At least one in six stars has an Earth-sized planet

The quest for a twin Earth is heating up. Using NASA's Kepler spacecraft, astronomers are beginning to find Earth-sized planets orbiting distant stars. A new analysis of Kepler data shows that about 17 percent of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way has about 100 billion stars, there are at least 17 billion Earth-sized worlds out there.

Kepler detects planetary candidates using the transit method, watching for a planet to cross its star and create a mini-eclipse that dims the star slightly. During the first 16 months of the survey, Kepler identified about 2,400 candidates. Astronomers then asked, how many of those signals are real, and how many planets did Kepler miss? .... http://www.astronomy.com