For years scientists have seen Saturn's rings as stable and slow to evolve—beautiful but, well, a bit boring. Not anymore.
The most detailed imagery of the rings yet is giving a very different and dynamic feel to the orbiting bands of ice chunks, according to two new studies in this week's issue of the journal Science.
By imaging the rings close up, in many wavelengths, and with unprecedented frequency, NASA's Cassini orbiter has revealed a slew of surprises. Among them are rings that rapidly rearrange themselves, high-speed collisions—not to mention an oxygen atmosphere.
(See Saturn pictures.)
"Here's this giant crystalline structure, stretching two-thirds of the distance from Earth to the moon, and yet parts of it change on a monthly or weekly time scale," said planetary scientist Jeff Cuzzi, from NASA's Ames Research Center in Moffett Field, California.
The edges of the thickest of Saturn's rings, A and B, for example, "kind of flop back and forth, sometimes pointing one way and sometimes another, sloshing around like water in a tank," said Cuzzi, co-author of one the new studies.
These fast-warping edges, he said, underscore the newfound, fluidlike nature of the rings.
Also, recent studies have uncovered dozens of mysterious moonlets, several kilometers in size, bouncing around like bumper cars in the slim, outermost ring, called F.
"These cannonballs are whizzing through the F ring and colliding with things," Cuzzi said. "What are these things? Where did they come from?
"This doesn't strike us as a particularly stable situation."
Oxygen Atmosphere Around Saturn Rings?
Scientists were also surprised to find that the atmosphere around Saturn's rings is largely made up of oxygen.
"Most people thought the ring atmosphere would be water molecules—H2O—and their breakdown products H [hydrogen] and OH [hydroxyl]," Cuzzi said. That the ring system would have the chemistry to turn hydrogen and hydroxyl into oxygen "was not foreseen by most."
The discovery could help solve a long-standing mystery of Saturn's rings: why some of them seem stained red.
Perhaps the color is imparted when metals in ring rocks interact with oxygen, he said. On Earth we have a name for it: rust.
Saturn Rings Hold Keys to Planet Birth?
Saturn's rings seem to be much like the dusty, rocky disks around stars where planets form, said Cassini team member Larry Esposito, of the University of Colorado in Boulder.
If the ring system is in fact a reasonable facsimile for a planet nursery, Saturn may change our understanding of how planetary disks behave. (Explore an interactive solar system map.)
Thanks to Cassini's close-up view of Saturn's rings, "we can see structures and phenomena that we would not have otherwise imagined existed in planetary disks," said Esposito, co-author of one the new Saturn studies.
One such phenomena is clumping, which Esposito called one of the most surprising things he's seen around Saturn. Cassini images reveal that gravity temporarily binds rocky ice chunks together, forming superchunks perhaps 30 feet (10 meters) across.
"The dynamics in the thicker A and B rings are much more complicated than we thought because of this clumpy nature," he said, "and those rings are more massive than we'd thought.
"When you know the mass you can say something about the origins of the rings," he said.
But that knowledge may have to wait until 2017, when Cassini is to measure the rings' masses as it plummets to destruction on Saturn.
So far, "Cassini has helped to refine the questions, but not provide the answers, on where the rings came from and when they were created," Esposito said. "And that is still my number one question."