A new theory on the formation and age of Saturn’s rings – rts.ch

A new study published September 15 in the journal Science seeks to provide a definitive answer to this burning question.

According to him, about 100 million years ago, an icy moon broke up after coming close to Saturn; The remnants of this satellite gradually settled into its orbit.

“Saturn’s rings were discovered by Galileo about 400 years ago and are one of the most interesting objects in the solar system to observe with a small telescope,” said Jacques Wisdom. study.

A “plausible” explanation

“It’s satisfying to find a plausible explanation,” says the professor of planetary science at the Massachusetts Institute of Technology.MIT)

Saturn is the sixth planet from the Sun and 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: about 100 million years ago.

A hypothesis reinforced by the study’s observations Cassini, launched in 1997 and decommissioned in 2017 after orbiting Saturn 294 times. He collected crucial data, including measurements of the planet’s gravity, which were key to this study.

“Some have questioned the logic” that led to their dating, explains Jack Wisdom, “because no one can find that these rings are 100 million years old.”

Every planet in our solar system is tilted on its axis. [JPL-Caltech/Richard Barkus – NASA]He and his colleagues have developed a complex model that not only explains their recent appearance, but also allows them to understand another characteristic of the planet: its tilt.

Saturn’s axis of rotation is actually tilted by 26.7 degrees from the vertical – this is called the declination. In comparison, our Earth is tilted 23.4 degrees. However, Saturn, a gas giant composed mainly of hydrogen and helium, would be expected to leave the accretion process of material that led to its formation perpendicular to the plane of its orbit.

Conflicting gravitational forces

The research team, which specifically modeled the interior of the planet for its calculations, started from a recent discovery: Titan, Saturn’s largest satellite – the planet has 83 known -, is moving slightly and quickly: eleven centimeters per year.

That may not seem like much, but it’s a long way in time, especially for such a large moon. Titan is the second largest moon in the Solar System: it is larger than Mercury, which is closest to the Sun.

According to the scientists’ model, this movement gradually changed the frequency at which Saturn’s axis of rotation makes a full turn perpendicular to the vertical—the imaginary cone formed as it rotates, similar to the axis of the spinning top. Pioneer.

An important detail because about a billion years ago this frequency became synchronized with the frequency of Neptune’s orbit. A powerful mechanism that must be maintained despite the continuing influence of Titan’s distance caused Saturn’s inclination to 36°.

But researchers have found that this sync between Saturn and Neptune – known as a vibration – is no longer accurate. Why?

Only a powerful event can interrupt it. Scientists hypothesized a moon with a chaotic orbit, gradually getting closer to Saturn, until contradictory gravitational forces caused its displacement: “It was torn into pieces, and these pieces fell back on themselves. The smaller ones formed rings”, even though the majority fell towards Saturn, explains Jacques Wisdom.

The continued retrograde Titan’s influence eventually reduced Saturn’s tilt, visible today.

>> Read More: Liquid on Titan, a moon of Saturn

Emerging from the chrysalis

The missing moon was christened the chrysalis – or chrysalide in French – by Jacques Wisdom, which resembles the wings of butterflies emerging from a nest, here the arrangement of rings.

Scientists estimate that Chrysalis is slightly smaller than our own moon and about the size of Saturn’s third largest moon, Ipedus, which is about 1,470 kilometers in diameter. Gold Ipedus Ice consists almost entirely of water.

>> 3D model of Saturn’s icy moon Ipedus:

“It is plausible to assume that the chrysalis is made of ice water, which is what we need to make the rings”, which makes up 99%, the professor notes.

Feel like the mystery of Saturn’s rings has finally been solved? “We made a good contribution,” he replied calmly. Before adding: The structure of Saturn and its moons still hides “many mysteries”.

Stéphanie Jaquet and agencies