Thermal non-equilibrium nucleation in exoplanet atmospheres

Recent observations bear evidence of clouds in exoplanet atmospheres. Large cloud opacities, especially in the visible wavelength range, impact the observed spectra by obscuring many atomic and molecular lines. Therefore, understanding cloud formation in exoplanet atmospheres is crucial to accurately model the observations. Cloud particles form when gas phase molecules condense onto cloud condensation nuclei (CCNs). In gaseous exoplanet atmospheres, homogeneous nucleation is an important pathway to form nano-sized CCNs. Here, we investigate the impact of thermal non-equilibrium on cluster nucleation using a kinetic nucleation model for non-uniform cluster temperatures. We use the model to study the nucleation of titania (TiO2) and discuss the impact of thermal non-equilibrium on the resulting number densities of TiO2-clusters.