Saturn's rings are made from the guts of a vanished moon that got a bit too close to the planet. That's the conclusion of a new study that claims not only to explain the formation of the rings but also the significant tilt at which the solar system's most-mooned planet rotates. "It ties together two puzzles that had previously been treated as separate," study co-author Dr. Francis Nimmo of the University of California, Santa Cruz, tells the Wall Street Journal. "It turns out that you can explain both in a single story." The story goes that an additional moon orbited the planet for billions of years, exerting a gravitation pull that kept it in resonance with Neptune, meaning the planets exerted periodic gravitational influence on each other.
Researchers have long suspected Saturn and Neptune are in resonance "as Saturn's tilt precesses, like a spinning top, at nearly the same rate as the orbit of Neptune," per MIT News. Neptune's axis of rotation is tilted 28.32 degrees from its plane of orbit around the Sun, while Saturn's is tilted 26.7 degrees. However, data from NASA's Cassini spacecraft indicated Saturn and Neptune were in resonance in the past, but no longer, pointing to a disruption some 100 million to 200 million years ago. Using simulations, researchers determined that as Saturn's largest moon Titan drifted outward, as it continues to do, it destabilized the orbit of a smaller but still large moon they dubbed Chrysalis, roughly 900 miles wide, sending it too close to the planet.
The moon made up mostly of water ice "would have been ripped apart by tidal forces," according to the study published Thursday in Science. Some 99% of the rubble was thrown into Saturn's atmosphere but the remaining 1% continued to orbit the planet and eventually flattened into the rings, researchers propose, per Reuters. Meanwhile, the loss of a moon like the proposed Chrysalis would have been enough to "remove Saturn from Neptune's grasp and leave it with the present-day tilt," per MIT News. "It's a pretty good story, but like any other result, it will have to be examined by others," says lead author Dr. Jack Wisdom of the Massachusetts Institute of Technology. "But it seems that this lost satellite was just a chrysalis, waiting to have its instability." (More Saturn stories.)
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