The first land animals still saw a ringless Saturn in the sky
Are Saturn's rings as old as the planet or much younger? A research group presents new arguments in favour of them having formed less than 400 million years ago.
They are Saturn's most striking feature and set it apart from all other planets in our solar system: its rings, which are clearly visible even with a simple telescope. However, the age of the ring system is hotly disputed among astronomers. While some assume that the discs consisting of chunks of ice and grains of dust formed together with Saturn 4.5 billion years ago, others are convinced that they are still quite young and formed less than 400 million years ago. In cosmic terms, that's the blink of an eye. Around that time, the first animals on Earth were just crawling out of the water onto land.
A team led by Sascha Kempf from the University of Colorado in the USA is now presenting new arguments in favour of the rings being a rather recent and very dynamic phenomenon. The research results, which were published in the journal "Science Advances", put the age of Saturn's rings at a maximum of 400 million years. This is based on data from the Cassini space probe, which orbited Saturn from 2004 to 2017. The research group claims to have drawn a line under the dispute.
The purity of the rings is at the centre of the analysis. This is because they consist mainly of frozen water. "This ice is only contaminated with a maximum of two per cent of other substances," says Sascha Kempf, according to a statement from the University of Colorado. "It is almost impossible to find anything so clean in space." The argument: after 4.5 billion years, the pollution with dust particles would have to be considerably greater than can actually be observed.
The researchers therefore investigated how quickly this layer of dust builds up. It's a bit like determining the age of a house by running your finger over the surface, explains Kempf. "Or imagine the rings like a carpet. If you lay out a clean carpet, all you have to do is wait. The dust will settle on the carpet over time. The same applies to the rings." To determine this dust influx, the team used an instrument called the Cosmic Dust Analyser on board NASA's Cassini space probe. A total of 163 particles were identified as new and from outside over the 13 years. That doesn't sound like much, but it is probably enough to make a valid extrapolation. And so the researchers conclude: "Saturn's current rings cannot be primordial."
This statement is clear - but not uncontroversial. When it was first suggested in 2019 that the rings were tens to hundreds of millions of years old, a research team led by Aurélien Crida" from the Côte d'Azur Observatory in the scientific journal "Nature Astronomy" point out that other processes may be keeping the rings "clean". Measurements by the Cassini space probe also showed that darker material from the ring system both rains down on the planet and flows outwards. This is enough to compensate for the influx of dust particles.
The almost transparent rings have fascinated researchers for more than 400 years. In 1610, the Italian astronomer Galileo Galilei observed the rings through a telescope for the first time. In his original drawings, the rings look a little like the handles of a jug of water. The Dutch astronomer and physicist Christiaan Huygens correctly described the rings as a ring system 45 years later.
And it could even be that the rings are already in the process of disintegrating. In an earlier study, NASA scientists reported that the ice is slowly raining down on the planet and could be completely gone in another 100 million years. "It's hard to believe, but we're probably incredibly lucky that we're seeing the rings now of all times - as short-lived and dynamic as they appear to be," said Kempf.
Spectrum of Science
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