Starship Asterisk*

First, the rings are bright and shiny like something new. Saturn’s radiation and dust particles would have darkened them if they were part of the original planetary formation.

Second, small moons that orbit through the outermost regions of the ring system are gaining angular momentum at the expense of the rings.
The spiral waves seen by Voyager are triggered by gravitational tugs from Saturn's moons -- the same ones that are sapping the rings' angular momentum. At some point in time the outer rings will fall in and the small outer moons will fly out of their orbits.

At this point, we've only been able to detect extrasolar planets "wobble-y" not visually.

Then in theory, if our optics were good enough, we may at some point in the future detect extra-solar planet systems younger with more developed rings and older systems with no rings. Or better yet, another system with rings of different stages of decline.

Of course, distance to and the nature of the central star, as well temperature gradients out to specific distances from the star would come into play.

How do they determine the age of the material or whether a ring system is diminishing?

As you've probably heard, there is no such thing as a stupid question, OK there are, questions that have not engaged the brain that conceived them, or those that the asker doesn't listen for the answer. You passed this test.

The reason the gas giants tend to have rings is - lots of gravity and their closer proximity to space debris. Rings are inherently unstable and without catastrophic events of the captured solar debris, they will disappear over millions of years; parts of Saturn's rings are thought to be only a few 100,000 years old so Saturn’s rings could look like Jupiter’s in a few million years
There is very little solar debris left near the rocky planets, with less area of space, the faster speeds of the inner orbits, and higher temps to vaporize icy objects, it's already swept clean, and, the gas giants catch most of what new debris is heading towards the inner space.

OK guys - another stoopid question

Is there anything about the gas giants that predisposes them to rings (all of them have rings, NONE of the terrestrials do)?

There is some chatter about one of Mar's moons potentially shattering into a ring system in about 100 million yrs, but I thought that the gas giant ring systems, like the asteroid belt on a larger scale, represent "failure to accrete" rather than large single object breakdown

Comments?