In 2026, an unmanned NASA spacecraft is scheduled to arrive at 16 Psyche, a massive, metallic asteroid floating somewhere between the orbits of Mars and Jupiter. Why is NASA so interested in this heavy metal asteroid? Are we going to mine all that metal, or build a giant space magnet? Linda T. Elkins-Tanton explains how the real answer can be found right under our feet. Lesson by Linda T. Elkins-Tanton, animation by Eoin Duffy.