Planetary Ring Systems

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Planetary Ring Systems
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Rings A B C
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4/4 Giant Worlds Have Rings

• Jupiter broad, dark, fine particles
• Saturn broad, bright, complex, icy particles
• Uranus narrow, dark, fine particles
• Neptune uneven, fine particles
• All consist of independently orbiting small
  chunks of material within very thin layers.
  Saturns rings span 100,000 miles, are only a few
  yards thick in places.

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Why rings?
Tidal forces destroy a large solid moon insides a
planets Roche limit. Ring systems are always
found inside the Roche limit (about 1.44 planet
diameters above the surface). Collisions make
rings the final configuration for swarms
of Individual particles in orbit they sap energy
but not momentum.
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Comet Shoemaker-Levy 9 following a 90-minute
excursion within Jupiters Roche limit.
This is not a large gravitationally- bound moon
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How do they stay there?
Random motions should make some particles leave
the rings and limit their lifetime. External
effects can help herd stragglers back. Main
example shepherd moons.
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Pan and Prometheus shepherd Saturns outer thin F
ring
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Internal structures
Rings can be very thin. Radial structures can be
produced by gravitational influences (such as
perturbations and tides from nearby moons).
Example Cassini division in Saturns rings.
Weaker disturbances and wave patterns can
divide a ring into myriads of ringlets.
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Wave patterns in Saturns rings (unprocessed Cassi
ni data, July 2004)
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Arcs of enhanced particle density in rings of
Neptune (Liberte, Egalite, Fraternite they
were found in 1989)
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Origins
Some ring systems are intimately tied to small
satellites as sources of particles. But where did
all that ice around Saturn come from?
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Puzzles

• Radial spokes in Saturns rings
• How long have rings been there? Are they part of
  a perpetual juggling act?

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Voyager 1 time-lapse movie (contrast enhanced) of
ring spokes