Would a single moon clarify some of the mysteries that Saturn holds? The hypothesis of an ancient and massive moon that would have collided with the planet of the rings could explain some things about this world that are still not entirely clear.
Saturn’s rings, apart from being spectacular, appear surprisingly young, only 150 million years old or so . If dinosaurs had telescopes, they could have seen Saturn without rings.
Spinning around the planet’s equator, Saturn’s rings are a dead giveaway that the planet is spinning at a certain tilt. Specifically, this gas giant rotates at an angle of 26.7 degrees relative to the plane in which it orbits the Sun. Astronomers have long suspected that this tilt is due to gravitational interactions with its neighbor Neptune, since Saturn’s tilt proceeds, like a top, almost at the same rate as Neptune’s orbit.
Is it so?
A new investigation, collected by the journal Science, points to another hypothesis. The team proposes that Saturn, which today has 83 moons, once hosted at least one more, an additional satellite they call Chrysalis. This other moon would have orbited Saturn for several billion years, tugging on the planet in a way that forced it to maintain obliquity” in resonance with Neptune. But what if this moon had disappeared?
a lost moon
Why don’t we see her anymore? The orbital chaos resulting from this situation could have led to the moon’s demise, shattering it to form the iconic rings that surround the planet today, scientists suggest. (Which would explain why the rings are only about 100 million years old or so, a long time after the rest of the solar system formed.)
“We like it because it’s a scenario that explains two or three different things that were previously not thought to be related,” says study co-author Jack Wisdom, a planetary scientist at MIT. “Rings are related to tilt, who would have guessed?”
What size was it?
The team ran hundreds of simulations, each with slightly different initial conditions, of the Saturn system , including this hypothetical moon, called Chrysalis. They found that this scenario fit the bill perfectly.
Scientists surmised that Saturn’s axial tilt might be affected by the loss of a moon, since this would have knocked it out of its resonance with Neptune. The event would have pushed Saturn out of resonance, lowering its axial tilt. To give rise to these phenomena, the hypothetical moon number 84, Chrysalis, would have to have been the size of the planet’s third largest moon, Iapetus.
The satellite in question would have experienced a series of close encounters with Iapetus and Titan, finally getting too close to Saturn around 160 million years ago. The collision ripped apart Chrysalis, allowing Saturn and Neptune to lose resonance as the moon’s gravitational influence disappeared. That is, the loss of the moon allowed the planet to escape resonance. A small fraction of Chrysalis’s mass remained suspended in orbit, breaking up into icy chunks and forming rings of debris.
“It’s a pretty good story, but like any other outcome, it will have to be scrutinized by others,” the authors explain. “But it seems that this lost satellite was just a chrysalis, waiting for its instability.”
That Saturn’s rings are made of an ancient and massive moon could also explain its axial tilt and the strangely rapidly expanding orbit of its largest moon, Titan.
Saturn in numbers:
Distance to the Sun : 1,434 billion km
Orbital period: 29 years
Surface: 42,700 million km²
Radius : 58,232 km
Time: 5,683 × 10^26 kg (95.16 M⊕)
Day length: 0d 10h 42m
Moons: 83 formal and countless additional moons
Referencia: Jack Wisdom, Loss of a satellite could explain Saturn’s obliquity and young rings, Science (2022). DOI: 10.1126/science.abn1234. www.science.org/doi/10.1126/science.abn1234
Maryame El Moutamid, How Saturn got its tilt and its rings, Science (2022). DOI: 10.1126/science.abq3184. www.science.org/doi/10.1126/science.abq3184