The Cosmic Collision That Formed Saturn’s Rings

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SAturn’s rings have captivated astronomers since Galileo first sighted them in the early 15th century. While the 13-year Cassini Saturn mission answered many questions about this iconic planetary feature, such as the age of the ring, it raised new ones about the planetary system.

Namely: Why are Saturn’s rings so young? Why do so many of Saturn’s 274 moons have unbalanced orbits? And if Saturn’s mass is so central, why does its axis wobble?

In 2022, astronomers from MIT and the University of California, Berkeley, proposed an elegant answer to all three questions: Saturn once had a moon that was ejected after contact with Titan and shattered to form the rings.

To test this hypothesis, researchers at the SETI Institute led by Matija Ćuk performed a series of computer simulations to determine whether this moon could get close enough to Saturn to form its rings. Although not yet published, their results have been accepted for publication in the Journal of Planetary Sciences.

The researchers noticed that Hyperion, another moon of Saturn, tended to disappear when the hypothetical moon in their simulations became unstable. And yet, it still exists, so what gives?

Read more: “When Earth had two moons”

“Hyperion, the smallest of Saturn’s main moons, has provided us with the most important clue to the system’s history,” Ćuk said in a statement.

Hyperion is an oblong, potato-shaped moon with a shaggy and chaotic orbit, but locked to Titan. According to the researchers, the Titan-Hyperion lock-up occurred only a few hundred million years ago, around the same time that the hypothetical extra-moon was disappearing.

The researchers therefore proposed an alternative scenario adapted to the facts. “Maybe Hyperion didn’t survive this upheaval, but it was a result of it,” Ćuk explained. “If the extra moon merged with Titan, it would likely produce fragments near Titan’s orbit. That’s exactly where Hyperion would have formed.”

In this scenario, a small “proto-Hyperion” and a large “proto-Titan” merged to form the moon we know as Titan while the debris became Hyperion. This would explain some strange things about Titan, like its eccentric orbit and the lack of impact craters on its surface, which would have formed in the event of a collision.

But what about rings?

If Titan formed from a merger, the researchers found, its eccentric orbit could destabilize Saturn’s smaller moons closer, sending them into a cosmic demolition derby. If this were the case, some debris from the collisions would have dispersed inward to form the rings.

While astronomers are still analyzing Cassini data, we will gain more information about Saturn in the coming decade. Launched in 2028, NASA’s Dragonfly mission is expected to reach Titan in 2034, when a nuclear-powered octocopter lands on the surface of the Moon, something Galileo could never have dreamed of.

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Main image: NASA/JPL-Caltech

• Jake Currie

  Published on February 13, 2026

  Jake Currie is a writer based in Brooklyn, New York.