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arXiv · 1111.5621

The Flat Transmission Spectrum of the Super-Earth GJ1214b from Wide Field Camera 3 on the Hubble Space Telescope

Zachory K. Berta·David Charbonneau·Jean-Michel Désert·Eliza Miller-Ricci Kempton·Peter R. McCullough·Christopher J. Burke·Jonathan J. Fortney·Jonathan Irwin·Philip Nutzman·Derek Homeier
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Abstract

Capitalizing on the observational advantage offered by its tiny M dwarf host, we present HST/WFC3 grism measurements of the transmission spectrum of the super-Earth exoplanet GJ1214b. These are the first published WFC3 observations of a transiting exoplanet atmosphere. After correcting for a ramp-like instrumental systematic, we achieve nearly photon-limited precision in these observations, finding the transmission spectrum of GJ1214b to be flat between 1.1 and 1.7 microns. Inconsistent with a cloud-free solar composition atmosphere at 8.2 sigma, the measured achromatic transit depth most likely implies a large mean molecular weight for GJ1214b's outer envelope. A dense atmosphere rules out bulk compositions for GJ1214b that explain its large radius by the presence of a very low density gas layer surrounding the planet. High-altitude clouds can alternatively explain the flat transmission spectrum, but they would need to be optically thick up to 10 mbar or consist of particles with a range of sizes approaching 1 micron in diameter.

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Zachory K. Berta, David Charbonneau, Jean-Michel Désert, Eliza Miller-Ricci Kempton, Peter R. McCullough, Christopher J. Burke, Jonathan J. Fortney, Jonathan Irwin, Philip Nutzman, Derek Homeier. 2011-11-23. The Flat Transmission Spectrum of the Super-Earth GJ1214b from Wide Field Camera 3 on the Hubble Space Telescope. https://doi.org/10.1088/0004-637x/747/1/35

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