Hidden water in magma ocean exoplanets

TL;DR

This paper introduces an advanced interior model for water-rich exoplanets with magma oceans, showing that volatile redistribution significantly affects radius estimates and can lead to underestimating planetary water content.

Contribution

It presents a novel model incorporating rock melting and water partitioning, revealing their impact on exoplanet radius and composition inference.

Findings

Water partitioning causes up to 16% radius deviation.

Neglecting mantle melting underestimates water content by up to tenfold.

Model is within current observational accuracy limits.

Abstract

We demonstrate that the deep volatile storage capacity of magma oceans has significant implications for the bulk composition, interior and climate state inferred from exoplanet mass and radius data. Experimental petrology provides the fundamental properties on the ability of water and melt to mix. So far, these data have been largely neglected for exoplanet mass-radius modeling. Here, we present an advanced interior model for water-rich rocky exoplanets. The new model allows us to test the effects of rock melting and the redistribution of water between magma ocean and atmosphere on calculated planet radii. Models with and without rock melting and water partitioning lead to deviations in planet radius of up to 16% for a fixed bulk composition and planet mass. This is within current accuracy limits for individual systems and statistically testable on a population level. Unrecognized mantle melting and volatile redistribution in retrievals may thus underestimate the inferred planetary bulk water content by up to one order of magnitude.