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By PAUL RECER AP Science Writer
WASHINGTON (AP) - Scientists have found a way to forecast powerful explosions on the sun that can cause power outages, block radio communications and scorch satellites in Earth orbit.
X-ray images captured by a Japanese scientific spacecraft show that an S-shaped structure develops on the face of the sun several days before an eruption of what is called a coronal mass ejection, scientists announced Tuesday.
The S-shaped sign, said Richard Canfield of Montana State University, Bozeman, can be used as a solar eruption warning signal. This would give power companies and satellite operators about three extra days to prepare for the effects of a coronal mass ejection.
Current technology detects the solar explosions as they happen. This gives some advanced warning since it takes three or four days for the explosive wave to reach Earth. The 'S' sign detected by the X-ray satellite would add days to the warning, Canfield said.
``The X-ray images will tell us when something is likely to happen,'' said Canfield, a co-author of research that detected the 'S' sign. ``It could be developed into a powerful predictive tool.
``We would go from three or four days of warning to six or seven days,'' he said.
Coronal mass ejections are massive eruptions of electrically charged plasma, or superheated gas, from the outer atmosphere of the sun. The sudden release of energy can hurl 10 billion tons of gas into space at speeds of up to 2 million miles an hour. The energy release can equal billions of megatons of TNT, said Canfield.
Such eruptions happen frequently and usually are harmless to the Earth. Occasionally, however, an explosion occurs on a side of the sun facing the Earth, sending a massive bubble of energy directly at the planet.
The Earth's magnetosphere shields the planet from most of the violence, but the planet's magnetic field lines can be charged suddenly with a powerful wave of electricity. Such surges of electricity along power lines have caused blackouts in the past, burning out transformers and disrupting service for thousands of people.
The wave of solar energy also can disrupt long-distance radio transmissions and can damage satellites that are in deep space, beyond the protective envelope of the Earth's magnetosphere.
George Withbroe, a NASA scientist, said the solar storm effects now are only a nuisance. Power companies protect their systems from the natural electrical surge, and satellites are affected only rarely.
However, Withbroe said solar eruptions could cause serious injury to astronauts traveling beyond the Earth's magnetosphere. He said astronauts in the Apollo program were at risk as they traveled between the Earth and the moon, but fortunately no serious solar storms occurred during that period.
When humans eventually return to the moon or voyage on to Mars, Withbroe said, the ability to predict solar storms could save lives.
``When we go to Mars, we will have to worry more about this,'' said Withbroe. He said it is likely that Mars-bound spacecraft will be equipped with a shielded compartment, which he called ``a storm cellar.'' If Mars voyagers were warned in advance of an approaching solar storm, he said, they could retreat to the shelter until the danger passed.
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