NASA's Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system, a milestone in the search for planets like the earth, the space agency said on Tuesday.
The planets, called Kepler-20e and Kepler-20f, are the smallest planets outside the solar system confirmed around a star like the Sun, NASA said in a statement.
The planets are too close to their star to be in the so-called habitable zone where liquid water could exist on a planet's surface.
The new planets are thought to be rocky. Kepler-20e is slightly smaller than Venus, measuring 0.87 times the radius of Earth.