An examination of Jupiter and Saturn systems shows that the formation and perseverance of rings may depend on the friendliness of planetary moons, among other factors.
Saturn, the second-largest planet in the Solar System, is adorned with a ring system so extensive that its loops of ice and rocky material differentiate it from the rest of the planets.
However, Saturn is not the only planet within the Solar System that has rings. In fact, planetary rings are a common feature of the giant planets orbiting around the Sun, with Jupiter, Uranus and Neptune also having them.
But it is Saturn that has the most extensive ring system, more spectacular and prominent than the others – the only one humankind never fails to depict.
One question arises, though: If the size of the planets is what determines the presence of planetary rings, then why is it that Jupiter – which is around 15 percent larger than Saturn – doesn’t have prevailing rings?
“It’s long bothered me why Jupiter doesn’t have even more amazing rings that would put Saturn’s to shame,” says astrophysicist Stephen Kane from the University of California, Riverside, as quoted by UCR news.
That led Kane and his graduate student Zhexing Li to conduct a dynamic computer simulation illustrating the behaviour of Jupiter and its four massive Galilean moons: Io, Europa, Ganymede, and Callisto.
They then examined that information, along with other data, and pinpointed what may be the primary reason of Jupiter’s modest ring system in a paper set to be published in the Planetary Science journal. Here’s what they found:
Galilean moons vs Jovian rings
The largest planet in the Solar System, Jupiter’s history must have included “significant impacts and other events that have resulted in raw material for substantial ring formation,” the authors write in their paper titled The Dynamical Viability of an Extended Jupiter Ring System.
But the rings of Jupiter, called the Jovian rings, are not substantial at all despite the planet’s eventful history.
That is because “the Galilean moons of Jupiter, one of which is the largest moon in our solar system, would very quickly destroy any large rings that might form,” Kane told UCR news.
“Massive planets form massive moons, which prevents them from having substantial rings,” Kane said.
One major difference between the Jupiter and Saturn systems is the presence of the massive Galilean moons around Jupiter. In particular, the Laplace resonance created by Io, Europa, and Ganymede lies within 15 Jupiter radii and has a significant perturbing effect. pic.twitter.com/mYNK0N9kkh— Stephen Kane (@ExoCytherean) July 15, 2022
Of Jupiter’s 79 moons, the Galilean moons have the largest gravitational force over potential ring particles, influencing the formation and sustainability of planetary rings.
Findings from Kane’s simulation show that these gravitational constraints might be making sure that any ring systems made up of dense material that creates spectacular planetary rings would not endure “beyond a few tens of millions of years”.
That means the gas giant might have had substantial planetary rings in certain points through time, although only for certain periods when the severity and frequency of events like significant impacts and collisions overcame the dynamical constraints of the Galilean moons.
That would, of course, last until the dynamical disruption by Io, Europa, Ganymede, and Callisto would prevail once again.
From these findings, the authors also suggest that Saturn’s local environment might just be an “optimal region” for the presence and sustainability of substantial planetary rings, becoming what can be considered an exception that proves the rule.
That relies on an intricate “balance between planet mass, the formation of massive moons, and the sustainability of significant ring mass,” the authors explain, while also mentioning that Saturn’s small moons contained in its rings might be “feeding” the rings, as well as “shepherding” them.