Scientists Solve Jupiter’s Rings
Solving a long-standing puzzle about the origin of Jupiter’s rings, Cornell astronomers announced Tuesday that the ghostly cosmic girdles are created by tiny nearby “mother moons” that continually supply them with dust kicked up in cometary collisions.
The new insight--from images taken by the Jet Propulsion Laboratory’s Galileo spacecraft--led to the discovery of a fourth, previously unknown, ring, which Cornell University astronomer Joseph Burns described as a “hula hoop around Jupiter’s fat waist.”
Moreover, the findings may help scientists better understand the dynamics of rings girdling other planets, including the ring of space debris now circling the Earth.
The gossamer clouds appear like smoke rings puffed out by Jupiter itself--each ring clearly bounded by the orbit of a tiny moon. “It’s a very gratifying result,” said University of Arizona astronomer Carolyn Porco, who heads the imaging team for NASA’s mission to Saturn’s much more substantial rings. dThe evidence from the pictures, she said, “is the next best thing to being there.”
The discovery that the tiny inner moons line up precisely at the sharp boundary of the gas giant’s gossamer rings provides clear evidence that the moons feed the rings, said astronomer Norman Murray of the Canadian Institute for Theoretical Astrophysics. “It looks like the proverbial smoking gun,” he said.
The Cornell astronomers who made the discovery were even more emphatic: “The how and why of Jupiter’s rings has been solved,” said Joseph Veverka. Galileo Project scientist Torrence Johnson at JPL in Pasadena hailed the discovery as “a slam-dunk.”
Unlike Saturn’s massive icy halos, Jupiter’s rings are so insubstantial that they would be invisible to someone standing inside them. “My house is a lot dustier,” Veverka said.
As with perfume, Burns said, a barely imperceptible amount of material can create a lot of excitement. “Here we have a contemporary laboratory for processes that took place eons ago,” he said at the news conference held at Cornell in Ithaca, N.Y., and broadcast to JPL.
Our solar system formed from just such a ring of debris, and ring systems continue to be formed today, Burns said.
Understanding the rings, said Porco, provides “a window into a process that operates slowly, but can cause great changes in the configuration of bodies in the solar system.”
Unlike planets, rings ebb and flow like candle flames, scientists now believe. “Rings are not eternal,” said Veverka. A hundred thousand years ago, the ring systems around Jupiter and Saturn were probably quite different.
While Saturn’s brightly colored hoops contain snowball-sized ice chunks, Jupiter’s rings are formed from fluffy flour-like particles. The dust particles are created as Jupiter’s huge mass sucks in small icy rocks from the surrounding space, and accelerates them toward the planet with enormous speeds.
The projectiles hit the moons and send up an enormous cloud of dust. “It’s like a bullet shooting into the sand, and the sand explodes,” said Cornell astronomer Maureen Ockert-Bell.
In a massive planetary recycling project, the dust rains downward toward Jupiter. On its way, it gets caught up in flat gossamer rings that orbit with the same tilt and radius as the moon that created them.
On a larger moon, such as Earth’s, dust stirred up by collisions gradually is pulled back by gravity and settles back down on the moon.
But the inner Jupiter moons are too small to hold onto the material, which then rains down toward the planet, forming into rings. Gradually, the particles cycle through the four-ring system, and eventually fall into Jupiter itself, to be replaced by new particles kicked off the moons.
Jupiter’s main ring--discovered by the Voyager satellites in 1979--also appears to be bounded by a small moon, Adrastea.
Only the planet’s inner “halo” is not tied to a moon. Instead, it seems to be created by sympathetic vibrations between the charged particles in the ring and the strong electromagnetic field of Jupiter.
While traces of all three rings were detected by Voyager, those missions spent too little time--and carried too little instrumentation--to discern details of the system.
Eventually, the continual bombardment will entirely whittle the mother moons away, said Burns. But even the tiniest moon, 5-mile-diameter Adrastea, contains enough material to last for 1,000 years or more. (The largest of these inner moons, Amalthea, is about the size of New York’s Long Island.)
Meanwhile, new rings are being created and destroyed throughout the solar system. Similar, even more tenuous rings, said Burns, are likely to be found around Mars.
In fact, he said, humans are in the process of producing rings of space debris around Earth--not only from the scraps of broken satellites, but also from fuel particles released into space. The same researchers who study cosmic dust rings, said Torrence, “are the leading researchers in problems of artificial debris.”
