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Saturn's Rings Formed Long After the Planet

A new study furthers the mystery of where the Saturn's sparkling ice rings came from.

By Matt Hrodey
May 15, 2023 8:30 PMMay 15, 2023 8:36 PM
Cassini and Saturn
Cassini in front of Saturn. (Credit: Dotted Yeti/Shutterstock)


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Saturn’s seven rings are much younger than the planet itself, concludes a paper that relied on data from the now-demolished Cassini spacecraft, which orbited the planet for 13 years.

While Saturn’s rings are like cosmic pearls – chunks of mostly water ice, the size of boulders and smaller – those pearls are slightly dirty and only getting dirtier. They collect the dust that flies through the solar system, at a certain rate. Scientists didn’t know what that rate was until Cassini pinned it down, which has helped scientists to date the rings.

How Cosmic Dust Dated Saturn's Rings

Cassini’s Cosmic Dust Analyzer, shaped like a bucket (albeit one with advanced sensors), scooped up dust and analyzed its trajectory and chemical makeup. Over 13 years, it found only 163 grains that had flown in from beyond Saturn’s environs, indicating that dust would have accumulated on the rings at a gradual rate.

“Think about the rings like the carpet in your house,” says Sascha Kempf, a physicist at the University of Colorado Boulder, in a press release. “Dust will settle on your carpet. The same is true for the rings.”

The researchers estimated the age of the rings based on the their current dirtiness and the level of dust that surrounded them. The result? The rings are somewhere between 100 and 400 million years old, much younger than the planet itself, which is 4.5 billion years old.

This makes the rings a recent phenomenon instead of something from the primordial past, raising new questions.

New Mysteries About Saturn and Its Rings

“If the rings are short lived and dynamical, why are we seeing them now?” he says. “It’s too much luck.”

The rings’ very ice presents a mystery as it's 98 percent (or more) pure water ice by volume, along with a very small amount of rocky matter. Added up, all this pristine ice equals about half the volume of Saturn’s moon Mimas.

“It’s almost impossible to end up with something so clean,” Kempf says.

It may not last forever – Saturn’s gravity is slowly pulling in the planet’s rings and cannibalizing them, according to NASA scientists. But the rings won’t disappear completely for at least another 100 million years. Every half hour, the planet nibbles more ice from the rings, about the equivalent of an Olympic-sized swimming pool, according to the space agency.

“We know approximately how old the rings are, but it doesn’t solve any of our other problems,” says Kempf. “We still don’t know how these rings formed in the first place.”

One theory suggests that the planet’s gravity tore apart one of its many moons (which may number as many as 145), and what we now see are the remnants.

Galileo and James Clerk Maxwell

Observation of Saturn began before the invention of telescopes, as it’s visible with the naked eye, but Galileo Galilei first spotted the rings through a telescope. He didn’t know what to make of them, at first, and drew flat loops on the sides of a planet in his notes.

In the 19th century, Scottish scientist and polymath James Clerk Maxwell concluded that these loops must be made of loose material and not solid bands. And so arose the need to explain when and where this material came from.

“In a way, we’ve gotten closure on a question that started with James Clerk Maxwell,” says Kempf.

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