Fro years, scientists have debated the origin of ultra-relativistic electrons, the extremely energetic particles in the Earth’s near-space environment. However, new research out of UCLA have finally resolved the controversy, and the findings are likely to influence our understanding of planetary magnetospheres throughout the universe as well.

One of the primary science objectives of the recently launched NASA Van Allen Probes mission is discovering the processes that control the formation and ultimate loss of these electrons in the Van Allen radiation belts. 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.

In research published Dec. 19 in Nature, lead author Richard Thorne, a distinguished professor of atmospheric and oceanic sciences in the UCLA College of Letters and Science, and his colleagues report on high-resolution satellite measurements of high-energy electrons during a geomagnetic storm on Oct. 9, 2012, which they have numerically modeled using a newly developed data-driven global wave model.

The team’s detailed modeling, together with previous observations of peaks in electron phase space density reported earlier this year by Geoff Reeves and colleagues in the journal Science, demonstrates the remarkable efficiency of natural wave acceleration in the Earth’s near-space environment and shows that radial diffusion was not responsible for the observed acceleration during this storm, Thorne said.

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. He thinks the new results from the detailed analysis of Earth will influence future modeling of other planetary magnetospheres.