The sun has dazed and confused scientists by triggering the biggest proton storm" to bombard the Earth for half a century, challenging many ideas about how to forecast space weather to protect astronauts and satellites. Ejections of material that are often linked to solar flares can also damage ground-based communications systems and power grids. Normally, it takes two or more hours for a dangerous shower of positively charged protons to reach maximum intensity at Earth after a solar flare and between one and four days for ejected solar material to arrive. But the particles from one vast flare earlier this year peaked about 15 minutes after the first signs. "The timing is incredibly fast," said Prof Peter Cargill of Imperial College London. The burst of radiation on Jan 20 accompanied a huge solar flare - the biggest explosions in the solar system. The solar flare tripped radiation monitors worldwide and scrambled detectors on spacecraft, marking "the largest solar radiation signal on the ground in nearly 50 years", said Dr Richard Mewaldt of the California Institute of Technology, Pasadena, a co-investigator on Nasa's Advanced Composition Explorer spacecraft. "But we were really surprised when we saw how fast the particles reached their peak intensity and arrived at Earth. That's important because it's too fast to respond with much warning to astronauts or spacecraft that might be outside Earth's protective magnetosphere."

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