This artist's concept shows what astronomers believe is an alien world just two-thirds the size of Earth — one of the smallest on record. It was identified by NASA's Spitzer Space Telescope. The exoplanet candidate, known as UCF-1.01, orbits a star called GJ 436, which is located a mere 33 light-years away. UCF-1.01 might be the nearest world to our solar system that is smaller than our home planet.
Image credit: NASA/JPL-Caltech