What Caused Saturn’s Rings and Tilt? Perhaps the Destruction of a Moon

Scientists propose that about 160 million years ago, the moon was torn apart, creating the planet’s iconic rings

A photo of Saturn showing its tilted axis and its rings
A photo of Saturn taken by NASA's Voyager 1 space probe from a distance of 34 million kilometers in 1980.  Smith Collection / Gado / Getty Images

Scientists have long struggled to explain some of Saturn’s quirks, such as how its rings were formed and why its axis of rotation is tilted by a steep 27 degrees.

In a new paper, published Thursday in Science, researchers hypothesize that the existence of a previously unknown moon could solve both of these mysteries at once.

From its orbit, the theoretical moon would have contributed to Saturn’s odd tilt. Then, around 160 million years ago, if the moon had flown too close to the planet and been torn apart, its icy remains would have formed the iconic rings, they propose.

“We like it because it’s a scenario that explains two or three different things that were previously not thought to be related,” Jack Wisdom, a planetary scientist at MIT and first author of the new study, tells Science News Lisa Grossman. “The rings are related to the tilt, who would ever have guessed that?”

Some scientists are not ready to completely accept the theory. Luke Dones, a planetary dynamicist at the Southwest Research Institute who did not contribute to the research, says to Science’s Eric Hand that while the idea is “clever,” he has some reservations. “I’m not sure how you would test this idea,” he says.

Now, Saturn is tilted 27 degrees, but based on when the planet formed, it should have a much smaller tilt, the researchers say. Jupiter, another gas giant, has a tilt that’s only about 3 degrees. When the gas giants arose, there’s no way such a deep tilt could have been created, per Science News, and 27 degrees is even too large to have been caused by a collision. “You can’t tilt Saturn over that much with the size of impactors that are believed to have been present,” Wisdom tells Science.

Scientists have thought that Saturn’s tilt is tied to Neptune’s, since the wobbling of these planets’ axes is synced together through a property called resonance. This resonance, along with the movement of Titan, Saturn’s largest moon, could have created the planet’s tilt, per New Scientist’s Leah Crane.

But data from NASA’s Cassini spacecraft indicated that Saturn has lost this relationship with Neptune, the researchers say. “Something kicked it out of the resonance,” Rola Dbouk, an MIT planetary scientist and a co-author of the paper, tells Science.

The team says that their hypothetical moon, dubbed Chrysalis, could be the cause, per New Scientist. If Chrysalis flew out of orbit or got destroyed by Saturn, it would have affected the planet's tilt. “When you have an event like that, the whole system would have shaken and tilted Saturn back up,” Maryame El Moutamid, an expert in orbital dynamics and celestial mechanics at Cornell University who wrote a companion piece to the study, tells New Scientist.

If Titan’s orbit had synced up with that of Chrysalis, it could have pushed the moon off its normal trajectory, per Science News. The researchers ran 390 computer simulations of this event, and in 17 of them, the moon grazed Saturn, according to Science. In those scenarios, Saturn would likely have engulfed almost all of Chrysalis, but the rest would have become suspended in orbit around the gas giant, forming its rings, per CNN’s Katie Hunt.

“With Chrysalis gone, Neptune no longer could change Saturn’s spin axis. So the planet was left spinning at an angle of 27 degrees,” study co-author Burkhard Militzer, a planetary scientist at the University of California, Berkeley, tells Reuters’ Will Dunham.

While the story holds together, it won’t be easy to prove. “It is hard to validate one unlikely event, and here there are two unlikely events that had to happen at the same time,” El Moutamid tells New Scientist.

“I think it’s all plausible, but maybe not so likely,” Larry Esposito, a planetary scientist at the University of Colorado Boulder who did not contribute to the research, tells Science News. “If Sherlock Holmes is solving a case, even the improbable explanation may be the right one. But I don’t think we’re there yet.”