Bridging the Gap: Using Brown Dwarfs to Examine Silicate Clouds in Giant Exoplanet Atmospheres

TL;DR

This study uses JWST observations and brown dwarf theory to analyze silicate clouds in hot Jupiter atmospheres, linking planetary formation chemistry with atmospheric composition and comparing exoplanet spectra to brown dwarfs.

Contribution

It introduces a novel approach of applying brown dwarf atmospheric models to interpret silicate cloud signatures in hot Jupiter atmospheres, supported by empirical stellar chemistry data.

Findings

Silicate cloud species align with host star Mg/Si ratios.

Atmospheric scenarios may deviate from stellar chemistry predictions.

Transit spectra show molecular absorption trends consistent with brown dwarf spectra.

Abstract

We present results from examining the silicate cloud modeling of four JWST-observed hot Jupiters in the context of brown dwarf theory to further explore signatures of formation in present-day atmospheres. We contextualize our understanding of protoplanetary disk refractory chemistry with empirical evidence from chondritic meteorites to show that giant planets forming and accreting in the outer disk adopt their stellar Mg/Si value. We show that current silicate cloud species determinations of WASP-17 b, WASP-107 b, WASP-39 b and HD 189733 b are in line with predictions laid out in Calamari et al. 2024 based on each system's host star Mg/Si ratio, further supporting this hypothesis. We discuss physical motivations for potential atmospheric scenarios where apparent silicate cloud species is not in agreement with that predicted by its host star chemistry. Additionally, we compare current transit spectroscopy for three of these four exoplanets against brown dwarf spectra to examine molecular absorption trends across the substellar mass temperature regime.