The Cassini images show an arc of bright material looping around the inside edge of the G ring, a tenuous 4,400-mile-wide band of dust-sized icy particles lying beyond the F ring by 16,800 miles. Cassini passed between the F and G rings in June 2004.

"We have seen the arc a handful of times over the past year," said Matt Hedman, Cassini imaging team associate at Cornell University. "It always appears to be a few times brighter than the rest of the G ring and very tightly confined to a narrow strip along the inside edge of the 'normal' G ring."

The researchers believe that feature is long-lived and may be held together by resonant interactions with the moon Mimas of the type that corral the famed ring arcs around Neptune.

"We've known since the days of Voyager that we had Jovian-type and Uranian-type rings within the rings of Saturn," said Cassini imaging team leader. Carolyn Porco. "Now it appears Saturn may be home to Neptunian-type rings as well."