There are several theories on how exactly Saturn's rings developed, and a recent discovery, published in the journal Nature, seems to bolster one of these. The sixth planet from the Sun and the second largest planet in the Solar System, Saturn, has clusters of "moonlets" which make up its trademark rings. The theory that large icy moons were slowly pulverized to form the ring system appears to be the most consistent with the findings published by University of Colorado researchers in Nature's Oct. 25 issue.

"The origin and evolution of planetary rings is one of the prominent unsolved problems of planetary sciences," write the study authors in this week's issue of the journal Nature.

The team, led by Miodrag Sremčević, a postdoctoral researcher at the University of Colorado in Boulder, found eight of the moonlets in Saturn's A ring were concentrated in a narrow belt, not scattered throughout the ring. This pattern suggests they were the result of a collision and not of a calmer process. "Some bigger moon was orbiting within the ring and was struck by a larger meteorite or comet," Sremčević said. "What we see today are remnants of that larger moon."

"I really did not expect that," Sremčević said. "I was thinking these moonlets are everywhere, and with more patience and observation we would find them throughout the rings."

The observed moonlets are between 160 and 500 feet across and were detected through the observation of eight propeller-shaped "wakes" in a thin belt of the outermost "A" ring. These "wakes" highlight areas of the belt where nearby material has been perturbed by the gravitational forces caused by individual moonlets. The discoveries were the made using images taken by Cassini, a joint NASA and European Space Agency spacecraft. Cassini is the size of a small bus and is in the last year of a four-year mission to investigate Saturn and its moons and rings.

Besides the researchers from UC Boulder, the study was also co-authored by Juergen Schmidt, Martin Seiss and Frank Spahn of the University of Potsdam in Germany and Heikko Salo of the University of Oulu in Finland.

Galileo Galilei first observed Saturn's rings in the 17th century, but has failed to understand them as such. Another 17th century scientist, Christiaan Huygens, was the first known person to suggest Saturn was surrounded by a ring. He was aided by a much better telescope than that used by Galilei. The first to understand that the rings could not be solid or they would become unstable was James Clerk Maxwell in 1859. Thus, four centuries have passed and we still cannot fully grasp the origin and composition of Saturn's famous rings.