New research provides explanation for the origin of Saturn’s rings and icy moons

by Haygen Warren

Recent research conducted by NASA and its partners using supercomputer simulations is shedding light on the origins of Saturn’s iconic rings and mysterious icy moons. Scientists believe the rings began forming from a massive impact between two icy moons, all the way back when dinosaurs were still roaming around the surface of Earth.

The massive amounts of debris from the collision were then caught by Saturn’s gravitational pull and then began wrapping around the planet to produce the rings we all know and love today. What’s more, debris that didn’t get caught in the rings likely went on to form some of Saturn’s icy moons.

“There’s so much we still don’t know about the Saturn system, including its moons that host environments that might be suitable for life. So, it’s exciting to use big simulations like these to explore in detail how they could have evolved,” said research scientist Jacob Kegerreis of NASA’s Ames Research Center in California.

From 1997 to 2017, NASA’s Cassini mission orbited Saturn and investigated its rings, icy moons, atmospheric properties, and more. One discovery Cassini made while at Saturn is that Sarurn’s rings are younger than originally expected (astronomically speaking). With this knowledge, scientists were able to better model Saturn’s rings and moons in the simulation.

To create the simulation, the team of scientists, led by Luis Teodoro, used the Distributed Research using Advanced Computing (DiRAC) supercomputing facility at Durham University in the United Kingdom. The scientists modeled the collision and the formation of the rings in nearly 200 different ways, as well as the different collisions between other moons and the debris. The resolution of the simulations was more than 100 times higher than previous studies into the formation of Saturn’s rings. Furthermore, the scientists used open-source simulation code, SWIFT.

Saturn’s current rings are situated close to the planet within Saturn’s Roche limit, which is the distance from a planetary body within which a second planetary body will disintegrate due to the tidal forces from the first planetary body exceeding the gravitational forces of the second planetary body. When simulating the collision and the formation of the rings, Teodoro et al. discovered that a significant amount of the collision scenarios scattered and distributed the right amount of debris around Saturn and within the Roche limit, which then led to the formation of the rings.

Nearly the entirety of Saturn’s rings is made of large chunks of ice, with there being very little rock and other material within the rings. Alternative explanations have been unable to explain why there’d be no rock in the rings, but the type of collision simulated using DiRAC places very little rock in the rings and could provide scientists with an explanation for the lack of rock.

Natural color image of Saturn’s outer C Ring and B Ring. (Credit: NASA/JPL-Caltech/SSI)

“This scenario naturally leads to ice-rich rings. When the icy progenitor moons smash into one another, the rock in the cores of the colliding bodies is dispersed less widely than the overlying ice,” said co-author Vincent Eke of the Department of Physics/Institute for Computational Cosmology at Durham University.

A cascade of collisions could’ve also occurred from the debris, with icy and rocky debris colliding with other moons around Saturn. This could have forced precursor moons out of the rings, which would have then allowed for the formation of the moons we see today.

As mentioned, scientists believe Saturn’s rings formed from the collision of two of Saturn’s former moons. But how did the moons collide in the first place?

Scientists believe that the extremely small effects of the Sun’s gravity on the moons could have added up to slightly destabilize their orbits around Saturn, leading to a collision. When moons are in the right orbital configuration around their planets, the extra gravitational pull exerted on the planet and its moons by the Sun can have a snowballing effect. This effect is called a resonance, and it can lead to the elongation and tilting of the moons’ orbits. In the case of Saturn’s two former moons, a resonance led to their orbits being changed to where their paths crossed, which led to the collision that formed Saturn’s rings and moons.

One of Saturn’s present-day moons, named Rhea, orbits just beyond the point at which a moon could encounter this resonance. Given that Saturn’s moons, like Earth’s moon, slightly move farther and farther from Saturn in every orbit they complete, Rhea had to have crossed the resonance recently. However, the moon’s orbit is still extremely flat and circular, which suggests that Rhea wasn’t subjected to the effects of the resonance and had to have formed more recently, astronomically speaking.

Rhea in front of Saturn and its rings. (Credit: NASA/JPL/SSI)

As aforementioned, scientists believe that Saturn’s rings formed more recently, and Teodoro et al.’s modeling agrees with this and is giving scientists insights into how ring systems and the moons around them form. However, there are still plenty of questions that need to be answered. For example, if some of Saturn’s current icy moons formed alongside the rings and are also young, what would that mean for icy moons like Enceladus that could potentially host life within their sub-surface oceans? As scientists continue to research Saturn and model the formation of its rings and moons, some of these questions could be answered — which would tell us more about Saturn and our solar system as a whole.

Teodoro et al.’s research, titled “A Recent Impact Origin of Saturn’s Rings and Mid-sized Moons,” was published in The Astrophysical Journal on Sept. 26.

(Lead image: Saturn, as imaged by Cassini in 2016. Credit: NASA/JPL-Caltech/SSI)

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