Chunks of smashed moon detected in Saturn's rings

WASHINGTON, Oct 25 (Reuters) Big chunks of a moon that was smashed long ago perhaps by a comet have been detected in Saturn's outermost ring, shedding light on the formation of the planet's grand ring system, scientists said.

A camera on NASA's Cassini spacecraft spotted wakes ahead of and trailing behind these fragments, where other ring material has been affected by the gravitational forces exerted by the pieces, they said yesterday.

The rings encircling Saturn are one of the most dramatic features of the solar system. The other gaseous planets in the solar system -- Jupiter, Uranus and Neptune -- also are encircled by rings, but they are not as spectacular.

The scientists called the fragments seen in this relatively narrow belt within Saturn's outermost ring ''moonlets.'' They were not directly observed by Cassini, but the scientists inferred their existence because of the eight propeller-shaped wakes.

It appears some of the fragments are as big as a sports stadium, the scientists said.

''There was probably a bigger moon of at least 32 km in diameter or larger orbiting at that place,'' Miodrag Sremcevic of the University of Colorado at Boulder's Laboratory for Atmospheric and Space Physics, one of the researchers, said in a telephone interview.

''And that moon had the unfortunate fate to be struck by a large meteoroid or comet and was destroyed into pieces. And now what we see today are the remaining shards of that moon,'' said Sremcevic, whose findings appear in the journal Nature.

The findings represent the first evidence of a ''moonlet'' belt in any of Saturn's rings, according to Sremcevic.

Saturn's innermost moon, Pan, is about the same size as the doomed moon, Sremcevic said. The collision that shattered it took place perhaps 100 million years ago.

There is a scientific debate over the origins of Saturn's rings. These findings support the idea that the material that makes up the rings is debris from collisions involving moons orbiting the giant planet that has spread out over time, said Nicole Albers, another researcher at the University of Colorado who worked on the study.

''This is another piece of the puzzle,'' Albers said.

Another theory holds that the rings were formed at the same time as Saturn and from some of the same material that created the second-largest planet in the solar system.

REUTERS SKB HS0949