Almost 400 extrasolar planets have been found to date (see PHYSICS TODAY, May 2009, page 46), but a new planet reported by Coel Hellier (Keele University) and colleagues stands out. Like many exoplanets, theirs, dubbed WASP-18b, is massive (10 times the mass of Jupiter) and has a small orbital radius (only 1/50th of Earth’s). But its orbital period of only 0.94 day is the shortest for any “hot Jupiter” yet observed. Moreover, its large mass and small orbit are predicted to cause the strongest tidal interactions of any known star–planet system. According to current theory, the tidal bulge that the planet raises on its host star exerts a torque that will drain angular momentum from the planet and cause it to spiral inward. (For more on tidal interactions, see Physics Today, August 2009, page 11). If the star’s tidal dissipation rate is comparable to what’s been...

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