Accurate Spitzer infrared radius measurement for the hot Neptune GJ 436b

M. Gillon, B. O. Demory, T. Barman, X. Bonfils, T. Mazeh, F. Pont, S. Udry, M. Mayor, D. Queloz

Research output: Contribution to journalArticlepeer-review

110 Scopus citations


We present Spitzer Space Telescope infrared photometry of a primary transit of the hot Neptune GJ 436b. The observations were obtained using the 8 μm band of the InfraRed Array Camera (IRAC). The high accuracy of the transit data and the weak limb-darkening in the 8 μm IRAC band allow us to derive (assuming M = 0.44 ±0.04 M for the primary) a precise value for the planetary radius (4.19-0.16+0.21 R ), the stellar radius (0.463-0.017+0.022 R) the orbital inclination (85.90° -0.18°+0.19°) and transit timing ((2454280.78186-0.00008+0.00015 HJD). Assuming current planet models, an internal structure similar to that of Neptune with a small H/He envelope is necessary to account for the measured radius of GJ 436b.

Original languageEnglish (US)
Pages (from-to)L51-L54
JournalAstronomy and astrophysics
Issue number3
StatePublished - Sep 2007


  • Eclipses
  • Infrared: general
  • Planetary systems
  • Stars: individual: GJ 436
  • Techniques: photometric

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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