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The results of a new analysis of Kepler data show that one in
six stars has an Earth-sized planet in a tight orbit. About a fourth of
all stars in the Milky Way have a super-Earth, and the same fraction
have a mini-Neptune. Only about 3 percent of stars have a large Neptune,
and only 5 percent a gas giant at the orbital distances studied.
Credit: F. Fressin (CfA)


The quest to determine if planets like Earth are rare or common is
taking another stride forward on the journey. Using NASA's Kepler
spacecraft, managed by NASA Ames Research Center, 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.




Francois Fressin, of the Harvard-Smithsonian Center for Astrophysics
(CfA), presented the analysis today 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.




The research team found that 50 percent of all stars have a planet of
Earth-size or larger in a close orbit. By adding larger planets detected
in wider orbits up to the orbital distance of the Earth, this number
increases to 70 percent.




Extrapolating from Kepler's currently ongoing observations and results
from other detection techniques, scientists have determined that nearly
all sun-like stars have planets.




Planets closer to their stars are easier to find because they transit
more frequently. As more data are gathered, planets in larger orbits
will be detected. In particular, Kepler's extended mission will enable
the detection of Earth-sized planets at greater distances, including
Earth-like orbits in the "habitable zone," the region in a planetary
system where liquid water might exist on the surface of an orbiting
planet.




Kepler is the first NASA mission capable of finding Earth-size planets
orbiting in or near the habitable zone of the host star. NASA's Ames
Research Center, Moffett Field, Calif., is the home organization of the
science principal investigator, and is responsible for the ground system
development, mission operations, and science data analysis.




NASA's Jet Propulsion Laboratory in Pasadena, Calif., managed Kepler
mission development. Ball Aerospace and Technologies Corp. in Boulder,
Colo., developed the Kepler flight system and supports mission
operations with JPL at the Laboratory for Atmospheric and Space Physics
at the University of Colorado in Boulder.




The Space Telescope Science Institute in Baltimore archives, hosts and
distributes the Kepler science data. Kepler is NASA's 10th Discovery
Mission and is funded by NASA's Science Mission Directorate at the
agency's headquarters.




To read more about the discovery, see the Harvard-Smithsonian Center for Astrophysics press release.




Read more about the Kepler Mission.


Michele Johnson
Ames Research Center, Moffett Field, Calif.
650-604-6982
michele.johnson@nasa.gov
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