About ten per cent of the known extrasolar planets are gas giants that orbit very close to their parent stars. The atmospheres of these ‘hot Jupiters’ are heated by the immense stellar irradiation1,2,3,4,5. In the case of the planet HD 209458b, this energy deposition results in a hydrodynamic state in the upper atmosphere, allowing for sizeable expansion and escape of neutral hydrogen gas2,3,4,5,6. HD 209458b was the first extrasolar planet discovered that transits in front of its parent star7. The size of the planet can be measured using the total optical obscuration of the stellar disk during an observed transit, and the structure and composition of the planetary atmosphere can be studied using additional planetary absorption signatures in the stellar spectrum. Here we report the detection of absorption by hot hydrogen in the atmosphere of HD 209458b. Previously, the lower atmosphere and the full extended upper atmosphere of HD 209458b have been observed2,6,8, whereas here we probe a layer where the escaping gas forms in the upper atmosphere of HD 209458b.
This is a preview of subscription content, access via your institution
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Tax calculation will be finalised during checkout.
Get time limited or full article access on ReadCube.
All prices are NET prices.
Burrows, A. & Lunine, J. Extra-solar planets — astronomical questions of origin and survival. Nature 378, 333 (1995)
Vidal-Madjar, A. et al. An extended upper atmosphere around the extrasolar planet HD209458b. Nature 442, 143–146 (2003)
Lecavelier des Etangs, A., Vidal-Madjar, A., McConnell, J. C. & Hébrard, G. Atmospheric escape from hot Jupiters. Astron. Astrophys. 418, L1–L4 (2004)
Yelle, R. Aeronomy of extra-solar giant planets at small orbital distances. Icarus 170, 167–179 (2004)
Yelle, R. Corrigendum to “Aeronomy of extra-solar giant planets at small orbital distances [Icarus 170 (2004) 167-179].”. Icarus 183, 508 (2006)
Vidal-Madjar, A. et al. Detection of oxygen and carbon in the upper atmosphere of the extrasolar planet HD 209458b. Astrophys. J. 604, L69–L72 (2004)
Henry, G. W., Marcy, G. W., Butler, R. P. & Vogt, S. S. A transiting “51-Peg-like” planet. Astrophys. J. 529, L41–L44 (2000)
Charbonneau, D., Brown, T. M., Noyes, R. W. & Gilliland, R. L. Detection of an extrasolar planet atmosphere. Astrophys. J. 568, 377–384 (2002)
Brown, T. M., Charbonneau, D., Gilliland, R. L., Noyes, R. W. & Burrows, A. Hubble Space Telescope time-series photometry of the transiting planet of HD209458. Astrophys. J. 552, 699–709 (2001)
Knutson, H., Charbonneau, D., Noyes, R. W., Brown, T. M. & Gilliland, R. L. Using stellar limb-darkening to refine the properties of HD 209458b. Astrophys. J. 655, 564–575 (2007)
Kurucz, R. HD209458 stellar model and associated spectra. 〈http://kurucz.harvard.edu/stars/HD209458/〉 (2005)
Mandel, K. & Agol, E. Analytic light curves for planetary transit searches. Astrophys. J. 580, L171–L175 (2002)
Carroll, B. W. & Ostlie, D. A. An Introduction to Modern Astrophysics Ch. 8 (Addison-Wesley, San Francisco, 1996)
Mihalas, D. Stellar Atmospheres 2nd edn, 99 (W.H. Freeman & Company, New York, 1978)
Deming, D., Seager, S., Richardson, L. J. & Harrington, J. Infrared radiation from an extrasolar planet. Nature 434, 740–743 (2005)
Claret, A. A new non-linear limb-darkening law for LTE stellar atmosphere models. Astron. Astrophys. 363, 1081–1190 (2000)
We thank J. Holberg for discussions, as well as R. Yelle for the atmospheric model of HD 209458b. Support for this work was provided by NASA through a grant from the Space Telescope Science Institute which is operated by AURA, under NASA contract.
Author Contributions The work required for this paper was equally shared between D.K.S. and G.E.B. F.H. suggested the Balmer jump spectral identification, and joined discussions.
Reprints and permissions information is available at www.nature.com/reprints. The authors declare no competing financial interests.
This file contains Supplementary Methods with details about data reduction, derivation of the photometric light curves, correction to systematic instrumental effects, corrections to the transit spectra accounting for the stellar limb-darkening; calculation of the Balmer jump absorption from hot (n=2) hydrogen based on a published model of HD209458b's upper atmosphere, Supplementary Figures 1-3 with Legends. (PDF 262 kb)
About this article
Cite this article
Ballester, G., Sing, D. & Herbert, F. The signature of hot hydrogen in the atmosphere of the extrasolar planet HD 209458b. Nature 445, 511–514 (2007). https://doi.org/10.1038/nature05525
This article is cited by
Nature Astronomy (2018)
Space Science Reviews (2016)
Experimental Astronomy (2015)
Astrophysics and Space Science (2011)