NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date

NASA - NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date: "MOFFETT FIELD, Calif. -- NASA's Kepler mission has discovered two new planetary systems that include three super-Earth-size planets in the "habitable zone," the range of distance from a star where the surface temperature of an orbiting planet might be suitable for liquid water."