Are there rings around... Miami?

New Scientist -- Saturn's sharp-edged rings revealed by Cassini -- Stephen Battersby -- 17:08 01 July 04

The main rings are extremely thin. They stretch 70,000 kilometres from their inner to outer edge, but are only about 100 metres thick. They are made of loose ice particles in all sorts of sizes.

"They go from the size of houses down to the finest ice particles, like the snow you might ski on in Utah" says Carolyn Porco, head of Cassini's imaging team and an expert on the rings.

Voyager showed that thousands of gaps break the main rings up into ringlets that are often only a few kilometres wide. In the new pictures from Cassini, it is clear that some ringlets are narrower still, maybe only half a kilometre or less.

The pictures also show that they have very sharp edges, even though the ice particles should be bouncing off each other and blurring the edges of the rings. "It's very mysterious - they must be held sharp by some mechanism," says Porco. "In some cases it is done by moons, but with many of the edges we don't know the mechanism."