'Moonlet' Found in Outer Saturn Ring

March 4, 2009 -- Scientists have found a new moon hidden in one of Saturn's dazzling outer rings. The international Cassini spacecraft spotted the small moon, which measures about a third of a mile wide.

The discovery of what appeared to astronomers as a faint, moving pinprick of light, was announced by the International Astronomical Union.

Researchers have long puzzled over the formation of Saturn's G ring, one of the planet's more mysterious arcs. They now think the G ring was likely formed from icy debris that scattered when meteorites crash into the newfound moon. The moonlet was found embedded within a partial ring, or ring arc, previously found by Cassini in Saturn's G ring.

Scientists confirmed the existence of the tiny moonlet last summer after analyzing images from Cassini. Saturn has over five dozen moons.

"Before Cassini, the G ring was the only dusty ring that was not clearly associated with a known moon, which made it odd," Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y., said in a press release. "The discovery of this moonlet, together with other Cassini data, should help us make sense of this previously mysterious ring."

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Working outward, Saturn's rings are named D, C, B, A, F, G and E (named in the order that they were discovered). The G ring is one of the outer rings. Within the faint G ring there is a bright and narrow 150-mile arc of ring material, which extends 90,000 miles, or one-sixth of the way around the ring's circumference. The moonlet moves within this arc.

Scientists imaged the moonlet on Aug. 15, 2008, and then they confirmed its presence by finding it in two earlier images. They have since had several more sightings of the moonlet, most recently on Feb. 20, 2009.

The moonlet is too small to be measured directly by Cassini's cameras, but scientists estimated its size by comparing its brightness to another small Saturnian moon, Pallene.

The new moonlet may have company in the G ring arc. Previous measurements with other Cassini instruments implied the existence of a population of particles, possibly ranging in size from 1 to 100 meters (about three to several hundred feet) across.

"Meteoroid impacts into, and collisions among, these bodies and the moonlet could liberate dust to form the arc," Hedman said in a release.

Early next year, Cassini's camera will take a closer look at the arc and the moonlet during the Cassini Equinox mission, an extension of the original four-year mission.

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