How did Saturn get rings?

This is a question that was not answered until just recently, mostly because of the data that has been returned by NASA's probes like Voyager.

Galileo was the first to observe Saturn's rings in 1610, but he didn't know what they were. It wasn't until 1655 that Huygens observed that they were rings that didn't touch Saturn and it wasn't until much later that theories about how they formed were proposed.
It turns out that all of the gas giants have rings, but it's only the magnificent rings of Saturn that are easily observed. The reason for this is easy: Saturn's rings are composed of ice crystals that reflect light. The rings are around 10 to a 1000 km thick and extend from 7000 km away from Saturn to 80,000 km and orbit around Saturn's equator.

There are many gaps in the rings, some of them are large, as much as 270 km wide, but this varies all over the place and it gives the rings a peculiar segmented look. Most people are familiar with the main gap, known as the Cassini Division, named for the astronomer who found it first. Some people may be familiar with the Huygens Gap at the inner edge of the Cassini Division. Some of the subdivisions in the rings are darker than others, while others are brighter. The detail in the rings is exquisite and quite beautiful. And, for centuries was very mysterious.

That was changed in 1980 when the Voyager probe went out to take a close look at Saturn's rings. Subsequent observations from the Cassini probe in 2009 gave us a much more detailed look at the ring structure.

But, how did these rings form? That's a question that's open to argument. One theory proposes that an icy moon of Saturn got too close (the Roche limit) to the planet and was ripped apart. Another theory suggests that an icy moon of Saturn suffered a collision that broke it apart. Obviously, both of these theories would involve moons that were composed of a lot of ice.

A recent variant of the collision theory is that a collision knocked the mantle off of a very large icy moon and its outer layers were stripped away and fell into Saturn. Most of the rings are composed of ice chunks along with a little rocky material, and they're very old, billions of years old, so any formation theory has to accommodate these facts.

Most astronomers believe that the rings were much larger at one time and have slowly eroded away because of Saturn's massive gravitational pull. Obviously, at an early phase, the rings consisted of rocky material that accreted into large moons, leaving a lot of the ice in the rings.

However, recent data on the purity of the ice in the rings suggest that rings are only a hundred million years old, but other astronomers dispute this and give as argument that the ice chunks often collide, revealing fresh surfaces that reflect better. See what I mean about how scientists argue a lot.

The fact that other gas giants also have rings, albeit very difficult ones to see, suggests that ring formation is not all that unusual. Voyager I first recorded Jupiter's rings in 1979. Jupiter's main ring is 6500 km wide but very difficult to see because it's composed of mostly dust, not ice like Saturn's rings. This dust comes from continuous collisions between larger bodies, and is continuously being sucked into Jupiter. A dust particle in Jupiter's ring only lasts around a thousand years or less.

James L. Elliot discovered the tenuous rings around Uranus in 1977, but Voyager 2 revealed their true extent. They consist mostly of dust. The same goes for Neptune's rings. Since both of these ring systems are mostly dust, observing them is difficult.

So, rings around the gas giants attest to the violent nature of planet and moon formation, and it demonstrates that you don't want to get too close to a big gas giant planet like Jupiter or Saturn lest you become broken into dust.

Thanks for reading.