An ancient moon that tore apart after spinning too close to Saturn could be the cause of the planet’s tilted rings, according to new research.
Saturn’s tilt has always been clear through its rings, which orbit the planet at a 26.7 degree angle to the planet’s orbit around the Sun.
Although this has long been thought to be related to the gravitational pull of Saturn’s neighbor Neptune, due to how closely Saturn’s rotation aligns with the pattern of Neptune’s orbit, astronomers believe now that the connection between the two planets has since been severed.
But if Saturn is not tilting to pull towards Neptune, what is the reason for its current tilt? And could it be related to the relatively recent formation of Saturn’s rings, which were estimated to be only 100 million years old?
Astronomers believe they’ve found an explanation that may answer for a number of these unexplained Saturn anomalies: an extra moon that died so the rings could form.
In a new study published Thursday in the journal Science, the authors dubbed this moon “Chrysalis.”
If Chrysalis existed as moon number 84, it would have helped keep Saturn in line with Neptune for several billion years, according to the study.
Then, around 160 million years ago, according to the researchers’ computer modelling, Chrysalis’ orbit became unstable and it brushed past the planet itself – a catastrophic event that would have separated the moon and also explain how Saturn was removed from its pattern with Neptune to acquire its current tilt.
The shattered pieces of Chrysalis that did not fall on Saturn were then thrown into orbit around it, eventually collapsing into small chunks of ice to make up the planet’s rings.
“Like a butterfly’s chrysalis, this satellite was dormant for a long time and suddenly became active, and the rings emerged,” said Jack Wisdom, professor of planetary sciences at the Massachusetts Institute of Technology and lead author of the new study, in a press release.
According to the researchers, this theory fixes a number of holes in previous explanations of Saturn’s orbit, rings, and tilt.
Neptune and Saturn were first suggested in the 2000s to be linked by a gravitational association, but when NASA’s Cassini flew to visit the planet from 2004 to 2017, his observations led to further complications.
Cassini’s observations of Titan, Saturn’s largest moon, led to the theory that this large moon was actually responsible for Saturn’s tilt, forcing it to align with Neptune. However, this only made sense if the mass of the gas giant was distributed in a particular way – since the composition of the planet prevents us from saying whether its mass is concentrated more towards the core or not, the moment of inertia of the planet is difficult to determine. .
Wisdom and his colleagues set out to see if Cassini’s latest observations — collected in the final moments of its existence as the spacecraft plunged toward Saturn’s surface — might shed some light on the question.
These final observations helped create a gravitational field of Saturn that allowed researchers to model how mass is distributed on the planet.
They found that the moment of inertia they were looking for meant Saturn was actually slightly out of alignment with Neptune. The planets were out of sync.
“Then we went looking for ways to get Saturn out of Neptune’s resonance,” Wisdom said.
After modeling numerous scenarios, the team discovered that the calculations balanced out if a new moon was added and then subtracted during a cataclysmic event.
They hypothesize that Chrysalis’ orbit became chaotic between 100 and 200 million years ago, and after having a few near misses with some of the other large moons such as Titan, it brushed past Saturn. herself, traveling too close to survive the encounter.
Chyrsalis would have had to be roughly the size of Iapetus, Saturn’s third-largest moon, to explain how its destruction and loss could have knocked Saturn out of resonance with Neptune.
“It’s a pretty good story, but like any other result, it will need to be looked at by others,” Wisdom says. “But it seems that this lost satellite was just a chrysalis, waiting for its instability.”