NASA finds Earth's twin? The first planet discovered in the habitable zone of a sun-like star
Planet Kepler-22b, approximately 2.4 times the size of Earth and 600 light-years away, is the first possible Earth twin planet that NASA has discovered among its over 1,000 new planet candidates. The NASA Kepler program has discovered other Earth-sized planets, but Kepler-22b represents the first of its kind in a habitable zone - a region whose distance to a sun makes it possible for liquid water to exist on a planet’s surface. By using the innovative technique of measuring the dips in the brightness of over 150,000 stars, Kepler discovers potential planets that cross or "transit" the stars. Once three transits have occurred, NASA confirms the interference to be a planet.
SOURCE: NASA Press Release