Space Mission To Improve Earth's Magnetic Image.
Most of us are aware that compasses swing towards the north because of the Earth's magnetic field. A lucky few will even have seen an aurora, the glorious, shimmering curtain of light which illuminates the night skies near the north and south poles. But, until now, no-one has been able to actually see what happens further out in space when streams of supersonic particles from the Sun arrive to batter our magnetic world.
This is about to change with the launch of NASA's IMAGE (Imager for Magnetopause-to-Aurora Global Exploration) spacecraft, the first satellite equipped to take pictures of the invisible magnetic bubble - the magnetosphere - which surrounds our planet. IMAGE will achieve this seemingly impossible feat by capturing atoms which are flying around inside the Earth's magnetic web.
"Near-Earth space resembles a giant game of billiards," explains Manuel Grande from the UK's Rutherford Appleton Laboratory, a Co-Investigator on the IMAGE mission. "Fast-moving charged particles, known as ions, smash into stationary atoms in the Earth's thin extended atmosphere (exosphere). This collision makes the atoms head off into space at high speed."
"Fortunately, the atoms are travelling in straight lines, so if they strike a detector on the IMAGE spacecraft, we can determine their energy and where they came from. In this way, we can build up a picture of the distribution of particles in the magnetosphere. By taking a series of pictures, about one every minute, we can build up a panorama of the doughnut-shaped magnetic bubble with the Earth in the centre."
Scientists are very excited by this new technique. Although the text books are filled with artists' impressions of the Earth's magnetic field, this will be the first time that anyone has ever seen what it really looks like. The view will extend some 75,000 km into near-Earth space, and although it will be fairly coarse in resolution compared with normal photography, it will be able to distinguish structure within the magnetosphere.
"In the past, we have only been able to sample the magnetosphere from satellites," explained Manuel Grande. "It was like trying to study a river by walking blindfold along the bank and dipping in a bucket from time to time."
"With IMAGE we will be able to look at the entire system and see where we've dipped in the bucket," he added. "By looking at the broader picture, we will be able to understand more about where the samples came from."
This means that scientists will be able to link the wide-angle pictures of the magnetosphere produced by IMAGE with more localised data returned from a scattered flotilla of spacecraft which is currently orbiting the Earth.
IMAGE data will also be of considerable value to scientists involved in the European Space Agency's Cluster II mission, which is scheduled for launch in June and July. For the first time, four identical spacecraft will be able to fly in close formation through the magnetosphere, providing three-dimensional samples of the fluctuating electrical and magnetic fields. Scientists from the UK are heavily involved in the unique Cluster II project, since three of the 11 instruments on each spacecraft have been provided by Britain.
The timing of the IMAGE mission is also particularly appropriate since it will be able to study the Sun-Earth interaction close to solar maximum. Increasing numbers of sunspots, solar flares and explosive coronal mass ejections are expected this year as our nearest star reaches the peak of its 11-year cycle of activity. At such times, the region inside the Earth's protective magnetic shield can feel the effects, resulting in frequent aurorae which are sometimes visible as far south as southern England. Other side-effects can be more serious, including power cuts, disruption to radio communications, damage to satellites and radiation hazards for astronauts.
Notes for Editors:
Following launch, the spacecraft will be inserted into a highly elliptical polar orbit which will take it up to 44,650 km (27,680 mls) above the Earth. The spin-stabilised spacecraft will be oriented so that its instruments scan the Earth during each spacecraft revolution. The mission is expected to last for two years.
During this period, the satellite's orbit will shift in space, enabling it to see the Earth from different viewpoints. At the beginning of the mission, it will reach its furthest point (apogee) at approximately 40 degrees north latitude and at dusk local time. After a year of operation, IMAGE will be at apogee over the north pole on the night side of the planet. The apogee will then begin to decrease until, two years into the mission, it is once again at 40 degrees north latitude.
IMAGE will use three different experimental techniques to carry out its mission: radio sounding, ultraviolet imaging, and neutral atom imaging. · The radio sounder - a type of radar system - will probe the boundaries of the magnetosphere by detecting 'echoes' from the sea of charged particles.