As the Sun's churning surface lets loose a belch of white-hot flame, it sends out a storm of radiation that washes over the solar system. Luckily for us, Earth's magnetic field shields us from most of these deadly rays. But overhead, something strange and lethal is happening when the solar wind bombards the Earth. A band of radioactive particles circling the planet, called the outer Van Allen belt, starts to charge up like a rail gun. It whips electrons along on its circular racetrack at a breakneck pace—near light speed. The powerful band ebbs and flows with solar radiation, but until today, nobody could be sure how it was creating such swift and energetic particles.
"This is like watching a natural particle accelerator in space," says Geoffrey Reeves, a magnetic field researcher at Los Alamos National Laboratory.
Reeves and a team of scientists published research today in the journal Science describing the bizarre way the outer Van Allen belt—which orbits around the Earth like a giant doughnut—accelerates electrons to more than 99.9 percent of the speed of light. Discounting light itself, Reeves says, "these electrons are the fastest things the Earth creates naturally." And they aren't simply a high-velocity curiosity: They pose a threat to the International Space Station and to commercial satellites. The particles can burst through the protective shielding—causing temporary computer failures—and cause degradation to vital onboard equipment such as solar panels.