Dave talks to Alan Stern and David Grinspoon, coauthors of Chasing Pluto: Inside The Epic First Mission to Pluto. When Voyager 2 flew by Neptune in 1989, it closed out the golden age of solar system exploration. But it left one unexplored body: Pluto. Stern was part of a group of scientists known as "The Pluto Underground." For years the proposed, lobbied and planned for a robotic mission to what was then, "the ninth planet." The mission that would be eventually called New Horizons went through decades of starts and stops. The story of how this mission ultimately succeeded in July 2015 is a triumphant tale of perseverence.