New supercomputer simulations have suggested the origin of Saturn’s rings lies in a massive collision in the recent history of the 4.5 billion-year-old Solar System. According to research involving NASA, Durham and Glasgow Universities, Saturn’s rings could have evolved from the debris of two progenitor icy moons that collided and shattered only a few hundred million years ago.
Most high-quality measurements of Saturn have come from the Cassini spacecraft, which spent 13 years studying the planetary system after entering Saturn’s orbit in 2004 to capture precise data, even diving into the gap between Saturn’s rings and the planet itself. Cassini found that the rings’ composition is almost pure ice; they have accumulated very little dust pollution since their formation, suggesting that they formed during the most recent few percent of the lifetime of the Solar System.
Motivated by the rings’ remarkable youth, the research team turned to the COSMA machine hosted by Durham University as part of the UK’s DiRAC (Distributed Research Utilising Advanced Computing) facility. The team modelled different collisions between precursor moons using hydrodynamical simulations conducted using the SWIFT open-source software, with a resolution more than 100x higher than previous studies, sufficient to give confidence in their accuracy.
According to Dr Vincent Eke, Associate Professor in the Department of Physics/Institute for Computational Cosmology at Durham University:
“We tested a hypothesis for the recent formation of Saturn’s rings and found that an impact of icy moons is able to send enough material near to Saturn to form the rings that we see now. This scenario naturally leads to ice-rich rings because when the progenitor moons smash into one another, the rock in the cores of the colliding bodies is dispersed less widely than the overlying ice.”
Saturn’s rings today live close to the planet, within the Roche limit – within which a planet’s gravitational force is strong enough to disintegrate orbiting bodies of rock or ice that get too close. Material orbiting farther out can still clump together to form moons. By simulating several hundred different versions of the impact, the researchers found that a wide range of collision scenarios could scatter just the right amount of ice inside Saturn’s Roche limit, where it could settle into rings as icy as those seen today. Since other elements of the Saturnian system have a mixed ice-and-rock composition, alternative explanations haven’t been able to explain why there would be almost no rock in the rings.
If correct, this scenario suggests we are lucky to be living at a time when Saturn’s youthful rings are such a spectacular sight (at the moment you can see Saturn as a bright object in the southern sky in the constellation of Aquarius – even a small telescope will clearly reveal the rings). Over time “ring rain” – detected by Cassini during its passage between rings and planet – will deplete the rings and ultimately diminish their splendour.
L.F.A.Teodoro, J.A.Kegerreis, P.R.Estrada, M.Ćuk, V.R.Eke, J.N.Cuzzi, R.J.Massey, and T.D.Sandnes