Evidence for a liquid silicate layer atop the Martian core.

Area of Science:

• Planetary Science
• Seismology
• Geophysics

Background:

• InSight mission seismic data indicated Mars's core is ~27% lighter than pure iron.
• Seismic and geophysical models suggest more volatile elements (H, C, S) than cosmochemically available.
• Discrepancy between core composition models and planetary formation constraints.

Purpose of the Study:

• To investigate Mars's core composition and structure using seismic data.
• To reconcile discrepancies between seismic, geophysical, and cosmochemical models of Mars's interior.
• To determine the properties of the core-mantle boundary and overlying layers.

Main Methods:

• Analysis of multiply diffracted P waves from InSight seismic recordings.
• First-principles computations of thermoelastic properties of liquid iron alloys.
• Inversion of differential body wave travel time data sensitive to the core-mantle boundary.

Main Results:

• Evidence for a stratified core-mantle boundary with a molten silicate layer.
• Decreased core radius (1,675 ± 30 km) and increased core density (6.65 ± 0.1 g/cm³).
• Molten silicate layer thickness (150 ± 15 km) and density (4.05 ± 0.05 g/cm³).
• Core composition: 85-91 wt% iron-nickel, 9-15 wt% light elements (S, C, O, H).

Conclusions:

• The inferred core properties resolve discrepancies between geophysical and cosmochemical requirements.
• A molten silicate layer above a smaller, denser core is consistent with seismic data.
• Martian magmatism products may reveal the chemical characteristics of this silicate layer.