Convective shutdown in the atmospheres of lava worlds

TL;DR

This study develops a 1D radiative-convective model to explore the stability of atmospheres over magma oceans on lava worlds, revealing conditions under which permanent magma oceans can exist without convection and how atmospheric composition affects observability.

Contribution

It introduces a coupled interior-atmosphere model to assess convective stability and magma ocean longevity on exoplanets, challenging previous assumptions that convection is necessary for atmospheric cooling.

Findings

HD 63433 d can sustain a magma ocean with a stable, deep isothermal atmosphere.

TRAPPIST-1 c likely solidified within 100 million years, with thick outgassed atmospheres.

Spectral features of CO2 and SO2 can indicate mantle redox state and magma ocean properties.

Abstract

Atmospheric energy transport is central to the cooling of primordial magma oceans. Theoretical studies of atmospheres on lava planets have assumed that convection is the only process involved in setting the atmospheric temperature structure. This significantly influences the ability for a magma ocean to cool. It has been suggested that convective stability in these atmospheres could preclude permanent magma oceans. We develop a new 1D radiative-convective model in order to investigate when the atmospheres overlying magma oceans are convectively stable. Using a coupled interior-atmosphere framework, we simulate the early evolution of two terrestrial-mass exoplanets: TRAPPIST-1 c and HD 63433 d. Our simulations suggest that the atmosphere of HD 63433 d exhibits deep isothermal layers which are convectively stable. However, it is able to maintain a permanent magma ocean and an atmosphere depleted in H2O. It is possible to maintain permanent magma oceans underneath atmospheres without convection. Absorption features of CO2 and SO2 within synthetic emission spectra are associated with mantle redox state, meaning that future observations of HD 63433 d may provide constraints on the geochemical properties of a magma ocean analogous with the early Earth. Simulations of TRAPPIST-1 c indicate that it is expected to have solidified within 100 Myr, outgassing a thick atmosphere in the process. Cool isothermal stratospheres generated by low molecular-weight atmospheres can mimic the emission of an atmosphere-less body. Future work should consider how atmospheric escape and chemistry modulates the lifetime of magma oceans, and the role of tidal heating in sustaining atmospheric convection