Program: GN-2011B-C-1

The carbon-to-oxygen ratio (C/O) in the atmosphere of the transiting Hot Jupiter Wasp-12b has recently been determined to be greater than unity from a study of the planet's dayside thermal emission. This is a surprising result because the solar C/O is significantly less than unity, and the naive expectation was that extrasolar gaseous planets would also have a similar abundance pattern. We propose to measure the transmission spectrum of Wasp-12b in the red optical to reveal the strength of expected water absorption features. We will observe two transits of the planet with Gemini-N/GMOS using a recently proved technique for obtaining space-telescope quality exoplanet transit spectroscopy from the ground. Our objective is to constrain Wasp-12b's C/O using the strength of the water features in transmission as an independent diagnostic of the planet's atmospheric composition. Furthermore, the combination of the proposed transmission spectrum measurements with the existing measurements of the dayside thermal emission will constrain the planet's overall metallicity.