The Van Allen radiation belts are two regions of space located about 20,000 kilometers above the Earth and filled with energetic particles coming from solar winds. The high energies of these particles, trapped by Earth's magnetic field, can reach millions of electron volts, and can represent a hazard to satellites and humans in space. Now, an international team of scientists has explained the activity of the two Van Allen radiation belts and this will help protect astronauts and spacecrafts. By studying the solar storms of 2003 which disrupted GPS and communications satellites, they found that the old theory, which stated that the electrons within the belts were accelerated by radial diffusion, was wrong. Instead, they discovered that very low frequency radio waves caused the particle acceleration and intensified the belts. With this new information, it will be possible to take measures to protect astronauts, according to the researchers.
"For a long time scientists have been trying to explain why the number of charged particles inside the belts vary so much. Our major breakthrough came when we observed two rare space storms that occurred almost back-to-back in October and November 2003. During the storms part of the Van Allen radiation belt was drained of electrons and then reformed much closer to the Earth in a region usually thought to be relatively safe for satellites," said Dr Richard Horne of the British Antarctic Survey (BAS)
You can see below the evolution of the waves of electrons on October 31, 2003, as observed by one of the four Cluster spacecraft (Samba) (Credit: British Antarctic Survey).
The wave electric field Ey, transverse to the ambient magnetic field is shown in (a), and the wave magnetic field By in (b). The colour bars on the right give the calibrated wave powerspectral density for the wave electric field (a), and relative wave power spectral density (in dB) for the wave magnetic field (b).
And here are more details given by Dr Richard Horne.
When the radiation belts reformed they did not increase according to a long-held theory of particle acceleration. Instead, by using scientific instruments in Antarctica and on the CLUSTER mission satellites, we showed that very low frequency radio waves caused the particle acceleration and intensified the belts.
This new information will help spacecraft operators and space weather forecasters who must predict when satellites and missions are most at risk from radiation events allowing them to take measures to protect instruments and systems from damage, and astronauts from risks to their health.
This research work has been published by Nature in its September 8, 2005 issue under the name "Wave acceleration of electrons in the Van Allen radiation belts" (Volume 437, Number 7056, Pages 227-230). Here are two links to the editor's summary and to the first paragraph of the paper.
As a final note, I understand that these scientists have found the mechanism behind these big waves of energy. But I don't really see why it will help to protect astronauts and spacecrafts. Any clues?
Sources: British Antarctic Survey news release, via EurekAlert!, September 7, 2005; and various web sites
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