Search for Earth’s twin shows promise
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. Because the Milky Way has approximately 100 billion stars, there are at least 17 billion Earth-sized worlds out there. Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics (CfA), presented the analysis Monday in a press conference at a meeting of the American Astronomical Society in Long Beach, Calif. A paper detailing the research has been accepted for publication in The Astrophysical Journal. 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. The first 16 months of the survey identified approximately 2,400 candidates. Astronomers then asked how many of those signals...