Cassini Found Tiny Moonlet within Saturn G-Ring Arc

NASA's Cassini spacecraft has found within Saturn's G ring an embedded moonlet that appears as a faint, moving pinprick of light. Cassini scientists believe it is likely a major source of the fine material composing Saturn's G ring and the G ring's bright ring arc. 

In each image, a small streak of light within the ring is visible. Unlike the streaks in the background, which are distant stars smeared by the camera's long exposure time of 46 seconds, this streak is aligned with the G ring and moves along the ring as expected for an object embedded in the ring.

Cassini scientists interpret the moving streak to be reflected light from a tiny moon half a kilometer (a third of mile) wide that is likely a major source of material in the arc and the rest of the G ring. Debris knocked off this moon forms a relatively bright arc of material near the inner edge of the G ring, the most visible part of the ring in these images. That arc, in turn, leaks material to form the entire ring.

Scientists imaged the moonlet on Aug. 15, 2008, and then they confirmed its presence by finding it in two earlier images. They have since seen the moonlet on multiple occasions, most recently on Feb. 20, 2009. 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.

*Note....

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-kilometer-wide (150-miles) arc of ring material, which extends 150,000 kilometers (90,000 miles), or one-sixth of the way around the ring's circumference.