Van Allen Probes Reveal How Radiation Belts Accelerate Super Speedy Particles

Two gigantic doughnuts of radiation surround our planet Earth. Yet what creates these circles, known as the Van Allen radiation belts, has long puzzled scientists. Now, though, the Van Allen Probes may shed some light on these radiation belts with some new data.

The inner Van Allen radiation belt remains relatively stable, but the outer one changes shape, size and composition over time. In fact, some of the particles within this belt zoom at almost the speed of light. Yet researchers are unsure exactly what accelerates these particles to such velocities. Data from the Van Allen Probes, though, suggest that there's a two-fold process involved: one mechanism gives the particles an initial boost and then a kind of electromagnetic wave, called Whistlers, does the final job to kick them up to high speed.

"It is important to understand how this process happens," said Forrest Mozer, first author of the new paper, in a news release. "Not only do we think a similar process happens on the sun and around other planets, but these fast particles can damage the electronics in spacecraft and affect astronauts in space."

The new Van Allen Probes data suggests that some mechanism speeds up particles already inhabiting the area of space around our Earth. In addition, the data reveals that once particles attain reasonably large energies of 100 keV, they are moving at speeds in synch with giant electromagnetic waves that can speed up the particles even more.

"This paper incorporates the Whistler waves theory previous embraced," said Shiri Kanekal, the deputy mission scientists for the Van Allen Probes. "But it provides a new explanation for how the particles get their initial push of energy."

The findings could help understand the belts a bit better, which could also allow scientists to develop strategies to protect nearby spacecraft.

The findings are published in the journal Physical Review Letters.