What is a Van Allen Radiation Belt?

Giant donut-shaped swaths of magnetically trapped, highly energetic charged particles surround Earth. James Van Allen, a physicist at the University of Iowa, discovered these radiation belts in 1958 after the launch of Explorer 1, the first U.S. satellite. The radiation belts were eventually named after him.

Van Allen's experiment on Explorer 1, which launched Jan. 31, 1958, had a simple cosmic ray experiment consisting of a Geiger counter (a device that detects radiation) and a tape recorder. Follow-up experiments on three other missions in 1958 — Explorer 3, Explorer 4 and Pioneer 3 — established that there were two belts of radiation circling the Earth.

While observations have continued for decades, our knowledge of the belts became more enhanced when the Van Allen Probes launched in 2012. They found that the belts were more complex than previously imagined. The probes showed that the shape of the belts depends on what particle is being studied. They also uncovered information hinting there is less radiation than imagined in certain parts of the Van Allen belts, which means spacecraft and humans would not need as much radiation protection if they are voyaging in that region.

On the 60th anniversary of Explorer 1, NASA said that studies of the Van Allen belts are even more important today. "Our current technology is ever more susceptible to these accelerated particles because even a single hit from a particle can upset our ever smaller instruments and electronics," said David Sibeck, Van Allen Probes mission scientist at NASA's Goddard Space Flight Center in Maryland, in a 2018 statement. "As technology advances, it's actually becoming even more pressing to understand and predict our space environment."

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