Search for rayleigh scattering in the atmosphere of GJ1214b

E.J.W. De Mooij, M. Brogi, R.J. De Kok, I.A.G. Snellen, B. Croll, R. Jayawardhana, H. Hoekstra, G.P.P.L. Otten, D.H. Bekkers, S.Y. Haffert, J.J. Van Houdt

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We investigate the atmosphere of GJ1214b, a transiting super-Earth planet with a low mean density, by measuring its transit depth as a function of wavelength in the blue optical portion of the spectrum. It is thought that this planet is either a mini-Neptune, consisting of a rocky core with a thick, hydrogen-rich atmosphere, or a planet with a composition dominated by water. Most observations favor a water-dominated atmosphere with a small scale-height, however, some observations indicate that GJ1214b could have an extended atmosphere with a cloud layer muting the molecular features. In an atmosphere with a large scale-height, Rayleigh scattering at blue wavelengths is likely to cause a measurable increase in the apparent size of the planet toward the blue. We observed the transit of GJ1214b in the B band with the FOcal Reducing Spectrograph at the Very Large Telescope and in the g band with both ACAM on the William Herschel Telescope (WHT) and the Wide Field Camera at the Isaac Newton Telescope (INT). We find a planet-to-star radius ratio in the B band of 0.1162 ± 0.0017, and in the g band 0.1180 ± 0.0009 and 0.1174 ± 0.0017 for the WHT and INT observations, respectively. These optical data do not show significant deviations from previous measurements at longer wavelengths. In fact, a flat transmission spectrum across all wavelengths best describes the combined observations. When atmospheric models are considered, a small scale-height water-dominated model fits the data best.

Original languageEnglish
Article number109
JournalThe Astrophysical Journal
Issue number2
Publication statusPublished - 10 Jul 2013
Externally publishedYes


  • planetary systems
  • stars: individual (GJ1214)
  • techniques: photometric


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