Saturn's Rings are Very Young

[lpetrich]

Young in geological terms, somewhere around 100 million years old, though much younger than the Solar System.
Saturn's spectacular rings are 'very young' - BBC News
Measurement and implications of Saturn’s gravity field and ring mass | Science The rings' mass is about 0.41 +- 0.13 times the mass of Saturn's moon Mimas.

This mass estimate supplies the missing piece of the puzzle in attempts to estimate the rings' age.

So something big much have happened some 100 million years ago, like an asteroid or a comet colliding with a moon, or else two moons colliding.

It also means that for much of its history, Saturn did not have a big ring system. But it may have had similar big rings in its past, rings that are now long gone.

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Scientists Finally Know What Time It Is on Saturn – Solar System Exploration: NASA Science -- the length of Saturn's bulk-rotation sidereal day: 10h 33m 38s +1m 52s -1m 19s
[1805.10286] Cassini Ring Seismology as a Probe of Saturn's Interior I: Rigid Rotation

The planet's magnetic field would be useful for that, but it is nearly aligned with the planet's spin axis, so it is not very useful. The Voyager spacecraft got 10h 39m 23s, while earlier Cassini results were 10h 36m to 10h 48m.

 

[Shake]

But as we also recently learned, the rings are disappearing. They've decided that this loss is going faster than previously thought, but not to worry, they'll still be around for many millions of years yet.

 

[James Brown]

The other gas giants have ring systems, albeit thin and wispy compared to Saturn's. That would suggest (to me) that ring systems are the default state of gas giants (probably not hot Jupiters, though.)

If Saturn's rings are truly young and short-lived, then could rings be cyclical?

 

[lpetrich]

Cyclical?

Ring systems would presumably be formed by collisions of moons and/or planetoids, and they would gradually dissipate.

 

[James Brown]

And a new system of rings from the way the previous set did? That's all I meant by cyclical.

For a four-billion year old planet to have a single set of rings that will exist for only 0.25% of its existence--when we happen to be around to observe them--seems like a big coincidence.