Source of "Killer Electrons" in Space Discovered, Study Says

Brian Handwerk
for National Geographic News
July 17, 2007
Scientists have discovered the force that creates "killer electrons," particles that pose a significant hazard to spacecraft and astronauts.

The supercharged particles are also a menace to satellites, which are increasingly vital to phones, television, and other communication systems.

Killer electrons are found in the outermost of Earth's doughnut-shaped radiation belts. The belts circle the Earth and are bound by the planet's magnetic fields.

Scientists have long pondered where the killer particles come from and how they accumulate in the radiation belts.

Some theories suggest that they originate in the sun, which produces similar particles, or are the remnants of cosmic rays from outside our solar system.

(See an interactive map of the solar system.)

But a team at New Mexico's Los Alamos National Laboratory may have solved the mystery, and their findings suggest the particles actually form much closer to home.

Using satellite detectors to probe the outer radiation belt, the team found that killer electrons occur extremely unevenly.

Such localized peaks in intensity, the researcher say, could only be caused by electromagnetic waves accelerating electrons to "killer" status within the radiation belt.

"I think we show conclusively they do not come from further out [in space]. They are accelerated in the radiation belt itself," said Reiner Friedel, co-author of a paper published in the July issue of the journal Nature Physics.

Coming Soon: Better Space Weather Forecasts?

The discovery may aid scientists in ongoing efforts to protect satellites and astronauts from the particles' damaging effects.

Killer electrons travel at near light speed, and each may be charged with a thousand times more energy than the average dental x-ray, scientists say.

"[The particles] pose a danger to humans because of cumulative radiation exposure and also by damaging the spacecraft on which they are dependent," said Mike Xapsos, a researcher at NASA's Goddard Space Flight Center unaffiliated with the new research.

When killer electrons collect in large numbers, they can penetrate a spacecraft and build up a significant electrical charge.

The charge is released as a type of electric bolt that can devastate sensitive equipment.

"One common effect is that they cause solar arrays to degrade, and those often supply power to spacecraft," Xapsos said.

Study co-author Friedel explained that magnetic storms and other "space weather" can dramatically impact killer electron levels.

(Read related story: "Space Weather Could Scrub Manned Mars Mission" [August 9, 2005].)

"In the outer radiation belts, things are very dynamic," he said.

"Particles can get lost, wiped out completely in a very fast time range, and they can become reaccelerated to levels far exceeding the average level—three orders of magnitude up—in just a couple of days."

"The main reason we're trying to come up with models of the radiation belt [is to] predict when these events are going to happen."

NASA's Xapsos said that understanding space weather remains difficult but our knowledge is increasing.

"We cannot control this kind of space weather any more than we can control the Earth's weather," he said.

"However, having a better understanding of the process helps us make more accurate predictions of when spacecraft can expect trouble and how to deal with it."

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