Exoplanet smaller than Earth Pasadena - Agencies   Astronomers say a planet two-thirds the size of Earth and 33 light-years away may be the nearest world to our solar system smaller than our home planet. Only a handful of exoplanets smaller than Earth have been found beyond the sun so far, astronomers said, and UCF-1.01 is the first ever identified with the Spitzer space telescope -- pointing to a possible role for the orbiting astronomy platform in helping discover potentially habitable, terrestrial-sized worlds -- NASA\'s Jet Propulsion Laboratory in Pasadena, Calif., reported. The hot, new-planet candidate was found unexpectedly in Spitzer observations by researchers studying a Neptune-sized exoplanet already known to exist around the red-dwarf star GJ 436. Spitzer data showed periodic dips in the light coming from the star, suggesting a second planet might be orbiting the star and blocking out a small fraction its light. Data indicate a diameter of approximately 5,200 miles, two-thirds that of Earth. UCF-1.01 would revolve quite tightly around GJ 436, with its \"year\" lasting only 1.4 Earth days. Being closer to its star than Mercury is to the sun, the exoplanet\'s surface temperature would be more than 1,000 degrees Fahrenheit, astronomers said. \"I hope future observations will confirm these exciting results, which show Spitzer may be able to discover exoplanets as small as Mars,\" Michael Werner, Spitzer project scientist at JPL, said.