New hope for endangered bald ibis

Bald ibis cling to survival in the Middle East and Africa

Two young adult bald ibis spotted in Syria could be mean new hope for the critically endangered species, Scottish-based conservationists report.

The bird, which was revered by the Egyptian Pharaohs, clings to survival in the Middle East and Africa.

RSPB staff picked up a report of two birds that did not have identification rings during a visit to Syria to study rare migratory species.

This would suggest the pair were previously unknown to conservationists.

Martin Scott, who works on the Western Isles and is one of four RSPB officers on the trip, said in an internet blog that it could also indicate there was an as yet undiscovered location where the bald ibis was surviving.

Hunters, poisonings and starvation have been blamed for the species' decline.

The RSPB officers were able to watch two tagged birds, nicknamed Sultan and Zenobia, on a reserve.

They have also observed sociable lapwings - another endangered bird - during their visit.

Giant laser experiment powers up

NIF is a step on what is still a very long road to fusion reality

The US has finished constructing a huge physics experiment aimed at recreating conditions at the heart of our Sun.

The US National Ignition Facility is designed to demonstrate the feasibility of nuclear fusion, a process that could offer abundant clean energy.

The lab will kick-start the reaction by focusing 192 giant laser beams on a tiny pellet of hydrogen fuel.

To work, it must show that more energy can be extracted from the process than is required to initiate it.

Professor Mike Dunne, who leads a European venture that is also pursuing nuclear fusion with lasers, told BBC News that if NIF was successful, it would be a "seismic event".

"It would mark the transition for laser fusion from 'physics' to 'engineering reality'," he said.

The world is looking to NIF to provide a clear, unequivocal demonstration that lasers can initiate fusion energy gain Prof Mike Dunne European Hiper project

The California-based NIF is the largest experimental science facility in the US and contains the world's most powerful laser. It has taken 12 years to build.

"This is a major milestone," said Dr Ed Moses, director of the facility.

"We are well on our way to achieving what we set out to do - controlled, sustained nuclear fusion and energy gain for the first time ever in a laboratory setting."

'Building blocks'

Experiments will begin in June 2009, with the first significant results expected between 2010 and 2012.

HOW TO MAKE A STAR ON EARTH A pea-sized spherical capsule is filled with fusion fuel This comprises a 150-microgram mix of deuterium and tritium The NIF laser set-up pulses for 20 billionths of a second For that time, it generates about 500 trillion watts That's equivalent to five million million 100-watt light bulbs All the laser power is focused on to the capsule's surface The fuel is compressed to a density 100 times that of lead It is heated to more than 100 million degrees Celsius Under these extreme conditions, fusion is initiated

"We have an incredible amount to do and an incredible amount to learn," added Dr Moses.

Fusion is looked on as the "holy grail" of energy sources because of its potential to supply almost limitless clean energy.

But the challenge of creating a practical fusion reactor has eluded scientists for decades. Now, however, they believe they are nearing their goal.

"We are now very close to the culmination of 50 years' effort," explained Professor Dunne.

There are currently several experimental facilities around the world aimed at demonstrating the building blocks of nuclear fusion.

In this process, two heavier forms of hydrogen, known as deuterium and tritium, are fused together to form helium.

Deuterium is commonly found in seawater, whilst tritium can be prepared from lithium, a relatively common element found in soil.

When these isotopes are combined at high temperatures, a small amount of mass is lost and a colossal amount of energy is released.

Energy gain

Fusion naturally occurs at the centre of stars where huge gravitational pressure allows the process to happen at temperatures of about 10 million Celsius.

At the much lower pressures on Earth, temperatures to produce fusion need to be much higher - above 100 million Celsius.

NIF will focus on a process known as inertially confined fusion, in which these extreme temperatures are achieved using ultra powerful lasers.

"When all NIF lasers are fired at full energy, they will deliver 1.8 megajoules of ultraviolet energy to the target," explained Dr Moses.

