Evidence for a liquid silicate layer atop the Martian core
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Date
2023-10-26
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Journal Article
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Abstract
Seismic recordings made during the InSight mission suggested that Mars’s liquid core would need to be approximately 27% lighter than pure liquid iron, implying a considerable complement of light elements. Core compositions based on seismic and bulk geophysical constraints, however, require larger quantities of the volatile elements hydrogen, carbon and sulfur than those that were cosmochemically available in the likely building blocks of Mars. Here we show that multiply diffracted P waves along a stratified core–mantle boundary region of Mars in combination with first-principles computations of the thermoelastic properties of liquid iron-rich alloys require the presence of a fully molten silicate layer overlying a smaller, denser liquid core. Inverting differential body wave travel time data with particular sensitivity to the core–mantle boundary region suggests a decreased core radius of 1,675 ± 30 km associated with an increased density of 6.65 ± 0.1 g cm⁻³, relative to previous models, while the thickness and density of the molten silicate layer are 150 ± 15 km and 4.05 ± 0.05 g cm⁻³, respectively. The core properties inferred here reconcile bulk geophysical and cosmochemical requirements, consistent with a core containing 85–91 wt% iron–nickel and 9–15 wt% light elements, chiefly sulfur, carbon, oxygen and hydrogen. The chemical characteristics of a molten silicate layer above the core may be revealed by products of Martian magmatism.
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published
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Volume
622 (7984)
Pages / Article No.
718 - 723
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Subject
Geochemistry; Geophysics; Inner planets; Seismology
Organisational unit
09495 - Murakami, Motohiko / Murakami, Motohiko
09784 - Sossi, Paolo Angelo / Sossi, Paolo Angelo
03476 - Giardini, Domenico / Giardini, Domenico
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Funding
ETH-06 17-2 - Exploring the shallow subsurface of Mars with seismic methods (ETHZ)