Modelling dynamically driven global cloud formation microphysics in the HAT-P-1b atmosphere

TL;DR

This paper introduces 'mini-cloud', an efficient microphysical cloud model for exoplanet atmospheres, coupled with a GCM to simulate 3D cloud structures, tested on HAT-P-1b, with promising implications for JWST observations.

Contribution

We developed and coupled an open-source microphysical cloud model to a GCM for 3D exoplanet cloud simulations, enabling detailed atmospheric analysis.

Findings

Complex 3D cloud structures were simulated.

Spectra suggest reduced cloud particle density fits observations.

Model shows promising JWST observation prospects.

Abstract

Insight into the formation and global distribution of cloud particles in exoplanet atmospheres continues to be a key problem to tackle going into the JWST era. Understanding microphysical cloud processes and atmospheric feedback mechanisms in 3D has proven to be a challenging prospect for exoplaneteers. In an effort to address the large computational burden of coupling these models in 3D simulations, we develop an open source, lightweight and efficient microphysical cloud model for exoplanet atmospheres. `Mini-cloud' is a microphysical based cloud model for exoplanet condensate clouds that can be coupled to contemporary general circulation models (GCMs) and other time dependent simulations. We couple mini-cloud to the Exo-FMS GCM and use a prime JWST target, the hot Jupiter HAT-P-1b, as a test case for the cloud formation module. After 1000+ of days of integration with mini-cloud, our results show a complex 3D cloud structure with cloud properties relating closely the dynamical and temperature properties of the atmosphere. Current transit and emission spectra data are best fit with a reduced cloud particle number density compared to the nominal simulation, with our simulated JWST NIRISS SOSS spectra showing promising prospects for characterising the atmosphere in detail. Overall, our study is another small step in first principles 3D exoplanet cloud formation microphysical modelling. We suggest that additional physics not included in the present model, such as coagulation, are required to reduce the number density of particles to appropriately observed levels.