Pluto


Barbara J. Feldman

On August 24, 2006, astronomers declared that Pluto is no longer a planet, thereby downsizing the solar system from nine planets to eight. After a week of debate, the International Astronomical Union stripped Pluto of planetary status because its orbit crosses Neptune’s and therefore fails one of three planetary requirements. Instead, Pluto (along with Ceres and Xena) is now classified as a dwarf planet.