Program: GN-2013A-C-1

A planet�s atmospheric composition holds important clues to its origin and interior, but only a handful of small extrasolar planets are amenable to atmospheric characterization. The recently discovered �warm Uranus� GJ 3470b provides the best opportunity yet to study the atmospheric composition and structure of cool, low-mass externally irradiated planets. We request two nights of UH88/OPTIC time to precisely measure the planetary radius in a broadband filter and and one night on Gemini/GMOS time to perform optical transmission spectroscopy. With these data we will test atmospheric models that predict the opaque hazes seen on hot Jupiters will be absent in cooler planets. These observations will provide an important benchmark for future studies of cool, low-mass planetary atmospheres and the first optical spectrum of an extrasolar ice giant.