Geophysical evidence for an enriched molten silicate layer above Mars’s core

Henri Samuel (), Mélanie Drilleau, Attilio Rivoldini, Zongbo Xu, Quancheng Huang, Raphaël F. Garcia, Vedran Lekić, Jessica C. E. Irving, James Badro, Philippe H. Lognonné, James A. D. Connolly, Taichi Kawamura, Tamara Gudkova and William B. Banerdt
Additional contact information
Henri Samuel: Université Paris Cité, Institut de physique du globe de Paris, CNRS
Mélanie Drilleau: Institut Supérieur de l’Aéronautique et de l’Espace ISAE-SUPAERO
Attilio Rivoldini: Royal Observatory of Belgium
Zongbo Xu: Université Paris Cité, Institut de physique du globe de Paris, CNRS
Quancheng Huang: Colorado School of Mines
Raphaël F. Garcia: Institut Supérieur de l’Aéronautique et de l’Espace ISAE-SUPAERO
Vedran Lekić: University of Maryland
Jessica C. E. Irving: University of Bristol
James Badro: Université Paris Cité, Institut de physique du globe de Paris, CNRS
Philippe H. Lognonné: Université Paris Cité, Institut de physique du globe de Paris, CNRS
James A. D. Connolly: ETH Zurich
Taichi Kawamura: Université Paris Cité, Institut de physique du globe de Paris, CNRS
Tamara Gudkova: Schmidt Institute of Physics of the Earth, Russian Academy of Sciences
William B. Banerdt: California Institute of Technology

Nature, 2023, vol. 622, issue 7984, 712-717

Abstract: Abstract The detection of deep reflected S waves on Mars inferred a core size of 1,830 ± 40 km (ref. 1), requiring light-element contents that are incompatible with experimental petrological constraints. This estimate assumes a compositionally homogeneous Martian mantle, at odds with recent measurements of anomalously slow propagating P waves diffracted along the core–mantle boundary2. An alternative hypothesis is that Mars’s mantle is heterogeneous as a consequence of an early magma ocean that solidified to form a basal layer enriched in iron and heat-producing elements. Such enrichment results in the formation of a molten silicate layer above the core, overlain by a partially molten layer3. Here we show that this structure is compatible with all geophysical data, notably (1) deep reflected and diffracted mantle seismic phases, (2) weak shear attenuation at seismic frequency and (3) Mars’s dissipative nature at Phobos tides. The core size in this scenario is 1,650 ± 20 km, implying a density of 6.5 g cm−3, 5–8% larger than previous seismic estimates, and can be explained by fewer, and less abundant, alloying light elements than previously required, in amounts compatible with experimental and cosmochemical constraints. Finally, the layered mantle structure requires external sources to generate the magnetic signatures recorded in Mars’s crust.

Date: 2023
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DOI: 10.1038/s41586-023-06601-8

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