Cassini Finds Possible Origin of One of Saturn’s Rings

Cassini Finds Possible Origin of One of Saturn’s Rings

Cassini scientists may have identified the source of one of Saturn’s more mysterious rings. Saturn’s G ring likely is 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.

The finding is evidence of the complex interaction between Saturn’s moons, rings and magnetosphere. Studying this interaction is one of Cassini’s objectives. The study is in the Aug. 2 issue of the journal Science and was based on observations made by multiple Cassini instruments in 2004 and 2005.

“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 Science paper.

Saturn’s rings are an enormous, complex structure, and their origin is a mystery. The rings are labeled 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 location of the G ring continued to defy explanation, until now.

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