Saturn’s rings have fascinated astronomers since Galileo first saw them in 1610, without being able to identify what they were. However, the planet did not always have them. This orderly amalgamation of particles of various sizes, from one centimeter to one meter, composed mostly of ice, was formed just a hundred million years ago. ‘Very recently’, if you take into account that Saturn is 4.5 billion years old, almost as old as the Solar System. Different hypotheses have tried to explain this late origin, without scientists having reached a consensus. Where did the rings come from?
In an article published this Thursday in the journal ‘Science’, researchers led by the Massachusetts Institute of Technology (MIT) point to the destruction of a old moon of saturn. According to the authors, the moon, which they have poetically called Chrysalis (Chrysalis), orbited the gas giant for several billion years until it became unstable and came too close. In the encounter, a part impacted with the planet, leaving it with the current inclination, very similar to that of the Earth. Other fragments continued in orbit until they broke into small pieces of ice that ended up forming the characteristic rings.
“Like a butterfly’s chrysalis, this satellite was dormant for a long time and suddenly it became active and the rings came into being,” says Jack Wisdom, professor of planetary sciences at MIT and lead author of the new study.
The researchers came to this conclusion using data obtained by NASA’s Cassini spacecraft, which orbited Saturn from 2004 to 2017. Specifically, they looked at some of its latest observations, taken during its ‘Grand Finale’, a phase of the mission during which the probe made an extreme approach to accurately map the gravitational field around the entire planet.
In this way, the team discovered that Saturn is no longer trapped in a resonance or gravitational association with Neptune, something that, in their opinion, would be explained by the loss of a moon that would be approximately the size of Iapetus, the third largest satellite. of Saturn
an unstable satellite
Along with its 83 sisters (Saturn’s current moons) Chrysalis orbited the planet for several billion years, tugging and tugging at it in a way that kept its tilt or ‘skewness’ in resonance with Neptune. But about 160 million years ago, Chrysalis became unstable. She entered a chaotic orbital zone, experienced a series of close encounters with the moons Iapetus and Titan, and finally got too close to Saturn, in a grazing encounter that tore her apart.
While most of Chrysalis’s shattered body may have collided with Saturn, a fraction of its fragments remained suspended in orbit, breaking up into small chunks of ice to form the planet’s characteristic rings. Not only the rings were formed. The loss of the moon was enough to knock Saturn out of Neptune’s ‘claws’ and leave it with its current tilt.
permanent change
“This theory constitutes an elegant confirmation of the complex effects of gravity on planetary systems and shows that the solar system is a rich and varied place subject to permanent change,” explains Ricardo Hueso Alonso, a researcher at the Department of Applied Physics and the Group of Planetary Sciences from the Bilbao School of Engineering (UPV/EHU) at SMC Spain.
For Santiago Pérez Hoyos, also from the Department of Applied Physics and the Planetary Sciences Group, the model fits “with the orbital variations of other satellites such as Titan and with the gravitational interactions that the entire Saturn system establishes with the nearby Neptune. The mass estimates also fit with the idea we have of the body that, when breaking off, could form the rings. In addition, the idea that a planet that today has more than eighty known moons could have had some satellite more or less is not far-fetched at all.
As indicated to SMC Spain, “although this hypothesis is apparently firm and resists a first detailed analysis, it will be necessary to continue studying both the rings of Saturn and the complicated gravitational interactions that are established between them, the planet, its numerous satellites and the neighboring planets. ». At the moment, no space mission will travel to Saturn to confirm this theory, so ground-based observatories and numerical calculations will have to do it.