‘Ten times faster than we thought’: Saturn is losing its rings

A portrait of Saturn from the Hubble telescope taken in June 2018, with its rings near maximum tilt toward Earth. Saturn was only approximately 1.36 billion miles from Earth, nearly as close to us as it ever gets.

A portrait of Saturn from the Hubble telescope taken in June 2018, with its rings near maximum tilt toward Earth. Saturn was only approximately 1.36 billion miles from Earth, nearly as close to us as it ever gets. Photo: NASA

If you’re planning to live for 100 million years, then you’ll be witness to Saturn losing the last of its famous 22 rings.

The rings are being broken up into a rain storm of ice particles and pulled into the planet’s gaseous atmosphere.

The break-up is driven by Saturn’s massive gravity and under the influence of the planet’s magnetic field – but it’s happening much faster than previously thought.

Indeed it’s occurring at the maximum pace based on measurements made decades ago by Voyager spacecraft observations, about 10,000 kilograms per second.

We’ve sort of known for years

It was the Voyager expeditions that first indicated the rings wouldn’t have a cosmically long lifespan.

NASA estimates that water products are draining out of the rings at a rate that could fill an Olympic-sized swimming pool in half an hour.

“From this alone, the entire ring system will be gone in 300 million years,” said James O’Donoghue of NASA’s Goddard Space Flight Center, in a prepared statement.

But when scientists added in the Cassini-spacecraft measurements of ring-material falling into Saturn’s equator, they found the rings have less than 100 million years to live.

“This is relatively short, compared to Saturn’s age of over 4 billion years,” Dr O’Donoghue said, lead author of a study on Saturn’s ring rain published this week in the journal Icarus.

More complex than just water

In 2013, Dr O’Donoghue was lead author of a paper published by Nature that showed for the first time that rain was falling from the rings.

The bad news comes from data gathered during the Cassini space probe’s fatal dive onto Saturn more than a year ago.

It was already understood that material from the rings was being pulled into Saturn by gravity under the influence of Saturn’s magnetic field.

Cassini showed that the intensity of the rainfall from the innermost ring was much higher than expected.

According to a study published in October in Science, Cassini found Saturn’s rings are more chemically complex – they include substantial amounts of methane, ammonia, molecular nitrogen, carbon monoxide, carbon dioxide, and impact fragments of organic nanoparticles.

“Turns out, ring rain is more like a ring downpour,” lead author Dr Hunter Waite said, principal investigator of Cassini’s Ion and Neutral Mass Spectrometer (INMS), in a prepared statement from the Southwest Research Institute.

“While INMS was designed to investigate gases, we were able to measure the ring particles because they hit the spacecraft at such high velocities they vaporised.

“Water ice, along with the newly discovered organic compounds, is falling out of the rings way faster than anyone thought — as much as 10,000 kilograms of material per second.”

Waite’s colleague and co-author, Dr Kelly Miller, said molecular hydrogen was, as expected, the most abundant atmospheric constituent.

The kind of chemicals used in a camping stove

“But the downpour coming from the rings included plenty of water as well as molecules like butane and propane – the kind of chemicals you might use for a grill or camping stove,” Dr Miller said.

The paper also shows that the innermost D ring of Saturn is flinging dust grains coated in a chemical cocktail into the planet’s upper atmosphere. This is happening at such a phenomenally fast rate that, over time, it may change the carbon and oxygen content of the atmosphere.

“This is a new element of how our solar system works,” said Thomas Cravens, professor of physics and astronomy at the University of Kansas, and also a co-author of the new paper.

A hole in the bucket

“Two things surprised me. One is the chemical complexity of what was coming off the rings – we thought it would be almost entirely water based on what we saw in the past, Dr Cravens said.

“The second thing is the sheer quantity of it – a lot more than we originally expected.”

In a prepared statement from the University of Kansas, Dr Cravens said: “We know that it’s bumping material out of the rings at least 10 times faster than we thought. If it’s not being replenished, the rings aren’t going to last – you’ve got a hole in your bucket.”

He said Jupiter probably had a ring that evolved into the current wispy ring, and it could be for similar reasons.

“Rings do come and go,” he said. “At some point, they gradually drain away unless somehow they’re getting new material.”

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