Atmosphere-interior exchange on hot rocky exoplanets

TL;DR

This paper models the atmosphere-interior exchange processes on hot rocky exoplanets, showing how surface composition and atmospheric pressure are influenced by temperature, planet properties, and initial composition, with implications for their variability.

Contribution

It introduces a basic model linking surface-interior exchange to planetary parameters, highlighting the effects of FeO content and temperature on magma pool composition and variability.

Findings

Atmosphere-interior exchange is faster with low FeO content.

Magma pools are well-mixed below 2400 K, variable above.

Surface compositions can be time-variable on magma planets.

Abstract

We provide estimates of atmospheric pressure and surface composition on short-period rocky exoplanets with dayside magma pools and silicate vapor atmospheres. Atmospheric pressure tends toward vapor-pressure equilibrium with surface magma, and magma-surface composition is set by the competing effects of fractional vaporization and surface-interior exchange. We use basic models to show how surface-interior exchange is controlled by the planet's temperature, mass, and initial composition. We assume that mantle rock undergoes bulk melting to form the magma pool, and that winds flow radially away from the substellar point. With these assumptions, we find that: (1) atmosphere-interior exchange is fast when the planet's bulk-silicate FeO concentration is low, and slow when FeO concentration is high; (2) magma pools are compositionally well-mixed for substellar temperatures $\lesssim$ 2400 K, but compositionally variegated and rapidly variable for substellar temperatures $\gtrsim$ 2400 K; (3) currents within the magma pool tend to cool the top of the solid mantle ("tectonic refrigeration"); (4) contrary to earlier work, many magma planets have time-variable surface compositions.