Planetary astronomer Mark Showalter is rabid about rings. While everyone knows about Saturn’s spectacular ring system, it’s often forgotten that Jupiter, Uranus, and Neptune are also encircled by fainter and narrower rings. Each of these systems interacts closely with a family of small, inner moons. Showalter works on some of NASA’s highest-profile missions to the outer planets, including Cassini, now orbiting Saturn, and New Horizons, which flew past Jupiter en route to its 2015 encounter with Pluto. He has even searched for the rings of Mars, although so far with no success. Known for his persistence in planetary image analysis, Mark's work on the earlier Voyager mission led to his discovery of Jupiter’s faint, outer “gossamer” rings and Saturn’s tiny ring-moon, Pan.
Mark was recently granted three more years to study the system of rings and moons orbiting Uranus with the Hubble Space Telescope. He has been leading a team of astronomers in this investigation off and on since 2002. This work has already led to the discovery of two small moons and two faint rings. He enjoyed the opportunity to name the moons "Mab" and "Cupid," after characters from Shakespeare's plays. For the next few years, he hopes that this work will illuminate the subtle interactions at work within a dense pack of moons and rings that circle the planet. The system shows signs of chaotic motion, which means that the orbits are slightly unpredictable and collisions between moons can occur on time scales as short as one million years. That may sound like a long time, but it is astonishingly short for a system that is more than 4 billion years old.
Rings and the faint moons that interact with them are more than just local anomalies. They serve as dynamical laboratories where we can observe some of the same processes that operate, albeit on much larger scales, in galaxies and during the formation of planetary systems.