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Earth-Sized Exoplanet Found Orbiting in Alpha Centauri System

Oct 17, 2012 09:27 AM EDT

European astronomers have found a exoplanet, with mass similar to Earth, orbiting a star in the Alpha Centauri system. 

Alpha Centauri is located outside our solar system about 4.3 light-years away and is the closest neighbor to Earth.

Alpha Centauri is a triple star system with two stars similar to the sun orbiting closely to each other, while the third star orbits at a farther distance. Alpha Centauri A and the slightly fainter Alpha Centauri B are orbiting each other and passing as close as nine billion miles every 80 years. The third star, a much fainter dwarf called Alpha Centauri C (Proxima Centauri), is circling the two stars some trillion miles away, reported The New York Times.

The newly found exoplanet (planets outside the solar system) called as Alpha Centuri Bb was found completing one revolution around the Alpha Centauri B star every 3.2 days at a distance of 3.6 million miles. "Our observations extended over more than four years using the HARPS instrument and have revealed a tiny, but real, signal from a planet orbiting Alpha Centauri B every 3.2 days," Xavier Dumusque, lead author of the paper, said in a release.

"It's an extraordinary discovery and it has pushed our technique to the limit!" he said.

The planet was detected using High Accuracy Radial Velocity Planet Searcher (HARPS). Using the HARPS instrument, astronomers observed tiny wobbles in Alpha Centauri B's movement that is created by the gravitational pull of the orbiting planet. The star wobbled around one mile per hour.

Astronomers have earlier found several exoplanets orbiting sun-like stars. But most of them are much bigger in size than the Earth. This is the first Earth-sized planet circling a sun-like star found outside our solar system and is our closest neighbor. The planet is too close to its star to be habitable, said the astronomers.

"This is the first planet with a mass similar to Earth ever found around a star like the Sun. Its orbit is very close to its star and it must be much too hot for life as we know it," Stéphane Udry (Geneva Observatory), a co-author of the paper and member of the team, said.

"But it may well be just one planet in a system of several. Our other HARPS results, and new findings from Kepler, both show clearly that the majority of low-mass planets are found in such systems, Udry said.

The findings of the study, "An Earth mass planet orbiting Alpha Centauri B," will appear online on OCt. 17 in Nature journal.

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