Narrator: NASA's Kepler Mission has discovered the
first Earth-size planet orbiting in the habitable
zone of a star outside of our solar system.
The newly discovered planet is called Kepler-186f
and is about 10 percent larger than Earth.
Elisa Quintana: Kepler-186f is the first validated
Earth-size planet in the habitable zone of its
star. It's the outmost of five planets to orbit a
star that is smaller and cooler than the sun.
This planet orbits its star every 130 days and so
this places it in the habitable zone, where it's
in a region where it could have liquid water
on its surface.
Narrator: Kepler-186f resides in the Kepler-186
system, about 500 light-years from Earth in the
constellation Cygnus.
Thomas Barclay: This planet, Kepler-186f, orbits
a star that is cooler and dimmer than the sun.
So while we may have found a planet that is
the same size as Earth and receives a similar
amount of energy as to what Earth receives,
it orbits a very different star.
So, perhaps instead of an Earth twin, we've
discovered an Earth cousin.
Narrator: On the surface of Kepler-186f, the
brightness of its star at high noon is only as
bright as our sun appears to us about an hour
before sunset.
Scientists believe Kepler-186f is likely to be a
rocky world, but are unable to confirm its mass
and density.
Thomas Barclay: This is one of the big milestones
that we've been looking for in our attempts to
find out if there are places just like home and if
there's life out there. One of the big steps is
to say "Is there somewhere that looks, to all
intents and purposes, like Earth?" Well, we don't
know just yet, but we know that there are at least
places that look similar.
Narrator: Managed by NASA's Ames Research Center,
the Kepler mission collected this data using a
space-based telescope to search one part of the
galaxy for potentially habitable planets.
(Electronic Sounds of Data Musical Tones)