The laser power will be focused on to a tiny pellet inside a small cylinder

NIF's beams are intended to deliver more than 60 times the energy of any previous laser system. When fired, the pulse will last just a few nanoseconds (billionths of a second) but it will impart an energy equivalent to 500 trillion Watts - more than the peak electrical generating power of the entire United States.

This intense energy will be focused on a ball-bearing-sized pellet of fuel, ablating the surface and compressing the remaining material inwards.

"This process will create temperatures of 100 million degrees and pressures billions of times greater than Earth's atmospheric pressure, forcing the hydrogen nuclei to fuse and release many times more energy than the laser energy required to spark the reaction," said Dr Moses.

This "energy gain", as it is known, is key. If it works, NIF will release 10 to 100 times more energy than the amount pumped into the lasers to kick-start the reaction.

Other experiments have shown that ignition is possible, but so far none have been able to demonstrate a net energy gain.

"The world is looking to NIF to provide a clear, unequivocal demonstration that lasers can initiate fusion energy gain," said Professor Dunne.

"This would lay the fundamental physics question to rest, allowing the community to focus on harnessing this energy."

Twin track

Although NIF is only at the beginning of its experimental life, scientists are already planning its successor, a European project known as Hiper (High Power Laser Energy Research).

"The technology of NIF allows the laser to fire every few hours," explained Professor Dunne, director of Hiper.

"This is right for the demonstration of the physics 'proof of principle', but does not meet the requirement of a laser fusion power plant, which needs to operate a few times per second."

Hiper aims to lay the foundations of this continuous fusion cycle by showing it can ignite a steady stream of fuel pellets.

Inside one of NIF's two laser bays

"This means a fundamentally different laser technology, a new approach to fuel pellet production, and a suite for robotic handling capability," said Professor Dunne.

In October 2008, Hiper received approximately 13m euros of funding to carry out a feasibility study. It also has access to European hardware and capability worth a further 50m euros.

If all goes well, engineers will begin to build the Hiper facility towards the end of the next decade, bringing the vision of a commercial fusion reactor one step closer to reality.

At approximately the same time, scientist will also get their hands on another mammoth fusion experiment, the International Thermonuclear Experimental Reactor (Iter), currently being built in Cadarache, France.

Iter will attempt to initiate fusion using a different method, known as magnetic confinement, in which a super-heated volume of gas is constrained by magnetic fields in a doughnut-shaped vessel known as a tokamak.

"We are entering a period when much of the technology development is common to both approaches," said Professor Dunne.

"We believe that the two-track approach is essential given the scale of the problem, and the predicted impact on society."

Evolution study focuses on snail

By Sarah Mukherjee Environment correspondent, BBC News

The banded snail has been studied for at least 60 years

Members of the public across Europe are being asked to look in their gardens or local green spaces for banded snails as part of a UK-led evolutionary study.

The Open University says its Evolution MegaLab will be one of the largest evolutionary studies ever undertaken.

Scientists believe the research could show how the creatures have evolved in the past 40 years to reflect changes in temperature and their predators.

The six-month study, starting in April, will ask people to submit data online.

'Ideal organism'

Professor Jonathan Silvertown, from the OU, said: "I was thinking about Darwin year and how we could help people get an idea of what Darwin was talking about.

"The banded snail has been studied for 60 or more years, so it's an ideal organism to use. It's something that's very common, we know what the genetics are and it's safe to handle."

Professor Silvertown said there were two main evolutionary drivers that affect where yellow and brown banded snails are found.

The first is climate - darker-shelled snails tend to be further north, and scientists believe this is because dark shells get warmer quicker than lighter ones.

Darker-shelled snails could also be active for longer - which would make a difference to how much they could eat and how many offspring they could have.

The second evolutionary driver is predation by thrushes.

The birds hunt by sight and they find it more difficult to find yellow-striped shells around grass and brown shells against brown leaves - so yellow-shelled snails have been more common in grassland and darker ones in areas with brownish background environments.

