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Saturn from Cassini Astronomy 161:
An Introduction to Solar System Astronomy
Prof. Richard Pogge, MTWThF 2:30

Lecture 41:
Planetary Rings

Key Ideas:

All Jovian planets have rings:

Ring properties:

All Jovian Planets have rings

Saturn's rings are bright and broad:

Uranus & Neptune have thin, dark rings:

Jupiter has faint, dusty rings:

Jupiter's Dusty Rings

Jupiter's rings are faint and dusty:

Divided into:

Dusty ring material may have been knocked off the moons of Jupiter by micrometeor impacts, or leftover from comets that crashed into Jupiter.

Saturn's Bright, Broad Rings

Saturn has the most elaborate of the Jovian ring systems:

The rings are very thin:

Orbiting Iceballs

Saturn's rings are not solid:

As the iceballs collide:

The constant collisions keep the iceballs bright and shiny. Old iceballs would gradually accumulate a dark "patina" of dust that would darken the rings.

Thin Rings of Uranus & Neptune

Uranus & Neptune have narrow, dark rings separated by large gaps.



Shepherd Moons

Thin rings should not last for very long:

Thin rings, however, can be gravitationally confined by a pair of Shepherd Moons:

Subsequent collisions between ring particles then damp out the eccentricities, resulting in the ring becoming confined between the Shepherd Moons.

[Review Lecture 19 on Orbits]

Rings and Resonances

Much of the fine structure within rings is governed by orbital resonances with the planet's moons.

Example: Saturn's Cassini Division.

The Origin of the Rings

The rings are not very massive:

Possible origins of the ring material:

Roche Radius

Distance at which the tidal forces from the planet on a moon equal the gravitational force holding the moon together: All rings are located inside the Roche Radii of their parent planets.
An excellent source for images of planetary rings and ring science is the Planetary Rings Node at the NASA Ames Research Center.
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Updated: 2007 November 19
Copyright Richard W. Pogge, All Rights Reserved.