Space satellites to study effect of Sun's lethal wind

A flying formation of four identical satellites will be launched by the European Space Agency later this month to watch the weather in space and study the effect on the Earth of storms on the surface of the Sun.

The "Cluster" space mission will probe how the Earth's magnetic field acts as a shield to divert the torrent of sub-nuclear particles streaming out from the Sun. These particles of the "solar wind" would otherwise hit the ground at speeds of 1.5-3 million km an hour.

According to professor Alan Johnstone, of the Mullard Space Science Laboratory at University College London, without the Earth's magnetosphere human life would not survive. It "protects us by shielding us from the radiation from the Sun. It's also helped us to hang on to our atmosphere".

Apart from Venus, no other planet is capable of sustaining life, professor Johnstone said, because they all lack protective magnetic fields.

The shield sometimes breaks. In March 1989 there was a power failure throughout Quebec, in Canada, when a solar storm tripped the entire electricity grid. But the breakdown can be breathtakingly beautiful when it takes the form of the shifting curtains of light in the high atmosphere over the Poles - the aurora borealis and australis.

Dr Paul Murdin, head of astronomy at the Particle Physics and Astronomy Research Council, said: "When the Sun sneezes, we on Earth have the possibility of catching cold and we want to learn how to turn our heads away and not get ill."

The researchers were speaking at a press conference in London yesterday revealing the scientific details of the Cluster mission.

Each satellite weighs about 1.2 tonnes and will be launched into geo- stationary orbit in the first lift-off by the latest and largest European rocket launcher, the Ariane 5. Europe hopes to steal a march on the Americans, Russians and Japanese with the Ariane 5, which will be its workhorse in the commercial satellite-launching business into the next century.

When Ariane 5 reaches orbit, the four Cluster satellites "will pop out like peas out of a pea-shooter", according to Dr Murdin. The satellites will then use their own on-board rocket motors to move into a highly elliptical orbit, which will take them over the North and South Poles of the Earth. They will fly in formation and their controllers on Earth will be able to vary the distance between the satellites from 600km to a few thousand kilometres. The Cluster satellites will carry a total of 44 instruments measuring magnetic storms, electrical currents, and particle accelerations that take place in the space around our planet. The mission will last for at least two years and has cost Europe and the US around pounds 500m over 10 years. (Graphic omitted)