Astronomers Say 1 in 6 Stars Has an Earth-Sized Planet
Posted on January 7, 2013
Astronomers analyzing Kepler data have determined that about 17% of stars have an Earth-sized planet in an orbit closer than Mercury. Since the Milky Way is estimated to have about 100 billion stars, this means there are at least 17 billion Earth-sized worlds in our galaxy.
Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics (CfA), presented the analysis in a press conference at a meeting of the American Astronomical Society in Long Beach, Calif. A research paper has been accepted for publication in The Astrophysical Journal.
Fressin says in a release, "There is a list of astrophysical configurations that can mimic planet signals, but altogether, they can only account for one-tenth of the huge number of Kepler candidates. All the other signals are bona-fide planets."
The astronomers have found that 50% of stars have a planet of Earth-size or larger in a close orbit. By adding larger planets, which have been detected in wider orbits up to the orbital distance of the Earth, this number climbs to 70%. Extrapolating from Kepler's currently ongoing observations and results from other detection techniques, the astronomers believe that practically all Sun-like stars have planets.
The researchers have grouped the planets into five different sizes. They found that 17% of stars have a planet 0.8 - 1.25 times the size of Earth in an orbit of 85 days or less. 25% of stars have a super-Earth (1.25 - 2 times the size of Earth) in an orbit of 150 days or less. 25% of stars has a mini-Neptune (2 - 4 times Earth) in orbits up to 250 days long. Larger planets are less common with only about 3% of stars have a large Neptune (4 - 6 times Earth), and only 5% of stars have a gas giant (6 - 22 times Earth) in an orbit of 400 days or less.