Mineral cloud formation above magma oceans in sub-Neptune atmospheres

TL;DR

This study models mineral cloud formation above magma oceans in sub-Neptune atmospheres, revealing how clouds form and influence atmospheric structure and spectral observations, with implications for understanding these exoplanets.

Contribution

It introduces a model for mineral cloud formation from refractory species outgassing at magma surfaces in sub-Neptunes, highlighting the impact of atmospheric mixing on cloud structure.

Findings

Mineral clouds form near the magma-atmosphere boundary and higher in the atmosphere.

Cloud vertical structure depends on atmospheric mixing strength.

Cloud opacity significantly affects the planet's thermal and spectral properties.

Abstract

The potential presence of a magma surface below a thick atmosphere primarily composed of hydrogen in some sub-Neptune exoplanets suggests a strong link between the interior composition and atmosphere through chemical coupling of volatile and refractory species. In this study, we aim to model the possibility for mineral cloud formation in the atmosphere of sub-Neptunes from outgassing of refractory species at the magma surface. In our specific cases, we find that mineral clouds easily form near the magma-atmosphere boundary, but also higher in the atmosphere once vapour is mixed to the cooler atmospheric regions. We find that the vertical cloud structure depends on the mixing profile of the atmosphere, with stronger mixing allowing particles to remain lofted in the atmosphere, while weak to moderate mixing produces larger, more sedimented cloud particle profiles. We suggest that due to the strong thermal feedback from cloud opacity, clouds may play an important role in the overall structure of the interior-surface-atmosphere coupled system in sub-Neptunes, as well as affect their observed spectral properties, especially at near-infrared wavelengths.