“This invisible shield” protects against a radiation belt


This image shows a colour-coded representation of ultra-relativistic electron fluxes

High above Earth’s atmosphere, electrons whiz past at close to the speed of light. Such ultrarelativistic electrons, which make up the outer band of the Van Allen radiation belt, can streak around the planet in a mere five minutes, bombarding anything in their path. Exposure to such high-energy radiation can wreak havoc on satellite electronics, and pose serious health risks to astronauts.

Now researchers at MIT, the University of Colorado, and elsewhere have found there’s a hard limit to how close ultrarelativistic electrons can get to the Earth. The team found that no matter where these electrons are circling around the planet’s equator, they can get no further than about 11,000 kilometres (6,800 miles) from the Earth’s surface – despite their intense energy.

What’s keeping this high-energy radiation at bay seems to be neither the Earth’s magnetic field nor long-range radio waves, but rather a phenomenon termed “plasmaspheric hiss” – very low-frequency electromagnetic waves in the Earth’s upper atmosphere that, when played through a speaker, resemble static, or white noise…

The team’s results are based on data collected by NASA’s Van Allen probes – twin crafts that are orbiting within the harsh environments of the Van Allen radiation belts. Each probe is designed to withstand constant radiation bombardment in order to measure the behaviour of high-energy electrons in space…

Instead, the group found that the natural barrier may be due to a balance between the electrons’ slow, earthward motion, and plasmaspheric hiss. This conclusion was based on the Van Allen probes’ measurement of electrons’ pitch angle – the degree to which an electron’s motion is parallel or perpendicular to the Earth’s magnetic field. The researchers found that plasmaspheric hiss acts slowly to rotate electrons’ paths, causing them to fall, parallel to a magnetic field line, into Earth’s upper atmosphere, where they are likely to collide with neutral atoms and disappear.

Useful for anyone up for near-Earth space research. One of the crappiest military/political notes in the research is a discussion of nuclear warheads that US military detonated in space to play with using artificially-created radiation belts to blind other nation’s satellites.

I guess we’re lucky once again to have survived War Department experiments which had a potential failure forecast which might have turned us all into mutants glowing in the dark.

Thanks, Mike

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