Madrid. – A new study led by Sasha Kempf, a physicist at the University of Colorado (USA), provides the strongest evidence to date that Saturn’s rings are exceptionally young, which may answer a question you’ve always wondered. has baffled scientists for over a century.
Research published in the journal Science Advances pegs the age of Saturn’s rings at no more than 400 million years. This makes them much younger than the planet, which is about 4.5 billion years old.
“In a way, we’ve solved a question that began with James Clerk Maxwell,” says Kempf, an associate professor at the University of California’s Laboratory for Atmospheric and Space Physics (LASP).
The researchers reached that conclusion by studying what might seem like an unusual subject, dust. Kempf points out that tiny particles of rocky material move almost continuously through Earth’s solar system. In some cases, this flow can leave a thin layer of dust on planetary bodies, including the ice that makes up Saturn’s rings.
In the new study, he and his colleagues determined Saturn’s rings by studying how quickly this layer of dust accumulated, much like finding out how old a house is by running your finger along its surface.
“Think of the rings as the rug in your house,” notes Kempf. If you have a clean carpet, just wait. Dust will settle on it. Same goes for rings.
From 2004 to 2017, the team used an instrument called the Cosmic Dust Analyzer aboard NASA’s defunct Cassini spacecraft to analyze specks of particles flying around Saturn.
During those 13 years, the researchers collected only 163 grains that originated outside the planet’s near field. But it was enough. According to their calculations, Saturn’s rings may have accumulated dust for only a few hundred million years.
In other words, the rings of a planet are new phenomena, appearing (and potentially disappearing) in the blink of an eye from a cosmic point of view. “We know roughly how old the rings are, but that doesn’t solve any of our other problems. We still don’t know how these rings form,” Kempf says.
Researchers have been fascinated by these apparently translucent rings for more than 400 years. In 1610, the Italian astronomer Galileo Galilei observed them through a telescope for the first time, although he did not know what they were. Galileo’s original drawings make the rings somewhat similar to the handles of a water jug.
In the 19th century, the Scottish scientist Maxwell came to the conclusion that the rings could not be solid, but were made up of many separate pieces.
Scientists now know that Saturn is home to seven rings made up of countless chunks of ice, most of which are no bigger than a rock on Earth. Altogether, this ice weighs half as much as Saturn’s moon Mimas and extends about 280,000 kilometers from the planet’s surface.
Kempf states that, for much of the 20th century, scientists believed that the rings probably formed at the same time as Saturn, but that idea raised some questions, such as whether the rings are ‘clean’. Observations show that they are composed of 98 percent water ice by volume, with only a small amount of rocky material. “Some are nearly impossible to clean,” says Kempf.
Cassini provided an opportunity to put a definite age on the rings of Saturn. The spacecraft first arrived at Saturn in 2004 and collected data until it intentionally crashed into the planet’s atmosphere in 2017.
Lasp engineers and scientists designed and built a more sophisticated dust analyzer for NASA’s upcoming Europa Clipper mission, scheduled for launch in 2024.
The team estimated that this interplanetary debris would contribute less than a gram of dust to each square meter of Saturn’s rings each year—a tiny pinch, but enough to accumulate over time. Previous studies also suggested that the rings may be young, but they did not include definitive measurements of dust accumulation.
The rings may have already disappeared. In an earlier study, NASA scientists reported that ice on the planet is slowly receding and could disappear completely in the next 100 million years.
That these short-lived features were present at a time when the Galileo and Cassini spacecraft could observe them sounds too good to be true, according to Kempf, and calls for an explanation of how the rings formed in the first place.
For example, some scientists believe that Saturn’s rings may have formed when the planet’s gravity tore down one of its moons. “If the rings are short-lived and dynamic, why do we see them now? It’s very fortunate,” Kempf concluded.