'Genuine study'

"We think [the snails] have changed in the last 40 or 50 years," said Professor Silvertown.

"Firstly, the climate has warmed up, so we think the distribution of colours has probably changed.

"Secondly, thrushes have become far less common in the last 30 years or so - so snail colouring in different habitats might be less important."

This is what the Evolution MegaLab, which will run from April to October, will be trying to discover.

"There's a lot of historical data on the website," said Professor Silvertown.

"We have data from the past on 8,000 or so snail populations, so if you submit your data on the website, it will automatically make a comparison telling you whether there's been any change in your area."

Professor Silvertown said this was a genuine scientific study and not just a public relations exercise.

It has been funded in part by the Royal Society and the British Council, and he and his team are hoping that a major report will be published on the data collected at the beginning of next year.

He also points out that this could be an invaluable tool for researchers of the future who will be able to look at this project and compare any further evolutionary changes.

'War' on poisonous Australia toad

Cane toads are only harmful to humans if their poison is swallowed

People in the Australian state of Queensland have taken part in a mass capture of poisonous cane toads as part of a collective effort at pest control.

The celebratory cull is known as Toad Day Out and was advocated by a Queensland politician, Shane Knuth.

The toads have to be captured alive and unharmed, examined by experts, and then killed humanely under the event rules.

Cane toads were introduced to Australia from South America in 1935 to eat beetles, but became a pest themselves.

"This is an example of how the war against cane toads can be won," said Mr Knuth, who hopes to take Toad Day Out nationwide.

Critics of the toads blame them for the deaths of crocodiles that may have feasted on them, inadvertently poisoning themselves.

Children also took part in collecting the creatures. "I've got no clue how many we've got but they're all fat!" said one boy involved in the hunt for the toads.

The majority of toads will be turned into fertiliser or donated to the science department of James Cook University.

But a few of the largest ones will be stuffed by a local Queensland taxidermist.

Nasa's Discovery returns to Earth

The shuttle took new solar panels to the International Space Station

Nasa's space shuttle Discovery has landed after a 13-day mission to the International Space Station.

The shuttle touched down at Kennedy Space Center in Florida, hours after its return was postponed because of concerns about poor weather conditions.

Discovery's seven crew members installed an extra pair of solar wings on the International Space Station.

The shuttle launched on 15 March, docking with the ISS to deliver the final set of solar arrays.

Sandra Magnus - who had been stationed at the ISS for four months - returned to earth on Discovery.

Meanwhile, a Russian space capsule with an American billionaire passenger on board has docked with the ISS.

The passenger, Charles Simonyi, is a software designer and is making his second trip as a space tourist.

He was accompanied by Russian and American astronauts.

Retirement

The shuttle undocked from the ISS on Wednesday after eight days there.

The crew spent five hours on Thursday inspecting the shuttle's outer surface using a laser and camera mounted on a 15m (50ft) boom connected to Discovery's robotic arm.

The shuttle, as seen from the ISS, includes a novel heat-shield tile

The images were then sent back to Mission Control as part of a routine procedure that ensures the integrity of the shuttle's heat-shield tiles.

The tiles are designed to dissipate heat as the orbiter returns to Earth through an increasingly thicker atmosphere.

Under the shuttle's left wing is a single tile that includes a "bump", which interrupts the normally smooth airflow around the tiles.

The disrupted airflow will increase the temperature of the tiles around it by a small amount and is part of a test of candidate tiles for future missions.

Current designs for those missions mean spacecraft will endure significantly more heat on re-entry than the space shuttles, which might be retired next year.

Nasa is preparing space shuttle Atlantis to be rolled out towards the launch pad on 31 March.

Atlantis is scheduled for a 12 May lift-off on a mission to service the Hubble Telescope. The mission has been delayed since October 2008.

