After Pluto was discovered in 1930, it enjoyed the title of planet for more than 75 years. But in 2006, that all changed. At a meeting in Prague, the International Astronomical Union adopted a new definition for planethood, leaving the solar system with only eight planets. But not everyone agrees with its decision. In this podcast, planetary scientist Alan Stern talks to us about Pluto's demotion, and why he thinks it should be back on list of planets.

Podcast produced by David Levin. NOVA is produced by WGBH in Boston. Funding for NOVA is provided by ExxonMobil, David H. Koch, the Howard Hughes Medical Institute, the Corporation for Public Broadcasting, and public television viewers.