If the dinosaurs had telescopes, they would have seen a ringless Saturn. By the time those iconic rings vanish entirely, Mars will have ripped apart a moon to grow its own.
Saturn’s rings, long assumed to have formed alongside the planet 4.5 billion years ago, are actually much younger. Data from the final orbits of NASA’s Cassini spacecraft in 2017 revealed that the rings formed only 10 to 100 million years ago.
They are also disappearing at a rapid pace. A phenomenon known as "ring rain" is draining the system. Saturn's magnetic field and intense gravity pull charged water-ice particles out of the rings and into the planet’s upper atmosphere at a rate of roughly 10,000 kilograms per second. At this rate, the rings have less than 100 million years to live. The entire lifespan of a massive ring system like Saturn's is likely no more than a few hundred million years—a brief blink in cosmic time.
The faint, dusty rings surrounding Jupiter, Uranus, and Neptune operate on an even tighter timeline. The fine dust that comprises them is driven by radiation pressure and gravity, causing the particles to spiral into the planets in just a few million years. These rings exist today only because micrometeorite impacts on tiny, embedded moons replenish them. Without these moons acting as a source of fresh debris, the outer planets would lose their halos.
New ring systems form to replace the ones that disappear. In about 20 to 40 million years, Mars’s largest moon, Phobos, will spiral close enough to the planet to cross the Roche limit. The tidal forces from Mars will shatter Phobos into rubble, creating a rocky ring system that will encircle the planet for tens of millions of years before eventually raining down onto the surface.