Saturn's sharp-edged rings revealed by Cassini
newscientist.com
The Cassini spacecraft has returned the most detailed images ever seen of Saturn's rings, just hours after passing through them and into orbit. The pictures should help scientists explain the enormous complexity of the rings, and perhaps how they formed.
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."
The rings are thought to be only a few hundred million years old. They may have been created when an old moon of Saturn was pulverised by an asteroid, or when a fragile comet strayed too close and was shredded by Saturn's gravity.
Some of the fine structures discovered by Cassini should help scientists work out how the rings develop dynamically and so work out their age much more precisely. That would give a clue to their origin.
The resolution in the image above is about 200 metres per pixel. The Sun is behind the rings and out of sight - the picture is taken from the dark side, and sees the only the diffuse light scattered through the rings.
It is also a raw image, as transmitted by Cassini, so it still shows electronic interference (the horizontal lines) and glitches where cosmic rays hit the camera. "Maybe it's the kind of picture only a ring scientist can love, but I think it's beautiful," says Porco. |
