Using real-time data from the MMS mission, which measures the interaction of Earth's magnetosphere with the solar wind, and the THEMIS/ARTEMIS mission, which studies the upstream plasma environment near the moon, the research team observed a large scale, time dependent (i.e. transient) phenomenon, upstream of Earth's bow shock, on December 17, 2017.
During this event, electrons in Earth's foreshock region—an area where the solar wind is predisturbed by its interaction with the bow shock—reached unprecedented energy levels, surpassing 500 keV.
This is a striking result given that electrons observed in the foreshock region are typically found at energies ~1 keV.
This research suggests that these high-energy electrons were generated by the complex interplay of multiple acceleration mechanisms, including the interaction of electrons with various plasma waves, transient structures in the foreshock, and Earth's bow shock.