The tiny moonlet Aegaeon is 0.5 km (about a third of a mile) across and is embedded within a partial ring, or ring arc, previously found by Cassini, the G ring. Aegaeon is believed to be a main source of the G ring and its single ring arc.
"Before Cassini, the G ring was the only dusty ring that was not clearly associated with a known moon, which made it odd," said Matthew Hedman, a Cassini imaging team associate at Cornell University in Ithaca, N.Y. "The discovery of this moonlet, together with other Cassini data, should help us make sense of this previously mysterious ring."
Saturn's rings were named in the order they were discovered. Working outward they are: D, C, B, A, F, G and E. The G ring is one of the outer diffuse rings. Within the faint G ring there is a relatively bright and narrow, 250-km-wide (150-miles) arc of ring material, which extends 150,000 km (90,000 miles), or one-sixth of the way around the ring's circumference.
Scientists imaged the moonlet on 15 August 2008, and then confirmed its presence by finding it in two earlier images. The
moonlet is too small to be resolved by Cassini's cameras, so its size cannot be measured directly. However, Cassini scientists estimated the moonlet's size by comparing its brightness to another small Saturnian moon, Pallene.
Hedman and his collaborators also have found that the moonlet's orbit is being disturbed by the larger, nearby moon Mimas, which is responsible for keeping the ring arc together.
Carl Murray, a Cassini imaging team member and professor at Queen Mary, University of London, said, "The moon's discovery and the disturbance of its trajectory by the neighboring moon Mimas highlight the close association between moons and rings that we see throughout the Saturn system. Hopefully, we will learn in the future more about how such arcs form and interact with their parent bodies."
How Aegaeon Got its Name:
Originally designated S/2008 S1, Aegaeon is named for a fierce giant with many heads and arms, who helped conquer the Titans.