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Radio Pollution Creates Space Shield for Satellites

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Human-caused space pollution can range from a hammer that floats away from a space station, to a nuclear weapons test in the atmosphere, and could damage nearby spacecraft. But one unexpected source of “pollution” helps many satellites. The special pollution protects spacecraft from “killer electrons,” in a region above the earth called the Van Allen belts. From Boulder, Colorado, Shelley Schlender reports.

People are big polluters, on the land, in the sea and even in outer space, that can include anything from a hammer that floats away from the space station, to radiation from a nuclear weapons test in the atmosphere.

"This can range from little chips of paint all the way up to spent rocket bodies and things like that," said Dan Baker, director of the Laboratory of Atmosphere and Space Physics at the University of Colorado, Boulder. "We’ve been trying to figure out how can we most effectively eliminate this debris without causing more of a problem."

NASA tracks more than 500,000 pieces of space debris as they orbit the Earth, each represented here by a dot.
NASA tracks more than 500,000 pieces of space debris as they orbit the Earth, each represented here by a dot.

Space debris travels so fast, even an orbiting chip of paint can poke a hole in a satellite. But Baker says something tinier, and natural, is a bigger hazard: It’s the highly charged "killer electrons" of the magnetized zone above the earth called The Van Allen Belts.

"We've observed them to cause very significant problems for spacecraft," Baker said.

Electro-magnetic planetary blanket

The doughnut-shaped Van Allen Belts around our planet protect life on earth from solar winds and cosmic rays. But their highly energetic charged particles can damage the circuitry in space stations, weather satellites and other machines that travel through that region of space.

Baker notes that "killer electrons" can also come from some human activities, like the atmospheric testing of nuclear weapons.

"Back in the 1950s and especially in the 1960s, there were nuclear explosions that put huge amounts of radiation into space that caused many satellites to 'die' because of radiation damage," he said. "And if that were to happen today, we know that there are over 1,400 satellites operating in space around the earth and all of those could be subject to very severe consequences."

Most nations adhere to treaties that prohibit atmospheric weapon testing. But Baker says that’s no guarantee.

"What is worrisome to us from a political standpoint today is that there are nations, for example, North Korea and others, that may be thinking once again, and who may not be adherent to such treaties, that this might be an interesting way to mess with modern technology," Baker said.

Mysterious space shield

Radiation particles in the Van Allen Belts already "mess" with modern technology. So when satellites must spend time in that region, they are built with thicker materials. That armor makes them heavier, and more expensive. Fortunately, spacecraft and satellites that orbit just under the Van Allen Belts don’t need this heavy shielding. Baker says that’s because, at the lower edge of the Van Allen Belts, the killer electrons abruptly stop.

He compares it to the shields that protected Captain Kirk's ship, the Enterprise, from phasers and asteroids on Star Trek.

VLF radio waves propagate into space, forming a shield that keeps killer electrons from leaving the Van Allen Belts.
VLF radio waves propagate into space, forming a shield that keeps killer electrons from leaving the Van Allen Belts.

Scientists have known for years that something here on the earth creates an invisible bubble that clears killer electrons from the lower edge of the Van Allen Belts. Just what makes that shield has been a mystery.

But recently, Baker’s teams figured out its source. The "bubble maker" is very low frequency radio transmissions, also known as VLF. Militaries use VLF to communicate with submarines underwater. It turns out those radio waves also travel up, through the atmosphere, to the Van Allen Belts.

"So the VLF bubble is made up of these intense waves. These waves act to sort of scatter and scrub the inner part of the Van Allen Belts," Baker said, admitting, "I would prefer that we not be messing with nature. However, in this particular case I would say that there is some evidence that this is beneficial."

John Bonnell, a researcher at the University of California Berkeley's Space Sciences Lab, agrees that VLF "pollution" is probably benign, and he points to the high-energy radiation emitted by lightning bolts as evidence.

"We’ve had natural clearing of the radiation Belts with lightning, for as long as we’ve had lightning. So in essence, you’ve had a long-running experiment that you can look at and say, 'Well, if we're going to do things on sort of a sporadic basis, whereas lightning's been doing it daily for hundreds of millions of years, the likelihood of there being a bad side effect is pretty minimal,'" he said.

Bonnell says that discovering a man-made way to clear killer electrons from the Van Allen Belt does not mean we will soon create "shields up" devices that use magnetics or radio transmissions. At least, he says, we’re not making them yet.

"It's a fascinating possibility and it's a fascinating technology that could enable us in the future, to explore more of the solar system with people, with robots. And so it's definitely something that people pick away at slowly over time," he said.

Bonnell says scientists, engineers and astronomers have teamed up to make amazing discoveries about how to study, and travel through, outer space. And while the future shape of space exploration is a mystery, our new understanding about the man-made "pollution" that shields satellites may be an important part of it.

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