Scientists at the University of Colorado at Boulder said new calculations, based on Cassini observations taken last May with the Ultraviolet Imaging Spectrograph, or UVIS, show the ring's opacity - or light-blocking capacity - is as much as 35 percent higher than previously reported.

Previous readings taken by the Voyager spacecraft in the early 1980s found the ring was more transparent, indicating it contained less material, said Joshua Colwell of CU-Boulder's Laboratory for Atmospheric and Space Physics.

Because of the uneven distribution of the ring particles - which range in size from dust grains to school buses - the transparency of the rings depends on the angle from which they are viewed, he explained. The particles are arranged essentially parallel in long stringy clumps as large as 60 feet across, 16 feet thick and 160 feet long, according to models produced from observation data, Colwell said.

Writing in the April 1 issue of Geophysical Research Letters, Colwell and colleagues said they have compiled a new image of the A-ring that shows the distribution of the material. The opaque B-ring has more material than the A-ring, located just outside it, and the A-ring is densest near its inner edge, the researchers said.

The A-ring particles are trapped in ever-changing clusters of debris that are regularly torn apart and reassembled by gravitational forces from the planet, Colwell said, adding his team deduced the size and behavior of the clusters by observing flickering light as the ring passed in front of a star in a process known as stellar occultation.

"The flickers are like a time-lapse movie of a car's headlights taken from the other side of a picket fence," Colwell said. "The flickering would provide us details about the pickets."

The observations of the particle clusters indicate the A-ring is primarily empty space. A close-up view of the rings would show as "short, flattened strands of spiral arms with very few particles between them," he said.

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