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Sunstruck. A quartet of satellites carries dozens of instruments to monitor various solar phenomena and their impact on Earth.

Earth's Turbulent Magnetic Field

PARIS--Four satellites flying in unison have revealed a hidden wild side to Earth's magnetosphere, the magnetic field enveloping the planet that acts like a gigantic deflector shield against blasts of solar radiation. The unprecedented view, unveiled here last week at the European Space Agency (ESA) headquarters, could help scientists devise better defenses against crippling magnetic storms.

ESA launched the quartet of identical spacecraft last summer, 4 years after the original set of satellites was lost in an explosion seconds after lift-off (Science, 28 June 1996, p. 1866). Each satellite of the resurrected mission carries 11 instruments designed to produce the first three-dimensional maps of the magnetic fields and plasmas surrounding Earth.

The Cluster spacecraft began gathering data soon after crossing the magnetopause--the outer edge of the magnetosphere, where the influence of the sun's magnetic field takes over--on 8 November. Already, Cluster has found that the magnetopause, thought to be smooth, is actually corrugated and undulates like an ocean wave buffeted by wind. "For years, we had been trying to find out what happens to this shield," says Nicole Cornilleau-Wehrlin of the Centre d'Etude des Environnements Terrestres et Planétaires in Vélizy, whose instruments detected waves in the magnetosphere that extended for 1000 kilometers.

Outside experts are impressed. "I am surprised the team has been able to extract such exciting observations so soon after launch," says Alan Gabriel of the Institut d'Astrophysique Spatiale in Orsay and president of the French sun-Earth research program.

Cluster's findings could soon have some practical benefits as well. The sun is entering the peak of its 11-year cycle of activity, which is expected to bring powerful solar flares that trigger magnetic storms in Earth's atmosphere. Such storms can disrupt radio and satellite communications. A better understanding of these processes, says project scientist André Balogh of Imperial College in London, could lead to the development of early warning systems that would enable satellite operators to shut off their equipment before electrical circuits are damaged.

Related site

ESA's Web site for Cluster