Some 7,200 miles above Earth, an invisible shield cloaking our planet is helping to protect us from damaging, super-fast “killer” electrons, scientists have found. This Star Trek style shield stops these whizzing electrons in their tracks, preventing them from harming astronauts and frying our satellites.
As described in the journal Nature, this invisible barrier is located within the Van Allen radiation belts. These are two doughnut-shaped rings around our planet that extend up to 40,000 kilometers above Earth. The inner zone is full of high-energy protons, whereas the outer zone is dominated by high-energy electrons.
The protective shield was discovered after scientists from the University of Colorado Boulder analyzed almost two years of data gathered by the twin NASA spacecraft, the Van Allen Probes, which orbit the rings to observe the behavior of high-energy electrons in this area.
The data revealed a sharp boundary at the very inner edge of the outer belt that appeared to be deflecting incoming highly charged electrons, called ultrarelativistic electrons. These particles whizz around Earth at near light-speed, travelling at approximately 160,000 kilometers per second. It was assumed that these electrons would make a smooth transition, gradually drifting into the upper atmosphere before being destroyed by collisions with air molecules. However, much to their surprise, a sharp cutoff was observed instead.
“It’s almost like these electrons are running into a glass wall in space,” lead author Professor Daniel Baker said in a news-release. “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.”
To attempt to identify this enigmatic force field, the researchers examined several different scenarios that could generate and maintain a barrier of this kind. They considered that the Earth’s magnetic field lines could be somehow trapping the electrons in place, or that radio signals from human devices on Earth could be somehow dispersing the electrons. But with what they were seeing, neither of these explanations made sense.
Instead, they suggest that a cloud of cold, electrically charged gas known as the plasmasphere could be playing a role. This giant cloud starts just 600 miles above Earth but stretches thousands of miles into the outer, high-energy electron dominated zone of the Van Allen belt. They propose that low frequency electromagnetic waves within the cloud which produce a phenomenon known as “plasmaspheric hiss” could be scattering the electrons at the boundary.
However, the team doesn’t think that the story ends there, and expects to find more pieces to the puzzle in the future. “I think the key here is to keep observing the region in exquisite detail,” said Baker, “which we can do because of the powerful instruments on the Van Allen probes.”