An orbital period of 0.94days for the hot-Jupiter planet WASP-18b

Research output: Contribution to journalArticlepeer-review


  • C. Hellier
  • D.~R. Anderson
  • A. Collier Cameron
  • M. Gillon
  • L. Hebb
  • P.~F.~L. Maxted
  • D. Queloz
  • B. Smalley
  • R.~G. West
  • D.~M. Wilson
  • S.~J. Bentley
  • B. Enoch
  • K. Horne
  • J. Irwin
  • T.~A. Lister
  • M. Mayor
  • N. Parley
  • F. Pepe
  • D.~L. Pollacco
  • D. Segransan
  • S. Udry
  • P.~J. Wheatley

Colleges, School and Institutes


The `hot Jupiters' that abound in lists of known extrasolar planets are thought to have formed far from their host stars, but migrate inwards through interactions with the proto-planetary disk from which they were born, or by an alternative mechanism such as planet-planet scattering. The hot Jupiters closest to their parent stars, at orbital distances of only 0.02 astronomical units, have strong tidal interactions, and systems such as OGLE-TR-56 have been suggested as tests of tidal dissipation theory. Here we report the discovery of planet WASP-18b with an orbital period of 0.94days and a mass of ten Jupiter masses (10M$_Jup$), resulting in a tidal interaction an order of magnitude stronger than that of planet OGLE-TR-56b. Under the assumption that the tidal-dissipation parameter Q of the host star is of the order of 10$^6$, as measured for Solar System bodies and binary stars and as often applied to extrasolar planets, WASP-18b will be spiralling inwards on a timescale less than a thousandth that of the lifetime of its host star. Therefore either WASP-18 is in a rare, exceptionally short-lived state, or the tidal dissipation in this system (and possibly other hot-Jupiter systems) must be much weaker than in the Solar System.


Original languageEnglish
Pages (from-to)1098-1100
Number of pages3
Publication statusPublished - 1 Aug 2009