Once upon a time, in the early days of the solar system, Saturn was a big planet that didn’t have any rings.
That might seem hard to believe now, as the planet’s rings are now its most noticeable feature. But four billion years ago, the Earth was young and mostly molten and Saturn was unadorned.
So how did it end up putting hundreds of rings on itself? A recently published study found that the rings of Saturn might have been built up over time as the planet’s gravity destroyed passing objects from the Kuiper Belt.
The researchers used computer simulations to model the conditions in the early Solar System, and found that dwarf planet-sized objects (roughly the size of Pluto) may have been torn apart by larger gas giants to form the rings that we now see today.
The Kuiper Belt is itself a ring of icy dwarf planets, comets, and asteroids on the outskirts of our solar system. As the solar system was forming, some of these objects (which hadn’t yet settled down into a stable orbit around the sun) ventured inside the solar system, where they often encountered other, larger objects (the planets and moons). So many objects pelted the solar system that this period of time came to be known as the Late Heavy Bombardment.
Now, thanks to this new study, researchers think that during that time, some of the icy objects that passed too close to Saturn were fragile enough that Saturn’s gravity pulled apart their icy shell, building the broken fragments into icy rings in its own orbit. Objects that passed close to the smaller but denser Neptune and Uranus fared even worse– the more intense tidal forces near those planets meant that the rocky cores of the passing dwarf planets were shredded and turned into rings.
The computer model explains why Saturn’s rings are made up of 90-95 percent water ice, while Neptune and Uranus have darker, more rocky rings.
Today, Saturn’s magnificent rings are 400,000 kilometers thick but only about 100 meters wide. They’re gorgeous but also a warning to any wayward asteroid: don’t mess with Saturn!