Scientists has recently discovered why a rapid variation in the number of 'small moons' or 'bright lumps' in the Saturn's ring keep occurring since it was pictured 30 year-old by the Voyager mission.
Robert French, Search for Extraterrestrial Intelligence (SETI) scientist, said that the F ring was a narrow, lumpy feature made entirely of water ice that lies just outside the broad, luminous rings A, B, and C, which has bright spots but it has fundamentally changed its appearance since the time of Voyager, as today, there are fewer of the very bright lumps.
He further explained that they believe the most luminous knots occur when tiny moons, no bigger than a large mountain, collide with the densest part of the ring and these moons are small enough to coalesce and then break apart in short order.
They found that there was a marked difference in the appearance of one of the rings, even over this cosmologically short interval, a difference that can be explained by the brief strut and fret of small moons.
The F ring was at a special place in the ring system, at a distance known as the Roche limit, named for French astronomer Edouard Roche who first pointed out that if a moon orbits too close to a planet, the difference in gravitational tug on its near and far side could tear it apart.
This happens at a distance dependent on the mass of the planet, and in the case of Saturn, happens to be at the location of the F ring. Consequently, material here was caught between the yin and yang of forming small moons, and having them pulled apart.
The moons in question are typically no more than 3 miles in size, and consequently could come together quickly. This chaotic region was given additional stir by Prometheus, a moon that's roughly 60 miles in size that orbits just inside the F ring. Every 17 years, Prometheus aligns with the F ring in a way that emphasizes its gravitational influence on the ring's particles, precipitating the formation of moonlets.