FAST, the Fast Auroral Snapshot Explorer, was the second Small Explorer mission. FAST investigated the behavior of ionized gas, called plasma, and particles during auroras. Auroras generally form when solar material causes a disturbance in near-Earth space, either in the form of a cloud called a coronal mass ejection or a variation in the sun’s constant outflow of material known as the solar wind. A complex interaction of particle acceleration, electric currents, and plasma waves propagate into Earth’s atmosphere, creating the brilliant light show known as the aurora. As FAST flew over the poles—the most common regions where auroras form—it took quick, high-resolution bursts of data on particles, electric and magnetic fields, and plasma.