Plot: When the American Museum of Natural History's Hayden Planetarium stopped calling Pluto a planet, director Neil deGrasse Tyson found himself at the center of a firestorm led by angry Pluto-loving elementary school students. What is it about Pluto—a cold, distant, icy rock—that captures so many hearts? Four years after the IAU (International Astronomical Union) officially reclassified the ninth planet as a plutoid, NOVA travels cross-country with Tyson to find out