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.

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