Chemical evolution of an evaporating lava pool

TL;DR

This study models the chemical evolution of lava pools and atmospheres on highly irradiated rocky exoplanets, revealing that their atmospheres reach a steady state reflecting the mantle composition, aiding future observational interpretation.

Contribution

Develops a simple chemical model of lava pool-atmosphere systems under mass loss, showing steady state evolution and implications for exoplanet atmosphere detection.

Findings

Atmospheres reach a steady state with mantle-like composition.

Dust tails likely reflect mantle material composition.

Evolved atmospheres may be undetectable due to low pressure.

Abstract

Many known rocky exoplanets are so highly irradiated that their dayside surfaces are molten, and `silicate atmospheres', composed of rock-forming elements, are generated above these lava pools. The compositions of these `lava planet' atmospheres are of great interest because they must be linked to the composition of the underlying rocky interiors. It may be possible to investigate these atmospheres, either by detecting them directly via emission spectroscopy or by observing the dust tails which trail the low mass `catastrophically evaporating planets'. In this work, we develop a simple chemical model of the lava pool--atmosphere system under mass loss, to study its evolution. Mass loss can occur both into space and from the day to the nightside. We show that the system reaches a steady state, where the material in the escaping atmosphere has the same composition as that melted into the lava pool from the mantle. We show that the catastrophically evaporating planets are likely to be in this evolved state. This means that the composition of their dust tails is likely to be a direct trace of the composition of the mantle material that is melted into the lava pool. We further show that, due to the strength of day-to-nightside atmospheric transport, this evolved state may even apply to relatively high-mass planets (>1 Earth Mass). Moreover, the low pressure of evolved atmospheres implies that non-detections may not be due to the total lack of an atmosphere. Both conclusions are important for the interpretation of future observations.