When Stardust was in particle-capturing mode, the return capsule was opened and an arm was extended away from the spacecraft. On this arm, which looked like a ten nis racket or catcher’s mitt, were flat mounted trays of Aerogel—a superlight, super-strong substance. When the particles struck the Aerogel, they would suddenly slow down from over ten thousand miles per hour to zero in a split second, embedding into the matrix without breaking or melting. When the particle collection was over, the arm retracted and the Aerogel was safely stored in the return capsule.