Saturn is surrounded by a number of concentric rings of ice and dust. Given that these ice and dust particles have mass, shouldn’t there be a gravitational attraction among them? Why don’t the particles in each ring conglomerate into single bodies (moons)? Or are they currently in the process of conglomerating, and it’s just taking an awful long time?
Any particle in orbit has a characteristic orbital speed for that altitude. If you have a collection of particles coalesced into a moon, all of the particles that make up the moon are forced to travel at the same speed. The particles higher or lower in altitude than the center of mass of the mass are forced to travel at a faster or slower speed than is the proper characteristic speed for that particular altitude. This leads to what are called “tidal” forces, which tend to counteract the gravitational force that the particles exert on each other.
Any body that is close enough to its primary where these tidal forces overcome the gravitational forces that tend to hold the body together will break up into individual pieces and spread into rings. Conversely, any collection of particles inside this limit will never coalesce into a moon. This is the case for Saturn’s rings.
Here’s wikipedia’s explanation:
The distance is called the Roche limit.
Maybe they are and it’s just taking a while?
On reading the linked article, I see that most of Saturn’s rings are within the Roche limit. I’m not surprised.
Well, there’s no known force in the Universe that can make small, uniform particles conglomerate into bigger ones 