Nightside clouds and disequilibrium chemistry on the hot Jupiter WASP-43b

TL;DR

This study uses JWST observations to reveal that the hot Jupiter WASP-43b has nightside clouds and disequilibrium chemistry, with significant temperature contrast and molecular composition variations across its orbit.

Contribution

First phase-resolved mid-infrared spectrum of WASP-43b showing evidence for nightside clouds and disequilibrium chemistry, advancing understanding of exoplanet atmospheric dynamics.

Findings

Large day-night temperature contrast (~1524K vs. 863K)

Presence of nightside clouds affecting thermal emission

Non-detection of methane on the nightside supports disequilibrium chemistry

Abstract

Hot Jupiters are among the best-studied exoplanets, but it is still poorly understood how their chemical composition and cloud properties vary with longitude. Theoretical models predict that clouds may condense on the nightside and that molecular abundances can be driven out of equilibrium by zonal winds. Here we report a phase-resolved emission spectrum of the hot Jupiter WASP-43b measured from 5-12 $\mu$m with JWST's Mid-Infrared Instrument (MIRI). The spectra reveal a large day-night temperature contrast (with average brightness temperatures of 1524$\pm$35 and 863$\pm$23 Kelvin, respectively) and evidence for water absorption at all orbital phases. Comparisons with three-dimensional atmospheric models show that both the phase curve shape and emission spectra strongly suggest the presence of nightside clouds which become optically thick to thermal emission at pressures greater than ~100 mbar. The dayside is consistent with a cloudless atmosphere above the mid-infrared photosphere. Contrary to expectations from equilibrium chemistry but consistent with disequilibrium kinetics models, methane is not detected on the nightside (2$\sigma$ upper limit of 1-6 parts per million, depending on model assumptions).