Cassini reveals Saturn's raucous rings
Images from the satellite show that Saturn's rings shift and tumble, changing their structure on very short time scales for astronomy: years, months or even days.
"This rambunctious system gives us a new feel for how an early solar system might have behaved," said Linda Spilker, a Cassini project scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif.
"This kind of deep, rich data can only be collected by an orbiting spacecraft, and we look forward to the next seven years around Saturn bringing even more surprises," she said.
Two studies of the Cassini data were published this week in the journal Science, one on the rings and one on Saturn's atmosphere.
The objects that made up the planet's rings are composed mostly of water ice, and collisions in the rings are routine, leaving trails of debris, the probe found. The chunks of ice are contaminated with a reddish substance that could be rusty iron compounds or organic molecules.
Cassini's data revealed how gravity from Saturn's moon and the planet itself toss and pull the micro-satellites around, preventing them from coalescing and forming moons themselves.
When sunlight hit Saturn's rings edge-on during the planet's equinox, Cassini saw that rings that were normally tens of metres thick were flipped up as high as mountains.
"It has been amazing to see the rings come to life before our very eyes, changing even as we watch, being colourful and taking on a tangible, 3-D nature," said Jeff Cuzzi, lead author of the ring study.
The scientists also looked at the magnetic fields surrounding the planet and found an unexpected source for the charged particles there.
Cassini found that the biggest source of charged particles is Saturn's moon Enceladus, not the sun or Saturn's largest moon, Titan. Enceladus also sprays water vapour and other gases from its south pole.
"We learned from Cassini that the Saturnian magnetosphere is swimming in water," said Tamas Gombosi of the University of Michigan in Ann Arbor. "This is unique in the solar system and makes Saturn's plasma environment particularly fascinating."
The Cassini spacecraft is the largest and most complex interplanetary spacecraft ever built. It's the result of a co-operative project that includes NASA, the European Space Agency and the Italian Space Agency. The mission is managed by the Jet Propulsion Laboratory.
The probe arrived in Saturn's neighbourhood in 2004, but it's not the first to look at the ringed planet. The Voyager missions flew by Saturn in the early 1980s.
Cassini is loaded with a dozen instruments, everything from cameras that take pictures in visible light to radar that can peer into the depths of planets' atmospheres. It can measure magnetic fields and analyze the quantity and composition of dust particles.
"Cassini has answered questions we were not even smart enough to ask when the mission was planned and raised a lot of new ones," Cuzzi said.
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