Skip to main content

Thank you for visiting nature.com. You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

The presence of methane in the atmosphere of an extrasolar planet

Abstract

Molecules present in the atmospheres of extrasolar planets are expected to influence strongly the balance of atmospheric radiation, to trace dynamical and chemical processes, and to indicate the presence of disequilibrium effects. As molecules have the potential to reveal atmospheric conditions and chemistry, searching for them is a high priority. The rotational–vibrational transition bands of water, carbon monoxide and methane are anticipated to be the primary sources of non-continuum opacity in hot-Jupiter planets1,2,3. As these bands can overlap in wavelength, and the corresponding signatures from them are weak, decisive identification requires precision infrared spectroscopy. Here we report a near-infrared transmission spectrum of the planet HD 189733b that shows the presence of methane. Additionally, a resolved water vapour band at 1.9 μm confirms the recent claim4 of water in this object. On thermochemical grounds, carbon monoxide is expected to be abundant in the upper atmosphere of hot-Jupiter planets, but is not identifiable here; therefore the detection of methane rather than carbon monoxide in such a hot planet5,6 could signal the presence of a horizontal chemical gradient away from the permanent dayside, or it may imply an ill-understood photochemical mechanism that leads to an enhancement of methane.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Calibrated measurements showing the primary eclipse event.
Figure 2: A comparison of observations with simulated water and methane absorption.

References

  1. 1

    Seager, S. & Sasselov, D. D. Theoretical transmission spectra during extrasolar giant planet transits. Astrophys. J. 537, L916–L921 (2000)

    ADS  Article  Google Scholar 

  2. 2

    Burrows, A. A theoretical look at the direct detection of giant planets outside the Solar System. Nature 433, 261–268 (2005)

    CAS  ADS  Article  Google Scholar 

  3. 3

    Fortney, J. J., Cooper, C. S., Showman, A. P., Marley, M. S. & Freedman, R. S. The influence of atmospheric dynamics on the infrared spectra and light curves of hot Jupiters. Astrophys. J. 652, 746–757 (2006)

    CAS  ADS  Article  Google Scholar 

  4. 4

    Tinetti, G. et al. Water vapour in the atmosphere of a transiting extrasolar planet. Nature 448, 169–171 (2007)

    CAS  ADS  Article  Google Scholar 

  5. 5

    Knutson, H. A. et al. A map of the day–night contrast of the extrasolar planet HD 189733b. Nature 447, 183–186 (2007)

    CAS  ADS  Article  Google Scholar 

  6. 6

    Cooper, C. S. & Showman, P. Dynamics and disequilibrium carbon chemistry in hot Jupiter atmospheres with application to HD 209458b. Astrophys. J. 649, 1048–1063 (2006)

    CAS  ADS  Article  Google Scholar 

  7. 7

    Richardson, L. J., Deming, D., Horning, K., Seager, S. & Harrington, J. A spectrum of an extrasolar planet. Nature 445, 892–895 (2007)

    CAS  ADS  Article  Google Scholar 

  8. 8

    Grillmair, C. J. et al. A Spitzer spectrum of the extrasolar planet HD 189733b. Astrophys. J. 658, L115–L118 (2007)

    ADS  Article  Google Scholar 

  9. 9

    Swain, M. R., Bouwman, J., Akeson, R. L., Lawler, S. & Beichman, C. A. The mid-infrared spectrum of the transiting exoplanet HD 209458b. Astrophys. J. 674, 482–498 (2008)

    ADS  Article  Google Scholar 

  10. 10

    Fortney, J. J. & Marley, M. S. Analysis of Spitzer spectra of irradiated planets: Evidence for water vapor? Astrophys. J. 666, L45–L48 (2007)

    CAS  ADS  Article  Google Scholar 

  11. 11

    Hubbard, W. B. et al. Theory of extrasolar giant planet transits. Astrophys. J. 560, 413–419 (2001)

    ADS  Article  Google Scholar 

  12. 12

    Gilliland, R. L. & Arribas, S. High signal-to-noise differential NICMOS spectrophotometry. Instrum. Sci. Rep. NICMOS 2003-001, 1–14 (2003)

    Google Scholar 

  13. 13

    Tinetti, G. et al. Infrared transmission spectra for extrasolar giant planets. Astrophys. J. 654, L99–L102 (2007)

    CAS  ADS  Article  Google Scholar 

  14. 14

    Pont, F. et al. Hubble Space Telescope time-series photometry of the planetary transit of HD189733: No moon, no rings, starspots. Astron. Astrophys. 476, 1347–1355 (2007)

