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Long-lost moon may be the origin of Saturn’s rings

Among all the planets in our solar system, Saturn is certainly the one that most awakens the imagination, due to its immense rings.

But there is no consensus among experts about his origin or training, not even about his age.

However, a study published this Thursday (15) in the prestigious journal Science tries to answer that question.

According to this research, 100 million years ago, a moon that got too close to Saturn broke up and its traces remained in the planet’s orbit.

“Saturn’s rings were discovered by Galileo some 400 years ago, and they are one of the most interesting objects to observe in the solar system through a small telescope”, explains Jack Wisdom, author of the study.

“It is satisfying to have found a plausible explanation” of its formation, this planetary science professor at the Massachusetts Institute of Technology (MIT) confided to AFP.

Saturn, the sixth planet around the Sun, formed 4.5 billion years ago, at the origins of the solar system.

But a few decades ago, scientists assured that Saturn’s rings appeared much later, some 100 million years ago.

This hypothesis was reinforced by observations from the Cassini spacecraft, launched in 1997 and retired in 2017.

“But since no one has been able to determine how these rings only appeared 100 million years ago, some have questioned the rationale,” explains Wisdom.

Wisdom and his colleagues then built a complex model that allows not only to explain its recent appearance, but also to understand the planet’s tilt.

Saturn’s axis of rotation is tilted 26.7° from its vertical. And since this planet is a gas giant, one would expect that the process of accumulating matter that led to its formation would have prevented this tilt.

Gravitational forces

Scientists have arrived at a recent discovery through complex mathematical models: Titan, Saturn’s largest satellite (of the more than 80 it has) is moving away at a rate of 11 centimeters per year.

This movement little by little changed the frequency with which Saturn’s axis of rotation makes a complete turn around the vertical, a bit like a tilted pawn.

An important detail, since a billion years ago, this frequency got in sync with the frequency of Neptune’s orbit; a powerful mechanism that caused Saturn to tilt up to 36°.

However, scientists observed that this synchrony between Saturn and Neptune (called resonance) was no longer exact and only a powerful event could disrupt it.

They hypothesized that a chaotic-orbiting Moon got too close to Saturn, until contradictory gravitational forces caused it to rupture.

“It broke into several pieces and these pieces, also displaced, gradually formed rings”, explains Wisdom.

The influence of Titan, which kept receding, finally reduced Saturn’s tilt to the level that can be observed today.


Wisdom named the moon Chrysalis (Chrysalis), comparing the appearance of Saturn’s rings to a butterfly emerging from a cocoon.

Scientists thought Chrysalis was slightly smaller than our Moon, and about the size of another satellite of Saturn, Iapetus, almost entirely made up of ice.

“It is, therefore, plausible to hypothesize that Chrysalis is also made of ice water, which is necessary to create the rings”, emphasizes the professor.

Do you believe you have solved the mystery of Saturn’s rings?

“We made a good contribution,” he replies, before adding that the system still contains “many mysteries.”

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