We memorized the planets as children, confident the solar system was a complete clockwork mechanism. But beyond Neptune, in the cold dim field of the Kuiper Belt, that familiar picture breaks down. This episode explores the strange orbits of distant objects like Sedna, which cluster together against overwhelming statistical odds, and examines how astronomers Konstantin Batygin and Mike Brown used these gravitational anomalies to reverse-engineer a hidden world. It traces the mathematics pointing to a super-Earth exiled to the outer dark, details the violent early history of our planetary neighborhood, and looks at the powerful telescopes now scanning the skies for a moving point of light a million times fainter than the dimmest visible star.

Some questions sound simple until you try to answer them. I wanted to understand how scientists can  ...