NASA's twin rovers, Spirit and Opportunity, have been exploring the surface of Mars for more than six years. It's an impressive fact, considering they were only designed to last for three months. But despite this longevity, recent mechanical failures have brought the Spirit rover to a standstill. In this podcast, we talked to Bruce Banerdt, the Project Scientist for the Mars rover missions, about the fate of this now-stationary rover.Podcast produced by David Levin. Original interview by Susan K. Lewis. 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.To learn more about the Mars rovers, go to pbs.org/nova/mars