Transit Signatures of Inhomogeneous Clouds on Hot Jupiters: Insights From Microphysical Cloud Modeling

TL;DR

This study models inhomogeneous cloud cover on hot Jupiters and predicts observable signatures in transmission spectra using JWST, revealing how cloud properties and temperature influence spectral features and inhomogeneities.

Contribution

It introduces a microphysical cloud modeling approach to predict limb inhomogeneities and their spectral signatures, enhancing interpretation of exoplanet transmission spectra.

Findings

Inhomogeneous clouds cause detectable limb-to-limb spectral differences.

Short wavelength slopes vary strongly with temperature, showing Rayleigh scattering.

Cloud spectral features are detectable even without optical spectral slopes.

Abstract

We determine the observability in transmission of inhomogeneous cloud cover on the limbs of hot Jupiters through post processing a general circulation model to include cloud distributions computed using a cloud microphysics model. We find that both the east and west limb often form clouds, but that the different properties of these clouds enhances the limb to limb differences compared to the clear case. Using JWST it should be possible to detect the presence of cloud inhomogeneities by comparing the shape of the transit lightcurve at multiple wavelengths because inhomogeneous clouds impart a characteristic, wavelength dependent signature. This method is statistically robust even with limited wavelength coverage, uncertainty on limb darkening coefficients, and imprecise transit times. We predict that the short wavelength slope varies strongly with temperature. The hot limb of the hottest planets form higher altitude clouds composed of smaller particles leading to a strong rayleigh slope. The near infrared spectral features of clouds are almost always detectable, even when no spectral slope is visible in the optical. In some of our models a spectral window between 5 and 9 microns can be used to probe through the clouds and detect chemical spectral features. Our cloud particle size distributions are not log-normal and differ from species to species. Using the area or mass weighted particle size significantly alters the relative strength of the cloud spectral features compared to using the predicted size distribution. Finally, the cloud content of a given planet is sensitive to a species' desorption energy and contact angle, two parameters that could be constrained experimentally in the future.