Saturn is tilted after one of its moons crashed into it, a new study has suggested.
Even in pictures, it is clear there is something off about our near neighbour: its rings swirl around at a roughly 25-degree angle to its orbit around the Sun. But it is less clear how it came to be tilted, with scientists thinking it probably has something to do with Neptune, its near neighbour, since the tilt is similar to its orbit.
Now scientists have suggested that the two were once in sync, orbiting in a neat alignment or resonance together.
That alignment was knocked off at some time in history, when a moon caused havoc between the two, a new study suggests.
Nowadays, Saturn has 83 moons. But in the past it may have had an extra, now missing satellite, that scientists have named Chrysalis.
Those many moons orbited around Saturn and kept it in neat alignment with Neptune, scientists say, with that smooth resonance lasting for billions of years.
About 160 million years ago, however, Chrysalis fell out of that neat alignment and strayed too close to Saturn itself. The moon was torn apart, and its loss pulled Saturn away from Neptune and left the planet off its alignment.
What’s more, Saturn’s rings may have been formed out of the chunks that Chrysalis was broken into.
That helps explain two mysteries at once. Chrysalis is the cause of the tilt and the unexplained age of the rings, which are only 100 million years old and much younger than the planet itself.
“Just like a butterfly’s chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged,” said Jack Wisdom, professor of planetary sciences at MIT and lead author of the new study.
The team used detailed data on Saturn – including measurements taken when the Cassini probe crashed into the planet – to construct a precise simulation of Saturn. Those models indicated that the planets could once have been synchronised together but had fallen out.
A moon could be enough to cause those problems, the scientists believe. It would have orbited around Saturn until 200 to 100 million years ago, when it fell into a chaotic orbit that took it near to other satellites and then grazed Saturn, which tore it apart.
“It’s a pretty good story, but like any other result, it will have to be examined by others,” Wisdom said. “But it seems that this lost satellite was just a chrysalis, waiting to have its instability.”
The research is described in a paper, ‘Loss of a satellite could explain Saturn's obliquity and young rings’, published in Science.