A Dance of Extrasolar Planets

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Science  01 Oct 2010:
Vol. 330, Issue 6000, pp. 47-48
DOI: 10.1126/science.1196505

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Launched in March 2009, the Kepler mission is tasked with searching for extrasolar planets. It continuously monitors 156,000 stars in a ∼100-squaredegree patch of sky covering a portion of the galactic disk centered on a direction lying in the constellation Cygnus (1). On page 47 of this issue, Holman et al. (2) report the discovery of a transiting planet whose orbit of 38.9 days varies by up to 1 hour due to the interaction with other planets in the system. This Saturn-sized world, known as Kepler-9c, circles a Sun-like star 2300 light-years away in the direction of the constellation Lyra, and is part of a bizarre system containing three transiting planets, whose mutual gravitational tugs generate an exquisitely choreographed orbital dance. Far from being mere curiosities, the planets of the Kepler-9 system may provide vital clues to the mechanisms of planetary formation and orbital evolution.