Transit spectrophotometry of the exoplanet HD 189733b: I. Searching for water but finding haze with HST NICMOS

D. K. Sing, J. M. Désert, A. Lecavelier Des Etangs, G. E. Ballester, A. Vidal-Madjar, V. Parmentier, G. Hebrard, G. W. Henry

Research output: Contribution to journalArticlepeer-review

122 Scopus citations


We present Hubble Space Telescope near-infrared transit photometry of the nearby hot-Jupiter HD 189733b. The observations were taken with the NICMOS instrument during five transits, with three transits executed with a narrowband filter at 1.87 μm and two performed with a narrowband filter at 1.66 μm. Our observing strategy using narrowband filters is insensitive to the usual HST intra-orbit and orbit-to-orbit measurement of systematic errors, allowing us to accurately and robustly measure the near-IR wavelength dependance of the planetary radius. Our measurements fail to reproduce the previously claimed detection of an absorption signature of atmospheric H2O below 2 μm at a 5σ confidence level. We measure a planet-to-star radius contrast of 0.15498±0.00035 at 1.66 μm and a contrast of 0.15517 ± 0.00019 at 1.87 μm. Both of our near-IR planetary radii values are in excellent agreement with the levels expected from Rayleigh scattering by sub-micron haze particles, observed at optical wavelengths, indicating that upper-atmospheric haze still dominates the near-IR transmission spectra over the absorption from gaseous molecular species at least below 2 μm.

Original languageEnglish (US)
Pages (from-to)891-899
Number of pages9
JournalAstronomy and astrophysics
Issue number2
StatePublished - Oct 2 2009


  • Binaries: eclipsing
  • Planetary systems
  • Stars: individual: HD 189733
  • Techniques: photometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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