My Ideas

Rings appear only around large planets and yet we recently discovered a ring around an asteroid or dwarf planet.  Why?   They last longer around large planets and they are more frequent the smaller the planet.   So we have two different causes and they are linear in that length of time a ring exists is proportional to the size of the planet and the frequency of rings is inversely proportional to the size of the planet.  We are talking about two different things at least the causes are different and each can be graphed as a line.  If you superimpose the two lines you will have a point at which the two lines cross and at that point is probably where the size of the planet is roughly similar to earth or the average rocky planet in our solar system.  Since one goes down and the other goes up the point where they cross will be where the planets with the least rings are likely to appear.