An artist's illustration of Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star, is seen in this undated handout picture released by NASA, December 5, 2011. Kepler-22b, the most Earth-like planet ever discovered is circling a star 600 light years away, a key finding in an ongoing quest to learn if life exists beyond Earth, scientists said on Monday. Kepler-22b joins a list of more than 500 planets found to orbit stars beyond our solar system. It is the smallest and the best positioned to have liquid water on its surface - among the ingredients necessary for life on Earth. REUTERS/NASA/Ames/JPL-Caltech/Handout
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