Contributors: University of Bristol, School of Earth Sciences; Department of Geology, University of Maryland; Institute of Geophysics ETH Zürich; Department of Earth Sciences Swiss Federal Institute of Technology - ETH Zürich (D-ERDW); Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich); Institut Supérieur de l'Aéronautique et de l'Espace (ISAE-SUPAERO); Royal Observatory of Belgium = Observatoire Royal de Belgique (ROB); Institut de Physique du Globe de Paris (IPGP (UMR_7154)); Institut national des sciences de l'Univers (INSU - CNRS)-Université de La Réunion (UR)-Institut de Physique du Globe de Paris (IPG Paris)-Centre National de la Recherche Scientifique (CNRS)-Université Paris Cité (UPCité); Institut de minéralogie, de physique des matériaux et de cosmochimie (IMPMC); Muséum national d'Histoire naturelle (MNHN)-Institut de recherche pour le développement IRD : UR206-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS); Jet Propulsion Laboratory (JPL); NASA-California Institute of Technology (CALTECH); Department of Earth, Planetary and Space Sciences Los Angeles (EPSS); University of California Los Angeles (UCLA); University of California (UC)-University of California (UC); Department of Applied Mathematics and Statistics & Department of Geophysics, Colorado School of Mines; Department of Electrical and Electronic Engineering, Imperial College London, South Kensington Campus, London, United Kingdom; Swiss Seismological Service ETH Zurich (SED); Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Eidgenössische Technische Hochschule - Swiss Federal Institute of Technology Zürich (ETH Zürich)-Department of Earth Sciences Swiss Federal Institute of Technology - ETH Zürich (D-ERDW); School of Earth Sciences Bristol; University of Bristol Bristol; Department of Applied Mathematics and Statistics & Department of Geophysics, Colorado School of Mines, Golden, CO, USA; Department of Geosciences, Virginia Tech, Blacksburg, VA; DLR Institute of Planetary Research; German Aerospace Center (DLR); Department of Geology, University of Illinois Urbana-Champaign, Urbana, IL, USA; Geosciences Barcelona - CSIC, Barcelona, Spain; Department of Geology, University of Maryland, College Park, USA; S-CAPAD/DANTE; ANR-19-CE31-0008,MAGIS,MArs Geophysical InSight(2019)
نبذة مختصرة : International audience ; 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 to Mars, 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 (PP, SS). SKS travels through the core as a compressional wave, providing information about its 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 = 1780-1810 km) and denser (core density = 6.2-6.3 g/cm 3) core compared to previous estimates, with a P-wave velocity of 4.9-5.0 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 20-22 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. Mars | Core evolution | Planetary structure ous estimation of a relatively low core density has motivated 29 questions about its composition: if only sulfur is considered as 30 an alloying element, an implausibly high core sulfur fraction 31 is required to match the core density whilst satisfying con-32 straints on mass, moment of inertia, and tidal response of the 33 planet (11). Though the observation of seismic waves ...
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