Water, methane, and carbon dioxide present in the dayside spectrum of the exoplanet HD 209458b

M. R. Swain, G. Tinetti, G. Vasisht, P. Deroo, C. Griffith, J. Bouwman, Pin Chen, Y. Yung, Adam S. Burrows, L. R. Brown, J. Matthews, J. F. Rowe, R. Kuschnig, D. Angerhausen

Research output: Contribution to journalArticlepeer-review

212 Scopus citations


Using the NICMOS instrument on the Hubble Space Telescope, we have measured the dayside spectrum of HD 209458b between 1.5 and 2.5 μm. The emergent spectrum is dominated by features due to the presence of methane (CH 4) and water vapor (H2O), with smaller contributions from carbon dioxide (CO2). Combining this near-infrared spectrum with existing mid-infrared measurements shows the existence of a temperature inversion and confirms the interpretation of previous photometry measurements. We find a family of plausible solutions for the molecular abundance and detailed temperature profile. Observationally resolving the ambiguity between abundance and temperature requires either (1) improved wavelength coverage or spectral resolution of the dayside emission spectrum or (2) a transmission spectrum where abundance determinations are less sensitive to the temperature structure.

Original languageEnglish (US)
Pages (from-to)1616-1621
Number of pages6
JournalAstrophysical Journal
Issue number2
StatePublished - 2009

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


  • Planetary systems
  • Techniques: spectroscopic


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