Transcript Moons and Rings

Moons and Rings
Jupiter’s Moons
• Jupiter is surrounded by 67 satellites.
– Four large Galilean satellites
– At least 16 over 5 km
Galilean moons
Captured moons
Captured Asteroids
• Jupiter’s immense gravity can capture passing asteroids
and comets.
• Some objects will remain as moons, others strike Jupiter.
• Captured moons may travel either direction around Jupiter.
incoming
asteroid
Captured retrograde
moon
Saturn’s Rings
• Galileo (1610) first saw
the rings, but thought they
were moons.
• Huygens (1659)
recognized that the shapes
on either side were due to
a ring.
Ring Structure
• The ice and dust is not that
close together.
– Groups in thin bands
with gaps
• The dust is pulled by
gravity of Saturn’s moons.
– Over 150 moons
identified
– Charged dust lines up in
magnetic field
Formation of Rings
• Ice and dust normally
accrete to form planets
and moons.
• Tidal force is too strong
inside the Roche limit.
– Saturn’s rings
Cassini-Huygens has
studied Saturn since 2004
Rings Around Planets
 Jupiter
 Uranus
 Neptune
Uranian Shepherds
• Uranus has the second largest ring system, possibly left
from past collisions.
– 27 known satellites
• Shepherd moons guide the ring particles.
Neptune’s Future Rings
• Neptune has a large moon, Triton, which revolves
retrograde.
– One of 14 known satellites
• Tidal forces will draw Triton in over time.
• When Triton reaches the Roche limit it will break up and
form rings larger than Saturn’s.