Space scientists have made a startling discovery regarding the two concentric rings of high-speed particles that encircle the Earth after they were discovered 55 years ago.

According to new data collected by NASA's twin Van Allen space probes, electrons within belts of radiation that circle Earth are excited by electromagnetic waves around the planet. The Van Allen belts, as the rings are known, are responsible for accelerating the particles, rather than collecting energetic particles that originated elsewhere. 

 In the future, this new information could help scientists learn how to better protect satellites and prevent them from sustaining damage from errant charged particles. Space scientists think that their latest findings could also account for the even more energetic belts circling Saturn and Jupiter, as well as high-energy radiation associated with worlds beyond the Solar System and even some Sun-like stars.

In a paper published in the July 25 issue of the online journal Science Express, researchers say they examined two possibilities: first, the long-accepted theory that the electrons get their energy as they make their way into the belts from outside them, or that they are accelerated inside the belts. Using measurements from NASA's twin Van Allen Probes mission satellites, the researchers determined that the electrons can also gain their energy inside the belts.

"Energetic electrons in the Van Allen radiation belts have been implicated in past satellite failures and so they are often referred to as 'killer electrons'," says UNH astrophysicist Harlan Spence, co-author on theScience paper and principal investigator on the Energetic Particle, Composition, and Thermal Plasma (ECT) instrument suite on board the twin Van Allen Probe spacecraft that made the precision particle measurements.

"A 50-year mystery of the radiation belts is, where, when and how these electrons are energized. With the Van Allen Probes, we have gone to the very scene of the crime, so to speak, and witnessed the unique, unambiguous fingerprints of a local acceleration process for the first time, revealing the culprit acting to create killer electrons," Spence said.

The researchers are now trying to understand exactly how the acceleration took place. Right now, the team believes that electromagnetic radio waves somehow excite the electrons into a higher-energy state, much like a microwave oven excites and heats water molecules.