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A ground-based transmission spectrum of the super-Earth exoplanet GJ 1214b


In contrast to planets with masses similar to that of Jupiter and higher, the bulk compositions of planets in the so-called super-Earth regime (masses 2–10 times that of the Earth) cannot be uniquely determined from a measurement of mass and radius alone. For these planets, there is a degeneracy between the mass and composition of both the interior and a possible atmosphere in theoretical models1,2. The recently discovered transiting super-Earth exoplanet GJ 1214b is one example of this problem3. Three distinct models for the planet that are consistent with its mass and radius have been suggested4. Breaking the degeneracy between these models requires obtaining constraints on the planet's atmospheric composition5,6. Here we report a ground-based measurement of the transmission spectrum of GJ 1214b between wavelengths of 780 and 1,000 nm. The lack of features in this spectrum rules out (at 4.9σ confidence) 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 the observed wavelengths at pressures less than 200 mbar. Alternatively, the featureless transmission spectrum is also consistent with the presence of a dense, water vapour atmosphere.

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Figure 1: Spectrophotometric data for transits of GJ 1214b.
Figure 2: The transmission spectrum of GJ 1214b compared to models.


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We thank D. Charbonneau, J.-M. Desert, J. Fortney, S. Seager, L. Rogers and D. Sasselov for discussions about this work. J.L.B. received funding from the European Commissions Seventh Framework Program as a Marie Curie International Incoming Fellow. J.L.B. and E.M.-R.K. acknowledge funding from NASA through the Sagan Fellowship Program. The results presented are based on observations made with ESO telescopes at the Paranal Observatories under programs 284.C-5042 and 285.C-5019.

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Authors and Affiliations



J.L.B. performed the observations and data analysis, and led the overall direction of the project. E.M.-R.K. calculated theoretical models for the planetary atmosphere. D.H. calculated the stellar limb darkening. J.L.B. and E.M.-R.K. wrote the telescope time proposals and the paper. All authors discussed the results and commented on the manuscript.

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Correspondence to Jacob L. Bean.

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The authors declare no competing financial interests.

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The data utilized in this work can be accessed at the ESO/ST-ECF science archive (

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Supplementary Information

This file contains Supplementary Methods comprising Observations, Data reductions and spectral extraction and Photometric corrections, Supplementary Figures 1-2 with legends and an additional reference. (PDF 383 kb)

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Bean, J., Kempton, ER. & Homeier, D. A ground-based transmission spectrum of the super-Earth exoplanet GJ 1214b. Nature 468, 669–672 (2010).

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