Abstract
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 born1,2, or by an alternative mechanism such as planet–planet scattering3. The hot Jupiters closest to their parent stars, at orbital distances of only ∼0.02 astronomical units, have strong tidal interactions4,5, and systems such as OGLE-TR-56 have been suggested as tests of tidal dissipation theory6,7. Here we report the discovery of planet WASP-18b with an orbital period of 0.94 days and a mass of ten Jupiter masses (10 MJup), 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 106, 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.
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Acknowledgements
We thank the South African Astronomical Observatory for hosting WASP-South and the UK’s Science and Technology Facilities Council for funding.
Author Contributions WASP-S construction, operation and candidate selection (C.H., D.R.A., D.M.W., P.F.L.M., B.S., S.J.B.); WASP-S design (D.L.P); WASP observatory software (J.I., D.R.A., P.F.L.M.); WASP-S data processing (D.R.A., D.M.W., B.S.); WASP data pipeline (A.C.C., T.A.L., N.P., K.H.); transit-search code (A.C.C., L.H., B.E.); WASP data archive (R.G.W., P.J.W.); Coralie/EulerCAM data (M.G., A.H.M.J.T., D.S., D.Q.); Euler/Coralie construction and upgrade (D.Q., M.M., S.U., F.P.); planet characterization (A.C.C., D.R.A., M.G.); host star characterization (B.S., L.H.); paper writing (C.H., A.C.C.).
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Hellier, C., Anderson, D., Cameron, A. et al. An orbital period of 0.94 days for the hot-Jupiter planet WASP-18b. Nature 460, 1098–1100 (2009). https://doi.org/10.1038/nature08245
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DOI: https://doi.org/10.1038/nature08245
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