At last, Earth-sized alien worlds
On Dec. 20, 2011, astronomers announced the discovery an alien solar system 950 light-years from Earth that is chock full of planets, including the first two extrasolar worlds ever confirmed to be the size of our own Earth or smaller.
Finding Earth-size planets has been a major goal for NASA’s Kepler space observatory, which spotted the small alien worlds and their larger cousins around a star known as Kepler 20. The two Earth-size planets (one is actually smaller than Earth) are known as Kepler-20e and Kepler-20f. See how the planets compare to Earth and the other planets in their alien star system in the infographic above.