A cloud of charged particles, known as a plasmasphere, surrounds the Earth, shown here in purple. Image Credit: NASA/Goddard, Andy Kale, University of Alberta
The Earth is surrounded by a near impenetrable barrier, protecting us from ‘killer electrons’.
NASA’s Van Allen Probes have found a sharp barrier at an altitude of over 11,000km that deflects the particles.
These fast, energetic particles could potentially fry satellites, harm astronauts and degrade space systems if they weren’t deflected.
The Van Allen belts are regions of charged particles surrounding the Earth, pinned in place by the planet’s magnetic field.
The region extends from 1,000 to 60,000km above the planet’s surface, though this can fluctuate if the solar wind changes.
Radiation is so intense in the region that it can cause problems for satellites as they pass through.
Researchers using the NASA probes found that there is a sharp barrier on the inner edge of the belt that prevents high-energy electrons from getting through.
Previously it was thought that these electrons were absorbed by the Earth’s atmosphere, but now it appears to be this field that protects us.
"It's almost like theses electrons are running into a glass wall in space," said Dan Baker, the study's lead author from University of Colorado Boulder.
"Somewhat like the shields created by force fields on Star Trek that were used to repel alien weapons, we are seeing an invisible shield blocking these electrons.
It's an extremely puzzling phenomenon."
The team of researchers are still unsure what could be causing the barrier.
Both the Earth’s magnetic field and man-made radio transmissions interacting with the charged electrons have been considered, but ultimately discounted.
One potential candidate is a plasmapheric ‘hiss’ that may be deflecting the particles.
"Nature abhors strong gradients and generally finds ways to smooth them out, so we would expect some of the relativistic electrons to move inward and some outward," said Baker.
"It's not obvious how the slow, gradual processes that should be involved in motion of these particles can conspire to create such a sharp, persistent boundary at this location in space."