December 13, 2010

Saturn’s Rings May Have Come From Killed Moon

New research suggests that the origin of Saturn's rings may be a case of cosmic murder.

According to a new theory published on Sunday in the journal Nature, the rings are the only evidence left of an unnamed moon of Saturn's that disappeared about 4.5 billion years ago

The report said that Saturn robbed its outer layer of ice as the moon made its death spiral, which then formed rings.

"Saturn was an accomplice and that produced the rings," study author Robin Canup, an astronomer at the Southwest Research Institute in Boulder, Colo, said in a press release.

Cornell astronomer Joe Burns, who was not involved in the study, told The Associated Press that Canup's new theory makes sense.

One of the leading theories has been that either some of Saturn's moons crashed into each other, or an asteroid crashed into some of them.  Canup said the problem is that Saturn's moons are half ice and half rock and the planet's seven rings are now as much as 95 percent ice and probably used to be all ice. 

She said that something had to have stripped away the outer ice.

A large disk of hydrogen gas circled Saturn and that helped create and destroy the moons.  Large inner moons probably made regular plunges into the planet.

These plunges took place for about 10,000 years and the key to understanding the rings' origins is what happened to them during that time.

Canup said that Saturn stripped the ice away from a huge moon while it was far enough from the planet that the ice would be trapped in a ring.

She said that the original rings were 10 to 100 times larger than they are now, but over time the ice in the outer rings has coalesced into some of Saturn's tiny inner moons. 

Canup said that this theory could help explain Tethys, an odd inner moon that did not quite fit other moon formation theories. 

According to Canup, this does not explain rings around other planets like Jupiter, Neptune and Uranus. 

She said that the rings and ice-rich inner moons are the last surviving remnants of this lost moon, "which is pretty neat."

Burns told AP that Canup's theory explains the heavy ice components of rings better than other possibilities.  Larry Esposito, who discovered one of Saturn's rings, said the new paper was "a very clever, original idea."

"I would call it more like cosmic recycling," Esposito told AP because the moon became rings which then became moons. "It's not so much a final demise, but a cosmic effort to reuse materials again and again."


Image Caption: The rings of Saturn (imaged here by Cassini in 2007) are the most conspicuous in the Solar System. Credit: NASA/JPL/Space Science Institute


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