Incompatibility of iron in post-perovskite and the stability of basal magma oceans in super-Earths
Abstract
Post-perovskite is expected to dominate much of the solid mantles of rocky exoplanets, yet iron partitioning between post-perovskite and silicate melt, which controls the compositional evolution and buoyancy of crystallizing magma oceans, is unconstrained at these pressures. We use first-principles molecular dynamics and thermodynamic integration to compute the Fe--Mg distribution coefficient KD between post-perovskite and (Mg,Fe)SiO3 liquid at 150--600~GPa and 6000--10000~K. Iron is strongly incompatible in post-perovskite and becomes increasingly so with pressure. Combining KD with equations of state, we find that iron enrichment of residual liquid reverses the solid--liquid density contrast, causing post-perovskite to become buoyant. Basal magma oceans are therefore gravitationally stable in super-Earth exoplanets up to 4 M⊕.
Related
- Water-rich sub-Neptunes and rocky super-Earths around different stars: Radii shaped by volatile partitioning, formation, and evolution
- “Mega-Earths” are Likely an Artifact of Stellar Activity
- "Mega-Earths" are likely an artifact of stellar activity
- Incorporation of atmospheric components in planetary magma oceans through bubble–metal compounds
- The Limits of Tidal Circularization and Atmospheric Escape for Mini-Neptunes and Super-Earths: The Case of TOI-2257 b
BibTeX
@misc{dragulet2026incompatibility,
title = {{Incompatibility of iron in post-perovskite and the stability of basal magma oceans in super-Earths}},
author = {Francis Dragulet and Lars Stixrude},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.13527},
eprint = {2609.13527},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.13527},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Incompatibility of iron in post-perovskite and the stability of basal magma oceans in super-Earths
AU - Francis Dragulet
AU - Lars Stixrude
PY - 2026
DA - 2026/09/11
PB - arXiv
DO - 10.48550/arxiv.2609.13527
UR - https://arxiv.org/abs/2609.13527
AB - Post-perovskite is expected to dominate much of the solid mantles of rocky exoplanets, yet iron partitioning between post-perovskite and silicate melt, which controls the compositional evolution and buoyancy of crystallizing magma oceans, is unconstrained at these pressures. We use first-principles molecular dynamics and thermodynamic integration to compute the Fe--Mg distribution coefficient K_D between post-perovskite and (Mg,Fe)SiO_3 liquid at 150--600~GPa and 6000--10000~K. Iron is strongly incompatible in post-perovskite and becomes increasingly so with pressure. Combining K_D with equations of state, we find that iron enrichment of residual liquid reverses the solid--liquid density contrast, causing post-perovskite to become buoyant. Basal magma oceans are therefore gravitationally stable in super-Earth exoplanets up to 4 M_⊕.
ER -