An icy moon is believed to be responsible for the formation of Saturn’s rings

Scientists have uncovered a vital part of Saturn’s history. The dislocation of an icy moon could explain the formation of its famous rings around 100 million years ago.

SPACE – While Saturn’s rings are beautiful to look at, they are also a colossal headache for scientists trying to study them. When and how did they manage to form around this giant gaseous planet? A new study published in the journal Science this Thursday, September 15, provides some answers.

“Saturn’s rings were discovered by Galileo about 400 years ago, and they are one of the most interesting objects to observe in the solar system”, enthusiastically launches Jack Wisdom, a specialist in planetary dynamics at the Massachusetts Institute of Technology (MIT) and lead author of the study. With his team, he developed a model, demonstrating that the famous rings appeared recently in our solar system, and even very recently on an astronomical scale.

Because that’s one of the big questions scientists ask about Saturn: Did these countless chunks of ice appear billions of years ago – and are therefore as old as the solar system itself? same – or only about 100 million years ago? This second hypothesis had gained weight in the scientific community after the observations of the Cassini probe in 2017.

The spacecraft had indeed discovered that the rings were exposed to a shower of soot dust from the solar system, which would tend to darken them over time. But then they are not “dirty” enough to be 4.5 billion years old. According to Jack Wisdom, these relatively intact rings must logically be young. But how do you explain what created the rings, especially so late in the history of the solar system?

Scientists were working on Saturn’s tilt

It is by looking at a completely different subject that scientists have found an explanation for the recent formation of these rings. They were indeed initially working on the astonishing inclination of Saturn.

Saturn’s axis of rotation is indeed inclined at 26.7° from the vertical. But Saturn being a gas giant, the process of accumulation of matter that led to its formation should have left it perpendicular to the plane of its orbit.

To find an explanation, the researchers started from a recent discovery: Titan, Saturn’s largest satellite, is gradually moving away from it… According to the researchers, this movement has gradually modified the axis of rotation of Saturn. But the observed tilt of the planet is greater than one would expect. Why ? Only a powerful event could interrupt it.

Scientists have therefore come up with a new hypothesis. The dislocation of a moon, formerly present in the system of Saturn, would have caused an additional imbalance. It would thus have modified the inclination of the planet about 160 million years ago, precisely at the time of the formation of the rings of Saturn. The team performed a total of 390 simulations of this event.

A named moon “Chrysalis”

In some scenarios, the lost moon collided with Titan or Iapetus, another natural satellite of the planet; in others, it was completely ejected from the Saturn system. But in 17 of the simulations, the moon brushed past Saturn, where it could have been shredded by gravitational forces, eventually becoming the iconic rings.

The missing Moon was baptized Chrysalis, Chrysalide in French, by Jack Wisdom, comparing the emergence of Saturn’s rings to a butterfly emerging from a cocoon. Scientists think Chrysalis was a bit smaller than our own Moon, and about the size of another Saturn satellite, Iapetus. However, the latter is almost entirely made up of ice water.

“So it is plausible to hypothesize that Chrysalis was also made of ice water, and that is what is needed to create the rings”, which are made up of 99% of them, notes the professor. Does he feel like he’s finally solved the mystery of Saturn’s rings? “We made a good contribution”he answers before adding: the system of Saturn and its satellites still conceal many mysteries ».

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