Van Allen probes resolve mystery in Earth`s upper atmosphere
Washington: Researchers have claimed to have resolved decades of scientific controversy over the origin of the extremely energetic particles known as ultra-relativistic electrons in the Earth`s near-space environment.
Discovering the processes that control the formation and ultimate loss of these electrons in the Van Allen radiation belts - the rings of highly charged particles that encircle the Earth at a range of about 1,000 to 50,000 kilometers above the planet`s surface - is a primary science objective of the recently launched NASA Van Allen Probes mission.
Understanding these mechanisms has important practical applications, because the enormous amounts of radiation trapped within the belts can pose a significant hazard to satellites and spacecraft, as well astronauts performing activities outside a craft.
Ultra-relativistic electrons in the Earth`s outer radiation belt can exhibit pronounced variability in response to activity on the sun and changes in the solar wind, but the dominant physical mechanism responsible for radiation-belt electron acceleration has remained unresolved for decades.
Two primary candidates for this acceleration have been "inward radial diffusive transport" and "local stochastic acceleration" by very low-frequency plasma waves.
Lead author Richard Thorne, a distinguished professor of atmospheric and oceanic sciences in the UCLA College of Letters and Science, and his team`s analysis reveals that scattering by intense, natural very low-frequency radio waves known as "chorus" in the Earth`s upper atmosphere is primarily responsible for the observed relativistic electron build-up.
The local wave-acceleration process is a "universal physical process" and should also be effective in the magnetospheres of Jupiter, Saturn and other magnetized plasma environments in the cosmos, Thorne said.
The new research has been published in the journal Nature.
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