The ringed planet Saturn, brilliant jewel of the night sky, has revealed new insights into the behavior of its rings for scientists studying signals from the Cassini spacecraft still flying through the Saturnian neighborhood after six years in orbit.
"We now have the clearest view of the rings' beautiful crystalline structure pasted onto the real night sky," said Jeffrey Cuzzi of NASA's Ames Research Center in Mountain View, leader of the Cassini-Huygens mission. "Gazillions of icy particles are constantly colliding with each other up there as they orbit the planet ... moving as waves under the influence of moonlets we've discovered orbiting inside gaps between the rings."Saturn's rings, through even the best of telescopes, look like series of thin flat discs grooved like an old phonograph record. But that's far from the truth: From Cassini's images and data, researchers have determined that each ring is a turbulent collection of orbiting particles - 95 percent water ice glistening in sunlight and the rest some strange kind of rubble tinged in red-brown here and there.
"That color may be some kind of organic materials," said Cuzzi, "but to me it looks like just plain rust - iron oxide. How it got there we don't yet know."
The ice chunks range in size from a few inches to tens of yards. As they orbit the planet, gravity turns some into huge clumps and pulls others apart, and they batter each other chaotically.
Beyond Saturn's major rings, Cassini scientists report they have detected several other faint rings that seem to be composed of minute amounts rubble and "microscopic dust."
The physics involved in their evolution suggests they are similar to the "protoplanetary discs" of rubble that on a much larger scale mark the earliest stages in the formation of the planets in the solar system.
But just how long ago the rings of Saturn formed and where their material came from originally remains a mystery, the scientists say.
The rings and the icy matter they contain are far from stable in their orbits around the planet. Instead, they appear to be changing constantly.
"Saturn's rings show dramatic variability (over) decades, years, even weeks," said the scientists.
Cassini's instruments have also revealed that strange objects occasionally shoot through the rings from far beyond the planet - comets, or asteroids, perhaps, but know one knows, Cuzzi said.
Each of Saturn's rings is labeled by a letter according date when it was discovered. Between Saturn's A and F rings lies a space 200 miles wide called the Encke gap. The gap holds several "ringlets" and gravity from a strange object named Pan, only 12 miles in diameter, disrupts the rings and causes waves along their edges.
Another gap exists between the thin ringlets of the Encke gap. It is called the Keeler gap, and here Cassini has discovered a lumpy little moonlet only 5 miles across that is also creating waves on the edges of Saturn's rings.
Amid all of Saturn's rings and ringlets lie 13 significant gaps, where Cassini mission scientists have been hunting for evidence of other moonlets. The absence of moonlets inside Saturn's C ring remains "baffling," the scientists say.
For now, the origin of the rings and much of their turbulent behavior will remain unknown, the scientists say, "until we have understood the powerful dynamical processes that have formed, and continue to shape, these elegant structures on time scales reaching from yesterday to billions of years" ago.
From http://www.sfgate.com/
