Did a Gigantic “Lost” Moon Create Saturn’s Rings?


One of the solar system's most evocative mysteries — the origin of Saturn's rings — may have been created by an unnamed moon of Saturn that disappeared about 4.5 billion years ago in a  forced plunge into Saturn leaving behind the planet's spectacular and rings. As the doomed moon made its death spiral, Saturn robbed its outer layer of ice, which then formed rings, according to a new theory.

"Saturn was an accomplice and that produced the rings," said study author Robin Canup, an astronomer at the Southwest Research Institute in Boulder, Colo. If the rings were formed by a moon-on-moon crash or an asteroid-on-moon, there would be more rocks in the rings. "Something had to have stripped away the outer ice of a large moon," Canup said.

Billions of years ago when the planets' moons were forming a large disk of hydrogen gas circled Saturn and that helped both create and destroy moons. Large inner moons probably made regular plunges into the planet, sucked in by the disk of gas.

These death spirals took about 10,000 years, during which  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.

According to Canup's model, 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, which explain Tethys, an odd inner moon that didn't quite fit other moon formation theories, she said.
But this doesn't explain rings on other planets in our solar system, such as Jupiter, Neptune and Uranus, which probably formed in a different way, Canup added.

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

Anéis de saturno

Image credit: The artist's rendering at top of page shows the biggest ring around Saturn, spotted by NASA's Spitzer Space Telescope. The inset shows an enlarged image of Saturn, as seen by the W.M. Keck Observatory at Mauna Kea, Hawaii, in infrared light. (Artist's rendering courtesy NASA's Jet Propulsion Laboratory/Associated Press)

Casey Kazan via nature.com


"The Galaxy" in Your Inbox, Free, Daily