It's been almost 20 years since Pluto lost its status as the ninth planet in our solar system. Now astronomers think they have identified a candidate to take its place. Katherine Volk with the Tucson-based Planetary Science Institute discusses a rare object that is orbiting the sun in step with the eighth planet, Neptune. In this extended episode, Katherine Volk spoke with Tim Swindle, professor emeritus in Planetary Science at the University of Arizona.