Three dwarf planets are shown to scale with Earth and the Moon in this artist's concept. Eris (left) and Pluto (bottom, with its largest moon, Charon) are the largest known objects in the Kuiper Belt, which is beyond the orbit of Neptune. Ceres (center) is the largest member of the asteroid belt, which is between Mars and Jupiter. The 2005 discovery of Eris, which is about the same size as Pluto, spurred the creation of the "dwarf planet" category. Five objects have official dwarf-planet status, with several candidates likely to join the list soon. [NASA]