Surprised scientists have found that the four small moons of Pluto—Styx, Nix, Kerberos, and Hydra—rotate faster than expected. Kerberos, pictured here, rotates once every 5.33 hours, the slowest of the four. But Hydra, the fastest, makes an unheard of 89 rotations per orbit of the dwarf planet. Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Southwest Research Institute