Samuel, H. ; Drilleau, M. ; Rivoldini, A. ; Xu, Z. ; Huang, Q. ; Garcia, R. F. ; Lekić, V. ; Irving, J. C. E. ; Badro, J. ; Lognonné, P. H. ; Connolly, J. A. D. ; Kawamura, T. ; Gudkova, T. ; Banerdt, W. B.

Poster presented at AGU 2013 San Fransisco on 2023-12-12

Abstract: The identification of deep reflected S-waves on Mars has led to the first seismic estimation of a core size of 1830±40 km [1]. However, this relatively large core size requires light element contents incompatible with experimental petrological constraints. In addition, this core size estimate assumes a compositionally homogeneous Martian mantle, at odds with measurements of anomalously slow propagating P-waves diffracted along the core-mantle boundary [2]. Alternatively, Mars' mantle may be heterogeneous as a result of a magma ocean solidification that formed a basal layer enriched in iron and heat-producing elements [3], resulting in the the presence of a molten silicate layer above the core, overlain by a partially molten layer [4]. To determine the planet structures compatible with observations, we performed a probabilistic inversion of seismic data. Our inversion relies on a parameterisation in terms of quantities that influence the thermo-chemical evolution of the planet composed of a liquid iron core, a silicate mantle (with or without a enriched Basal Mantle Layer), and an evolving lithosphere and crust [5]. We show that such a layered Martian mantle is compatible with all geophysical data including (1) deep reflected and diffracted seismic phases from the mantle, (2) weak shear attenuation at seismic frequencies, and (3) Mars' dissipative behaviour at Phobos tides. In particular, our results point to a revised core size of 1650±20 km implying a density of 6.5 g/cm3, 5-8% larger than previous seismic estimates. Using a core equation of state that reproduces experimental data, we show that Mars' core can be explained by fewer, and less abundant, alloying light elements than previously required, in amounts compatible with experimental and cosmochemical constraints. The new density structure is compatible with measurements of Mars' rotation [6]. The layered mantle structure requires external sources to generate the magnetic signatures recorded in Mars' crust. [1] Stähler, S. et al., Science 373 (2021) [2] Posiolova L. et al. Science, 378 (2022) [3] Elkins-Tanton, L. et al., JGR., doi: 10.1029/2005JE002480 (2003) [4] Samuel, H. et al., JGR, doi:10.1029/2020JE006613 (2021) [5] Drilleau, M. et al., JGR, doi:10.1029/2021JE007067 (2022) [6] Le Maistre et al., Nature, doi:10.1038/s41586-023-06150-0 (2023)

Note: DI23B-0034
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Funding: 3PRODPLANINT/3PRODPLANINT/3PRODPLANINT