spacetoday.net: Astronomers discover Earth-sized planet in star's habitable zone

Posted: Fri, Apr 18, 2014, 7:09 AM ET (1109 GMT)
Kepler-186f illustration (NASA)

Astronomers announced Thursday the discovery of a planet approximately the size of the Earth orbiting in the habitable zone of its star. The planet, Kepler-186f, is near the outer edge of the habitable zone of the M-class star it orbits. The planet is about 10% larger than the Earth based on its radius, but astronomers noted they do not know the planet's mass, and thus its density. The planet is the first world about the size of the Earth found in a planet's habitable zone, although scientists cautioned that does not mean the planet is Earth-like since it receives only about one-third the flux from its star as the Earth does from the Sun. Astronomers detected the planet in transits observed by NASA's Kepler spacecraft; observations by the Gemini and Keck telescopes ruled out other phenomena, like a background star or stellar companion, that could have caused a signal like that detected by Kepler.