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-HuygensCassini-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.