Detection of two Earth-sized exoplanets

Planetary science update from Nature

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Planetary science: Detection of two Earth-sized exoplanets (AOP)
DOI: 10.1038/nature10780

The discovery of two Earth-size planets orbiting a Sun-like star called Kepler-20 is reported online this week by Nature. The paper describes observations made by the Kepler spacecraft and methods used to determine that the signals detected are planets. Moreover, the researchers go on to predict that these planets are rocky, with possible Earth-like compositions.

Since the discovery of the first extrasolar giant planets orbiting Sun-like stars around two decades ago, steady improvements in observational capabilities have brought us closer to detecting Earth-like planets. François Fressin and co-workers report the detection of the smallest exoplanets discovered so far, orbiting around Kepler-20 — a star already known to host three larger transiting planets. The authors rule out hypotheses that the signals might not be planets, and calculate the size of the planets as they pass in front of (transit) the parent star. One of these planets, Kepler-20 f, has a radius almost identical to Earth’s and the other, Kepler-20 e, is slightly smaller at 0.87 times the radius of Earth.

Fressin and colleagues infer that the planets may have bulk compositions similar to Earth, such as a 32% iron core and a 68% silicate mantle, based on their Earth-like radii. Furthermore, they suggest that the outer planet (Kepler-20 f) may have developed a thick water-vapour atmosphere.

CONTACT

François Fressin (Harvard-Smithsonian Center for Astrophysics, Cambridge, MA, USA)
Tel: +1 617 496 7299; E-mail: [email protected]

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Published: 22 Dec 2011

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