Nasa delays space shuttle landing

The shuttle took new solar panels to the International Space Station

Nasa has delayed attempts to land space shuttle Discovery due to concerns about heavy winds and cloud-cover.

The shuttle had been scheduled to land at Kennedy Space Center in Florida and controllers have one more opportunity on Saturday if the weather clears.

Its seven crew members had packed away their equipment as they made final preparations to come home.

Discovery launched on 15 March, docking with the International Space Station to deliver a final set of solar arrays.

As and when it finally returns to earth, the orbiter will have Sandra Magnus on board. She has been stationed at the ISS for four months.

Meanwhile a Russian space capsule with an American billionaire passenger on board has docked with the ISS.

The passenger, Charles Simonyi, is a software designer and is making his second trip as a space tourist.

He was accompanied by Russian and American astronauts.

On the tiles

The shuttle undocked from the ISS on Wednesday after eight days there.

The crew spent five hours on Thursday inspecting the shuttle's outer surface using a laser and camera mounted on a 15m (50ft) boom connected to Discovery's robotic arm.

The shuttle, as seen from the ISS, includes a novel heat-shield tile

The images were then sent back to Mission Control as part of a routine procedure that ensures the integrity of the shuttle's heat-shield tiles.

The tiles are designed to dissipate heat as the orbiter returns to Earth through an increasingly thicker atmosphere.

Under the shuttle's left wing is a single tile that includes a "bump", which interrupts the normally smooth airflow around the tiles.

The disrupted airflow will increase the temperature of the tiles around it by a small amount and is part of a test of candidate tiles for future missions.

Current designs for those missions mean spacecraft will endure significantly more heat on re-entry than the space shuttles, which might be retired next year.

Nasa is preparing space shuttle Atlantis to be rolled out towards the launch pad on 31 March.

Atlantis is scheduled for a 12 May lift-off on a mission to service the Hubble Telescope. The mission has been delayed since October 2008.

World cities begin big switch-off

Auckland, New Zealand, was one of the first cities to switch off

Millions of people worldwide are being urged off lights for an hour, in what is described as the biggest climate change protest ever attempted.

The initiative, Earth Hour, was begun in Sydney two years ago by green campaigners keen to cut energy use.

Correspondents say the aim is to create a huge wave of public pressure to influence a meeting in Copenhagen later this year to seek a new climate treaty.

Critics describe the event as a symbolic and meaningless gesture.

The switch-off is expected to take place in more than 3,400 towns and cities across 88 countries, at 2030 in each local time zone.

Earth Hour was launched in 2007 as a solo event in Sydney, Australia, with more than two million people involved. Last year's event claimed the participation of 370 cities.

This time Sydney was one of the first places to switch off. The BBC's Nick Bryant described a city where skyscrapers were hard to make out against the night sky.

Locations taking part this time include Edinburgh Castle in Scotland, the Bird's Nest Stadium in Beijing and the Egyptian Pyramids.

Fast-food giant MacDonald's has pledged to dim its "golden arches" at 500 locations, while celebrities such as actress Cate Blanchett and Archbishop Desmond Tutu have promised support.

UN Secretary-General Ban Ki-moon backed the initiative in a video posted this month on the event's YouTube channel.

"Earth Hour is a way for the citizens of the world to send a clear message," he said. "They want action on climate change."

People are invited to provide blogs and short video clips on how they spend their time.

World prepares for big switch-off

This photo shows Sydney before and after switching off last year

Millions of people worldwide are being urged to switch off lights for an hour, in what is described as the biggest climate change protest ever attempted.

The initiative, Earth Hour, was begun in Sydney two years ago by green campaigners keen to cut energy use.

Correspondents say the aim is to create a huge wave of public pressure to influence a meeting in Copenhagen later this year to seek a new climate treaty.

Critics describe the event as a symbolic and meaningless gesture.

The switch-off is expected to take place in more than 3,400 towns and cities across 88 countries, at 2030 in each local time zone.

