Huge solar flares hit far-flung craft

From Montreal, at a joint meeting of the American and Canadian Geophysical Unions

Spacecraft distributed throughout the solar system, including one launched more than a quarter-century ago and now billions of kilometers from Earth, have detected material spewed into space by a spate of huge solar flares late last year.

In October 2003, large, chaotic regions of magnetic activity on the sun began triggering what became a series of at least 60 solar flares, says Nat Gopalswamy of NASA’s Goddard Space Flight Center in Greenbelt, Md. The active regions, known as sunspots, covered about 0.6 percent of the sun’s face. Four of the flares that erupted from these areas are among the strongest ever recorded.

Early salvos in the solar barrage disrupted as many as 20 satellites in Earth orbit and totally disabled at least one of them. Strong magnetic fields associated with some of the flares caused a major power outage in southern Sweden and stifled high-frequency radio communications in some parts of the Arctic. Some of the flares were so strong that the Mars Radiation Environment Experiment—an instrument on the Odyssey craft that’s been orbiting the Red Planet since October 2001—was permanently knocked out by the very phenomenon it was designed to measure.

Instruments on board the Ulysses probe, which swung by Jupiter in February 1992 and is now in orbit around the sun, detected a gust of solar particles that was spurred by a flare that erupted on Nov. 7. Before the gust struck the craft, which is about 775 million kilometers from the sun, the normal flow of charged particles, called solar wind, was speeding past at 832 kilometers per second, says Curt A. de Koning of the Los Alamos (N.M.) National Laboratory.

As the flare’s remains swept by the craft on Nov. 15, instruments clocked solar-wind speeds as high as 993 km/sec. The Cassini probe, more than 1.3 billion km from the sun and headed for Saturn, detected similar surges in the solar wind on Nov. 10 and Nov. 16.

Vestiges of the sun’s fiery burps will probably reach the edge of the solar system soon. Sensors on the Voyager 2 craft, now more than 10.6 billion km away from Earth, discerned a boost in solar-wind speed from 460 km/sec to 520 km/sec on April 28, says John D. Richardson of the Massachusetts Institute of Technology. Computer models suggest that shock waves from the flares will strike the Voyager 1 probe, now nearly 13.8 billion km away from Earth, on June 26.

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