Earth's Van Allen radiation belts double as particle accelerator

The Earth's magnetic field traps high energy particles -- mostly from the sun -- in what are known as the Van Allen radiation belts, named for the astronomer who discovered them.

In 2012, NASA launched a pair of spacecraft, called the Van Allen Probes, to study the mechanics of the magnetosphere. The probes observed plasma waves and measured the speed and trajectory of a wide range of particles.

Data collected by the Van Allen Probes showed electrons in the radiation belts can achieve ultra-relativistic energies -- or reach high speeds. Because the electrons move so fast, their energy of motion is greater than their energy of rest, causing the flow of time to significantly slows down for these particles.

Previously, scientists estimated that only two mechanisms could explain such tremendous speeds: the acceleration particles moving from the outer to the inner regions of the magnetosphere or local acceleration via plasma waves.

The new analysis, conducted by researchers in Germany, suggests electrons are accelerated locally, in the heart of the Van Allen radiation belts.

"Here, we present a unique way of analyzing satellite observations which demonstrates that local acceleration is capable of heating electrons," researchers wrote.

The research suggests electrons derive their tremendous energies from plasma waves in the magnetosphere. Plasma waves in the radiation belts work like extremely efficient particle accelerators.

By studying particle acceleration closer to Earth, scientists hope to improve their understanding of particle acceleration phenomena in more distant environs -- like in the sun's atmosphere.