Today the International Astronomical Union (IAU) decided that Pluto will not be keeping its "planet" title. Instead, Pluto, as well as asteroid Ceres and the larger-than-Pluto 2003 UB313 are now classified as "dwarf planets." According to the IAU, a "planet" is rounded by self gravity and has cleared its orbital zone, a "dwarf planet" is rounded by self gravity but has NOT cleared its orbital zone, and "small solar system bodies" are not rounded by self gravity. Because Pluto is part of the Kuiper belt and Ceres is part of the asteroid belt, neither has "cleared" its neighborhood, so they don't qualify as planets.

Nagi