Far beyond its original goal of the planet Jupiter, the venerable Pioneer 10 spacecraft fed us data from 1972 until 2003. But there was something interesting about those data—an anomaly in Pioneer’s velocity.

In the new ebook The Pioneer Detectives, Konstantin Kakaes tells the story of some very smart people who came to believe the Pioneer anomaly could change our understanding of the universe. For this New America Foundation podcast, I talked to him about what made the Pioneer anomaly so significant, and what happens when scientists are faced with a discovery that challenges their fundamental beliefs in gravity.

Future Tense is a partnership of Slate, the New America Foundaiton, and Arizona State University.