Saturn’s largest moon, the smog-enshrouded Titan, could possibly be the results of a dramatic merger between two different moons that initiated a cavalcade of results — together with the formation of Saturn’s stunning rings.
When the Cassini–Huygens mission arrived within the Saturnian system in 2004, it was greeted by a menagerie of mysterious moons with weird properties. Titan, the second largest moon within the photo voltaic system, can also be the one moon in our cosmic neighborhood to sport an environment, one redolent in natural molecules. Then, there’s Hyperion, a battered and bruised physique that appears like a large pumice stone tumbling round Saturn. In the meantime, the yin-yang world of Iapetus, with its two-toned hemispheres believed to end result from passing by way of Saturn’s E ring — which is shaped by materials spewed out from Enceladus‘s geysers — has essentially the most inclined orbit of any of Saturn’s principal moons, angled at 15.5 levels to Saturn’s equatorial aircraft.
Now, astronomers led by Matija Ćuk of the SETI Institute have come to suspect the creation of the Titan that we know today via a collision and merger of two moons could have triggered a series of events that led to all of Saturn’s other peculiarities that 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 inside Saturn itself. This moment of inertia is a controlling factor in how much Saturn’s axis of rotation wobbles, like a spinning top, a phenomenon known as precession. It had been thought that the period of Saturn’s precession matched the period of distant Neptune‘s orbit, creating a gravitational resonance that began to pull Saturn over at an angle of 26.7 degrees relative to the plane of its orbit around the 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 slightly more of Saturn’s mass was concentrated in the center than had been thought. This therefore changes Saturn’s moment of inertia, which takes it marginally out of resonance with Neptune’s orbit.
Seemingly, something had pulled Saturn out of sync with Neptune, resulting in mass to become redistributed inside Saturn. But what could have done that?
Despite being far less massive than Saturn, the ringed planet’s moons can have a surprisingly large effect on the planet. Originally, to explain what took Saturn out of resonance with Neptune, scientists came up with a theory that once upon a time Saturn had another icy moon, which they named Chrysalis. This moon, they said, could have had its orbit perturbed following a close encounter with Titan and got too close to Saturn, where gravitational tidal forces ripped it apart about 100 million years ago. While most of the debris fell into Saturn, some remained in orbit, forming the rings. Meanwhile, the interaction with Chrysalis would have been the trigger to cause Titan’s orbit to expand, which in turn would have pulled Saturn out of sync with Neptune.
It was a nice theory, but when Ćuk’s team put it to the test in simulations, they found that the vast majority of the time Chrysalis collided with Titan instead. However, instead of being a dead end for the Chrysalis hypothesis, the simulations opened another door, and the key was another moon of Saturn, 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 that Titan makes, Hyperion makes exactly three orbits, tumbling disorderly around the ringed planet.
“Hyperion, the smallest among Saturn’s major moons, provided us the most important clue about the history of the system,” said Ćuk in a statement. “In simulations the place the additional moon grew to become unstable, Hyperion was usually misplaced and survived solely in uncommon circumstances. We acknowledged that the Titan–Hyperion lock is comparatively younger, only some hundred million years outdated. This dates to about the identical interval when the additional moon disappeared. Maybe Hyperion didn’t survive this upheaval, however resulted from it. If the additional moon merged with Titan, it might produce fragments close to Titan’s orbit. That’s precisely the place Hyperion would have shaped.”
Ćuk is suggesting that Chrysalis was actual, and did certainly collide and merge with the proto-Titan 100–200 million years in the past, and that it was this collision that formed a lot of what we see within the Saturnian system.
For instance, earlier than the collision Titan could have been extra like Jupiter’s icy, airless moon Callisto, with an historical and battered floor. The collision would have seen Titan’s complete floor cleaned, which might clarify why there are so few craters on Titan beneath its thick ambiance. And that ambiance would have leaked out from Titan’s inside in the course of the collision. The collision knocked Titan in its orbit round Saturn, inflicting its orbit to widen and change into extra elongated. It’s only now starting to steadily develop extra round once more.
The change in Titan’s orbit would have seen its tidal forces wreak havoc on the interior mid—sized moons, prompting them to collide too, in accordance with additional simulations by scientists on the College of Edinburgh and NASA Ames Analysis Heart. Whereas the moons reformed from a lot of the particles, among the icy particles would have settled round Saturn to kind its ring methods.
The simulations additionally present that Chrysalis would have perturbed Iapetus’s orbit, resulting in its excessive inclination.
It’s a good, neat speculation — however at present, that’s all it’s. Whereas the thought matches the info, there isn’t any direct proof but. NASA’s Dragonfly mission to Titan, which is ready to launch in 2028, could possibly be the primary to search out such proof by searching for additional indicators that Titan’s floor is younger, indicating the upheaval that adopted the collision with Chrysalis over 100 million years in the past.
The findings from Ćuk’s staff have been accepted for publication in Planetary Science Journal, and a preprint is accessible on the arXiv paper repository.
