A small, newly discovered moon embedded in a bright arc of Saturn's outer G ring is likely to be the source of that ring, researchers with NASA's Cassini mission announced this week.

The Cassini imaging team, including several Cornell faculty and staff members, published the finding March 3 in an International Astronomical Union circular.

Unlike Saturn's other dusty rings, which have embedded or nearby moons that can provide and confine source material, the G ring's origin has long been mysterious. The newfound moon, first spotted in Cassini images in August 2008, could help unravel that mystery, said co-author Matthew Hedman, a Cornell research associate.

The object, about 500 meters (one-third of a mile) across, is Saturn's 61st identified moon. It is embedded in a bright arc that makes up one-sixth of the G ring's circumference and orbits the planet in resonance with the shepherd moon Mimas, 15,000 kilometers away.

In 2007 in the journal Science, Hedman and colleagues reported that debris from collisions between micrometeorites and objects within the arc are the likely source for the material that makes up the G ring.

"We had evidence that there were big particles in the arc, and thought that collisions between these objects and various micrometeoroids could release the dust that formed the ring," Hedman said. "[This moon is likely] one of the objects that dust is knocked off of to form the ring."

The arc probably contains other smaller moonlets, he added, "but this is quite likely the biggest thing in there by a fair fraction."

Cassini's cameras caught sight of the moon when the spacecraft's orbit placed it so that the G ring could be imaged with the sun directly behind the cameras -- ideal conditions for spotting small objects in the rings, Hedman said.

Besides finding this moonlet embedded in the G ring arc, Cassini researchers have also recently discovered that faint arcs of debris surround two other small moons, Anthe and Methone, whose orbits are also influenced by the gravitational pull of Mimas. Comparisons between these rings and moons are expected to provide insights into the connections between them.

Early next year, Cassini's camera will have the opportunity to take a closer look at the G ring moonlet. The Cassini Equinox mission, an extension of the original four-year mission, is expected to continue until fall 2010.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory (JPL), a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington, D.C. The imaging operations center and team leader are based at the Space Science Institute in Boulder, Colo.