Earth Hour was launched in 2007 as a solo event in Sydney, Australia, with more than two million people involved. Last year's event claimed the participation of 370 cities.

Locations taking part this time include Sydney's Opera House, Edinburgh Castle in Scotland, the Bird's Nest Stadium in Beijing and the Egyptian Pyramids.

Fast-food giant MacDonald's has pledged to dim its "golden arches" at 500 locations, while celebrities such as actress Cate Blanchett and Archbishop Desmond Tutu have promised support.

UN Secretary-General Ban Ki-moon backed the initiative in a video posted this month on the event's YouTube channel.

"Earth Hour is a way for the citizens of the world to send a clear message," he said. "They want action on climate change."

People are invited to provide blogs and short video clips on how they spend their time.

Space shuttle ready to head home

The shuttle took new solar panels to the International Space Station

The seven crew members on space shuttle Discovery are spending their last day in space packing away equipment and making final preparations to come home.

The crew will also speak with students at a school in Hawaii on Friday, as two of the team are former teachers.

Discovery launched on 15 March, docking with the International Space Station (ISS) to deliver new solar panels.

The shuttle is scheduled to land at Kennedy Space Center in Florida on Saturday afternoon.

The shuttle will return with Sandra Magnus on board, who has been stationed at the ISS for four months.

As Discovery heads toward Florida, the Soyuz capsule launched onThursday is on its way to take Discovery's place at the space station.

On the tiles

The shuttle undocked from the space station on Wednesday after eight days there.

The crew spent five hours on Thursday inspecting the shuttle's outer surface using a laser and camera mounted on a 50-foot boom connected to Discovery's robotic arm.

The shuttle, as seen from the ISS, includes a novel heat-shield tile

The images were then sent back to Mission Control as part of a routine procedure that ensures the integrity of the shuttle's heat-shield tiles.

The tiles are designed to dissipate heat as the shuttle returns to Earth through an increasingly thicker atmosphere.

Under the shuttle's left wing is a single tile that includes a "bump", which interrupts the normally smooth airflow around the tiles.

The disrupted airflow will increase the temperature of the tiles around it by a small amount and is part of a test of candidate tiles for future missions.

Current designs for those missions mean spacecraft will ensure significantly more heat on re-entry than the space shuttles, which might be retired next year.

"We have returned to using the space shuttle as a research vehicle," said Nasa shuttle programme manager John Shannon.

"We're trying to learn more and more about space flight and hypersonic re-entry."

On the ground, Nasa is preparing space shuttle Atlantis to be rolled out toward the launch pad on 31 March.

Atlantis is scheduled for a 12 May launch for the Hubble Telescope's final servicing mission, which has been delayed since October 2008.

Millions of fish shoal in seconds

A 'critical threshold' causes the fish to form shoals covering many kilometres

Researchers in the US have recorded the point at which hundreds of millions of herring coalesce into a vast shoal.

The team used equipment, which they also invented, that uses sound waves to remotely monitor movement of the fish.

They found that, when the herring numbers reach a tipping point, or "critical threshold", this triggers a chain reaction whereby the shoal forms within seconds.

The findings are reported in the journal Science.

Herring form shoals to migrate during the autumn spawning season.

The shoal moves in a "highly organised fashion" and hundreds of millions of herring travel together to shallower waters to spawn.

The very ordered movement of the fish has reinforced an earlier theory that very large groups of migrating animals - swarms or shoals - act as one.

Fibre optic ocean

The technology the researchers used is called Ocean Acoustic Waveguide Remote Sensing.

This produces an image of the whole shoal by bouncing sound waves off the bodies of the fish.

With this equipment, measurements could be taken at such a high speed that the team was able to create a moving image of the forming shoal.

Using sound waves to monitor animals in the darkness of the ocean is not new.

But traditionally, a single survey vessel sends high-frequency sound beams into the ocean - taking a snapshot of a relatively small area.

