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It seems to be a given that gas giants have rings. However,Saturn has rings that are far larger than any others in the Solar System, and far more visible as well. What is unique to Saturn that it has such a large and complex ring system? Images from Wikipedia, in order of planet, Jupiter, Saturn, Uranus, and Neptune.

Jupiter

Saturn

Uranus Ring System

Neptune Ring System

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There are two factors at work here:

  1. The rings of Saturn are made of much more reflective material (water ice) than those of Jupiter, Uranus or Neptune.
  2. They simply have much more matter in them. This wikipedia article and this one suggest a mass for Saturn's rings ($1-3\times 10^{19}$kg) which is at least 1000 times greater than that of Jupiter's rings ($10^{14}$ -- $10^{16}$kg) including possible small moons embedded in the rings.

The question of why this arose is, as far as I know, more or less completely open, especially given that we don't even have much of an idea whether these ring systems have been around since the planets formed, or are much more recent. It could be pure chance, perhaps related in part of the sizes and orbits of the moons. It might relate to how far from the Sun the planets formed, and how they got to their present positions, which is still very much under active discussion.

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source:Wikipedia This image shows that the rear side of Saturn rings is dark.

source:astrobobThese images show the variation of the rings' brightness: the closer Saturn is to Earth, the brighter its rings appear.

The rings of Saturn consist of 99% of water and the remainder are various impurities.

The water is in the form of water ice. Since ice is a crystalline structure, it reflects and refracts light, making the rings appear bright.

But the brightness also depends upon the intensity of incident light: the closer Saturn is to the Sun the bright its rings.

The reason the rings of Jupiter appear dull (even though it is on average closer to Earth than Saturn is) is that they are composed of dust, which is darker than ice.

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    $\begingroup$ This is almost a good answer, but a bit incoherent... $\endgroup$ – PearsonArtPhoto Oct 3 '13 at 16:45

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