Analysis of spitzer spectra of irradiated planets: Evidence for water vapor?

Jonathan J. Fortney, Mark S. Marley

Research output: Contribution to journalArticlepeer-review

41 Scopus citations


Published mid-infrared spectra of transiting planets HD 209458b and HD 189733b, obtained during secondary eclipse by the InfraRed Spectrograph (IRS) aboard the Spitzer Space Telescope, are predominantly featureless. In particular, these flux ratio spectra do not exhibit an expected feature arising from water vapor absorption shortward of. Here we suggest that in the absence of flux variability, the spectral data for HD 189733b 10 mm are inconsistent with 8 mm photometry obtained with Spitzer's InfraRed Array Camera (IRAC), perhaps an indication of problems with the challenging reduction of the IRS spectra. The IRAC point, along with previously published secondary eclipse photometry for HD 189733b, are in good agreement with a one-dimensional model of HD 189733b that clearly shows absorption due to water vapor in the emergent spectrum. We are not able to draw firm conclusions regarding the IRS data for HD 209458b, but spectra predicted by 1D and 3D atmosphere models fit the data adequately, without adjustment of the water abundance or reliance on cloud opacity. We argue that the generally good agreement between model spectra and IRS spectra of brown dwarfs with atmospheric temperatures similar to these highly irradiated planets lends confidence in the modeling procedure.

Original languageEnglish (US)
Pages (from-to)L45-L48
JournalAstrophysical Journal
Issue number1 PART 2
StatePublished - 2007
Externally publishedYes


  • HD 209458)
  • Planetary systems
  • Radiative transfer
  • Stars: Individual (HD 189733

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


Dive into the research topics of 'Analysis of spitzer spectra of irradiated planets: Evidence for water vapor?'. Together they form a unique fingerprint.

Cite this