National Geographic News
The Hubble Space Telescope above Earth.
A satellite such as the Hubble Space Telescope (pictured) could be disabled by a solar megastorm.

Photograph courtesy NASA

Ker Than

for National Geographic News

Published September 20, 2011

Earth-orbiting satellites are designed to withstand the sun's explosions—but they may not be strong enough to ride out a solar "megastorm," a new study says.

If hit by a powerful onslaught of solar energy and particles, Earth's atmosphere would be flooded with high-energy electrons accelerated to nearly the speed of light, according to a new computer model.

This would hinder operations of low-Earth orbiting, or LEO, satellites. The satellites wouldn't immediately start falling out of the sky following a megastorm, but they would malfunction much faster than previous models suggested.

"What we concluded based on our calculations is that a very strong storm would decrease the lifetime of a typical LEO satellite by a factor of ten," said study leader Yuri Shprits, a geophysicist at the University of California, Los Angeles.

Though the results are still preliminary, Shprits predicts that a majority of the LEO satellite fleet could be lost within a few years of such an event.

What's more, the effect could last for up to a decade, the model showed.

(See "Solar Flare Sparks Biggest Eruption Ever Seen on Sun.")

Magnetic Waves Would Give Electrons a Boost

Satellite problems, and even failures, have been reported during solar storms before, but the danger usually passes within a few days.

A megastorm would be different, because electrons and other particles ejected by the sun would get accelerated after penetrating Earth's inner Van Allen radiation belts. (See pictures of solar eruptions.)

The Van Allen belts are two doughnut-shaped rings of charged particles—one nestled inside the other—that encircle our planet.

According to the computer model, solar electrons that reach the inner belt would get a burst of speed through interactions with traveling magnetic waves.

The model simulated a solar storm stronger than the so-called Halloween solar superstorms of 2003 and investigated what effect the resulting flux of electrons would have on LEO satellites.

Such "chorus waves" form in a region of space that lies just above the plasmasphere, a section of Earth's protective magnetic bubble filled with plasma, or electrically charged gas.

Normally, such electron acceleration is difficult or impossible because the plasmasphere's high plasma density prevents the chorus waves from efficiently interacting with particles.

But during a megastorm, the plasmasphere becomes severely eroded, thinning to the point that chorus waves interact with and accelerate electrons.

After several years, the inner-belt electron density would return to normal, the model suggests. Until that happens, though, satellites traversing the inner belt would be in danger of having their innards zapped by stray, high-energy electrons.

"It's hard and expensive to shield from them," Shprits said. "They penetrate shielding and get deposited in semiconductors, where they can create electrical surges that damage electronics."

Weather, communications, and military satellites are the most likely to be affected, because many of them pass through the inner belt, he added.

(Related: "As Sun Storms Ramp Up, Electric Grid Braces for Impact.")

Megastorms as Rare in Snow in LA

A solar megastorm has never been observed during the space age, although a solar storm that was triggered by a megaflare on the sun in 1859 and famously known as the Carrington Event is thought to have been powerful enough to qualify.

(Read what would happen if the Carrington Event happened today.)

Many scientists think it's only a matter of time before another megastorm erupts. Shprits compared the odds of another megastorm happening with the likelihood of snow in southern California. "It's rare, but it does happen," said Shprits, whose study was published recently in the journal Space Weather.

Richard Behnke, a space scientist at the National Science Foundation, said the new study could help  both improve space-climate forecasts and design mitigation strategies for satellites.

"If a solar [megastorm] were to occur, there is no doubt in my mind that there will be an extensive impact on satellite lifetimes," said Behnke, who was not involved in the study.

Janet Green, a researcher at the Space Weather Prediction Center at the National Oceanic and Atmospheric Administration, called the new computer model a "very necessary first step" for planning and preparing for a solar megastorm.

The model shows "there is probably a threat to satellites during [megastorms]," Green said in an email. She cautioned, however, that the model is based on many assumptions and simplifications that will have to be tested further.

Study leader Shprits noted that NASA's Radiation Belt Storm Probe mission, scheduled to launch in 2013, will help scientists better understand how radiation belt particles are energized and dissipated.

For more on solar flares, sunspots, and solar wind, read "The Sun—Living With a Stormy Star," from National Geographic magazine >>

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