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

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

111 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
Pages (from-to)L51-L54
JournalAstronomy and Astrophysics
Issue number3
StatePublished - Sep 2007


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


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