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Recent observations of the super-Earth GJ 1214b show that it has a relativelyfeatureless transmission spectrum. One suggestion is that these observationsindicate that the planet's atmosphere is vertically compact, perhaps due to awater-rich composition that yields a large mean molecular weight. Anothersuggestion is that the atmosphere is hydrogen/helium-rich with clouds thatobscure predicted absorption features. Previous models that incorporate cloudshave included their effect without a strong physical motivation for theirexistence. Here, we present model atmospheres of GJ 1214b that includephysically-motivated clouds of two types. We model the clouds that form as aresult of condensation in chemical equilibrium, as they likely do on browndwarfs, which include KCl and ZnS for this planet. We also include clouds thatform as a result of photochemistry, forming a hydrocarbon haze layer. We use aphotochemical kinetics model to understand the vertical distribution andavailable mass of haze-forming molecules. We model both solar andenhanced-metallicity cloudy models and determine the cloud properties necessaryto match observations. In enhanced-metallicity atmospheres, we find that theequilibrium clouds can match the observations of GJ 1214b if they are loftedhigh into the atmosphere and have a low sedimentation efficiency (fsed=0.1). Wefind that models with a variety of hydrocarbon haze properties can match theobservations. Particle sizes from 0.01 to 0.25 micron can match thetransmission spectrum with haze-forming efficiencies as low as 1-5%.

Quantitatively Assessing the Role of Clouds in the Transmission Spectrum of GJ 1214b