NASA's Kepler mission has
discovered the first Earth-size planets orbiting a sun-like star outside
our solar system. The planets, called Kepler-20e and Kepler-20f, are
too close to their star to be in the so-called habitable zone where
liquid water could exist on a planet's surface, but they are the
smallest exoplanets ever confirmed around a star like our sun.
Kepler-20e is slightly smaller than Venus, measuring 0.87 times the
radius of Earth. Kepler-20f is slightly larger than Earth.