Redox hysteresis of super-Earth exoplanets from magma ocean circulation

TL;DR

This paper explores how magma ocean circulation influences redox reactions in super-Earth exoplanets, affecting core formation, atmospheric composition, and planetary evolution through turbulent diffusion and convective processes.

Contribution

It introduces a scaling analysis showing turbulent diffusion in magma oceans can entrain iron droplets, impacting core formation and redox state in super-Earths.

Findings

Turbulent diffusion can kinetically entrain liquid iron droplets.

Redox control is linked to planetary heat flow and size.

Magneto-chemical memory of accretion history may be retained.

Abstract

Internal redox reactions may irreversibly alter the mantle composition and volatile inventory of terrestrial and super-Earth exoplanets and affect the prospects for atmospheric observations. The global efficacy of these mechanisms, however, hinges on the transfer of reduced iron from the molten silicate mantle to the metal core. Scaling analysis indicates that turbulent diffusion in the internal magma oceans of sub-Neptunes can kinetically entrain liquid iron droplets and quench core formation. This suggests that the chemical equilibration between core, mantle, and atmosphere may be energetically limited by convective overturn in the magma flow. Hence, molten super-Earths possibly retain a compositional memory of their accretion path. Redox control by magma ocean circulation is positively correlated with planetary heat flow, internal gravity, and planet size. The presence and speciation of remanent atmospheres, surface mineralogy, and core mass fraction of atmosphere-stripped exoplanets may thus constrain magma ocean dynamics.