Saturn is known by the nickname the Lord of the Rings because of the characteristic rings that surround it. Although it is not the only one to have them – they are on the four gaseous planets: Jupiter, Neptune, Uranus and Saturn itself – it is distinguished by the fact that they are the only ones visible from Earth. There are seven of them and they are fundamentally formed by small fragments of ice and rock with a thickness of half a kilometer – in some points it is only ten meters – and a diameter of 270,000 kilometers, more than half the distance that separates our planet from the Moon. Specialists have been debating his age for a long time. For a long time it was thought that they emerged at the same time as the planet, about 4.5 billion years ago – the same as calculated for the Earth and the rest of the Solar System – but a study published in ‘Science’ in 2019 lowered that figure to leave it at ‘only’ one hundred million, very little on an astronomical scale. Now, another work reflected in ‘Science Advances’ has adjusted the calculation to take it up to 400 million years.
To reach this conclusion, scientists analyzed the cosmic dust that ‘floats’ around the planet for thirteen years – between 2004 and 2017 – with a special instrument mounted on NASA’s Cassini probe. «Think of the rings as the carpet in your house. The dust will settle on it,” the authors explain graphically. It would be something like determining the age of a house by running your finger over the dust accumulated on some of its walls or furniture. The result, the aforementioned 400 million years.
The theory that pointed to a formation in parallel to that of Saturn itself argued that it would be the remains of ice that remained from the formation of the solar system or that it was material ‘captured’ from the so-called Kuiper belt, a ring of icy bodies located outside the orbit of Neptune and where Pluto is located, or of a comet that had been reduced to fragments. For its part, the one that estimated its age at 100 million was based on data obtained by the aforementioned Cassini probe. This, in its final flight before disintegrating, entered between the planet and its rings and was able to precisely measure the amount of material that makes them up – around 40% of the moon Mimas, one of the 82 that Saturn has. From the data obtained, they came to the conclusion that the famous rings would have been formed a hundred million years ago.
The first, Galileo Galilei
In addition to his age, there is also debate about his origin. There is no definitive explanation, but they may be the result of an ancient icy moon crashing into the planet. This is the theory put forward last year by scientists from the Massachusetts Institute of Technology (MIT) and the University of Berkeley. According to them, one of these satellites that orbited Saturn for billions of years became unstable and came too close to the planet, a giant with a mass 95 times greater than that of Earth. Much of it was absorbed by it, while the small remaining part broke into small pieces of ice that would end up forming the characteristic rings.
The first to see these was Galileo Galilei in 1610. The famous Italian astronomer mistakenly thought they were satellites. Shortly afterwards, with better means, his Dutch colleague Christiaan Huygens assured that it was a single flat ring. Already in 1859, the mathematician and physicist James Clerk Maxwell – best known for formulating the classical theory of electromagnetism – demonstrated that they could not be a single solid object, but rather a group of millions of smaller particles.
Denominated as D, C, B, A, F, G and E according to their proximity to the planet, the particles that form the ring ‘float’ around Saturn due to a kind of balance between its gravity, which attracts them, and their orbital speed, which pushes them into space. However, the first will end up making them disappear in about 100 million years, according to NASA calculations. The reason is that the smallest particles that make it up can become electrically charged, among other causes, by ultraviolet light from the sun. When this happens, they are attracted to Saturn’s magnetic field and vaporized to form a kind of shower of ice particles enough to fill an Olympic-size swimming pool in just half an hour.