Three distinct models for the recently discovered super-Earth (masses 2–10 times that of Earth) planet GJ 1214b that are consistent with its mass and radius have been suggested. Breaking the degeneracy between these models requires obtaining constraints on the planet's atmospheric composition. Here, a ground based measurement of the transmission spectrum of GJ 1214b between 780 and 1,000 nm is reported. The lack of features in this spectrum rules out cloud free atmospheres composed primarily of hydrogen. If the planet's atmosphere is hydrogen-dominated, then it must contain clouds or hazes that are optically thick at pressures <200 mbar. Alternatively, the data are also consistent with the presence of a dense water vapour atmosphere.
- Jacob L. Bean
- Eliza Miller-Ricci Kempton
- Derek Homeier