The new system uses much lower frequency sound that can travel much farther.

The fish form a shoal covering tens of kilometres within tens of minutes Nicholas Makris MIT

"It's like using the ocean as a fibre optic cable," explained Nicholas Makris, the Massachusetts Institute of Technology (MIT) professor who led the research.

"The low frequency beams stay trapped in the water column and can cover a 100km area in a minute and a half."

This, says Professor Makris, is a vast improvement over conventional techniques, which Makris compared to "watching one pixel on a movie screen" while the new technology allows you to "see the entire movie."

'Cities of fish'

The herring's initial movement seems to be triggered by the reduction in light as the sun sets.

"When the light fades, it's safer for the fish to move away from the seabed," says Professor Makris.

"Once they have a certain number of other fish in their sphere of perception, they suddenly come together - forming a shoal covering tens of kilometres within tens of minutes."

The herring gather in such huge numbers, and under cover of darkness, for "synchronised spawning". This helps protect them from predators.

The ordered movement of the shoal means the fish can reach their spawning ground more quickly and more safely.

"This is truly a commute," says Professor Makris. "And there are truly cities of fish down there."

Slower spin 'made moon's bulge'

By Paul Rincon Science reporter, BBC News, The Woodlands, Texas

The Cassini flyby returned exquisite pictures of the bulge

Scientists have come up with a novel theory to explain the unexplained terrain on one of Saturn's icy moons.

The most striking feature of Iapetus is a bulging ridge, which encircles the moon's equator and reaches an altitude of 20km in places.

A new theory suggests the ridge formed when the moon went from a relatively fast-spinning body to one spinning more slowly.

Details were presented at the Lunar and Planetary Science Conference in Texas.

The results are based on computer models of the interior of Iapetus created by James Roberts and his colleagues at the Johns Hopkins University Applied Physics Laboratory (JHUAPL).

Referring to the ridge on Iapetus, Mr Roberts explained: "It looks like somebody screwed two halves of the moon together and did a very bad job soldering the joint.

The ridge is unparalleled in the geology of Solar System bodies. At up to 20km high in places, it dwarfs Mount Everest, which stands only 8km high. The Olympus Mons volcano on Mars stands some 25km tall.

But Mr Roberts points out that Mars is over four times the diameter of Iapetus: "Proportionally, this is the tallest feature in the Solar System with respect to its host body," he said.

Spin cycle

Today, the 1,500km-wide Saturnian satellite spins at a rate of about once every 79 days. But Mr Roberts' data suggest Iapetus could have been rotating as fast as once every 16 hours early in its history.

Over time, tidal interactions with Saturn caused the moon's rotation to slow down until it matched the time taken to complete one orbit of its planet.

This process is known as "de-spinning", reaching a condition where the moon always keeps the same face towards its host planet.

Spinning celestial bodies tends to flatten out at the poles and bulge at the equator. The amount of flattening is controlled by the object's rotation rate: if the rotation slows, the flattening decreases.

De-spinning can cause compression along the equator, but it cannot have formed the ridge on Iapetus because this compression is acting in the wrong direction.

The nature of Iapetus' surface colouring has also proved enigmatic

However, the computer modelling work carried out at JHUAPL shows that de-spinning also dissipates more heat at the equator than elsewhere.

Mr Roberts suggested that warm, buoyant ice rose to the surface from Iapetus' interior and pushed the brittle surface ice outward, forming a ridge around the equator.

The slowing down of Iapetus' spin is estimated to have taken 100 million years or so, at which point the heating stopped. As the moon cooled down, the ridge was frozen in place.

Extreme case

A number of other theories have previously been advanced to describe the development of the ridge.

One group has proposed that Iapetus oence had its own ring system, just as Saturn does today, and that these rings collapsed, falling on to the equator.

It has also been theorised that as the moon de-spun, forces created so-called thrust faults to appear in Iapetus, causing a ridge to pop up around the equator.

