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The planet that shouldn't exist

University of Warwick researcher Peter Wheatley is one of a team of physicists who have discovered a planet with ten times the mass of Jupiter, but which orbits its star in less than one Earth-day.

The discovery, reported in this week's Nature by Peter Wheatley, Coel Hellier and colleagues, poses a challenge to our understanding of tidal interactions in planetary  systems.

The planet, called WASP-18b, belongs to a now-common class of extrasolar planets known as 'hot Jupiters' - massive planets  that are thought to have formed far from their host stars, and migrated inwards over time. WASP-18b is so massive, and so close to its star - only about three stellar radii away - that tidal interactions between star and planet should have caused the planet to spiral inwards to its destruction in less than a million years.

Yet, as the authors of the paper show, the WASP-18 parent star is about a billion years old - making the likelihood of observing WASP-18b about one in a thousand.Dr  Peter Wheatley said: "The discovery of this planet is surprising and it will help us understand how planets and stars interact with each other".

How can this unlikely discovery be explained? One possibility is that the tidal dissipation in the WASP-18 system is a thousand times less than in our Solar System; this and other possible explanations are discussed by Douglas Hamilton in an accompanying News and Views article in Nature.

Notes to editors

For more information please contact Dr Peter Wheatley, 02476 574330, 0786 772 8114.The paper is published in Nature, due out Thursday 27 August, 2009