More Strange Holes Found in Saturn's Rings

By Ker Than, Staff Writer

posted: 24 October 2007 01:00 pm ET

: Scientists have found evidence for a belt of moonlets in Saturn's outermost "A" ring (top image, outer purple band). The moonlets in the belt were detected by gravity "wakes" 10 miles to 20 miles across (boxed in bottom image) by NASA's Cassini spacecraft. Credit: NASA/JPL/Space Science Institute/ University of Colorado

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The discovery of more oddly shaped gaps in Saturn's rings strengthens the case that one of the planet's moons was smashed to bits in an ancient collision.

Shaped like airplane propellers, the gaps likely formed when "moonlets" as large as football stadiums plowed through Saturn's ring particles while orbiting the planet, scientists say. The propeller voids had been predicted from computer models, but they weren't observed until 2004, when NASA's Cassini spacecraft revealed four of them.

Scientists recently found evidence for eight more propellers by examining Cassini images snapped in 2005.

The discovery, detailed in the Oct. 25 issue of the journal Nature, lends further support to the theory that a comet or asteroid collided with one of the small Saturnian moons about 100 million years ago, creating "thousands and thousands" of boulder-sized moonlets, said study team member Miodrag Sremcevic of the University of Colorado at Boulder.

The moonlets are hard to discern because of their small size. "You need such a large zoom that even having spacecraft there, we can't see these individual moonlets because they are so tiny," Sremcevic said. "But we can see these propellers, or 'wings,' that flank the moonlets."

Each propeller is about 10 miles (16 kilometers) long, and the moonlets are thought to range in size from semi-trailers to sports arenas.

The new moonlets all float at a distance of about 81,000 miles (130,000 kilometers) from Saturn in a relatively narrow band only 2,000 miles (3,218 kilometers) wide, or only about 1/80th the diameter of Saturn's total ring system.

"We all expected they would be everywhere in the ring," Sremcevic told SPACE.com. "Our study shows they are concentrated in certain regions in the ring like a belt."