A slot region in the magnetosphere of Jupiter.

Abstract

Understanding the balance between charged particle acceleration and loss is central to radiation belt research. Jupiter's Galilean moons orbit within its intense radiation environment and can act both as sources and sinks of energetic particles. Using observations from the Juno spacecraft, we identify large-scale depletions of energetic electrons along Europa's orbit. These depletions are too deep to result from direct absorption by the moon alone. Here we show that rapid electron losses, occurring within a timescale shorter than Jupiter's rotation, are driven by pitch angle scattering via whistler-mode waves co-located with Europa's orbit. This suggests that Europa maintains a plasma environment capable of sustaining a slot-like region, similar to the one seen in Earth's Van Allen belts. However, this Jovian slot only partially extends along Europa's path, implying that additional, unidentified acceleration mechanisms may act to refill the region and maintain high radiation levels close to Jupiter.