New Simulations Shed Light on the Origins of Saturn’s Rings and Icy Moons

saturn rings ice

Saturn’s rings, those gigantic, fascinating structures, have long been shrouded in mystery, raising many questions as to their origin. Recent research, combining advanced simulations and data from the Cassini probe, suggests an unexpected origin for these iconic structures.

A collision between two icy natural satellites could be the key to their birth, offering a renewed perspective on Saturn’s evolution and paving the way for new explorations of the potentially habitable conditions of its moons.

The work of researchers from NASA, Durham University, and Glasgow University is published in The Astrophysical Journal.

Young Rings

Still image from a computer simulation of an impact between two icy moons orbiting Saturn.
Still image from a computer simulation of an impact between two icy moons orbiting Saturn. The collision ejects debris that could evolve into the planet’s iconic and remarkably young rings. The simulation involved over 30 million particles. Image: NASA, Durham University, University of Glasgow.

The revelations of the Cassini mission have been crucial in understanding the composition of Saturn’s rings. The data collected showed that these rings are predominantly made up of ice, with a minimal presence of dust. This composition suggests that they are relatively young, especially compared to the age of the solar system, estimated at 4.5 billion years.

This indication of youth was a trigger for scientists, prompting them to investigate their origins further. They sought to determine whether these structures could indeed have a recent origin, namely the collision of natural satellites. To do this, they relied on state-of-the-art hydrodynamic simulations carried out with supercomputers using SWIFT software to model the conditions and processes that could have led to the formation of the rings.

Essential Modelling

Presentation of the collision between moons that created Saturn’s rings. NASA/Durham University/University of Glasgow/Jacob Kegerreis/Luís Teodoro.

The research team carried out a series of simulations, examining nearly 200 different collision scenarios. The aim of these simulations was to determine whether impacts between celestial objects could generate enough icy debris to create rings similar to those of Saturn. Their size would probably have been similar to that of two of Saturn’s current moons, Dione and Rhea.

Above all, they studied how this debris would be projected into Saturn’s Roche limit, a region around the planet where tidal forces are strong enough to break objects down into smaller fragments.

The results of these simulations were revealing. They showed that many collision scenarios could indeed throw up enough ice to form rings. Vincent Eke, from Durham University and co-author of the paper, explains in a press release: “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“.

Ice and rocky debris would also have collided with other moons in the system, potentially triggering a cascade of collisions. Such a multiplier effect could have disrupted any other natural precursor satellite outside the rings, from which Saturn’s present moons could have formed.

What Was the Triggering Event?

Orbits of p-Rhea and p-Dione around Saturn before an impact, in a specific scenario. Saturn is shown in gray. Zooms detail the velocities of the moons before impact, and a panel illustrates the orientation and velocity for the impact simulation, with a time to impact of 1 hour. L. F. A. Teodoro et al. 2023
Orbits of p-Rhea and p-Dione around Saturn before an impact, in a specific scenario Saturn is shown in gray. Zooms detail the velocities of the moons before impact, and a panel illustrates the orientation and velocity for the impact simulation, with a time to impact of 1 hour. Image: Iop Science.

Two of Saturn’s ancient moons could have been pushed into a collision by the generally weak effects of the Sun’s gravity “adding up” to destabilize their orbits around the planet. In the right configuration of orbits, the Sun’s extra pull can have a snowball effect—a “resonance”—that lengthens and tilts the moon’s generally circular, flat orbits until their paths cross, resulting in a high-speed impact.

Saturn’s natural satellite, Rhea, today orbits just beyond the point where a moon would encounter this resonance. Like Earth’s Moon, Saturn’s satellites migrate outward from the planet over time. So, if Rhea were ancient, it would have crossed the resonance in the recent past. However, Rhea’s orbit is very circular and flat. This suggests that it did not undergo the destabilizing effects of resonance and that it formed more recently.

The new research is consistent with evidence that Saturn’s rings formed recently, but big questions remain. If at least some of Saturn’s icy moons are also young, what could this mean for the potential for life in the oceans beneath the surface of worlds like Enceladus? Future research based on this work will help us learn more about this planet and the icy worlds orbiting it.