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Last Updated: Monday, 23 April 2007, 15:33 GMT 16:33 UK
Spacecraft return 3D Sun pictures
To get the full effect, 3D glasses are needed to view the images

The US space agency (Nasa) has released the first 3D images of the Sun.

The pictures are built from data obtained by its twin Stereo orbiters which were launched in October.

The new views of our star will advance scientists' understanding of solar physics and improve their ability to model and forecast "space weather".

Of particular concern are explosive events that hurl billions of tonnes of charged particles at Earth, disrupting power grids and satellites.

These Coronal Mass Ejections (CMEs), as they are known, can also be hazardous to astronauts in space.

Stereo is an international mission led by Nasa and the Johns Hopkins University Applied Physics Laboratory in Maryland.

The UK has a significant role on the mission, having provided all the camera systems on board the spacecraft. It has also delivered a Heliospheric Imager (HI) for each orbiter.

These instruments follow the progress of a CME through space by tracing its reflected light.

Strength in depth

The Stereo twins follow a long line of observatories trained on the Sun - but their 3D capability adds a remarkable new dimension to the investigation of solar phenomena.

"The improvement with Stereo's 3D view is like going from a regular X-ray to a 3D CAT scan in the medical field," said Dr Mike Kaiser, the Stereo project scientist at Nasa's Goddard Space Flight Center.

Stereo spacecraft - artist's impression

Since their launch last year, the identical Stereo spacecraft have been moving to widely displaced positions - one in front of the Earth as it goes around the Sun, the other just behind.

It is these different vantage points - when combined into a single view - that give the mission its strength. Just as the slight offset between a person's eyes provides depth perception, the separation of the spacecraft allows them to create 3D images.

The pictures, which can be run together to make mini movies, should provide new insight into the mechanisms that trigger CMEs.

"The mission has gone extraordinarily well so far," said Dr Russell Howard of the Naval Research Laboratory, Washington, the principal investigator for the Secchi (Sun Earth Connection Coronal and Heliospheric Investigation) suite of telescopes on each spacecraft.

"We saw filaments of plasma on the centre of the Sun's disc that had such fine strands that you would not have thought of them as being particularly unusual. Only when you see them in 3D do these filaments - which connect two regions of opposite polarity - pop out at you," he told BBC News.

"CMEs often don't have any disc counterpart - we don't know why that is - and perhaps it's these kinds of things we've ignored in the past that may lead us to an explanation."

South polar region on the Sun (Nasa)
In this Stereo image, material can be seen erupting off the Sun

A CME cloud is laced with magnetic fields, and CMEs directed towards Earth smash into the field created by our own planet.

If the CME magnetic fields have the proper orientation, they dump energy and particles into the Earth's system, causing magnetic storms that can overload power line equipment and radiation storms that disrupt satellites.

We've also taken pictures of planets and stars - simply great astronomical images that are really just a by-product of our main mission
Prof Richard Harrison, RAL
With our increasing dependence on spacecraft in orbit - for communications and navigation - the Stereo mission comes not a moment too soon.

The Earth's magnetic field gives the planet and its inhabitants a good measure of protection; but with space agencies seemingly intent on sending astronauts to the Moon and even to Mars in the next few decades, there is a pressing need for a fuller understanding of the Sun's activity.

Moon or Mars bases will have to be carefully designed shelters, and astronauts will need very good advice before deciding to venture too far from such protection.

The new information is expected to lengthen the advance warning space weather forecasters are able to give of dangerous events - from the current few hours to a couple of days.

Tail to tell

At the moment, the twins view the Sun with only a small angle of separation.

This means the new 3D images are being built largely from data obtained by the ultraviolet telescopes on the platforms. These are looking at structures that play out close to the Sun.

In time, as the separation grows, the spacecraft will be able to follow more distant events - tracking the movement of CME clouds all the way from the Sun to Earth.

The UK's Heliospheric Imagers are producing great pictures

At that stage, the UK's Heliospheric Imagers will make their major contribution.

They employ a system of precision baffles to protect their camera optics from the direct glare of sunlight. This allows the HIs to pick out much fainter objects than would otherwise be possible in the flood of light from the star.

"We won't come into our own for several months but already we've managed to do some amazing science," explained Professor Richard Harrison from the Rutherford Appleton Laboratory, Oxfordshire.

"We opened the door on one spacecraft and immediately a comet - Comet McNaught - went screaming through the field of view. It revealed a highly structured tail that tells us something about the presence of iron.

"We've also seen asteroids which are tiny things right on the borders of the intensity levels we can detect. That's fantastic because it tells us our instruments will do what they are supposed to," he told BBC News.

"We've also taken pictures of planets and stars - simply great astronomical images that are really just by-products of our main mission."

As well as RAL, the University of Birmingham has been heavily involved in the Stereo project, together with the University of Wales Aberystwyth which has been one of the first UK institutions to work on exploiting the data to produce 3D simulations.

Orbit of Stereo spacecraft
The twins were launched on a trajectory that went past the Moon
The lunar swingby positioned the probes in widely spaced orbits
One leads the Earth in its orbit, the other lags behind
Over the course of their mission, the twins will continue to separate
Their different views are combined to make 3D movies of CMEs

The first 3D pictures of the Sun are unveiled

Scientists unveil 3D Sun images
23 Apr 07 |  Mid Wales
Spacecraft return Sun panoramas
02 Mar 07 |  Science/Nature
Probe's close-up of Sun eruption
29 Nov 06 |  Science/Nature
Spacecraft go to film Sun in 3D
26 Oct 06 |  Science/Nature
Mission guide: Stereo
26 Oct 06 |  Science/Nature
Sun probe sends back first data
03 Nov 06 |  Science/Nature

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