A Cloudy Fit to the Atmosphere of WASP-107 b

TL;DR

This study models the atmosphere of WASP-107 b using JWST data, demonstrating that silicate clouds can form in its upper atmosphere due to turbulence, and providing insights into its composition and cloud formation processes.

Contribution

It presents a self-consistent cloud and temperature profile fitting approach that explains silicate cloud features without relying on parametrized temperature profiles.

Findings

Silicate cloud feature at 10 um explained without parametrized temperature profile.

Moderate vertical diffusivity (Kzz = 10^9 cm^2 s^-1) uplifts cloud particles to upper atmosphere.

Model suggests a metallicity 17 times solar for WASP-107 b.

Abstract

Context. WASP-107 b has been observed comprehensively by JWST in the near- and mid-IR bands, making it an ideal planet to probe the composition and internal dynamics. Recent analysis reveals a 8-10 um silicate feature, but it still remains uncertain how silicate clouds form on this planet. Aims. We aim at fitting the complete JWST spectrum of WASP-107 b, from 0.9 um to 12 um with a physically motivated cloud model and self-consistent temperature profile. Methods. Two-stream radiative transfer is coupled to a cloud formation model until convergence between cloud and temperature profiles is reached. We search a model grid spanning metallicity, turbulent diffusivity, internal heat flux and nucleation parameters to find the best fit model. Results. The silicate cloud feature at 10 um and the near-IR molecular band strength can be simultaneously and naturally explained without assuming a parametrized temperature profile. A moderate vertical diffusivity of Kzz = 10^9 cm^2 s^-1 is needed to bring the cloud particles to the upper atmosphere of WASP-107 b. This Kzz is favored by the joint fitting of the near-IR water feature and mid-IR silicate feature -- both sensitive to clouds. From the strength of H2O and CO2 bands, our model suggests a metallicity 17 times solar. Conclusions. Even in warm planets such as WASP-107 b, silicate clouds can form in the relatively cool upper atmosphere because turbulence uplifts vapor and cloud particles. Despite having considerably fewer degrees of freedom, the self-consistent modeling approach successfully fits WASP-107 b's multi-wavelength data, instilling confidence in the derived physical parameters.