Schematic illustration of local electron acceleration by chorus The top panel shows electron fluxes before (left) and after (right) a geomagnetic storm. The injection of low-energy plasma sheet electrons into the inner magnetosphere (1) causes chorus wave excitation in the low-density region outside the cold plasmasphere (2). Local energy diffusion associated with wave scattering leads to the development of strongly enhanced phase space density just outside the plasmapause (3). Subsequently, radial diffusion can redistribute the accelerated electrons inwards or outwards from the developing peak (4). Credit: Jacob Bortnik/UCLA

New research using data from NASA’s Van Allen Probes mission helps resolve decades of scientific uncertainty over the origin of ultra-relativistic electrons in the Earth’s near space environment, and is likely to influence our understanding of planetary magnetospheres throughout the universe. See: Scientists solve a decades-old mystery of Earth’s Van Allen radiation belts