planetary ring systems. rings: a b c 4/4 giant worlds have rings jupiter: broad, dark, fine...
TRANSCRIPT
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. Saturn’s rings span 100,000 miles, are only a few yards thick in places.
Why rings?
Tidal forces destroy a large solid moon insides a planet’s 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 ofIndividual particles in orbit; they sap energy but not momentum.
Comet Shoemaker-Levy 9 following a 90-minute excursionwithin Jupiter’s Roche limit.
This is not a large gravitationally-bound moon
How do they stay there?
Random motions should make some particles leave therings and limit their lifetime. External effects can helpherd stragglers back. Main example: shepherd moons.
Internal structures
Rings can be very thin. Radial structures can be producedby gravitational influences (such as perturbations and tidesfrom nearby moons). Example: Cassini division in Saturn’srings. Weaker disturbances and wave patterns can dividea ring into myriads of ringlets.
Arcs of enhancedparticle density inrings of Neptune(Liberte, Egalite,Fraternite; they werefound in 1989)
Origins
Some ring systems are intimately tied to small satellitesas sources of particles. But where did all that ice aroundSaturn come from?
Puzzles
• Radial spokes in Saturn’s rings
• How long have rings been there? Are they part of a perpetual juggling act?