It may surprise you that all four giant planets in the Solar System have rings because none are as spectacular as those of Saturn. Why does Jupiter, the largest planet, not simply have the biggest rings? A new study has put forward an answer to that mystery. The blame is to be placed squarely upon Jupiter’s four largest moons.
According to simulations published in the Planetary Science Journal, the Galilean moons, as they are called – Io, Europa, Ganymede, and Callisto – are so big and influential that they would quickly destroy any large ring system.
“It’s long bothered me why Jupiter doesn’t have even more amazing rings that would put Saturn’s to shame,” lead author Stephen Kane, from the University of California Riverside, said in a statement “If Jupiter did have them, they’d appear even brighter to us, because the planet is so much closer than Saturn.”
Jupiter's rings are thin and flimsy. They're made of dust, which is not a great reflector of light, so are much harder to see.
The simulations looked at the orbit of Jupiter and the orbits of its four largest moons, playing out possible scenarios looking at how rings would have formed over astronomical ages. Kane and graduate researcher Zhexing Li found it unlikely that Jupiter ever had a large ring system at any point in the past. The huge moons keep rock and dust from accumulating around Jupiter in the way they do around Saturn.
“We found that 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 added. “Massive planets form massive moons, which prevents them from having substantial rings.”
This work has interesting implications for exoplanets, as a lack of rings might indicate massive moons or vice versa, as well as the history of the Solar System. Uranus's rings for example are an intriguing mystery that could be related to the many peculiarities of the planet.
Unlike every other planet in the Solar System, Uranus orbits on its side. The reason behind this weirdness is believed to be a massive impact that rocked the planet billions of years ago. The rings might be key evidence of that impact.
“For us astronomers, they are the blood spatter on the walls of a crime scene. When we look at the rings of giant planets, it’s evidence something catastrophic happened to put that material there,” Kane said.
The researchers will now run similar simulations on the lifetime of Uranus’s rings to work out if they could be the results of a major impact or if they are unrelated to the dramatic past of this ice giant.