Of all the planets in our solar system, Saturn is by far the most striking due to its enormous rings.
But even today, experts do not all agree either with the origin of their education, or even with age.
To this burning question, a new study, published on Thursday in the prestigious journal Science, aims to give a convincing answer.
About 100 million years ago, the icy moon broke apart after getting too close to Saturn, and the moon’s remnants then gradually entered orbit around it, she said.
“The rings of Saturn were discovered by Galileo about 400 years ago, and they are one of the most interesting objects to observe with a small telescope in the solar system,” said Jack Wisdom, lead author of the study.
“It’s nice to find a plausible explanation” for their formation, this professor of planetary sciences from the Massachusetts Institute of Technology (MIT) modestly admits to AFP.
Saturn, the sixth planet from the Sun, formed four and a half billion years ago at the beginning of the solar system.
But a few decades ago, scientists suggested that Saturn’s rings appeared much later: only about 100 million years ago.
A hypothesis supported by observations of the Cassini probe, which launched in 1997 and ceased operation in 2017.
“But because no one could find the process leading to these rings being only 100 million years old, some questioned the reasoning” that led to their dating, explains Jack Wisdom.
Thus, he and his colleagues built a complex model that allows not only to explain their recent appearance, but also to understand another characteristic of this planet: its tilt.
Saturn’s axis of rotation is actually tilted 26.7° from vertical (this is called tilt). However, since Saturn was a gas giant, one would expect that the process of accumulation of matter that led to its formation left it perpendicular to the plane of its orbit.
– Forces of gravity –
The researchers, who famously modeled the bowels of the planet for their calculations, proceeded from a recent discovery: Titan, the largest satellite of Saturn (and the planet has more than 80 of them), is gradually moving away from it … or rather quickly.
According to their model, this movement gradually changed the speed at which Saturn’s axis of rotation makes a full rotation around the vertical – just as the axis of a spinning top forms an imaginary cone, slightly tilted (we are talking about precession) during rotation.
An important detail, because about a billion years ago this frequency entered into synchronization with the frequency of the orbit of Neptune. A powerful mechanism that must be maintained, despite the constant influence of the remoteness of Titan, caused Saturn to tilt up to 36 °.
But researchers have found that this synchronization between Saturn and Neptune (called the resonance) is no longer accurate today. Why?
Only a strong event could interrupt it.
So they hypothesized a moon with a chaotic orbit that gradually got too close to Saturn until conflicting gravitational forces caused it to shift.
“It’s broken into several pieces, and those pieces are still displaced by themselves and little by little form rings,” although most of it falls on Saturn, explains Jack Wisdom.
The influence of Titan, which continued to wane, eventually reduced Saturn’s obliquity to what it is today.
– Coming out of the chrysalis –
Jack Wisdom dubbed the missing moon Chrysalis (chrysalis in French) by analogy with the wings of butterflies flying out of a cocoon – as here the unfolding of rings.
Scientists believe that Chrysalis was slightly smaller than our Moon and about the size of Saturn’s other moon, Iapetus.
However, the latter is almost entirely composed of ice water.
“Therefore, it is plausible to assume that Chrysalis was also made of ice water, and that is what we need to create rings” that are 99% composed of it, the professor notes.
Does it feel like the mystery of Saturn’s rings has finally been solved?
“We made a good contribution,” he soberly replies. Before I add: the system of Saturn and its moons is still fraught with “many mysteries.”