The idea of heat driving upwelling currents in the ice has already been proposed as a mechanism for pushing the surface up at the equator.

But Mr Roberts' theory shows that heat generated at the equator by de-spinning can result in the pattern of convection required to cause these currents in the ice.

Most moons are thought to have undergone de-spinning. But why this process should have caused a ridge around Iapetus, and not around the equatorial regions of other satellites, remains an open question, Mr Roberts told BBC News.

However, he added, going from 16-hour rotation to 79 days could mean Iapetus presents the most extreme case of de-spinning in the Solar System.

Slower spin 'made moon's bulge'

By Paul Rincon Science reporter, BBC News, The Woodlands, Texas

The Cassini flyby returned exquisite pictures of the bulge

Scientists have come up with a novel theory to explain the unexplained terrain on one of Saturn's icy moons.

The most striking feature of Iapetus is a bulging ridge, which encircles the moon's equator and reaches an altitude of 20km in places.

A new theory suggests the ridge formed when the moon went from a relatively fast-spinning body to one spinning more slowly.

Details were presented at the Lunar and Planetary Science Conference in Texas.

The results are based on computer models of the interior of Iapetus created by James Roberts and his colleagues at the Johns Hopkins University Applied Physics Laboratory (JHUAPL).

Referring to the ridge on Iapetus, Mr Roberts explained: "It looks like somebody screwed two halves of the moon together and did a very bad job soldering the joint.

The ridge is unparalleled in the geology of Solar System bodies. At up to 20km high in places, it dwarfs Mount Everest, which stands only 8km high. The Olympus Mons volcano on Mars stands some 25km tall.

But Mr Roberts points out that Mars is over four times the diameter of Iapetus: "Proportionally, this is the tallest feature in the Solar System with respect to its host body," he said.

Spin cycle

Today, the 1,500km-wide Saturnian satellite spins at a rate of about once every 79 days. But Mr Roberts' data suggest Iapetus could have been rotating as fast as once every 16 hours early in its history.

Over time, tidal interactions with Saturn caused the moon's rotation to slow down until it matched the time taken to complete one orbit of its planet.

This process is known as "de-spinning", reaching a condition where the moon always keeps the same face towards its host planet.

Spinning celestial bodies tends to flatten out at the poles and bulge at the equator. The amount of flattening is controlled by the object's rotation rate: if the rotation slows, the flattening decreases.

De-spinning can cause compression along the equator, but it cannot have formed the ridge on Iapetus because this compression is acting in the wrong direction.

The nature of Iapetus' surface colouring has also proved enigmatic

However, the computer modelling work carried out at JHUAPL shows that de-spinning also dissipates more heat at the equator than elsewhere.

Mr Roberts suggested that warm, buoyant ice rose to the surface from Iapetus' interior and pushed the brittle surface ice outward, forming a ridge around the equator.

The slowing down of Iapetus' spin is estimated to have taken 100 million years or so, at which point the heating stopped. As the moon cooled down, the ridge was frozen in place.

Extreme case

A number of other theories have previously been advanced to describe the development of the ridge.

One group has proposed that Iapetus oence had its own ring system, just as Saturn does today, and that these rings collapsed, falling on to the equator.

It has also been theorised that as the moon de-spun, forces created so-called thrust faults to appear in Iapetus, causing a ridge to pop up around the equator.

The idea of heat driving upwelling currents in the ice has already been proposed as a mechanism for pushing the surface up at the equator.

But Mr Roberts' theory shows that heat generated at the equator by de-spinning can result in the pattern of convection required to cause these currents in the ice.

Most moons are thought to have undergone de-spinning. But why this process should have caused a ridge around Iapetus, and not around the equatorial regions of other satellites, remains an open question, Mr Roberts told BBC News.

However, he added, going from 16-hour rotation to 79 days could mean Iapetus presents the most extreme case of de-spinning in the Solar System.