Earth-size planets outside solar system

National Aeronautics and Space Administration's(NASA) Kepler mission has discovered the first Earth-size planets orbiting a sun-like star outside our solar system on Tuesday Dec 20,2011.The planets, called Kepler-20e and Kepler-20f, are the smallest planets outside the solar system confirmed around a star like the Sun.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.

Kepler-20f is slightly larger than Earth, measuring 1.03 times its radius. Both planets are in a five-planet system called Kepler-20, about 1,000 light-years away in the constellation Lyra.

Kepler-20e orbits its parent star every 6.1 days and Kepler-20f every 19.6 days.

Kepler-20f, at 800 degrees Fahrenheit, is similar to an average day on the planet Mercury. The surface temperature of Kepler-20e, at more than 1,400 degrees Fahrenheit, would melt glass.