The 10-day space tempest in November 2003 was stirred by huge solar flares -- mass ejections of highly energised particles blasted out from the Sun -- a few days earlier.

American astronomers say the so-called Halloween Storm "compressed dramatically" the Van Allen belts, two magnetic belts which girdle the Earth and protect the planet from electron bombardment by trapping charged particles.

The inner Van Allen belt lies 3,000-6,000 kilometers (1,900-3,700 miles) from the equator, and the outer belt lies 20,000-25,000 kilometers (12,500-15,600 miles) away.

The region in between is normally devoid of particles, which is why it is a favourite slot for satellites.

From November 1-10 2003, the outer Van Allen bet was so squeezed by the electron assault that its centre was only about 10,000 kilometersmiles) from the equator, and the normally peaceful region in between was seething with solar radiation, the astronomers say.

For people on Earth, there was no risk, and for people in northerly latitudes there was a remarkable display of the celestial shimmering known as the Northern Lights, as charged particles collided with the atmosphere. The phenomenon was seen as far south as El Paso, Texas.

But for electronic equipment in orbit, it was a different matter.

Several satellites broke down completely and circuitry failed on others.

Even though the event was very rare, its severity should be a lesson for satellite designers to shield their circuitry, the study says.

"The presence of very energetic electrons in the Earth's magnetosphere constitutes a 'space weather' hazard to spacecraft operating in near-Earth space," it says.

"Future models and design strategies need to take account of possible extreme events."

The study, which appears on Thursday in the British weekly science journal Nature, is lead-authored by Daniel Baker of the Laboratory for Atmospheric and Space Physics at the University of Colorado.

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