Astrogeology

Earth And Mars Interior Structures Set By Re-melting Of The First Solid Mantle

By Keith Cowing

Press Release

May 8, 2026

Filed under astrogeology, Earth, geology, magma ocean, Mantle, Mars, tectonics

Earth And Mars Interior Structures Set By Re-melting Of The First Solid Mantle — Sensitivity of the Fe anomaly of the overturned silicate layer with respect to the rest of the mantle. (a) Sensitivity of this anomaly vs. mantle thickness. Mars and Earth sizes are represented for clarity. Note that the final anomaly is expected to be maximum when the thickness of the mantle is that of the critical Rayleigh number DRac and tends to 0 at infinite thickness. (b) Sensitivity of the Fe# anomaly vs. the bulk Fe# of the mantle. Earth and Mars compositions are represented for clarity. We extend compositions to lower bulk Fe# than Earth according to (R. J. Spaargaren et al. 2023) (dotted line, see text). All other properties remain fixed at Earth-like values except for gravity acceleration which is scaled linearly to planet size (assumed to be proportional to mantle thickness). The density anomaly secondary axis is valid for both, panel (a) and (b). — astro-ph.EP

Magma ocean crystallisation sets up the early structure and long-term evolution of terrestrial planets. Recent seismic evidence signals the presence of a silicate layer at the base of Mars’ mantle.

Magma-ocean crystallisation and subsequent overturn has been invoked as a hypothesis for this layer’s origin. However, while a magma ocean existed in both Earth and Mars, there is no seismic evidence for a basal layer in present-day Earth. In this study, we apply a parameterized-convection model to study whether the effect of partial melting in the growing mantle on overlying magma ocean composition can explain this discrepancy.

Melts from the mantle buffer the crystallising magma ocean, limiting progressive differentiation, iron enrichment and the density anomaly of the overturned layer. This buffering is more efficient for larger planets with more vigorous mantle convection and for planets that are originally less enriched in iron.

Consequently, a shallow magma ocean is more iron enriched and denser on Mars than on Earth, providing an explanation for the Mars-Earth difference in present-day structure of the mantle. We also predict a dichotomy in terrestrial-exoplanet interior structures, with a population with small, stratified mantles and another with large, mostly-homogeneous mantles.

Antonio Manjón-Cabeza Córdoba, Maxim D. Ballmer, Oliver Shorttle

Comments: Main text: 7 Pages, 3 Figures. 3 Appendixes: 5 Pages, 5 Figures. References: 2 Pages (Total 14 Pages) Submitted to Astrophysical Journal Letters
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Geophysics (physics.geo-ph)
Cite as: arXiv:2605.04840 [astro-ph.EP] (or arXiv:2605.04840v1 [astro-ph.EP] for this version)

https://doi.org/10.48550/arXiv.2605.04840
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Submission history
From: Antonio Manjon Cabeza Cordoba
[v1] Wed, 6 May 2026 12:37:07 UTC (26,734 KB)
https://arxiv.org/abs/2605.04840
Astrobiology, Astrogeology,

Keith Cowing

Biologist, Explorers Club Fellow, ex-NASA Space Biologist and Payload integrator, Editor of NASAWatch.com and Astrobiology.com, Lapsed climber, Explorer, Synaesthete, Former Challenger Center board member 🖖🏻

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