Week 7: Planetary Ring System

Question 1

Describe Jupiter’s rings

Answer 1

• Consists of 3 rings: Halo, main, and Gossamer rings
• All rings are optically thin, extremely faint, and consist of micron-sized dust
• All rings are made from ejecta from surrounding moons
  
  • This is because Jupiter has deep gravity well, which attracts small impactors that strike its moons, causing them to release dust
  • Halo rings spread away North-South from the equator due to Jupiter’s electromagnetic influence on dust grains, and are truncated by magnetostatic interactions

Question 2

State similarities and differences between Neptune’s and Uranus’ rings

Answer 2

Similarities:
- Both are characterized by many narrow and faint bands
- Both planets are immersed in dusty environment
- Both are more visible when back-lit on the night side

Differences:
- All of Neptune’s rings are optically thin, but Uranus contains one optically thick E ring.

Question 3

Explain how gravitational force from Saturn’s moons affect its rings.

Answer 3

• Responsible for sharp edges, density variations, vertical warps, and arcs
• Strongest at resonances
  
  • Moon’s perturbations can cause outer edge to move in/out. If the period of in/out motion = whole number ratio times moon’s orbital period, this results in Lindblad Resonance.
  • If the particle’s orbital periods = whole number ratio times the moon’s radial motion period, this results in Corotation Resonance which forms arcs
  • Resonances can also cause localized disturbances that changes the rings’ apparent brightness

Question 4

Explain how Vertical Resonance affect Saturn’s rings.

Answer 4

• When the moon’s orbit is inclined relative to the ring’s plane, the moon can pull ring particles up and down
  
  • If the period of the particles’ vertical motion = whole number ratio times the moon’s orbital period, this results in Vertical Resonance.
  • This produces warps in the rings that cast shadows near equinox

Question 5

Describe how Saturn’s rings form and evolve/ dynamics of Saturn’s rings

Answer 5

Formation:
- Saturn has a deep gravity well that attracts stray bodies into its orbit
- This results in satellite fragmentation due to disruptions and impacts, which adds to/ replenish ring particles

Evolution:
- The ring evolve from shear motion which causes radial spreading
- Gravitational forces from the moons keep ring edges sharp with clear gaps

Question 6

Describe how Saturn’s E ring and Phoebe ring form

Answer 6

E ring:
- Formed from icy grains ejected from the South pole of Enceladus that has reached escape v

Phoebe ring:
- Originates at an outer moon Phoebe, which ejects dust into space due to micrometeoroid impacts

Question 7

Describe what Spokes are and how they are formed

Answer 7

• Spokes are small dust grains levitating above Saturn’s rings
• Formed from thunderstorms on Saturn, where lightning strike the rings and charges dust, causing it to levitate