Sidereal Messenger: Study suggests explanation for the formation of Saturn’s rings

They are one of the great postcards of the Solar System. But how did Saturn’s intriguing rings form? A new study presents a plausible hypothesis, capable of explaining several peculiar features of the Saturn system. Playing against her, uncertainties and her own low probability.

It’s a complicated story. It starts with the peculiar tilt of Saturn’s axis of rotation: 26.7 degrees, slightly greater than that of Earth. The difficult thing is to explain where it came from, since, from birth, Saturn would tend to come out more like Jupiter (3.1 degrees). One idea that helps to explain it is to think that the pattern of oscillation of Saturn’s axis of rotation, synchronized with the fluctuation of Neptune’s orbit and combined with the movement of Titan, the largest of the Saturnian moons (which little by little moves away from the planet, as the Moon does to the Earth), could have induced the increase in tilt. I said it was complicated.

Enter the new study by the team of Jack Wisdom, from MIT (Massachusetts Institute of Technology), published in Science. Modeling Saturn’s interior with the most accurate information available from the Cassini spacecraft, the group calculated the likely pattern of wobble of the spin axis and found that it would not today be in resonance with the precession of Neptune’s orbit — but almost, 1 % difference.

How to explain? The group then assumed that indeed this resonance had been at work in the past, but then something happened to subtly undo it. And then the only way out that they found is that, in the past, a hypothetical additional moon of Saturn had its orbit destabilized, which destroyed it or ejected it away.

Wisdom and colleagues ran 390 simulations that added the presence of this moon, dubbed Chrysalis, with minimal changes to initial conditions. At 19, she was indeed ejected from the system. In another 17, it grazed Saturn to the point of being destroyed. And that’s where the rings come in. Or rather, that’s where they would be born, according to the researchers. The peculiar structures would be all that remained of poor Chrysalis, after being destroyed by the powerful tidal effect generated in a fatal and close flyby by Saturn.

The hypothesis aligns well with the growing understanding that the rings, rather than being something that was born with the planet 4.5 billion years ago, are much more recent. By the way, the Wisdom team’s simulations suggest that its formation, with the destruction of Chrysalis, took place “only” 100 million years ago – dinosaurs could have seen it live.

Note that it is still too early to say that this closes the question. Scientists are still not all convinced that the rings are “recent”. There is also no consensus that the resonance between Saturn and Neptune is not yet at work (1%, based on model, is very little). Finally, the simulations themselves have this outcome less than 5% of the time. But that sounds like a believable scenario, it seems.

This column is published on Mondays, in Folha Corrida.

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