Moonlets are constantly being born and dying in the F ring surrounding Saturn. The process was witnessed by the Cassini spacecraft orbiting the Ringed Planet.

SETI Institute astronomers studied a pair of observations made three decades apart. The oldest of these was recorded by the Voyager spacecraft, launched in the 1970's. They found significant differences between the two recordings. These changes, which took place over an incredibly short period of time in astronomical terms, could be explained by the creation and destruction of tiny moons in the ring.

"The F ring is a narrow, lumpy feature made entirely of water ice that lies just outside the broad, luminous rings A, B, and C. It has bright spots. But it has fundamentally changed its appearance since the time of Voyager. Today, there are fewer of the very bright lumps," Robert French of the SETI Institute, said.

Bright spots seen in the F ring appear and disappear over the course of a few days. Astronomers believe this effect may be caused by moonlets, the size of mountains, form and then collide with particles in the densest part of the F ring. Bodies this big are the right size to coalesce and be broken apart over the course of a few days.

Edouard Roche was a French astronomer who lived in the 19th Century. He first proposed the idea that a moon orbiting closer than a certain distance from its parent planet would be torn apart by gravitational forces. This critical distance, which is dependent on the mass of the larger world, is known as the Roche limit.

Saturn's F-ring is located on the outside of the main ring system, at the Roche distance from the giant planet. Gravitational forces here can cause collections of rocks to coalesce until they are a few miles in diameter. With millions of bodies orbiting in close proximity to each other, collisions are common, and can tear these bodies apart.

Prometheus, a moon of Saturn discovered by the Voyager 1 spacecraft in 1980, orbits just inside the F-ring. Once every 17 years, this 60-mile diameter moon aligns with the ring in such a way that gravity encourages the creation of large numbers of moonlets. Further research, studying Cassini data, will determine if conditions over the last few years have produced a greater number of moonlets than normal. Discovery of a large number of tiny bodies in the ring would lend credence to the theory that Prometheus is fueling the creation of the mountain-sized moonlets.

Discovery of changes in Saturn's F-Ring and research into how Prometheus may affect the system was profiled in the journal Icarus.