Determine the dominant nucleation pathway in gas-giant exoplanet atmospheres

Determine whether cloud nucleation in gas-giant exoplanet atmospheres occurs through bottom-up nucleation, in which cloud-forming material is diffusively replenished from the planetary interior, or through top-down nucleation, in which cloud-forming materials are supplied from higher atmospheric layers.

Background

The paper identifies a fundamental unresolved issue in exoplanet cloud modelling: whether cloud particles form predominantly through bottom-up or top-down nucleation. Bottom-up models such as CARMA and Nimbus replenish cloud-forming material by diffusion from the planetary interior, whereas top-down models such as DRIFT parameterize the supply of cloud-forming material through a relaxation timescale and produce cloud condensation nuclei at high altitudes.

The authors note that observations of WASP-107 b and PSO J318 show evidence for high-altitude nucleation and propose that ablation of interplanetary dust particles may provide a source of high-altitude cloud condensation nuclei. However, the relative dominance and physical mechanism of the competing nucleation pathways remain unresolved.