) operations at ETH are supported by ETH Research grant ETH-06 17-02. M.D., H.S., D.A., R.G., T.K., P.L., E.S., and Z.X. acknowledge the support of CNES for SEIS operation and science analysis, with an additional support of ANR (MAGIS, ANR-19-CE31-0008-08). H.S., T.K., P.L. E.S., and Z.X. additionally acknowledge the support from the IdEx Université Paris Cité (ANR-18-IDEX-0001). M.D. and H.S. were granted access to the HPC resources of CINES under the allocation A0110413017, made by the GENCI. Numerical computations were partly performed on the S-CAPAD/DANTE platform, IPGP, France. D.A. has received funding from the European Research Council under the European Union’s Horizon 2020 research and innovation program (grant agreement 724690); D.A. also acknowledges the support by CNES, focused on the SEIS instrument of the InSight mission. A.R. was financially supported by the Belgian PRODEX program managed by the European Space Agency in collaboration with the Belgian Federal Science Policy Office. E.B. and Q.H. were funded by NASA InSight PSP grant #80NSSC18K1680. C.B. and J.L. were funded by NAS