Scientists detected an invisible shield roughly 7,200 miles above the Earth's surface that is protecting us from harmful, super-fast electrons flying close to the speed of light.
It may sound like Star Trek tech, but this mysterious protective barrier isn't science fiction. The findings, described in the journal Nature, could help scientists better understand the complex dynamics of the Van Allen radiation belts.
The Van Allen radiation belts, discovered in 1958, are two doughnut-shaped rings of energetic particles circling the Earth up to about 25,000 miles above the surface, and are held in place by the planet's magnetic fields. Scientists have found that there appears to be an inner zone full of high-energy protons and an outer zone full of high-energy electrons. These belts are thought to be fed by cosmic rays and the solar wind, and they can swell and shrink over time in response to changes in space weather.
The high-energy "killer electrons" in the belt can wreak havoc with the sensitive electronics of orbiting satellites and even potentially harm the health of astronauts in space. So how is it that these high-speed particles, traveling faster than 100,000 miles per second, don't regularly cause problems at the Earth's surface?
To find out why the particles don't seem to reach Earth, scientists studied the belt using NASA's twin Van Allen Probes. As it turns out, there seems to be a sharp cutoff of high-energy electrons around the 7,200-mile mark – almost as if the particles are hitting a glass wall, lead author Daniel Baker, director of the University of Colorado Boulder's Laboratory for Atmospheric and Space Physics, said in a statement.
"The presence of such a clear, persistent and seemingly impenetrable barrier to inward transport of ultrarelativistic electrons at this very specific location presents a substantial puzzle," the study authors wrote.
The sharp cutoff took the scientists by surprise – they had expected to see a more natural, smooth transition. Previous theories suggested that the magnetic fields might be holding the electrons in place, or that human-generated radio signals from the ground were somehow blocking the onslaught. But now, given what the scientists were seeing, those theories didn't make sense.
The researchers think it could have to do with electrically charged cold gas in a zone called the plasmasphere, which starts around 600 miles above the Earth and stretches thousands of miles into the outer, electron-dominated zone in the Van Allen belt. The low-level, hissing white noise generated by low frequency electromagnetic waves coming from the gas could be scattering the electrons at the gas' border, the scientists said.
The findings provide fresh insight into the complex workings of plasma physics – and could give engineers a better idea about where to safely park their orbiting satellites.