Scientists Solve Mystery in Earth's Upper Atmosphere: Origin of Ultra-Relativistic Electrons

A mystery has plagued researchers for decades when it comes to Earth's upper atmosphere. Now, that mystery may finally be solved. Scientists have discovered the origin of the extremely energetic particles known as ultra-relativistic electrons in Earth's near-space environment. The findings are likely to influence our understanding of planetary magnetospheres throughout the universe.

Ultra-relativistic electrons in Earth's outer radiation belt can exhibit pronounced variability in response to activity on the sun and changes in the solar wind. That said, 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 order to figure out exactly what was happening, the researchers used high-resolution satellite measurements of high-energy electrons during a geomagnetic storm. They numerically modeled this data using a newly developed data-driven global wave model. In the end, their analysis revealed that scattering by intense, natural very low-frequency radio waves known as "chorus" in Earth's upper atmosphere is primarily responsible for the observed relativistic electron build-up. This detailed modeling in particular shows the remarkable efficiency of natural wave acceleration in Earth's near-space environment and shows radial diffusion was not responsible for the observed acceleration during the storm.

The local wave-acceleration process is actually a "universal" physical process. It should be effective in the magnetospheres of Jupiter, Saturn and other magnetized plasma environments. The results from this particular study could influence future modeling of other planetary magnetospheres.

The findings are also important for practical applications. Because the enormous amounts of radiation trapped within the belts can pose a significant hazard to satellites and spacecraft, as well as astronauts performing activities outside a craft, it's crucial to better understand the mechanisms behind these ultra-relativistic electrons.

The findings are published in the journal Nature.