The Earth is protected from fast-moving “killer electrons” by an invisible plasma shield, which is located thousands of miles above the planet’s surface, according to researchers at the Massachusetts Institute of Technology (MIT) and the University of Colorado Boulder.

High above the Earth’s atmosphere, harmful electrons that make up the outer band of the Van Allen radiation belt travel at nearly the speed of light, pelting everything in their path. Exposure to such high-energy radiation can harm satellite electronics and pose serious health risks to astronauts. However, despite their intense energy, these electrons -- circling around the planet’s equator -- cannot come below 7,200 miles from the Earth’s surface due to the shield, scientists said in a study, published in the journal Nature on Thursday.

“It’s almost like theses electrons are running into a glass wall in space,” Daniel Baker of the University of Colorado Boulder and the study’s lead author said, in a statement. “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 invisible shield, dubbed the “plasmaspheric hiss,” is made up of very low-frequency electromagnetic waves in the Earth’s upper atmosphere. Scientific data and calculations have helped researchers deduce that the hiss deflects incoming electrons, causing them to smash into neutral gas atoms in the Earth’s upper atmosphere, and ultimately disappear.

“It’s a very unusual, extraordinary, and pronounced phenomenon,” John Foster, associate director of MIT’s Haystack Observatory, said in a statement. “What this tells us is if you parked a satellite or an orbiting space station with humans just inside this impenetrable barrier, you would expect them to have much longer lifetimes. That’s a good thing to know.”

The latest study is based on data collected by NASA’s Van Allen Probes that are orbiting within the harsh environments of the Van Allen radiation belt. During the study, the researchers observed an “exceedingly sharp” barrier against harmful electrons, which was steady enough to withstand a solar wind shock in October 2013. To determine what could create and maintain such a barrier, the researchers considered a few possibilities, including effects from the Earth’s magnetic field and radio signals from human transmitters on Earth.

“It’s like looking at the phenomenon with new eyes, with a new set of instrumentation, which give us the detail to say, ‘Yes, there is this hard, fast boundary,’” Foster said.