Stunning images from Saturn probe

By Richard Black
BBC science correspondent

The UV images show interior rings of red "dirt"

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The Cassini-Huygens mission which reached Saturn last week has sent back startling images of the planet's famous rings viewed in ultraviolet light.

The pictures processed by University of Colorado researchers depict the famous feature in shades of turquoise and red.

The different colours are indications of the rings' varied composition.

Cassini scientists say the spacecraft's four-year tour of the Saturnian system may tell them how the rings formed and if they are just a temporary feature.

Space scientists refer to the rings by letter, listing the major regions (from the inside) D, C, B, A, F, G, E. Cassini-Huygens actually passed between F and G when it arrived at the planet on 1 July.

Images taken during that orbit insertion by Cassini's Ultraviolet Imaging Spectrograph show up details the spacecraft's two main cameras cannot detect looking in the visible part of the spectrum.

The red indicates sparser ringlets believed to be made of particles that are "dirty" and possibly smaller than those in the denser, icier ringlets, which are shown in turquoise.

A faint stream of material appears to connect the F ring to Prometheus, the white blob at the bottom (Nasa/JPL/SSI)

The dirt probably contains silicates and organic material, scientists say. The ice is likely to be a mixture of water and other substances such as ammonia.

Some of this dirt seems to be the same material which dominates the surface of the outer moon Phoebe, adding weight to the theory that the rings formed from the demolition of a previous moon.

The Cassini-Huygens mission is living up to its billing, delighting researchers with the quality and abundance of data it is able to return to Earth.

The spacecraft has shown how the rings ripple and shimmy - in one image, the thin outer F-ring snakes across the Saturn sky like a newly cracked whip.

"We knew there was a pair of moons, one on each side, that were somehow interacting with the ring," says Professor Carl Murray from Queen Mary University of London.

"So I was sitting looking at the images, and I noticed that there appeared to be like a stream of material coming from the F-ring to the inner of the two moons, Prometheus," he says.

Outer rings, shown in turquoise, contain more ice

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"That was confirmation of a theory that had been produced over four years ago; that's very satisfying."

Saturn's biggest moon, Titan, is believed to be the only body in the Solar System other than Earth with liquid on the surface.

Cassini has already been able to peer through its dense clouds, photographing a large crater, deposits of ice, and lines and circles of unknown origin.

The images of Titan and Phoebe are strangely reminiscent of photos of the Earth and our own Moon, taken decades ago by the earliest space missions.

They are so clear that you struggle to remember that they are coming from a distance of one-and-a-half-billion km.