Fascinating and plausible.
Scientists propose a lost moon of Saturn, which they call Chrysalis, pulled on the planet until it ripped apart, forming rings and contributing to Saturn's tilt. . . . the team proposes that Saturn, which today hosts 83 moons, once harbored at least one more, an extra satellite that they name Chrysalis. Together with its siblings, the researchers suggest, Chrysalis orbited Saturn for several billion years, pulling and tugging on the planet in a way that kept its tilt, or "obliquity," in resonance with Neptune.
But around 160 million years ago, the team estimates, Chrysalis became unstable and came too close to its planet in a grazing encounter that pulled the satellite apart. The loss of the moon was enough to remove Saturn from Neptune's grasp and leave it with the present-day tilt.What's more, the researchers surmise, while most of Chrysalis' shattered body may have made impact with Saturn, a fraction of its fragments could have remained suspended in orbit, eventually breaking into small icy chunks to form the planet's signature rings.The missing satellite, therefore, could explain two longstanding mysteries: Saturn's present-day tilt and the age of its rings, which were previously estimated to be about 100 million years old -- much younger than the planet itself.
From Science Daily citing Jack Wisdom, et al., "Loss of a satellite could explain Saturn’s obliquity and young rings." 377 (6612) Science 1285 (2022). DOI: 10.1126/science.abn1234
4 comments:
I find it hard to believe that rearrangements of moons could affect the tilt of a gas giant. But I also find it hard to believe that the authors could screw up a basic celestial mechanics calculation...
"How did Saturn get its rings?
Saturn’s rings are about 100 million years old, but it is unclear how they could have formed so recently. Wisdom et al. propose that the Saturn system previously contained an additional moon, the orbit of which was perturbed by the orbital migration of Titan, Saturn’s largest moon (see the Perspective by El Moutamid). The authors used numerical simulations to show that the perturbation would have eventually destabilized the system, scattering the additional moon. If it came too close to Saturn, the moon would have been ripped apart by tidal forces, forming the rings. The scenario explains several otherwise puzzling properties of Saturn’s tilt and the orbits of its other moons and is consistent with the measured age and mass of the rings. —KTS"
"Abstract
The origin of Saturn’s ~26.7° obliquity and ~100-million-year-old rings is unknown. The observed rapid outward migration of Saturn’s largest satellite, Titan, could have raised Saturn’s obliquity through a spin-orbit precession resonance with Neptune. We use Cassini data to refine estimates of Saturn’s moment of inertia, finding that it is just outside the range required for the resonance. We propose that Saturn previously had an additional satellite, which we name Chrysalis, that caused Saturn’s obliquity to increase through the Neptune resonance. Destabilization of Chrysalis’s orbit ~100 million years ago can then explain the proximity of the system to the resonance and the formation of the rings through a grazing encounter with Saturn."
Related article abstract:
"How did Saturn get its rings?
Saturn’s rings are about 100 million years old, but it is unclear how they could have formed so recently. Wisdom et al. propose that the Saturn system previously contained an additional moon, the orbit of which was perturbed by the orbital migration of Titan, Saturn’s largest moon (see the Perspective by El Moutamid). The authors used numerical simulations to show that the perturbation would have eventually destabilized the system, scattering the additional moon. If it came too close to Saturn, the moon would have been ripped apart by tidal forces, forming the rings. The scenario explains several otherwise puzzling properties of Saturn’s tilt and the orbits of its other moons and is consistent with the measured age and mass of the rings. —KTS"
There is no preprint on arXiv at this time.
An earlier theory of where the tilt came from
https://skyandtelescope.org/astronomy-news/why-is-saturn-tipsy/
The theory of Wisdom et al seems to be similar, except that Saturn's biggest moons affect the response of the Saturnian system to the Neptunian influence.
I guess the tilt change happens first to a hard Saturnian core, then gets transmitted to the atmosphere?
Another oddity is that Saturn has a 10 hour day. Is that just atmospheric, or should it be the core's rotation speed too?
Guess I should read the article...
Another new paper looks at the origins of the tilt of Uranus, attributing it to the migration of an ancient satellite. https://arxiv.org/abs/2209.10590
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