Saturn's rings haven't always been there - CNN

When NASA's Cassini spacecraft plunged into the planet's atmosphere to end its 20-year mission in 2017, it dived between the planet and its rings. This last act before the spacecraft disintegrated allowed the instruments to precisely measure the amount of material in Saturn's rings.

Knowing that weight also allowed scientists to determine the age of the rings. The material in the rings weighs about 40% of Saturn's moon Mimas. The smooth, round moon has an impact crater that caused people to compare it to the Death Star from the "Star Wars" films.

Scientists now believe the rings formed less than 100 million years ago, or even as recently as 10 million years ago.

The age of the rings has been a debate among scientists for years. Some believed they formed when the planet did 4.5 billion years ago, using icy debris leftover from the formation of the solar system. And others thought the rings were captured material from the Kuiper belt or a comet, reduced over time to rubble orbiting Saturn.

What Cassini found as it plunged into Saturn a year ago

"These measurements were only possible because Cassini flew so close to the surface in its final hours," said a statement from Burkhard Militzer, study author and professor of Earth and planetary science at the University of California, Berkeley. "It was a classic, spectacular way to end the mission."

But in order to even get the right measurements, the scientists had to account for deep flowing winds in Saturn's atmosphere. These flows look like massive clouds about 6,000 miles deep. The surface clouds at Saturn's equator rotate 4% faster than this deep layer.

"The discovery of deeply rotating layers is a surprising revelation about the internal structure of the planet," said Cassini project scientist Linda Spilker of NASA's Jet Propulsion Laboratory. "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."

They also determined that the planet's rocky core is between 15 and 18 times the mass of Earth.

This adds to previous science results from Cassini's "death dive" that are unlocking the mysteries of Saturn.

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