Scientists unveil moon crash theory to explain the rings of Saturn

Image of Saturn taken by the Voyager Spacecraft at a distance of 21.1 million miles.
Saturn's famous rings may have been a recent addition in the planet's 4.5 billion year history - Bettmann

Saturn’s rings were created when two icy moons crashed together unleashing a frozen debris field that encircled the planet, a new study suggests.

Previous theories have suggested that the rings were made from pieces of comets or asteroids that were torn apart by Saturn’s powerful gravity, and left suspended in orbit soon after the planet formed.

But new research by Nasa and the universities of Durham and Glasgow suggests that the rings were created when two ice moons collided and shattered only a few hundred million years ago.

It means that for most of its existence, Saturn did not have rings.

Experts say the two culprits would have been similar in size to two of Saturn’s current moons, Dione and Rhea, which have a radius of 348 and 474 miles respectively.

Dr Vincent Eke, associate professor in the Department of Physics at Durham University, said: “We tested a hypothesis for the recent formation of Saturn’s rings and have found that an impact of icy moons is able to send enough material near to Saturn to form the rings that we see now.”

Saturn has seven rings composed of chunks of ice, most no bigger than a boulder. They were first spotted by Italian astronomer Galileo Galilei in 1610 and in the 1800s Scottish scientist James Clerk Maxwell determined that they were made up of individual pieces.

Although Saturn is around 4.5 billion years old, recent data from Nasa’s Cassini mission has shown that the rings are almost pure ice and relatively dust free, suggesting they are far younger than the planet.

Dust is a good indicator of how long an object has been in place because it accumulates in layers over time; like a carpet, or a disused shelf, that becomes dustier the longer it has been left exposed to the elements.

But the icy chunks in Saturn’s rings are sparkling clean, meaning they cannot have been there since the birth of the planet.

For the new study, the team simulated nearly 200 different collision scenarios and found that two moons coming together would scatter the right amount of ice to allow the formation of rings.

Previous explanations involving comets and asteroids have struggled to explain why there is almost no rock in Saturn’s rings.

Experts believe that rocky debris ended up orbiting further out, and could have clumped together to form Saturn’s present moons.

‘Puzzle’ of Saturn’s rings

Dr Luis Teodoro, an honorary research fellow at the University of Glasgow, added: “The apparent geological youth of Saturn’s rings has been a puzzle since the Voyager probes sent back their first images of the planet.

“This collaboration has allowed us to examine the possible circumstances of their creation, with fascinating results.”

Dr Jacob Kegerreis, a Durham University graduate who is now a research scientist at Nasa’s Ames Research Center, said: “There’s so much we still don’t know about the Saturn system, including its moons that host environments that might be suitable for life, so it’s exciting to use big simulations like these to explore in detail how they could have evolved.”

Recent research by Nasa has shown that the rings may be fleeting. The ice that forms them is slowly raining down on the planet and could disappear altogether in the next 100 million years.

The new research is published in The Astrophysical Journal.

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