Cassini gets a ringside seat to solve Saturn's ancient riddle

Ever since the 17th century, when they were spotted by a Dutch astronomer, Saturn's rings have delighted and perplexed stargazers in equal measure. Delighted, because of the spectacular appearance of the shining girdle of the solar system's second largest planet. Perplexed, because nobody has been able to establish what they are made of.

Ever since the 17th century, when they were spotted by a Dutch astronomer, Saturn's rings have delighted and perplexed stargazers in equal measure. Delighted, because of the spectacular appearance of the shining girdle of the solar system's second largest planet. Perplexed, because nobody has been able to establish what they are made of.

Today, we may be a little closer to finding the answer. After a seven-year, two billion-mile journey, the Cassini spacecraft is now in orbit around Saturn. And that journey, completed yesterday, represents the best chance yet of unravelling the mystery.

Over the next four years, the £1.6bn space probe will make 76 orbits of the planet and its 31 moons in the closest examination yet of the planet and its rings.

Cassini will examine their gravitational fields, determine their chemical composition, and measure any ultraviolet energy they give off. Scientists think the rings are mainly frozen water, but they could contain rock from the beginnings of the solar system.

From Earth, we can only see two prominent rings ­ called A and C. But there are many more; the spacecraft today sneaked through the F and G rings. Although they look continuous in the photos, astronomers reckon if you compressed them into a single body it would be no more than 60 miles across. That is because each ring is made of innumerable tiny particles, each orbiting independently. And though they are 150,000 miles across, they're no more than a mile thick ­ infinitesimal in astronomical terms.

The ring particles can't form into a new body, nor drift away; so they are held in a dance, "shepherded" by some of the dozens of moons that pass around and through the rings.

The rings' origin is unknown. They might have been there since the planet's formation, about six billion years ago, at the birth of the solar system. The ring systems must be replenished by some destructive process ­ probably the break-up, through tidal forces, of larger orbiting bodies, which are torn apart as the outside pieces try to move more quickly than those on the inside of the orbit.

"I can tell you it feels awfully good to be in orbit around the lord of the rings," said Charles Elachi, the director of the US space agency Nasa's Jet Propulsion Laboratory, and a Cassini radar team member, as the spacecraft allowed itself to be caught by Saturn's gravity.

Having passed just 12,500 miles above Saturn's clouds, the bus-sized lander fired its thrusters for 90 minutes. The firing finished just one minute early, to the relief of those watching live in California and at the European Space Agency's headquarters in Darmstadt, Germany. Without braking, the spacecraft would have sailed on into deep space.

"If you miss that operation, the mission is lost," said Gaele Winters, the ESA's director of operations. "Now it's right on target ­ it's perfect."

The ESA has put roughly £400m into the mission, which is the result of nearly 20 years' work by scientists in 17 countries, and the most ambitious uncrewed space mission in history.

Britain is playing a key role, providing half of the 12 instruments on board the Nasa orbiter, and two of the six instruments on the Huygens probe. The Huygens lander will detach on Christmas Eve and should land on the moon Titan three weeks later.

Start your day with The Independent, sign up for daily news emails
PROMOTED VIDEO
ebooks
ebooksA special investigation by Andy McSmith
Latest stories from i100
Have you tried new the Independent Digital Edition apps?
Independent Dating
and  

By clicking 'Search' you
are agreeing to our
Terms of Use.

iJobs Job Widget
iJobs General

Tradewind Recruitment: English Teacher

Negotiable: Tradewind Recruitment: My client is an excellent, large partially ...

Tradewind Recruitment: Science Teacher

£90 - £140 per day: Tradewind Recruitment: I am currently working in partnersh...

Tradewind Recruitment: Year 3 Primary Teacher

£100 - £150 per day: Tradewind Recruitment: Year 3 Teacher Birmingham Jan 2015...

Ashdown Group: Lead Web Developer (ASP.NET, C#) - City of London

£45000 - £50000 per annum + Excellent benefits: Ashdown Group: Lead Web Develo...

Day In a Page

Isis hostage crisis: The prisoner swap has only one purpose for the militants - recognition its Islamic State exists and that foreign nations acknowledge its power

Isis hostage crisis

The prisoner swap has only one purpose for the militants - recognition its Islamic State exists and that foreign nations acknowledge its power, says Robert Fisk
Missing salvage expert who found $50m of sunken treasure before disappearing, tracked down at last

The runaway buccaneers and the ship full of gold

Salvage expert Tommy Thompson found sunken treasure worth millions. Then he vanished... until now
Homeless Veterans appeal: ‘If you’re hard on the world you are hard on yourself’

Homeless Veterans appeal: ‘If you’re hard on the world you are hard on yourself’

Maverick artist Grayson Perry backs our campaign
Assisted Dying Bill: I want to be able to decide about my own death - I want to have control of my life

Assisted Dying Bill: 'I want control of my life'

This week the Assisted Dying Bill is debated in the Lords. Virginia Ironside, who has already made plans for her own self-deliverance, argues that it's time we allowed people a humane, compassionate death
Move over, kale - cabbage is the new rising star

Cabbage is king again

Sophie Morris banishes thoughts of soggy school dinners and turns over a new leaf
11 best winter skin treats

Give your moisturiser a helping hand: 11 best winter skin treats

Get an extra boost of nourishment from one of these hard-working products
Paul Scholes column: The more Jose Mourinho attempts to influence match officials, the more they are likely to ignore him

Paul Scholes column

The more Jose Mourinho attempts to influence match officials, the more they are likely to ignore him
Frank Warren column: No cigar, but pots of money: here come the Cubans

Frank Warren's Ringside

No cigar, but pots of money: here come the Cubans
Isis hostage crisis: Militant group stands strong as its numerous enemies fail to find a common plan to defeat it

Isis stands strong as its numerous enemies fail to find a common plan to defeat it

The jihadis are being squeezed militarily and economically, but there is no sign of an implosion, says Patrick Cockburn
Virtual reality thrusts viewers into the frontline of global events - and puts film-goers at the heart of the action

Virtual reality: Seeing is believing

Virtual reality thrusts viewers into the frontline of global events - and puts film-goers at the heart of the action
Homeless Veterans appeal: MP says Coalition ‘not doing enough’

Homeless Veterans appeal

MP says Coalition ‘not doing enough’ to help
Larry David, Steve Coogan and other comedians share stories of depression in new documentary

Comedians share stories of depression

The director of the new documentary, Kevin Pollak, tells Jessica Barrett how he got them to talk
Has The Archers lost the plot with it's spicy storylines?

Has The Archers lost the plot?

A growing number of listeners are voicing their discontent over the rural soap's spicy storylines; so loudly that even the BBC's director-general seems worried, says Simon Kelner
English Heritage adds 14 post-war office buildings to its protected lists

14 office buildings added to protected lists

Christopher Beanland explores the underrated appeal of these palaces of pen-pushing
Human skull discovery in Israel proves humans lived side-by-side with Neanderthals

Human skull discovery in Israel proves humans lived side-by-side with Neanderthals

Scientists unearthed the cranial fragments from Manot Cave in West Galilee