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Saturn didn’t always have rings, according to new analysis of Cassini data

Saturn’s rings are younger than previously believed and could have been formed in the relatively recent past, according to new data gathered from the Cassini mission.

The Cassini spacecraft that was orbiting Saturn is no more, but before it expired it took a loop between the planet and its rings, acting as a gravity probe and uncovering data about the composition of the rings. By looking at the strength of the gravitational pull of the rings, scientists were able to estimate the amount of mass they contained, which turns out to be about 40 percent of the mass of Saturn’s moon Mimas. For reference, Mimas is 2,000 times smaller than Earth’s moon, meaning there is relatively little material in Saturn’s rings

Artist’s concept of the Cassini spacecraft shown against a real photo of Saturn and its rings as Cassini crossed the ring plane. NASA/JPL-Caltech

This indicates that Saturn’s distinctive rings are a relatively recent development as ring mass is correlated with ring age, meaning that the rings are certainly less than 100 million years old and perhaps as young as 10 million years old. Scientists had debated whether the rings were formed from icy debris at the same time as the planet, 4.5 billion years ago, or whether the rings were younger and were formed when Saturn’s gravity captured a comet or a Kuiper Belt object and pulverized it into rocks which orbited the planet. Now the evidence is in that Saturn was ring-less for a considerable time after its formation, and the rings were a later addition.

Scientists also used the data to understand Saturn’s surface and interior composition. They discovered that there were deep flowing winds in Saturn’s atmosphere, which were impossible to observe from space and which explain the gravitational fluctuations between planet and rings. The surface clouds around the equator of Saturn rotate four percent faster than the deep layer of clouds, which is around 6,000 miles deep.

“The discovery of deeply rotating layers is a surprising revelation about the internal structure of the planet,” said Linda Spilker, Cassini project scientist at NASA’s Jet Propulsion Laboratory in a statement. “The question is what causes the more rapidly rotating part of the atmosphere to go so deep and what does that tell us about Saturn’s interior.”

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