Dr. Mark Showalter

December 21, 2006

SETI Institute Principal Investigator

Anyone who has ever looked at Saturn through a telescope surely remembers the sight of its magnificent and intricate rings, and close-up views from Voyager and now Cassini show a system that only gets more surprising the closer we look.  However, it is often forgotten that Saturn's  is only oe of four planetary ring system.  Jupiter, Uranus, and Neptune are also encircled by rings that are less ostentatious but no less puzzling.  Jupiter's ring system consists of fine dust leaking off of a family of embedded moons and then dispersing under the influence of Jupiter's intense magnetic field.  Uranus and Neptune have narrow rings and even incomplete arcs, demonstrating subtle aspects of the interplay between ring material and nearby satellites.   What all four ring systems have in common is that they show bizarre features, some with names like "braids", "spokes", and "wakes", that no theorist would ever have imagined if we hadn't seen them in our telescopes first.

Planetary astronomer Mark Showalter sees ring-moon systems as dynamical laboratories where we can observe some of the same processes that also operate, on much larger scales of space and time, in galaxies and during the formation of planetary systems.  His research draws on observations from Voyager, Galileo, Cassini, the Hubble Space Telescope, and ground-based observatories to understand these processes.  Back in 1990 he studied a set of wiggles on the edge of the Encke Gap, a 300-km wide opening in Saturn's rings, and used his results to predict, and then discover, a small moon (now called Pan) embedded in the middle of the gap.  By pushing to the limit the capabilities of the Hubble Space Telescope, he recently discovered two tiny moons, each about the size of San Francisco, orbiting Uranus.  He is also participating in the Cassini mission to Saturn, using infrarred data to understand the dynamics and composition of its innumerable ring particles, ranging in size from the tiniest micron-sized motes to boulders the size of houses.

- SETI Institute Explorer, Special Edition 2005


Lectures and Presentations