How Rings Form around a Planet
This is a crude model of the formation of a ring around a planet, such as Saturn in our solar system. An asteroid, comet, or moon is broken into a number of fragments. Their positions are slightly different and, because of Kepler's third law, the periods of the inner fragments are smaller. This produces the large-scale effect of the fragments spreading out over the whole orbit.
Based on the contents of the site "Los Anillos de un Planeta" (in Spanish).