抖阴旅行射

A new study led by physicist Sascha Kempf at 抖阴旅行射 Boulder has delivered the strongest evidence yet that Saturn鈥檚 rings are remarkably young鈥攑otentially answering a question that has boggled scientists for well over a century.听

The research, , pegs the age of Saturn鈥檚 rings at no more than 400 million years old. That makes the rings much younger than Saturn itself, which is about 4.5 billion years old.

鈥淚n a way, we鈥檝e gotten closure on a question that started with James Clerk Maxwell,鈥� said Kempf, associate professor in the (LASP) at 抖阴旅行射 Boulder.

The researchers arrived at that closure by studying what might seem like an unusual subject: dust.听

Kempf explained that tiny grains of rocky material wash through Earth鈥檚 solar system on an almost constant basis. In some cases, this flux can leave behind a thin layer of dust on planetary bodies, including on the ice that makes up Saturn鈥檚 rings.

In the new study, he and his colleagues set out to put a date on Saturn鈥檚 rings by studying how rapidly this layer of dust builds up鈥攁 bit like telling how old a house is by running your finger along its surfaces.

鈥淭hink about the rings like the carpet in your house,鈥� Kempf said. 鈥淚f you have a clean carpet laid out, you just have to wait. Dust will settle on your carpet. The same is true for the rings.鈥�

It was an arduous process: From 2004 to 2017, the team used an instrument called the aboard to analyze specks of dust flying around Saturn. Over those 13 years, the researchers collected just 163 grains that had originated from beyond the planet鈥檚 close neighborhood. But it was enough. Based on their calculations, Saturn鈥檚 rings have likely been gathering dust for only a few hundred million years.

The planet鈥檚 rings, in other words, are new phenomena, arising (and potentially even disappearing) in what amounts to a blink of an eye in cosmic terms.听

鈥淲e know approximately how old the rings are, but it doesn鈥檛 solve any of our other problems,鈥� Kempf said. 鈥淲e still don鈥檛 know how these rings formed in the first place.鈥�

From Galileo to Cassini

Researchers have been captivated by these seemingly translucent rings for more than 400 years. In 1610, Italian astronomer Galileo Galilei first observed the features through a telescope, although he didn鈥檛 know what they were. (Galileo鈥檚 original drawings make the rings look a bit like the handles on a water jug). In the 1800s, Maxwell, a scientist from Scotland, concluded that Saturn鈥檚 rings couldn鈥檛 be solid but were, instead, made up of many individual pieces.听

Today, scientists know that Saturn hosts seven rings comprised of countless chunks of ice, most no bigger than a boulder on Earth. Altogether, this ice weighs about half as much as Saturn鈥檚 moon Mimas and stretches nearly 175,000 miles from the planet鈥檚 surface.听

Kempf added that for most of the 20th Century, scientists assumed that the rings likely formed at the same time as Saturn.听

But that idea raised a few issues鈥攏amely, Saturn鈥檚 rings are sparkling clean. Observations suggest that these features are made up of roughly 98% pure water ice by volume, with only a tiny amount of rocky matter.听

鈥淚t鈥檚 almost impossible to end up with something so clean,鈥� Kempf said.

Cassini offered an opportunity to put a definitive age on Saturn鈥檚 rings. The spacecraft first arrived at Saturn in 2004 and collected data until it purposefully crashed into the planet's atmosphere in 2017. The Cosmic Dust Analyzer, which was shaped a bit like a bucket, scooped up small particles as they whizzed by.听

Engineers and scientists at LASP designed and built a much more sophisticated dust analyzer for NASA鈥檚 upcoming Europa Clipper mission, which is scheduled to launch in 2024.

The team estimated that this interplanetary grime would contribute far less than a gram of dust to each square foot of Saturn鈥檚 rings every year鈥攁 light sprinkle, but enough to add up over time. Previous studies had also but didn鈥檛 include definitive measures of dust accumulation.

Stroke of luck

The rings might already be vanishing. In听previous research, NASA scientists reported that the ice is slowly raining down onto the planet and could disappear entirely in another 100 million years.

That these ephemeral features existed at a time when Galileo and the Cassini spacecraft could observe them seems almost too good to be true, Kempf said鈥攁nd it begs an explanation for how the rings appeared听in the first place. Some scientists, for example, have posited that Saturn鈥檚 rings may have formed when the planet鈥檚 gravity tore apart one of its moons.

听鈥淚f the rings are short lived and dynamical, why are we seeing them now?鈥� he said. 鈥淚t鈥檚 too much luck.鈥�

Co-authors on the new study include Nicolas Altobelli of the European Space Agency; J眉rgen Schmidt of the Freie Universit盲t Berlin; Jeffrey Cuzzi and Paul Estrada of the NASA Ames Research Center; and Ralf Srama of the Universit盲t Stuttgart.