Observability of Evaporating Lava Worlds

TL;DR

This paper models the atmospheres of lava worlds to identify spectral features detectable by JWST, focusing on silicate signatures like SiO and SiO2 to understand their composition and thermal structure.

Contribution

It provides the first comprehensive models of silicate atmospheres for lava worlds, predicting observable spectral features with JWST and exploring atmospheric evolution and melt compositions.

Findings

SiO and SiO2 features are detectable with JWST's MIRI instrument.

Detection of these features constrains atmospheric thermal structure and melt composition.

Certain species like TiO may indicate different melt classes and surface dynamics.

Abstract

Lava worlds belong to a class of short orbital period planets reaching dayside temperatures high enough to melt their silicate crust. Theory predicts that the resulting lava oceans outgas their volatile components, attaining equilibrium with the overlying vapour. This creates a tenuous, silicate-rich atmosphere that may be confined to the permanent dayside of the planet. The launch of JWST will provide the much needed sensitivity and spectral coverage to characterise these worlds. In this paper, we assess the observability of characterisable spectral features by self-consistently modelling silicate atmospheres for all the currently confirmed targets having sufficient substellar temperatures (> 1500 K). To achieve this we use outgassed equilibrium chemistry and radiative transfer methods to compute temperature-pressure profiles, atmospheric chemical compositions and emission spectra. We explore varying melt compositions, free of highly-volatile elements, accounting for possible atmospheric evolution. Our models include a large number of neutral and ionic species, as well as all up-to-date opacities. The results indicate that SiO and SiO2 infrared features are the best, unique identifiers of silicate atmospheres, detectable using MIRI instrument of JWST. Detection of these two species in emission would allow for strong constraints on atmospheric thermal structure and possibly the composition of the melt. We also propose that certain species, e.g., TiO, may be directly tied to different classes of melts, possibly revealing surface and interior dynamics. Currently, there are nearly a dozen confirmed lava planets ideal for characterisation of silicate atmospheres using JWST, with two of these already accepted for the initial General Observers program.