Given its similarities to its neighbor Saturn, it seems natural to wonder why Jupiter doesn’t also have a magnificent and extensive visible ring system.
Unfortunately, it is not the reality. Although Jupiter has rings, they are thin, faint, fragile things of dust, visible only when the Sun illuminates them thoroughly.
According to new research, these discount rings lack brightness because Jupiter’s Galilean moons prevent disks of rock and dust from accreting like they do around Saturn.
“It’s long bothered me why Jupiter doesn’t have even more amazing rings that put Saturn’s to shame,” said astrophysicist Stephen Kane of the University of California, Riverside.
“If Jupiter had them, they would appear even brighter to us, because the planet is much closer than Saturn.”
To question the idea of a giant ring system forming around Jupiter at some point in its history, Kane and his colleague, UC Riverside astrophysicist Zhexing Li, conducted a series of simulations of objects orbiting the Jovian system.
These simulations took into account Jupiter’s orbital motion and the motions of its four largest moons, also known as the Galilean moons: Ganymede (which is larger than Mercury and the largest moon in the Solar System), Callisto , Io and Europe. Into this mix, the team added how long it might take for a ring system to form.
According to this model, Jupiter cannot have Saturn-style rings, and it is unlikely that it ever did, the researchers said.
“Massive planets form massive moons, which prevents them from having substantial rings,” Kane explained. “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.”
Jupiter’s rings, currently fragile, are made mostly of dust ejected from some of its moons, possibly including material thrown into space by impact events.
Saturn’s rings, on the other hand, are mostly made of ice; perhaps fragments of comets or asteroids, or an icy moon that was torn apart by Saturn’s gravity or collided in such a way that the ejecta formed rings.
We know that Saturn’s moons play an important role in the formation and maintenance of its rings. But a large enough moon (or moons) can also gravitationally disrupt the rings, sending the ice out of planetary orbit to who knows where.
Although Saturn is the planet we all think of as having rings, rings around planets are actually quite common, even here in the Solar System.
There is Jupiter, of course, as we just discussed. The ice giants Neptune and Uranus also have thin, faint dust rings.
Uranus is also tilted on its side, relative to the other planets, with its orbital axis nearly parallel to the orbital plane. His rings are believed to be related to this in some way; either something hit Uranus and knocked it sideways, or it had absolutely huge rings, which could have caused it to tilt sideways.
And rings aren’t even limited to planets. A small body about 230 kilometers (143 miles) in diameter, called Chariklo, orbiting between Jupiter and Uranus has rings. So does the dwarf planet Haumea, which is in the Kuiper Belt with Pluto. The simulations suggest that rings around icy bodies are not unusual, due to gravitational interactions that lift ice from the surface of these bodies to form an orbiting ring around them.
Mars may also occasionally have rings. Its moon Phobos approaches the red planet only a little each year; in 100 million years, it will be close enough to be torn apart by Mars’ gravity, forming a short-lived ring that could become a moon again. Even Saturn’s rings are probably temporary, meant to slowly rain down on the planet.
If we can examine them in sufficient detail, the rings can be used to piece together certain violent aspects of a planet’s history.
“For us astronomers, it’s the blood spatter on the walls of a crime scene,” Kane said. “When we look at the rings of the giant planets, it’s evidence that something catastrophic happened to put that material there.”
Anyway, it might as well be that Big Jupe doesn’t have spectacular rings. Let Saturn have his. After all, Jupiter has already approached the hexagons.
The research has been accepted into the Planetary Science Journal and is available on arXiv.