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An orbital period of 0.94days for the hot-Jupiter planet WASP-18b
The `hot Jupiters' that abound in lists of known extrasolar planets arethought to have formed far from their host stars, but migrate inwardsthrough interactions with the proto-planetary disk from which they wereborn, or by an alternative mechanism such as planet-planet scattering.The hot Jupiters closest to their parent stars, at orbital distances ofonly ~0.02 astronomical units, have strong tidal interactions, andsystems such as OGLE-TR-56 have been suggested as tests of tidaldissipation theory. Here we report the discovery of planet WASP-18b withan orbital period of 0.94days and a mass of ten Jupiter masses(10MJup), resulting in a tidal interaction an order ofmagnitude stronger than that of planet OGLE-TR-56b. Under the assumptionthat the tidal-dissipation parameter Q of the host star is of the orderof 106, as measured for Solar System bodies and binary starsand as often applied to extrasolar planets, WASP-18b will be spirallinginwards on a timescale less than a thousandth that of the lifetime ofits host star. Therefore either WASP-18 is in a rare, exceptionallyshort-lived state, or the tidal dissipation in this system (and possiblyother hot-Jupiter systems) must be much weaker than in the Solar System.
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