Home News The long goodbye to the rings of Saturn – Marina Koren

The long goodbye to the rings of Saturn – Marina Koren

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The long goodbye to the rings of Saturn – Marina Koren

09 Apr 2022 08:53

Of all the planets in our solar system, Saturn is perhaps the most beautiful. About those rings! They are composed of bands of frozen water with traces of rock particles, which take the form of a delicate halo. Up close, they glow in soft pink, gray and brown, and glow in the dark. It is difficult to imagine Saturn without its rings. But they are not a permanent feature of the planet, and are indeed disappearing.

Each year, Saturn’s rings lose some of their material. The micrometeorites that hit them and the solar radiation disturb the tiny dusty fragments of the rings and charge them with electrical energy. The suddenly transformed particles tune into the lines of force of Saturn’s magnetic field and begin to spiral along those invisible trajectories. When the particles get too close to the outermost layer of Saturn’s atmosphere, gravity pulls them in, and they evaporate into the planet’s clouds.

Astronomers call it ring rain, or “annular rain”, and over time this and other phenomena will contribute to dissolve the distinctive element that, for us, makes Saturn what it is, until there is nothing left. But now? “We see the rings of Saturn in their golden age,” explains James O’Donoghue, a planetary scientist at Jaxa, the Japanese space agency. A magnificent spectacle that from our perspective seems immutable, but which on a large scale is fleeting.

The Voyager 1 grand tour
It might help to know that it will take a while: O’Donoghue and other scientists estimate that the rings will disappear in about 300 million years. The inhabitants of the Earth still have a lot of time to marvel at their beauty and to study them. Because, even if astronomers have understood that the rings are an endangered species, they still don’t know everything about these bands, starting with how they formed.

Saturn’s rings have fascinated observers for centuries, but we were only able to really see them up close in the early 1980s, when NASA’s Voyager 1 spacecraft passed us during a big ride of the outer planets (as planets beyond the earth’s orbit are called). At the time, scientists imagined that the rings may have formed about 4.6 billion years ago, when the solar system was young and turbulent. At that time, rocky bodies flew everywhere, and a new planet could easily have intercepted some, have them go into orbit around its own equator, and let gravity flatten them.

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Final measurements by the Cassini spacecraft confirmed that the rings were not massive enough to be billions of years old

But Voyager’s close passing suggested a different story. The high-resolution images sent by the spacecraft revealed that the mass of the rings was less than that predicted by the researchers, so they could not have been billions of years, but they must have been much younger, probably between ten million and one hundred million years. “The results were absolutely disconcerting and bizarre,” confirms Jeff Cuzzi, a NASA researcher and expert on planetary rings.

It was previously believed that Saturn’s rings were as old as the solar system itself; now it seemed they didn’t exist when the dinosaurs began to roam the Earth. The solar system had then calmed down, so where did Saturn find the raw material? “The odds that in recent times an event has led to the formation of rings” (in the language of astronomers in recent times it means in the last hundred million years or so) “are very low,” says Paul Estrada, a NASA researcher. studying the rings of Saturn. Still, observations made in recent years support this hypothesis. In 2017, NASA’s Cassini probe touched Saturn’s rings and sent us as much information as possible before plunging into the planet’s atmosphere and being destroyed. The final measurements confirmed what the two Voyager missions had found, namely that the rings are not massive enough to be ancient.

Spatial sensations
The scientific community does not agree on their origin. But assuming that they are really “young”, according to scientists it is likely that they formed when one of Saturn’s moons, itself very old, got too close to the planet and was torn to pieces. It is likely that the moon was small – by comparison, thousands of Saturn-like ring systems could be made from our moon, O’Donoghue says.

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The story of Saturn’s rings reminds us that the worlds of our solar system, however immobile and static they may seem to us, are actually dynamic places with dramatic stories. “We think that the universe out there – unlike this one, where we live and where everything is chaotic, messy and constantly changing – is a kind of immutable crystal,” comments Cuzzi. From a distance, Saturn’s rings look so solid, like a ledge from which you could swing your legs. But they are not at all. “The particles from which they are composed move slowly and collide with each other,” says Linda Spilker, planetologist at NASA’s Jet propulsion laboratory who worked on the Cassini mission. “And there are trails created by small moons.” When the Cassini spacecraft squeezed between Saturn and the rings, “we were able to measure the amount of material from each ring making its way to the planet,” she says. The Voyager mission, on which Spilker also worked, had already collected evidence on the detachment of materials from the rings in the direction of Saturn, but with the Cassini astronomers were able to really study the phenomenon and elaborate more precise estimates on the duration of the rings.

A few hundred million years is a very long time. Yet I feel a sharp pang of sadness at the idea that Saturn will lose its rings. The same goes for some of the astronomers I spoke to, and for other people who are not astronomers at all but who grew up with a very clear image of Saturn as “the planet with the rings”. I experienced a similar emotion when I learned that the Moon is slowly moving away from the Earth; that a small drone attempted unsuccessfully to take off in the atmosphere of Mars; that an interstellar comet has traveled for millions of years without feeling the heat of a star. I have come to regard these reactions as “spatial sensations”. None of these events have any real bearing on our daily life, yet they touch our hearts on cosmic levels. “It is very sad to think that rings have to disappear in the future,” says O’Donoghue. But “I am very happy because we are lucky enough to see them”.

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Maybe someday, after they dissolve, the universe will provide Saturn with a new set of rings. “Perhaps thanks to an event of some kind – the destruction of another moon, a comet that gets too close – it could start all over again,” comments Spilker. “Perhaps we will still see rings around Saturn.”

After all, the cosmos is a jewelry designer: Jupiter, Uranus and Neptune also have rings. They’re thin and fluffy, but they’re there, and it’s likely they were significantly more massive long ago, before a mysterious mechanism reduced them, O’Donoghue argues. The forces of the cosmos are already at work on the next feature to add to the solar system. Between twenty million and eighty million years from today, Phobos, a small moon of Mars, will likely disintegrate. The fragments will swirl around the red planet and take on a beautiful new arrangement. Imagine Mars with rings.

(Translation by Davide Musso)

This article appeared in the US monthly The Atlantic.

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