Evidence against an edge-on disk around the extrasolar planet, 2MASS1207b and a new thick-cloud explanation for its underluminosity

Since the discovery of the first directly imaged, planetary-mass object, 2MASS1207b, several works have sought to explain a disparity between its observed temperature and luminosity. Given its known age, distance, and spectral type, 2MASS1207b is underluminous by a factor of ∼10 (∼2.5mag) when compared to standard models of brown-dwarf/giant-planet evolution. In this paper, we study three possible sources of 2MASS1207b's underluminosity. First, we investigate Mohanty et al.'s hypothesis that a near edge-on disk, comprising large, gray-extincting grains, might be responsible for 2MASS1207b's underluminosity. After radiative transfer modeling, we conclude that the hypothesis is unlikely due to the lack of variability seen in multi-epoch photometry and unnecessary due to the increasing sample of underluminous brown dwarfs/giant exoplanets that cannot be explained by an edge-on disk. Next, we test the analogous possibility that a spherical shell of dust could explain 2MASS1207b's underluminosity. Models containing enough dust to create ∼2.5 mag of extinction, placed at reasonable radii, are ruled out by our new Gemini/T-ReCS 8.7 μm photometric upper limit for 2MASS1207b. Finally, we investigate the possibility that 2MASS1207b is intrinsically cooler than the commonly used AMES-DUSTY fits to its spectrum, and thus it is not, in fact, underluminous. New, thick-cloud model grids by Madhusudhan et al. fit 2MASS1207b's 1-10 μm spectral energy distribution well, but they do not quite fit its near-infrared spectrum. However, we suggest that with some "tuning," they might be capable of simultaneously reproducing 2MASS1207b's spectral shape and luminosity. In this case, the whole class of young, underluminous brown dwarfs/giant exoplanets might be explained by atmospheres that are able to suspend thick, dusty clouds in their photospheres at temperatures lower than field brown dwarfs.