for National Geographic News
We've long known that Saturn has dozens of moons, ranging from gigantic Titan (about as big as the planet Mercury) to asteroid-size chunks only a few kilometers in diameter.
There are also uncounted ring particles, varying from marble size to the size of a small house.
Now scientists have found the first evidence of millions of "missing link" moonletsbigger than ring particles but small enough to fit inside a football stadium.
The international team found signs of four such moonlets in one small segment of Saturn's brightest ring, called the A ring, according to a report in this week's issue of the journal Nature.
When they made the discovery, the scientists were examining the high-resolution photos taken by NASA's Cassini probe shortly after it reached Saturn in 2004.
"Since we hadn't ever seen the rings in this kind of detail, we were looking for phenomena we'd never seen before," said Carolyn Porco, head of the Cassini imaging team at the Space Science Institute in Boulder, Colorado.
What the scientists found were pairs of bright streaks shaped like two-bladed propellers. The streaks weren't big, only about 3 miles (4.8 kilometers) wide.
But they looked familiar.
Computer simulations produce similar structures, Porco said, when the motions of ring particles are simulated in the presence of small moonlets within the ring.
The presence of two Saturn moons, Pan and Daphnis, has created gaps that circle the entire ring systemempty bands in the striped ring pattern. But Pan is 19 miles (30 kilometers) wide and Daphnis is 4 miles (7 kilometers).
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