Encircling Earth are two enormous rings — called the Van Allen radiation belts — of highly energized ions and electrons. Various processes can accelerate these particles to relativistic speeds, which endanger spacecraft unlucky enough to enter these giant bands of damaging radiation. Scientists had previously identified certain factors that might cause particles in the belts to become highly energized, but they had not known which cause dominates.
Now, with new research from NASA’s Van Allen Probes and Time History of Events and Macroscale Interactions during Substorms — THEMIS — missions, published in Geophysical Research Letters, the verdict is in. The main culprit is a process known as local acceleration, caused by electromagnetic waves called chorus waves. Named after their characteristic rising tones, reminiscent of chirping birds, chorus waves speed up the particles pushing them along like a steady hand repeatedly pushing a swing. This process wasn’t a widely accepted theory before the Van Allen Probes mission.
Establishing the main cause of the radiation belt enhancements provides key information for models that forecast space weather — and thus protect our technology in space.
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