Chemistry of Silicate Atmospheres of Evaporating Super-Earths

TL;DR

This paper models the composition of silicate atmospheres on volatile-free super-Earths, predicting dominant gases and potential observable Na and K clouds that could be detected around such planets.

Contribution

It provides the first detailed modeling of silicate atmospheres on hot super-Earths, including effects of vaporization, cloud formation, and observational implications.

Findings

Atmospheres mainly consist of Na, O2, O, and SiO gases.

Cloud condensation reduces atmospheric element abundances except Na and K.

Large Na and K clouds could be observable around hot super-Earths.

Abstract

We model the formation of silicate atmospheres on hot volatile-free super-Earths. Our calculations assume that all volatile elements such as H, C, N, S, and Cl have been lost from the planet. We find that the atmospheres are composed primarily of Na, O2, O, and SiO gas, in order of decreasing abundance. The atmospheric composition may be altered by fractional vaporization, cloud condensation, photoionization, and reaction with any residual volatile elements remaining in the atmosphere. Cloud condensation reduces the abundance of all elements in the atmosphere except Na and K. We speculate that large Na and K clouds such as those observed around Mercury and Io may surround hot super-Earths. These clouds would occult much larger fractions of the parent star than a closely bound atmosphere, and may be observable through currently available methods.