Ring Systems

demonstrate an understanding that some planets have satellite systems with a variety of origins and structures (including Mars and Neptune)
describe the appearance, physical nature and composition of planetary ring systems.

We have seen how our moon was probably the result of a collision between the Earth and another large object. There are other ways that planets can come to have moons.

Mars Phobos and Deimos, the two tiny moons of Mars, are thought to be captured asteroids	Neptune Neptune has 13 known moons but the largest by far is Triton. Triton has a retrograde orbit. This suggests that it is probably a captured Kuiper belt object (as it formed at a different time to the planet it orbits). Triton is officially the coldest object in the solar system.

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Ring Systems

Jupiter, Saturn, Uranus and Neptune all have ring systems. One of the most spectacular features of our solar system are the the rings of Saturn. Here are some facts about them.

• They are about 95% ice.

• Made of small particles from millionths of a metre to several metres.    

• Average thickness is only 20m.

• The outer A ring is separated from the B ring by the dark Cassini division.

If a moon's orbit decays beyond a certain point then it gets ripped apart, by gravitational forces, into lots of little pieces. It is thought that this is the origin of Saturn's rings.