    ADS  Article  Google Scholar 

  15. 15

    Claret, A. A new non-linear limb-darkening law for LTE stellar atmosphere models. Calculations for -5.0 ≤ log[M/H] ≤ +1, 2000≤Teff≤50000 K at several surface gravities. Astron. Astrophys. 363, 1081–1190 (2000)

    CAS  ADS  Google Scholar 

  16. 16

    Winn, J. N. et al. The transit light curve project V. System parameters and stellar rotation period of HD 189733. Astron. J. 133, 1828–1835 (2007)

    ADS  Article  Google Scholar 

  17. 17

    Hauschildt, P. H., Allard, F. & Baron, E. The NextGen model atmosphere grid for 3000 <Teff <10,000 K. Astrophys. J. 512, 377–385 (1999)

    CAS  ADS  Article  Google Scholar 

  18. 18

    Borysow, A., Jorgensen, U. G. & Fu, Y. High temperature (1000–7000K) collision induced absorption of H2 pairs computed from first principles, with application to cool and dense stellar atmospheres. J. Quant. Spectrosc. Radiat. Transf. 68, 231–255 (2001)

    ADS  Article  Google Scholar 

  19. 19

    Barber, R. J., Tennyson, J., Harris, G. J. & Tolchenov, R. A high accuracy computed water line list. Mon. Not. R. Astron. Soc. 368, 1087–1094 (2006)

    CAS  ADS  Article  Google Scholar 

  20. 20

    Rothman, L. S. et al. The HITRAN 2004 molecular spectroscopic database. J. Quant. Spectrosc. Radiat. Transf. 96, 139–204 (2005)

    CAS  ADS  Article  Google Scholar 

  21. 21

    Nassar, R. & Bernath, P. Hot methane spectra for astrophysical applications. J. Quant. Spectrosc. Radiat. Transf. 82, 279–292 (2003)

    CAS  ADS  Article  Google Scholar 

  22. 22

    Burrows, A., Sudarsky, D. & Hubeny, I. Theory for the secondary eclipse fluxes, spectra, atmospheres and light curves of transiting extrasolar giant planets. Astrophys. J. 650, 1140–1149 (2006)

    CAS  ADS  Article  Google Scholar 

  23. 23

    Pont, F., Knutson, H., Gilliland, R. L., Moutou, C. & Charbonneau, D. Detection of atmospheric haze on an extrasolar planet: The 0.55 – 1.05 micron transmission spectrum of HD189733b with the Hubble Space Telescope. Mon. Not. R. Astron. Soc. (in the press)

  24. 24

    Brown, T. M. Transmission spectra as diagnostics of extrasolar giant planet atmospheres. Astrophys. J. 533, 1006–1026 (2001)

    ADS  Article  Google Scholar 

  25. 25

    Liang, M.-C., Seager, S., Parkinson, C. D., Lee, A. Y.-T. & Yung, Y. L. On the insignificance of photochemical hydrocarbon aerosols in the atmospheres of close-in extrasolar giant planets. Astrophys. J. 605, L6–L64 (2004)

    Article  Google Scholar 

Download references

Acknowledgements

We thank D. Deming for contributions to the original proposal and for suggestions for clarifying the material presented in the manuscript. We thank T. Wiklind, N. Pirzkal and other members of the Space Telescope Science Institute staff for assistance in planning the observations and for advising how the observations could be optimized. We also thank K. Jahnke for suggesting the long-wavelength NICMOS grism, F. Pont for discussions concerning the treatment of the data, M.-C. Liang for discussions on photolysis, and J. Tennyson and R. Barber for suggestions on the methane data lists. G.T. was supported by the UK Sciences & Technology Facilities Council and the European Space Agency. The research described in this paper was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA.

Author Contributions M.R.S. was the PI of the project and led the overall direction of the research. G.V. led the data analysis and G.T. led the modelling. All authors contributed equally to the writing of the paper.

Author information

Affiliations

Authors

Corresponding author

Correspondence to Mark R. Swain.

Supplementary information

Supplementary Information

The file contains Supplementary Notes with Supplementary Figures 1-9.and Supplementary Table 1.. (PDF 711 kb)

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Swain, M., Vasisht, G. & Tinetti, G. The presence of methane in the atmosphere of an extrasolar planet. Nature 452, 329–331 (2008). https://doi.org/10.1038/nature06823

Download citation

Further reading

Comments

By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.

Search

Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing