Did a titanic moon crash create Saturn’s iconic rings?

When you purchase through links on our articles, Future and its syndication partners may earn a commission.

Saturn’s largest moon, Titan, shrouded in smog, could be the result of a spectacular merger between two other moons that triggered a cavalcade of effects, including the formation of Saturn’s magnificent rings.

When the Cassini–Huygens mission arrived in the Saturnian system in 2004, it was greeted by a menagerie of mysterious moons with weird properties. Titanthe second largest moon of the solar systemis also the only moon in our cosmic neighborhood to have an atmosphere reminiscent of organic molecules. Then there’s Hyperion, a battered and bruised body that looks like a giant tumbling pumice stone. Saturn. Meanwhile, the yin-yang world of Iapetus, with its two-colored hemispheres believed to result from passing through Saturn’s E ring – which is formed by material spewed out by Saturn’s E ring. EnceladusSaturn’s Geysers – has the most inclined orbit of all of Saturn’s main moons, tilted 15.5 degrees to Saturn’s equatorial plane.

And of course there is Saturn’s ringsunrivaled in the solar system; today their age is estimated to be “young” 100 million years, but their origins unfortunately remain mysterious.

Today, astronomers led by Matija Ćuk of the SETI Institute have come to suspect that the creation of the Titan we know today via a collision and merger of two moons could have triggered a series of events that led to all the other features of Saturn we see today.

The clue to all this came from Cassini’s measurements of Saturn’s “moment of inertia,” which is governed by the distribution of mass within Saturn itself. This moment of inertia is a determining factor in how Saturn’s spin axis wobbles like a top, a phenomenon known as precession. It was thought that the period of Saturn’s precession corresponded to the period of distant NeptuneSaturn’s orbit, creating a gravitational resonance that began to pull Saturn at an angle of 26.7 degrees to the plane of its orbit around Saturn’s orbit. sun. This tilt has the added benefit of allowing us to see Saturn’s rings more clearly from Earth.

But Cassini’s measurements of the internal mass distribution showed that a little more of Saturn’s mass was concentrated at the center than previously thought. This therefore modifies Saturn’s moment of inertia, which takes it slightly out of resonance with Neptune’s orbit.

Apparently, something had knocked Saturn out of sync with Neptune, resulting in a redistribution of mass inside Saturn. But what could have done this?

Although they are much less massive than Saturn, the ringed planet’s moons can have a surprisingly large effect on the planet. Originally, to explain what stopped Saturn from resonating with Neptune, scientists proposed a theory that Saturn once had another icy moon, which they named Chrysalis. This moon, they said, could have had its orbit disrupted following a close encounter with Titan and gotten too close to Saturn, where gravitational tidal forces tore it apart about 100 million years ago. While most of the debris fell on Saturn, some remained in orbit, forming the rings. Meanwhile, the interaction with Chrysalis would have been the trigger for the expansion of Titan’s orbit, which in turn would have knocked Saturn out of sync with Neptune.

It was an interesting theory, but when Ćuk’s team tested it in simulations, they found that the vast majority of the time Chrysalis collided with Titan. However, instead of being a dead end for the Chrysalis hypothesis, the simulations opened another door, and the key was another Saturn moon, Hyperion, which orbits just beyond Titan.

Titan and Hyperion are another example of gravitational resonance. Their orbits are locked together: for every four orbits of Saturn made by Titan, Hyperion completes exactly three orbits, rotating haphazardly around the ringed planet.

“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. statement. “In simulations where the extra moon became unstable, Hyperion was often lost and only survived in rare cases. We recognized that the Titan-Hyperion lock is relatively young, only a few hundred million years old. from Titan’s orbit. This is exactly where Hyperion would have formed.

Ćuk suggests that Chrysalis was real and that it actually collided and merged with proto-Titan 100 to 200 million years ago, and that it was this collision that shaped much of what we see in the Saturnian system.

For example, before the collision, Titan may have looked more like Callisto, Jupiter’s icy, airless moon, with an old, battered surface. The collision would have seen Titan’s entire surface erased, which would explain why there are so few craters on Titan beneath its thick atmosphere. And this atmosphere would have escaped from Titan’s interior during the collision. The collision threw Titan into its orbit around Saturn, causing its orbit to widen and lengthen. Only now is this system starting to gradually become more circular again.

Titan’s shift in orbit would have seen its tidal forces wreak havoc on the mid-sized inner moons, prompting them to collide as well, according to further simulations by scientists at the University of Edinburgh and NASA’s Ames Research Center. While the moons reformed from most of the debris, some ice particles would have been deposited around Saturn to form its ring systems.

The simulations also show that Chrysalis would have disrupted Iapetus’ orbit, leading to its strong inclination.

It’s an interesting and interesting hypothesis – but currently, that’s all it is. Although the idea fits the facts, there is no direct proof yet. NASA’s Dragonfly mission to Titan, scheduled to launch in 2028, could be the first to find such evidence by searching for other signs that Titan’s surface is young, indicating the upheaval that followed the collision with Chrysalis more than 100 million years ago.

Ćuk’s team’s results have been accepted for publication in Planetary Science Journal, and a preprint is available on the arXiv paper repository.