Pluto: The Dwarf Planet

Pluto: Facts - NASA Science

Ever wondered why Pluto was demoted from being a planet? When Pluto was discovered in 1930, it was hailed as the ninth planet. But in 2006, the International Astronomical Union redefined what qualifies as a planet: It must orbit the sun, be spherical, and clear its orbit of other debris. Pluto met the first two rules, but it shares its orbit with objects in the Kuiper belt, failing the third. Instead, it was reclassified as a dwarf planet. The debate still sparks emotions, but scientifically, Pl