Three hundred and ten miles above our planet’s surface, near-Earth space is abuzz with action. Here begin the Van Allen Belts, a pair of concentric rings of fast-moving particles and intense radiation that extends more than 30,000 miles farther into space. For the most part these particles are confined to this special region, spiraling along Earth’s magnetic field lines. But sometimes they come too close and crash into our atmosphere—creating the eye-catching diffuse red aurora, but also potentially interfering with critical communications and GPS satellites that we depend on every day.