An ancient moon which was torn apart after it spun too close to Saturn may be the cause of the planet鈥檚 tilted rings, according to new research.
Saturn鈥檚 lean has always been clear through its rings, which spin around the planet at a 26.7-degree angle compared to the planet鈥檚 orbit around the Sun.
While this was long thought to be connected to the gravitational force of Saturn鈥檚 neighbour, Neptune, due to how closely the spin of Saturn aligns with the pattern of Neptune鈥檚 orbit, astronomers now believe that connection between the two planets has since been broken.
But if Saturn isn鈥檛 tilting to pull toward Neptune, what is the reason behind its current tilt? And could it be connected to the relatively recent formation of Saturn鈥檚 rings, which have previously been estimated to be only 100 million years old?
Astronomers believe they have found an explanation that could answer a number of these unexplained Saturn anomalies: an extra moon which died so the rings could form.
In a new study published Thursday in the journal Science, authors have dubbed this moon 鈥淐hrysalis.鈥�
If Chrysalis existed as moon number 84, it would鈥檝e assisted in keeping Saturn in line with Neptune for several billion years, the study suggests.
Then, around 160 million years ago, according to researchers鈥� computer modelling, Chrysalis鈥檚 orbit became unstable and it grazed the planet itself 鈥� a catastrophic event which would鈥檝e pulled the moon apart, and would also explain how Saturn was pulled from its pattern with Neptune to acquire its current tilt.
The shattered pieces of Chrysalis which didn鈥檛 fall to Saturn were then flung into orbit around it, eventually crumbling into smaller icy pieces to make up the planet鈥檚 rings.
鈥淛ust like a butterfly鈥檚 chrysalis, this satellite was long dormant and suddenly became active, and the rings emerged,鈥� Jack Wisdom, professor of planetary sciences at Massachusetts Institute of Technology and lead author of the new study,
This theory patches a number of holes in previous explanations for Saturn鈥檚 orbit, rings and tilt, researchers say.
It was first suggested in the 2000s that Neptune and Saturn were bound in a gravitational association, but when NASA鈥檚 Cassini flew out to visit the planet from 2004 to 2017, its observations brought new complications.
Cassini鈥檚 observations of Titan, Saturn鈥檚 largest moon, led to the theory that this large moon was actually responsible for Saturn鈥檚 tilt, forcing it into alignment with Neptune. However, this only made sense if the gas giant鈥檚 mass was distributed in a particular way 鈥� since the planet鈥檚 composition makes it difficult for us to tell if its mass is concentrated more towards the core or not, the planet鈥檚 moment of inertia is hard to pinpoint.
Wisdom and his colleagues set out to see if Cassini鈥檚 final observations 鈥� gathered in the last moments of its existence as the spacecraft plunged towards the surface of Saturn 鈥� could shed light on the issue.
These final observations made it possible to create a gravitational field of Saturn that allowed researchers to model the way mass is distributed across the planet.
They found that the moment of inertia they鈥檇 been searching for meant that Saturn was actually slightly out of alignment with Neptune. The planets were no longer in sync.
鈥淭hen we went hunting for ways of getting Saturn out of Neptune鈥檚 resonance,鈥� Wisdom said.
After modelling numerous scenarios, the team discovered that the math balanced out if a new moon was added and then subtracted in a cataclysmic event.
They theorize that Chrysalis鈥� orbit became chaotic between 100-200 million years ago, and that after it had some near misses with some of the other large moons such as Titan, it grazed by Saturn itself, travelling too close to survive the encounter.
Chyrsalis would鈥檝e had to be about the size of Iapetus, Saturn鈥檚 third-largest moon, to explain how its destruction and loss could鈥檝e pulled Saturn out of resonance with Neptune.
鈥淚t鈥檚 a pretty good story, but like any other result, it will have to be examined by others,鈥� Wisdom says. 鈥淏ut it seems that this lost satellite was just a chrysalis, waiting to have its instability.鈥�
