Scientists Might Have Solved Mystery of Saturn's Famous Rings

They theorize it has to do with the gas giant's missing moon.

Eric Mack Contributing Editor
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Eric Mack
3 min read
An illustration in dark, sort of ominous, tones that showcase a small, bright star in the background in space. In the foreground is a large planet that seems to have rings like Saturn.

Saturn's rings might really be the remnants of a lost satellite. 

University of Sheffield

Saturn's rings aren't the kind of bling you come by easily -- and a new theory suggests they were formed when one of the gas giant's own moons treaded too close to the massive planet. 

This unfortunate satellite might've gotten caught in its host's intense gravitational field, which then literally pulled it apart. The resulting debris, scientists believe, might've formed much of the rings we see today. At least that's what a team of researchers led by MIT's Jack Wisdom, who dubbed the lost moon "Chrysalis," suggest. An outline of the team's theory can be found in a paper published in the latest issue of the journal Science. 

Wisdom says this story also helps explain the unusual tilt of Saturn's axis and why the rings are thought to only be over 100 million years old, when Saturn itself formed over 4 billion years ago. 

"The tilt is too large to be a result of known formation processes in a protoplanetary disk or from later, large collisions," Wisdom said in a statement. "A variety of explanations have been offered, but none is totally convincing. The cool thing is that the previously unexplained young age of the rings is naturally explained in our scenario."

Finding the lost moon of Saturn

Saturn orbits the sun tilted over 26 degrees to one side, a position even more dramatic than Earth's tilt, which oscillates between 22.1 and 24.5 degrees. The most likely explanation for this has long been that Saturn's tilt comes from a sort of gravitational dance the planet is engaged in with Neptune.

But Wisdom and colleagues, aided by data from NASA's Cassini spacecraft, ran some new models which suggest that, while Saturn and Neptune were once in resonance in the past, something changed about 160 million years ago. And that something basically removed Saturn from Neptune's influence. 

From a number of simulations, the one that fit all the data best was a hypothetical instance in which Saturn lost a relatively large moon. 

See Saturn's secrets through NASA Cassini's finest views

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Today, the giant's planetary system hosts 83 moons; Chrysalis would have been about the size Iapetus, currently Saturn's third-largest moon. The new study's scientists theorize that between 200 and 100 million years ago, the forgotten moon started to get pushed around by the gravitational field of Titan, Saturn's largest moon. In turn, this would have disrupted Chrysalis' orbit, sending it on a chaotic path that included nearly colliding with Iapetus and Titan and eventually coming too close to Saturn itself. 

Such an encounter, the researchers say, could have ripped the moon to bits, with much of the remains probably being consumed by Saturn and a small fraction forming what we now know today as those magnificent rings. It seems to be the perfect explanation, solving two cosmic mysteries at once, but Wisdom cautions that it remains a theory. 

"Like any other result, it will have to be examined by others," he said, adding that it makes for a great story in the meantime.

"Just like a butterfly's chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged."