A Gnarly New Theory About Saturn's Rings

Saturn has quite the collection of moons, more than any other planet in the solar system. There's Enceladus, blanketed in ice, with a briny ocean beneath its surface. There's Iapetus, half of which is dusty and dark, and the other shiny and bright. There are Hyperion, a rocky oval that bears a striking resemblance to a sea sponge, and Pan, tiny and shaped just like a cheese ravioli. But one moon might be missing. From a report: According to a new study, Saturn once had yet another moon, about the same size as Iapetus, which is the third-largest satellite in Saturn's collection. The moon orbited the ringed planet for several billion years, minding its own business, doing moon things, until about 100 million to 200 million years ago, when other Saturnian moons started messing with it. The interactions between them pushed the unlucky moon closer to Saturn -- too close to remain intact. Gravity shredded it to bits. Something remarkable might have come out of all this. While most of the moon debris fell into Saturn's atmosphere, some of the pieces hung back, whirling around the planet until they splintered further and flattened into a thin, delicate disk. This lost moon, the authors of the study say, is responsible for Saturn's trademark feature: the rings. These astronomers didn't set out to find a missing moon. They were trying to better understand why Saturn is the way it is now -- specifically, why the planet is tilted just so. "Planetary tilts are an interesting indicator of a planet's history," Zeeve Rogoszinski, an astronomer at the University of Maryland who was not involved in this recent work but who studies orbital dynamics, told me. Most of the planets in our solar system spin at an angle relative to the plane in which they orbit the sun. Earth's tilt, for example, is a result of the collision that scientists believe might have created our moon. Mars's tilt is chaotic, thanks to the influence of next-door neighbor Jupiter. Uranus likely got its dramatic lean after the planet was whacked with a massive rocky object a few billion years ago.

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