Planetary astronomer Mark Showalter studies the dynamics of rings and small moons in the Solar System. Known for his persistence in planetary image analysis, Mark's early work with Voyager data led to the discoveries of Jupiter's faint, outer "gossamer" rings and Saturn's tiny ring-moon, Pan. His work with the Hubble Space Telescope starting in 2003 has led to the discoveries of "Mab" and "Cupid," small moons of Uranus now named after characters from Shakespeare's plays. His work also revealed two faint outer rings of dust encircling the planet. In 2011, Mark initiated a Hubble observing program focused on Pluto, which has led to the discoveries of two tiny moons. Their names, "Kerberos" and "Styx", were selected through an international naming campaign. Most recently, Mark discovered the 14 known moon of Neptune, which is designated "S/2004 N 1" until its permanent name can be selected. He is a co-investigator on NASA's Cassini mission to Saturn and its New Horizons mission to Pluto.