Saturday science subject: Broken moon

New findings by the Cassini spacecraft suggest one of Saturn's rings was created by the disintegration of an ancient moon, as the New Scientist reports.
Saturn's faint G ring lies beyond the planet's main set of rings and has puzzled scientists since it was first detected by NASA's Pioneer spacecraft in 1979. They wondered how it could continue to survive with no moon nearby to feed it with debris or stop its dust from dispersing – the nearest moon, 400-kilometre-[250-mile-]wide Mimas, lies more than 15,000 km [9,321 miles] away.

Now, images captured by the Cassini spacecraft are providing an important clue. They reveal a bright arc at its inner edge that is thought to consist of bigger chunks of debris, some a metre [3.3 feet] in diameter. As they are bombarded by micrometeorites, dust flies off these large chunks "and spreads out to form this ring", says team leader Matthew Hedman of Cornell University in Ithaca, New York, US.

If the chunks were unified into a single object, they would form a 100-metre-[110-yard-]wide icy moonlet – a body that astronomers believe actually existed at one time.

The New Scientist says the gravitational influence of Mimas, one of Saturn's remaining moons, controls the G ring's movement. As Jeff Cuzzi of NASA's Ames Research Center tells the publication, "We think of these outer planets as pristine and unchanging, but they're really not." He adds, "There's a lot of action going on out there."
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