E-Mail IMAGE: The contours in color show the intensities of the radiation belts. Grey lines show the trajectories of the relativistic electrons in the radiation belts. Concentric circular lines show the trajectory... view more Credit: Ingo Michaelis and Yuri Shprits, GFZ New study found that electrons can reach ultra-relativistic energies for very special conditions in the magnetosphere when space is devoid of plasma. Recent measurements from NASA's Van Allen Probes spacecraft showed that electrons can reach ultra-relativistic energies flying at almost the speed of light. Hayley Allison, Yuri Shprits and collaborators from the German Research Centre for Geosciences have revealed under which conditions such strong accelerations occur. They had already demonstrated in 2020 that during solar storm plasma waves play a crucial role for that. However, it was previously unclear why such high electron energies are not achieved in all solar storms. In the journal