There are two main theories regarding the origin of Saturn's inner rings. One theory, originally proposed by Édouard Roche in the 19th century, is that the rings were once a moon of Saturn (named Veritas, a Roman goddess who hid in a well) whose orbit decayed until it came close enough to be ripped apart by tidal forces. A variation on this theory is that this moon disintegrated after being struck by a large comet or asteroid. The second theory is that the rings were never part of a moon, but are instead left over from the original nebular material from which Saturn formed.

Source :Wikipedia

It's now known that there are thousands of individual rings made up of billions of particles of rock, ice, and debris - just a few metres thick.

They were extensively photographed by NASA's Cassini mission (archived) which discovered that rings must have been formed between 10 million and 100 million years ago, rather than at the same time as the planet, as had previously been assumed.

Nevertheless, their origin still remains obscure.

Also see :Planet formationplugin-autotooltip__plain plugin-autotooltip_bigPlanet formation

"The origin of planets is a vast, complex, and still quite mysterious subject. Despite decades of space exploration, ground-based observations, and detailed analyses of meteorites and cometary grains (the only space samples available in our laboratories),