Adapted and reprinted with permission from "Saturn's dynamical rings," by Carl D. Murray, Physics Today, August 2007, page 74. Cassini image courtesy of NASA/JPL/Space Science Institute; larger image
The Alphabet Soup of Saturn's Rings
The objects that make up Saturn's rings are in gravitational orbits about the planet, so the closer-in objects are moving faster than those further out (just as with the planets in the solar system or the moons of Jupiter). The image shows the gap swept out of the A ring by Saturn's moon Daphnis, and the disturbances it creates in the ring material in the nearby edges of this gap. The red arrows show the velocities of the material in the rings and also of Daphnis, and the black arrows show the relative velocities in Daphnis' frame of reference. You can watch an animation of Daphnis traveling through the gap here.
-- Since Daphnis moves faster than the particles in the ring just outside it, the disturbance on the outside looks like a wake, behind Daphnis.
-- Since Daphnis moves more slowly than the particles in the ring just on the inside, the disturbance on the inside is ahead of of Daphnis.
(This feature was updated on February 18, 2014.)
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