Planetary Rings

1
Planetary Rings
2
Rings are swarms of orbiting particles

• Orbits have to be very circular
• Elliptical orbits will result in collisions,
  destroying the ring

3
Rings Have to be Very Flat

• Inclined orbits will result in collisions and
  destruction of the ring

4
Rings have to be Equatorial

• Tilted orbits precess the plane of the orbit
  rotates due to the planets equatorial bulge,
  other satellites, and the Suns gravity

5
A tilted ring wont stay flat very long

• Particle orbits will precess at different rates
• Collisions will soon destroy the ring

6
Rings, Gaps, and Resonances

• When two objects return to the same relative
  positions regularly, they are said to be in
  resonance
• Some resonances are stable. Mercurys 32
  resonance between its rotation and its orbit is
  an example.
• Plutos period is 3/2 that of Neptunes. This
  resonance keeps the two planets from ever
  colliding even though their orbits cross.

7
Rings, Gaps, and Resonances

• Some resonances create gaps. There are no
  asteroids with one-half Jupiters period because
  repeated pulls by Jupiter eventually would change
  the asteroids orbit.
• Gaps in Saturns rings are due to resonances with
  Saturns satellites.

8
Shepherd Moons

• Shepherd Moons help maintain the sharp edges of
  rings

9
A Shepherd Moon Outside a Ring Tends to Drag
Stray Particles Back, Causing Them to Fall Back
Into the Ring
10
Outer Shepherd Moon
11
(No Transcript)
12
(No Transcript)
13
(No Transcript)
14
(No Transcript)
15
(No Transcript)
16
A Shepherd Moon Inside a Ring Tends to Speed
Stray Particles Up, Causing Them to Rise Back
Into the Ring
17
Inner Shepherd Moon
18
(No Transcript)
19
(No Transcript)
20
(No Transcript)
21
(No Transcript)
22
(No Transcript)
23
Rings Are Probably Short-Lived

• Gravity of the Sun and planets satellites
  constantly disturbs orbits of particles
• Collisions probably happen frequently
• Particles should drift out of the ring
• Rings around outer planets have probably come and
  gone repeatedly during history of Solar System

24
(No Transcript)