Saturn’s rings are surprisingly young, forming within the last 100 million years

Saturn’s rings are only about 100 million years old, meaning they formed long after the first dinosaurs and mammals walked the Earth.

TL;DR

NASA’s Cassini spacecraft made daring dives between Saturn and its rings during its Grand Finale, providing groundbreaking data that revealed Saturn’s rings are only 10 to 100 million years old—much younger than the planet itself. Precise measurements of Saturn’s gravitational field, achieved during these maneuvers, allowed researchers to determine the rings’ relatively low mass. The cause of the rings’ formation remains unknown, though theories include a catastrophic event like a collision. Cassini’s data also offered insights into Saturn’s interior, including the depth at which uniform rotation begins and the size of its core.

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Exploring Saturn’s Rings

During NASA’s Cassini spacecraft’s Grand Finale, the craft daringly dove between Saturn and its rings, gathering groundbreaking insights about the planet and unveiling the unexpected youthfulness of Saturn’s rings. Recent studies reveal that these majestic rings are much younger than Saturn itself, likely forming in just the last 100 million years.

Initially, Cassini orbited Saturn outside its rings, which complicated efforts to distinguish the gravitational pull of the rings from that of the planet, a crucial step in determining the rings’ mass. Scientists had long theorized that the rings’ mass could reveal their age, but precise measurements had to wait until Cassini’s final, bold maneuvers.

As Cassini dove between Saturn and its rings, researchers meticulously monitored a radio link between the spacecraft and Earth. This allowed for an accurate measurement of Saturn’s gravitational field, unobstructed by the influence of the rings, as explained by study author Luciano Iess of the Sapienza University of Rome.

Upon finding that the rings possess a relatively low mass, scientists concluded that Saturn’s rings are only 10 to 100 million years old—far younger than Saturn, which is estimated to be 4.5 billion years old. Iess noted, “There were already clues from Voyager and Cassini measurements that the rings had not formed with Saturn, but now we have much more concrete evidence, which was only possible to obtain during the final phase of the mission.”

Saturn’s Mysteries

While these findings pinpoint the age of Saturn’s rings, the exact cause of their recent formation remains a mystery. “A catastrophic event like a collision looks to me the most obvious explanation, but there may be problems with that too,” Iess stated. He added, “The origin of the rings has to be put in the broader context of the dynamics of the Saturnian system. There are colleagues who think that even the inner moons of Saturn are young, and they are migrating [outward].”

Cassini’s close passes didn’t just reveal the rings’ age; they also provided deeper insights into Saturn’s gaseous interior. Saturn, primarily composed of hydrogen and helium, has a unique atmospheric rotation where the outer layers move faster than the inner layers. With this new data, researchers were able to quantify this difference and discovered that uniform rotation begins at a depth of about 5,592 to 6,214 miles (9,000 to 10,000 km) below the surface.

The study also sheds light on the size of Saturn’s core, revealing it to be composed of heavy elements and accounting for about 15 to 18 Earth masses, or 15 percent of Saturn’s total mass. According to Iess, understanding the core’s size could provide key insights into the formation of Saturn and its moons.

This work is published in the journal Science.