QUANTITATIVELY ASSESSING THE ROLE OF CLOUDS IN THE TRANSMISSION SPECTRUM OF GJ 1214b

Abstract

Recent observations of the super-Earth GJ 1214b show that it has a relatively\nfeatureless transmission spectrum. One suggestion is that these observations\nindicate that the planet's atmosphere is vertically compact, perhaps due to a\nwater-rich composition that yields a large mean molecular weight. Another\nsuggestion is that the atmosphere is hydrogen/helium-rich with clouds that\nobscure predicted absorption features. Previous models that incorporate clouds\nhave included their effect without a strong physical motivation for their\nexistence. Here, we present model atmospheres of GJ 1214b that include\nphysically-motivated clouds of two types. We model the clouds that form as a\nresult of condensation in chemical equilibrium, as they likely do on brown\ndwarfs, which include KCl and ZnS for this planet. We also include clouds that\nform as a result of photochemistry, forming a hydrocarbon haze layer. We use a\nphotochemical kinetics model to understand the vertical distribution and\navailable mass of haze-forming molecules. We model both solar and\nenhanced-metallicity cloudy models and determine the cloud properties necessary\nto match observations. In enhanced-metallicity atmospheres, we find that the\nequilibrium clouds can match the observations of GJ 1214b if they are lofted\nhigh into the atmosphere and have a low sedimentation efficiency (fsed=0.1). We\nfind that models with a variety of hydrocarbon haze properties can match the\nobservations. Particle sizes from 0.01 to 0.25 micron can match the\ntransmission spectrum with haze-forming efficiencies as low as 1-5%.\n