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Van Allen surprise: fewer nasty particles than NASA expected

Spacecraft might need lighter rad-shields, which means more payload!

By Richard Chirgwin, 16 Mar 2017

Video After a three-year search, NASA's Van Allen Probes have worked out there's far fewer high-energy electrons in the Van Allen Belts than previously thought.

That's good news, because electrons moving at relativistic speeds are a danger to navigation, as NASA explains in a paper that's just landed in the Journal of Geophysical Research (abstract here).

The Van Allen Belts are a pair of toroidal radiation regions (inner and outer) that surround the Earth and are influenced by solar activity that stirs up a complex local space weather system.

Scientists have long known the belts contain a lot of energy, but what's been of concern to space scientists is that nobody quite knows the proportion of the electronics-zapping relativistic electrons among the soup of charged particles.

The Van Allen Probes, launched in 2012, carry Magnetic Electron and Ion Spectrometer (MagEIS) instruments that can distinguish between protons and electrons in the belt. MagEIS uses its own magnetic field to sort particles by charge and energy, and that's what's yielded the new results.

“We’ve known for a long time that there are these really energetic protons in there, which can contaminate the measurements, but we’ve never had a good way to remove them from the measurements until now,” explains Seth Claudepierre, lead author and Van Allen Probes scientist at the Aerospace Corporation in El Segundo, California.

The outer belt, naturally enough, takes the big hits in a solar storm, while the inner belt was assumed to be more stable. Not so: measurements gathered during major solar storms in 2015 let probes gather observations of high-energy electrons getting pushed into the inner belt, as visualised in this video:

Youtube Video

Knowing that high-energy electrons are rare in the inner belt, NASA says spacecraft designers could get the chance to trim back on the protections they've always assumed were needed in the Van Allen Belt.

The scientists will also take more measurements of the belts to get a better idea of when electrons penetrate the inner region, and to see if more intense geomagnetic storms push more intense or energetic electrons into the inner belt. ®

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