New theory to explain Saturn's rings
Image of the moon Titan in orbit around the planet Saturn, obtained by combining six photos taken by the Cassini spacecraft on May 6, 2012.
Of all the planets in the solar system, Saturn is certainly the one whose representation strikes the most imagination, thanks to its huge rings.
But, even today, astronomers do not all agree on the origin of their formation, or even their age.
To this burning question , a study published in the journal Science intends to provide a convincing answer.
According to it, about 100 million years ago, a moon ice broke apart after getting a little too close to Saturn, and the remnants of this satellite then gradually orbited around it.
Saturn's rings were discovered by Galileo about 400 years ago, and they are one of the most interesting objects to observe through a small telescope in the Solar System, notes Jack Wisdom, lead author of the x27;study.
It is satisfying to have found a plausible explanation for their formation, confides to AFP this professor of planetary sciences in Massachusetts Institute of Technology (MIT).
Saturn, the sixth planet from the Sun, was formed 4.5 billion years ago, at the beginning of the solar system.
But there A few decades ago, scientists argued that Saturn's rings appeared much later: only about 100 million years ago. A hypothesis reinforced by observations of the Cassini probe, launched in 1997 and which bowed out in 2017.
But, since no one could find a process that resulted in these rings being only 100 million years old, some have questioned the reasoning behind their dating, says Jack Wisdom.
< p class="e-p">He and his colleagues have built a complex model that not only explains their recent appearance, but also helps to understand another characteristic of this planet: its tilt.
Saturn's axis of rotation is indeed tilted at 26.7 degrees from the vertical (known as its obliquity).
Now, Saturn being a gas giant, it would have been expected that the process of accumulation of matter that led to its formation would have left it perpendicular to the plane of its orbit.
< p class="e-p">The researchers, who notably modeled the interior of the planet for their calculations, started from a recent discovery: Titan, the largest satellite of Saturn (the planet has more of 80), gradually moves away from her… and rather quickly.
According to their model, this motion gradually changed the rate at which Saturn's axis of rotation makes a complete turn around the vertical, much like the axis of Saturn's axis. #x27;a top forming an imaginary cone when it rotates slightly tilted (we speak of precession).
An important detail, because about a billion years ago this frequency entered into synchronization with the frequency of Neptune's orbit. A powerful mechanism, which to be maintained despite the continued influence of Titan's remoteness, caused Saturn to tilt, up to 36 degrees.
But researchers have found that this synchronization between Saturn and Neptune (called resonance) is no longer accurate today. Why?
Only a powerful event could interrupt it. They thus hypothesized that the Moon had a chaotic orbit, having gradually approached too close to Saturn, until the contradictory gravitational forces caused its dislocation.
It is demolished into multiple pieces, and these pieces are themselves still dislocated, and little by little form the rings, although the majority of them fall toward Saturn, says Jack Wisdom.
The influence of Titan, which continued to recede, then eventually reduced Saturn's tilt, down to that seen today.
The vanished moon was baptized Chrysalis (chrysalis in French) by Jack Wisdom, an analogy to the wings of a butterfly emerging from a cocoon, as here the unfolding of the rings.
Scientists believe that Chrysalis was a bit smaller than our Moon, and about the size of another Saturn satellite, Iapetus, made almost entirely of ice water.< /p>
So it's plausible to hypothesize that Chrysalis was also made of ice water, and that's what is needed to create the rings, 99% of which are made up of them, notes the professor.
Does he feel like he has finally solved the mystery of Saturn's rings?
We have provided a good contribution, d he asks soberly. Before I add: the system of Saturn and its satellites still holds many mysteries.