New Saturn Ring Is Largest Known; May Solve Moon Puzzle

October 7, 2009

A newly discovered, dark ring around Saturn is the largest known planetary ring in the solar system, a new study says.

If the new ring were visible from Earth, it would look twice as wide as the full moon.

Until now, that title of largest planetary ring belonged to Saturn's E ring, which orbits Saturn at a distance of about 400,000 miles (640,000 kilometers). The new Saturn ring is about 20 times farther—about 8 million miles (13 million kilometers) from Saturn (Saturn pictures).

Scientists think the new ring is made from dust-size particles kicked up as comets and other space debris slam into Saturn's outer moon Phoebe.

(Flashback picture: new Saturn ring found in 2006.)

Saturn Ring Hiding in the Dark

The ring has avoided detection until now because it's made from the same dark, carbon-rich material as Phoebe.

Though the new ring is dark, it's anything but cold—and it's that heat that gave the ring away this February, with a little help from NASA's infrared Spitzer Space Telescope.

"When you have dark objects sitting in the sun, they warm up and reemit that heat like a black car in the sun," said study team member Douglas Hamilton of the University of Maryland.

New Ring Solves Saturn Mystery?

The new ring could explain a long-standing mystery about the strange two-tone coloration of Phoebe's neighbor Iapetus, another Saturn moon (picture of Saturn moon Iapetus).

Half of walnut-shaped Iapetus is icy and bright. The other half appears to be covered in a soot-like material of mysterious origin.

Now the researchers think the dark coating comes from particles from the newly discovered ring.

It's no accident Iapetus is essentially half black and half white. The moon is gravitationally locked to Saturn like our moon is with Earth, so one side of Iapetus constantly faces Saturn.

That arrangement means the dark side of Iapetus is continually bombarded by particles from the new ring as the moon orbits Saturn, the study says.

"The dark material," Hamilton said, "hits the leading face of Iapetus like bugs on a windshield."

The new Saturn ring research is to be published in tomorrow's issue of the journal Nature.

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