Washington, Aug 3 : The NASA/ESA/ASI Cassini spacecraft may have identified the source of one of Saturn's more mysterious rings.

Astronomers believe Saturn's G ring is likely produced by relatively large, icy particles that reside within a bright arc on the ring's inner edge.

The particles are confined within the arc by gravitational effects from Saturn's moon Mimas. Micrometeoroids collide with the particles, releasing smaller, dust-sized particles that brighten the arc. The plasma in the giant planet's magnetic field sweeps through this arc continually, dragging out the fine particles, which create the G ring.

Scientists say the finding is evidence of the complex interaction between Saturn's moons, rings and magnetosphere.

"Distant pictures from the cameras tell us where the arc is and how it moves, while plasma and dust measurements taken near the G ring tell us how much material is there," said Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y., and lead author on the paper.

Saturn's rings compose an enormous, complex structure and their origin is a mystery.

The rings are labelled in the order they were discovered. From the planet outward, they are D, C, B, A, F, G and E. The main rings--A, B and C--from edge-to-edge, would fit neatly in the distance between Earth and the moon. The most transparent rings are D--interior to C--and F, E and G, outside the main rings.

Unlike Saturn's other dusty rings, such as the E and F rings, the G ring is not associated closely with moons that either could supply material directly to it--as Enceladus does for the E ring--or sculpt and perturb its ring particles--as Prometheus and Pandora do for the F ring.

The Cassini images further show that the bright arc within the G-ring extends one-sixth of the way around Saturn and is about 250 kilometres wide, much narrower than the full 6,000-kilometer (3,700-mile) width of the G ring. A gravitational disturbance caused by the moon Mimas also exists near the arc.