10:45 AM - 11:00 AM
[PPS07-24] Modeling Dust Cloud Structure in Super-Earth GJ1214b: Implications for the Atmospheric Metallicity
Keywords:super-Earth, Dust Clouds, Atmospheric Metallicity
In this study, we aim to understand the relationship between the atmospheric metallicity and the vertical extent of dust clouds. Recently, we have developed a new cloud model that takes into account the vertical transport of condensate particles and particle growth via both condensation and coalescence (Ohno & Okuzumi 2017). With our cloud model, we examine the vertical distributions of dust clouds in GJ1214b as a function of atmospheric metallicity.
We find that the cloud top reaches beyond 10-3 bar for atmospheric metallicities of ≥ 10× solar abundance, but does not reach the height of 10-5 bar for all choices of the model parameters. From timescale arguments, we find that the dust cloud structure can be classified into three regimes: Condensation–Diffusion regime, Coagulation– Diffusion regime, and Coalescence–Sedimentation regime. The maximum height of the cloud top occurs at the transition of the Coagulation–Diffusion and Coalescence–Diffusion regimes. Comparison between the maximum height of the cloud top predicted from our model and the height indicated from the observations of GJ1214b rules out atmospheric metallicities of 1–100× solar abundance for this particular exoplanets. Consequently, our results suggest that the atmosphere of GJ1214b is depleted in hydrogen as suggested by previous independent modeling, or the cloud in GJ1214b is composed of haze particles produced by photochemical reactions at high altitude.