Astronomers discover the smallest known transiting extrasolar planet: finding could provide clues to composition and structure.

Astronomers have found an extrasolar planet no more than 11 Earth masses, with a diameter about twice that of Earth's. The discovery of the planet, dubbed COROT-Exo-7b, may ultimately provide groundbreaking information about the composition and structure of terrestrial planets beyond the solar system.

Once the team can refine an estimate of the planet's mass, "this could be a potentially huge discovery," comments theorist Sara Seager of MIT. "I'm excited to see what more the team will find out about this prospective terrestrial planet."

Located about 450 light-years from Earth, the planet is too small for imaging. Classified as a hot superEarth, it lies too close to the heat of its parent star to support life. The planet whips about its star in just 20 hours, has a surface temperature between 1,000[degrees] and 1,500[degrees] Celsius and might be covered by lava or water vapor.

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Although scientists have found a few extrasolar planets with smaller masses, the newly found body is the tiniest known that periodically passes between its parent star and Earth, blocking a tiny fraction of starlight during each transit.

These minieclipses yield a planet's radius and, in combination with another technique, provide a trove of information, including the exact mass, density and composition of a body, notes Daniel Rouan of the Observatory of Paris in Meudon, France. He and his colleagues reported the find February 3 at a symposium in Paris about the European Space Agency's COROT satellite, the craft that detected the planet's transits. Rouan says an accurate mass for the planet, which will soon be available, can help determine its density and composition.

"For the very first time in human history, we can study a solid planet located outside our solar system," says team member Michael Gillon of the Observatory of Geneva in Sauverny, Switzerland. "This is a major step towards the detection and study of actual Earth twins orbiting other stars."