Jupiter: Eat My Dust

The rings around the largest planet are a movable feast

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The controversy over Jupiter's rings is over. The process that created them, however, is not. Cornell University researchers announced Tuesday that the gossamer-thin disks, first discovered by the Voyager spacecraft in 1979, were in fact space dust thrown up by micrometeorites bombarding the inner moons of Jupiter; they are not, as previously thought, particles of a moon that died or never had a chance to form. The bombardment, says TIME space writer Jeffrey Kluger, continues even now: "These moons continue to be pummeled." It's a good thing, too. "The rings need to be refreshed periodically," Kluger explains. "Otherwise, they'd just fall down to the planet."

Indeed, gravity -- or the lack of it -- also plays a big part in the rings' creation. The moons are so small and weightless that chunks of rock can fly off them with ease -- an effect we couldn't hope to repeat back home. "A similar explosion on Earth would release a lot of debris, but it would fall back to the ground," says Kluger. Indeed, the only rings astronomy buffs can ever hope to see themselves are those around Saturn; Jupiter's shroud will forever remain invisible to the Earth-bound.