NASA using its planet-hunting Kepler space telescope has discovered a new catalog of exoplanet candidates, it was announced on Thursday.The catalog adds more than 500 new possible planets to the 4,175 already found by the famed space-based telescope, Xinhua reported.The new catalog includes 12 candidates that are less than twice the Earth's diameter, orbiting in the so-called habitable zone of their star. This zone is the range of distances at which the energy flux from the star would permit liquid water to exist on the planet's surface.Kepler 452b is the first to be confirmed as a planet of these candidates. At a distance of 1,400 light-years, Kepler 452b accompanies a star whose characteristics are very similar to the Sun: It is 4 percent more massive and 10 percent brighter. Kepler 452b orbits its star at the same distance as the Earth orbits the sun.