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Solar Blast Reveals Clues About Threats to and Effects on Planets

Posted on: Saturday, 17 July 2004, 06:00 CDT

Some of the most powerful solar storms ever recorded stripped away part of Mars' atmosphere last fall as they combined into a blast wave now rolling toward the edge of the solar system.

A fleet of spacecraft deployed from Earth to far beyond Pluto are giving scientists the best understanding yet of how such blasts and the radiation in their wake buffet planets, disrupt communications and endanger astronauts. The solar weather report also may shed light on how Mars lost its water and how the solar system will temporarily expand.

The storms occurred over a two-week period around Oct. 31. About 17 eruptions on the face of the sun ejected billions of tons of electrified gas into space, merging into a blast wave that raced toward Earth at 5 million mph.

"All of these explosions combine and form an amazing blast wave that spreads throughout the entire solar system," Eric Christian of NASA's solar-physics division said at a NASA news conference last week.

Now slowed to about 1.5 million mph, the blast wave is approaching the boundary between the solar system and interstellar space.

On Earth, which escaped the brunt of the wave, the solar storms were watched closely by NASA, pilots whose planes were rerouted and astronauts aboard the International Space Station, who took shelter from the storms' high radiation. Some long-distance radio communications were disrupted, some areas suffered power outages, and orbiting spacecraft were put into "safe" mode.

But mostly, the Earth's magnetosphere did its job in safeguarding against the bombardment of high-energy particles. The magnetosphere peeled away from the poles just enough to allow Floridians to see auroras typical of northern climes.

Things got even more interesting just a couple of days later, when the blast wave hit Mars, which has no global magnetic field to deflect it.

As the blast pummeled the orbiting Mars Odyssey and disabled the onboard radiation recorder, it ripped away part of the planet's thin upper atmosphere. The action, repeated over the planet's 3.5- billion-year history, may account for the water lost on Mars, one scientist said.

Mars once had plenty of water, based on evidence from rovers and orbiters, noted Thomas Zurbuchen of the University of Michigan, a scientist who participated in some of the missions for spacecraft that tracked the solar storms.

As the blast wave rolled on, other spacecraft, including Cassini and Ulysses, recorded days of disrupted magnetic fields around Jupiter, Saturn and Neptune, the scientists said.

This spring, the twin Voyager spacecraft, the most distant human- made objects, spotted the wave, which is now 9 million miles from the sun.

In about 10 months, the blast wave will reach the boundary between the solar system and interstellar space. The blast will bulge the boundary outward by about 400 million miles, creating a radio signal that NASA hopes to hear relayed by Voyager.

The bulge will rebound to nearly its current position in about a year or two, said Ed Stone, physicist with NASA's Jet Propulsion Laboratory.

The extensive effects such solar storms can have on space weather demonstrates the need to learn how to predict them to better protect the Earth, the scientists said.

"Space-weather forecasting is still in development but is needed to better protect our space infrastructure and future human and robotic explorers," said former astronaut Carl Walz of NASA's Project Prometheus.

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