WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star

F. Faedi*, S. C C Barros, D. R. Anderson, D. J A Brown, A. Collier Cameron, D. Pollacco, I. Boisse, G. Hébrard, M. Lendl, T. A. Lister, B. Smalley, R. A. Street, A. H M J Triaud, J. Bento, F. Bouchy, O. W. Butters, B. Enoch, C. A. Haswell, C. Hellier, F. P. KeenanG. R M Miller, V. Moulds, C. Moutou, A. J. Norton, D. Queloz, A. Santerne, E. K. Simpson, I. Skillen, A. M S Smith, S. Udry, C. A. Watson, R. G. West, P. J. Wheatley

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

64 Citations (Scopus)


We present the discovery of WASP-39b, a highly inflated transiting Saturn-mass planet orbiting a late G-type dwarf star with a period of 4.055259 ± 0.000008 d, Transit Epoch T0 = 2 455 342.9688 ± 0.0002(HJD), of duration 0.1168 ± 0.0008d. A combined analysis of the WASP photometry, high-precision follow-up transit photometry, and radial velocities yield a planetary mass of Mpl = 0.28 ± 0.03 M J and a radius of Rpl = 1.27 ± 0.04 RJ, resulting in a mean density of 0.14 ± 0.02 ρJ. The stellar parameters are mass M= 0.93 ± 0.03 M, radius R= 0.895 ± 0.23 R, and age 9+3-4Gyr. Only WASP-17b and WASP-31b have lower densities than WASP-39b, although they are slightly more massive and highly irradiated planets. From our spectral analysis, the metallicity of WASP-39 is measured to be [Fe/H]= -0.12 ± 0.1 dex, and we find the planet to have an equilibrium temperature of 1116+33-32K. Both values strengthen the observed empirical correlation between these parameters and the planetary radius for the known transiting Saturn-mass planets.

Original languageEnglish
Article numberA40
Pages (from-to)1-8
Number of pages8
JournalAstronomy and Astrophysics
Publication statusPublished - 2011
Externally publishedYes


  • planetary systems
  • stars: individual: WASP-39
  • techniques: photometric
  • techniques: radial velocities


Dive into the research topics of 'WASP-39b: a highly inflated Saturn-mass planet orbiting a late G-type star'. Together they form a unique fingerprint.

Cite this