As of 1989, mankind had successfully sent craft to every known planet in the solar system except one: Pluto. Located in an mysterious region called the Kuiper Belt, Pluto is a scientific goldmine, and could hold clues to the formation of our solar system. Alan Stern explains how NASA's New Horizons mission is going to allow us to see Pluto for the first time. Lesson by Alan Stern, animation by Eoin Duffy.