Why are there rings around certain planets?

Answer 1

We're not sure why ring systems form. At one time, astronomers thought that ring systems would be rare, and that Saturn was a magnificent freak of nature here in our own backyard, so to speak. But there are partial ring systems around ALL of the larger planets.

Among the various explanations are that these are collections of matter that never managed to collect themselves into a proper moon, and so orbit independently. Or that the rings are remnants of where a moon was destroyed by tidal forces, and the debris scattered in the orbital path of the old moon.