In 2006, a group of astronomers gathered in Prague and made a decision that shocked the world: Pluto was no longer a planet.

But the story of Pluto is far more complicated—and far more fascinating—than that single vote.

In this episode of Star Trails, we reopen the case. From Percival Lowell’s search for the mysterious “Planet X” to Clyde Tombaugh’s painstaking discovery using a blink comparator, we trace the strange history of the ninth planet. We’ll examine the discoveries that led to Pluto’s controversial demotion, meet the astronomers who helped redefine what a planet is, and follow NASA’s New Horizons spacecraft as it revealed Pluto to be a dynamic and surprisingly complex world.

Along the way we explore Pluto’s bizarre orbit, its giant moon Charon, its icy surface and hidden mysteries—and the poetic moment when the ashes o ...