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Scientists read sun signs for danger

By David L. Chandler, Globe Staff, 03/10/99

ometimes the sun blows its stack, sending explosive outbursts of energy out into space and occasionally right toward Earth. This can cripple satellites, cause power blackouts, and threaten astronauts heading into space, but scientists yesterday reported a dramatic new discovery that should help them to see such blasts brewing a week in advance.

''It's a breakthrough discovery in forecasting the largest explosions in the modern-day solar system,'' said a space scientist, George Withbroe.

The discovery came from detailed pictures of the sun's X-ray emissions, taken by a Japanese-built satellite called Yohkoh, which revealed that a characteristic S-shaped formation usually appears on the sun's surface just before these tremendous explosions, called Coronal Mass Ejections.

''S marks the spot,'' said Alphonse Sterling of Virginia-based Computational Physics Inc., who has been working on the project for the Japanese space science agency ISAS. Whenever these S-shaped regions appear on the sun, he said, it is ''like a loaded gun that we know has a high probability of going off.''

The resulting explosions unleash as much energy as billions of nuclear explosions, the scientists said yesterday at a National Aeronautics and Space Administration press conference announcing the discovery.

While such events can occur as often as once or twice a day, only a small fraction of them are aimed toward Earth, and even those that do reach us have most of their energy blocked by Earth's magnetic field so that none reaches the ground in a form that can directly harm people.

But indirect effects can cause damage, especially as the world becomes more dependent on electrical power distribution and on satellites used for communications, navigation, and weather prediction. A so-called coronal mass ejection ten years ago, for example, caused a major power blackout in Quebec and temporarily disrupted some satellites.

That event happened during the last peak in the sun's 11-year cycle of activity. The next peak of activity, already starting to build up, is expected about a year from now.

Astronauts aboard a space shuttle or on a space station would be protected by Earth's magnetic field. But any astronauts who leave Earth's environs would be vulnerable to deadly radiation from such solar outbursts.

During the Apollo moon missions, ''we were lucky that nothing bad happened,'' said Withbroe, who is NASA's science director for sun-Earth connections. ''If we go to Mars, we'll have to worry more than we do now.''

With enough warning, astronauts heading to Mars could simply ride out the storm by huddling together in a small ''storm cellar,'' a heavily shielded compartment inside the spacecraft. But without such warning, Withbroe said, the radiation from such solar outbursts ''can be extremely hazardous - can be deadly, in fact.''

Aside from the practical results of the new finding in terms of enabling better forecasts, it should also help scientists to better understand how the sun itself works. Many features that can be seen on the sun's surface, said Richard Canfield, a physicist at Montana State University, ''are related to events going on deep inside.''

The S-shaped structures seen on the sun's surface are probably magnetic field lines emanating from the ''solar dynamo'' at its center, a swirling mass that theorists believe produces the sun's intense magnetic field. The S shapes may be places where ''you twist the magnetic field up like you twist a rubber band, and it's ready to release,'' said Withbroe.

These distinctive shapes on the surface ''are important because they give us an indication of the twistedness of the magnetic field and its likeliness to erupt,'' said Sarah Gibson, a theorist at Cambridge University in England.

So far, calculations about the amount of energy built up and expelled by each of these outbursts closely match calculations based on ideas of the sun's structure, said David McKenzie of Montana State University. ''It's tending to confirm a very important, fundamental understanding about the sun,'' he said. ''It can be developed into a very powerful prediction tool.''

This story ran on page A08 of the Boston Globe on 03/10/99.
© Copyright 1999 Globe Newspaper Company.

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