NASA's Kepler program has a found a planet similar to Earth in size and distance to its star, and while it's not quite a twin, some scientists are calling it a "cousin."
The planet, called Kepler 186f, is about 500 light-years away, and the space agency suspects that its surface is rocky like Earth's — though it hasn't been confirmed. What they do know is that the planet is only 10-percent larger than Earth, and is in the habitable zone: a safe enough distance from its star that water can pool on its surface, and life, as we know, may be able to survive given the right atmosphere. NASA found four other planets in Kepler 186f's solar system, but they're a great deal larger than Earth and orbit their star in under three weeks. Kepler 186f orbits the star in about 130 days.
“Kepler 186f is the first, validated, Earth-size planet in the habitable zone of another star,” said Elisa Quintana of the SETI Institute and NASA’s Ames Research Center. “It has the right size and is at the right distance to have properties similar to our home planet.”