Since its discovery in 1930, the ninth planet - Pluto - has held a warm place in the public imagination. So, when the American Museum of Natural History's Hayden Planetarium stopped calling Pluto a planet, a great controversy ensued. Hayden Planetarium's Director Neil deGrasse Tyson found himself at the center of a firestorm led by angry, Pluto-loving elementary school students. But why has a cold, distant rock captured so many hearts? This episode of NOVA joins Tyson as he recounts the amazing story of Pluto's discovery and the captivating science that surrounds this former planet, including the possibility of finding more Pluto-like celestial bodies in the mysterious Kuiper belt, an area of icy rocks at the edge of the solar system. From the scientists trying to re-classify Pluto to die-hard Pluto-philes, Tyson meets a fascinating cast of characters with just one thing in common: strong opinions about Pluto.

Encoded with permission for digital streaming by Infobase on August 21, 2011. Learn360 is distributed by Infobase for Films for the Humanities & Sciences, Cambridge Educational, Meridian Education, and Shopware.

Overview & Sponsors: The Pluto Files (1:37) -- Pluto Declassified (4:25) -- Pluto: Oddball or Planet? (6:42) -- History of Pluto (3:53) -- Pluto's Name (4:26) -- Discoverer of Pluto: Clyde Tombaugh (2:08) -- Planet Discovery Timeline (1:34) -- A Visit to the Tombaugh Family (5:34) -- Pluto: Planet or Kuiper Belt Object? (3:42) -- In Search of More Plutos (3:09) -- New Definition of Planet (5:21) -- Pluto: Dwarf Planet (3:49) -- New Horizons Spacecraft (2:14) -- Controversy Over Definitions (3:23) -- Credits and Sponsors: The Pluto Files (1:27).