First Earth-size planet in the "habitable zone" discovered by NASA's Kepler Mission. 

An Earth-like planet? Our Kepler spacecraft discovered first Earth-size planet in the habitable zone of another star! The artist's concept depicts Kepler-186f , the first validated Earth-size planet to orbit a distant star in the habitable zone—a range of distance from a star where liquid water might pool on the planet's surface. The discovery of Kepler-186f confirms that Earth-size planets exist in the habitable zones of other stars and signals a significant step closer to finding a world similar to Earth. 

The size of Kepler-186f is known to be less than ten percent larger than Earth, but its mass, density and composition are not known. Previous research suggests it's likely rocky. Kepler-186f orbits its star once every 130 days and receives one-third the energy that Earth does from the sun, placing it near the outer edge of the habitable zone. If you could stand on the surface of Kepler-186f, the brightness of its star at high noon would appear as bright as our sun is about an hour before sunset on Earth. Kepler-186f is about 500 light-years from Earth in the constellation Cygnus. The system is also home to four inner planets, seen lined up in orbit around a host star that is half the size and mass of the sun.

Details: http://go.nasa.gov/1itJMsQ