A cloudy fit to the atmosphere of WASP-107 b

Context. WASP-107 b has been observed comprehensively by JWST in the near- and mid-IR bands, meaning we can probe its composition and internal dynamics. Recent analyses reveal a 8 − 10 μm silicate feature, but it remains uncertain how silicate clouds form on this planet. Aims. We aim to fit the complete JWST spectrum of WASP-107 b, from 0.9 μm to 12 μm with a physically motivated cloud model and self-consistent temperature profile. Methods. We coupled two-stream radiative transfer to a cloud formation model until convergence between cloud and temperature profiles was reached. We searched a model grid that included metallicity, turbulent diffusivity, internal heat flux, and nucleation parameters to find the best-fit model. Results. The silicate cloud feature at 10 μm 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 = 109 cm2 s−1 is needed to bring the cloud particles into 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 of which are sensitive to clouds. Based on the strength of the H2O and CO2 bands, our model suggests a metallicity of 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 multiwavelength data, instilling confidence in the derived physical parameters.