The rings of Saturn are raining down up to 10,000 kg (22,000 pounds) of frozen material on the gas giant every second.
Astronomers discovered that the rings are dropping ten times more hail to the planet’s surface than was previously thought.
Data from the kamikaze Cassini spacecraft, which plunged into the planet in September 2017, revealed the complexity of the trademark rings.
Scientists say the findings could redefine what we know about how planetary rings form and revolutionise our understanding of the solar system’s mechanics.
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Saturn (pictured) is the second largest planet in our solar system and has a series iconic rings around its equator. Scientists now believe , thanks to data from the Cassini mission, that up to 10,000 kg of frozen material on the gas giant every second
‘Turns out, ring rain is more like a ring downpour,’ said Dr. Hunter Waite, the paper’s lead author and principal investigator of Cassini’s Ion and Neutral Mass Spectrometer (INMS).
The team found the rings to be composed of water, methane, ammonia, carbon monoxide, molecular nitrogen and carbon dioxide.
‘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,’ said Dr Waite.
‘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.’
The variety of compounds found in the space between the planet’s atmosphere and its rings surprised the researchers.
‘Molecular hydrogen was, as expected, the most abundant atmospheric constituent,’ said Dr Kelly Miller, who coauthored the paper published today in the journal Science.
‘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.’
Cassini was a Nasa mission which spent 20 years in space and 13 years in the Saturn system.
In the twilight of its operational lifespan the probe was running out of fuel and the space agency decided to use its last orbits to analyse the upper atmosphere and skirt the edge of the inner rings.
These final 22 orbits allowed instruments on board Cassini to measure the composition of Saturn’s upper atmosphere and its chemical interactions with material originating in the rings.
After this part of the mission was complete the spacecraft plunged into Saturn’ and was destroyed by the planet’s dense atmosphere.
‘For its final adventure, Cassini dove into the unknown region between Saturn’s rings and its atmosphere,’ explained Dr Kelly Miller, who works for the Southwest Research Institute in Texas.
‘Based on previous work, scientists expected water was raining from the rings into Saturn’s atmosphere, so the spacecraft used its radio antenna as an umbrella to protect it from debris.’
Cassini was travelling at such rapid speeds compared to Saturn’s atmosphere that it allowed the analysis to take place.
This immense velocity also complicated the interpretation of the data, the scientists reveal.
Molecules and particles would likely shatter upon impact with the detector so the various organic compounds detected by INMS are likely fragments.
The observations also suggest that regions in Saturn’s innermost D ring are materially variable, either over time or by locality.
‘While INMS was one of the last instruments collecting data to the mission’s end, getting these results was not easy,’ said Rebecca Perryman, the paper’s second author.
‘The large mass of infalling material has implications for ring evolution, hinting that material from the C ring repeatedly replenishes the neighbouring D ring,’ Dr Waite said.
Astronomers also discovered that the rings are dropping ten times more hail to the planet’s surface than was previously thought. They say the findings could redefine what we know about how planetary rings form and our understanding of the solar system’s mechanics
Researchers say this infalling material may also 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 co-author of the paper.
‘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.
‘The second thing is the sheer quantity of it – a lot more than we originally expected.
‘The quality and quantity of the materials the rings are putting into the atmosphere surprised me.’
Dr Cravens says the team fully expected to discover the rings were made of water, but some of the other compounds they detected were very unexpected.
‘What was a surprise was the mass spectrometer saw methane – no one expected that.
‘Also, it saw some carbon dioxide, which was unexpected.
‘The rings were thought to be entirely water. But the innermost rings are fairly contaminated, as it turns out, with organic material caught up in ice.’
Data from the kamikaze Cassini mission has revealed the complexity of Saturn’s rings (pictured) and what they are made from. The team found the rings to be composed of water, methane, ammonia, carbon monoxide, molecular nitrogen and carbon dioxide
WHAT DID CASSINI DISCOVER DURING ITS 20-YEAR MISSION IN SPACE?
Cassini launched from Cape Canaveral, Florida in 1997, then spent seven years in transit followed by 13 years orbiting Saturn.
An artist’s impression of the Cassini spacecraft studying Saturn
In 2000 it spent six months studying Jupiter before reaching Saturn in 2004.
In that time, it discovered six more moons around Saturn, three-dimensional structures towering above Saturn’s rings, and a giant storm that raged across the planet for nearly a year.
On 13 December 2004 it made its first flyby of Saturn’s moons Titan and Dione.
On 24 December it released the European Space Agency-built Huygens probe on Saturn’s moon Titan to study its atmosphere and surface composition.
There it discovered eerie hydrocarbon lakes made from ethane and methane.
In 2008, Cassini completed its primary mission to explore the Saturn system and began its mission extension (the Cassini Equinox Mission).
In 2010 it began its second mission (Cassini Solstice Mission) which lasted until it exploded in Saturn’s atmosphere.
In December 2011, Cassini obtained the highest resolution images of Saturn’s moon Enceladus.
In December of the following year it tracked the transit of Venus to test the feasibility of observing planets outside our solar system.
In March 2013 Cassini made the last flyby of Saturn’s moon Rhea and measured its internal structure and gravitational pull.
Cassini didn’t just study Saturn – it also captured incredible views of its many moons. In the image above, Saturn’s moon Enceladus can be seen drifting before the rings and the tiny moon Pandora. It was captured on Nov. 1, 2009, with the entire scene is backlit by the Sun
In July of that year Cassini captured a black-lit Saturn to examine the rings in fine detail and also captured an image of Earth.
In April of this year it completed its closest flyby of Titan and started its Grande Finale orbit which finished on September 15.
‘The mission has changed the way we think of where life may have developed beyond our Earth,’ said Andrew Coates, head of the Planetary Science Group at Mullard Space Science Laboratory at University College London.
‘As well as Mars, outer planet moons like Enceladus, Europa and even Titan are now top contenders for life elsewhere,’ he added. ‘We’ve completely rewritten the textbooks about Saturn.’
Saturn’s innermost ring, known as the D ring, is the main culprit for expelling hailstones on to the planet and the researchers observed proof of another phenomena.
Cassini’s mass spectrometer showed large amounts of chemicals from Saturn’s D ring is flung into the planet’s upper atmosphere.
This happens because the ring is spinning faster than the planet’s atmosphere itself.
‘We saw it was happening even though it’s not fully understood,’ Dr Cravens revealed.
‘What we saw is this material, including some benzine, was altering the uppermost atmosphere of Saturn in the equatorial region.
‘There were both grains and dust that were contaminated.’
Dr Cravens said the findings could cast new light on mechanisms underpinning our solar system as well as other solar systems and exoplanets – and also prompt a host of new scientific questions.
‘This could help us understand, how does a planet get rings? Some do, some don’t,’ he said.
‘What’s the lifetime of a ring? And what’s replenishing the rings? Was there a time when Saturn didn’t have rings? How did that composition get into there in the first place? Is it left over from the formation of our solar system? Does it date back to proto pre-solar nebula, the nebula that collapsed out of interstellar media that formed the sun and planets?’
According to the researchers, because the rings are expelling matter at a higher-than-expected rate, the experts believe the lifespan of the ring may be briefer than previously thought.
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. Jupiter probably had a ring that evolved into the current wispy ring, and it could be for similar reasons.
‘Rings do come and go. At some point they gradually drain away unless somehow they’re getting new material.’