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Predicting solar eruptions.

If astronauts had been on the Moon in early August 1972, they would have been at best terribly queasy, and at worst--dead. A burst of charged particles that was released from the Sun would have caused severe radiation sickness, dosing the unlucky moonwalkers with about 400 rem--about 50,000 times the radiation dose you get from a chest X-ray. Fortunately the burst, known as a coronal mass ejection (CME), erupted in-between Apollos 16 and 17, so no astronauts were harmed.

But as NASA looks to send astronauts back to the Moon and on to Mars, the health hazards posed by solar explosions are a serious concern. CMEs hurl billions of tons of charged particles into space at hundreds of kilometers per second (millions of miles per hour). Thanks to Earth's magnetosphere and atmosphere, these extremely energetic clouds pose little danger to us. But astronauts outside Earth's protective envelopes would have to shield themselves from the radiation, a problem complicated by the fact that no one knows when CMEs will erupt.

Now a team led by Zoran Mikic (Science Applications International Corporation, San Diego) has developed a model that can accurately predict the behavior of the corona, the Sun's hot outer atmosphere. At a recent solar-physics meeting, Mikic and his colleagues reported that their model had accurately predicted the structure of the corona during the March 29th solar eclipse. And though the model still cannot predict CMEs, researchers think that predicting the corona's structure is the first step.

"It's a real breakthrough," says space-weather researcher Janet Luhmann (University of California, Berkeley). "I do not know of another coronal model with this level of realism. From now on, the corona can routinely be described more accurately, which is just what we need to go to the next step of modeling CMEs."

Researchers have been trying to simulate the corona for decades, but none have been able to take into account how energy is transferred within it. The new model, tested on two supercomputers, allows researchers to map pressure and density changes and to predict the corona's large-scale magnetic structure. Such maps are key to predicting how magnetic-field lines will behave and when potentially dangerous CMEs will erupt.

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Title Annotation:news notes; Zoran Mikic develops a model to predict space weather
Author:Cull, Selby
Publication:Sky & Telescope
Geographic Code:1USA
Date:Oct 1, 2006
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