spacetoday.net: Kepler discovers first Earth-sized planets around Sun-like stars

Posted: Wed, Dec 21, 2011, 10:53 AM ET (1553 GMT)
Kepler-20e exoplanet illustration (NASA/Ames/JPL-Caltech)

Astronomers announced Tuesday the discovery of the first planets similar in size to the Earth around a Sun-like star. The planets, designated Kepler-20e and Kepler-20f, orbit a Sun-like star 1,000 light-years away. Kepler-20e has a radius of 0.87 Earth radii, making it slightly smaller than Venus, while Kepler-20f is slightly larger, at 1.03 Earth radii. The two planets closely orbit their star, with orbital periods of 6.1 and 19.6 days, putting them well inside the star's habitable zone. Scientists hailed the discovery, though, as the first time a planet as small as the Earth has been found around a star similar to the Sun. The discovery was made using data collected by NASA's Kepler spacecraft as it observed transits of the planets across the star. Three other planets, larger than Earth but smaller than Neptune, have aslo been detected in Kepler observations of the star.