Upward, MeV‐Class Electron Beams Over Jupiter's Main Aurora.

Jupiter's poleward (Zone II) main aurora exhibits bi‐directional electron acceleration; upward acceleration dominates but downward acceleration generates strong aurora. During Juno's first perijove (PJ1), the upward acceleration manifested as narrow electron angular beams (within ∼5° of the magnetic field) over the 30–1,200 keV energy range of Juno's Jupiter Energetic Particle Detector Investigation (JEDI). These beams can be simply connected (non‐uniquely) to >10 to perhaps 100's of MeV electrons that penetrated the radiation shielding of the camera head of the Magnetometer Investigation's Advanced Stellar Compass (ASC). The most intense of those multiple MeV populations are shown to have been highly directional and propagating upwards. How auroral processes generate such beams is unknown. With azimuthal symmetry assumed (not demonstrated here), these beams provided >1026 s−1 of >30 keV electrons to Jupiter's vast magnetosphere, a possibly critical and dominating source of energetic electrons to that region and ultimately to Jupiter's radiation belts. Plain Language Summary: Aurora at Earth and Jupiter are generated by electron acceleration processes occurring at relatively low altitude above the polar atmospheric regions emitting the auroral lights. While downward electron acceleration causes the auroral emissions, upward electron acceleration can occur in a fashion that populates the distant planetary space environments (or "magnetospheres"). We find with NASA's Juno spacecraft that upward auroral electron acceleration at Jupiter has unique features. It is often more energetic and powerful than is the downward acceleration. The resulting electron beams are unexpectedly collimated along the magnetic field lines connecting the auroral regions to the spacecraft. The beams can extend in energy to unexpectedly high values, greater than 20 million electron volts (MeV). Finally, the quantity of energetic electrons coming from Jupiter's auroral regions is possibly a major, if not dominate, source of energetic electrons for Jupiter's vast magnetosphere. Key Points: Intense, narrow (±∼5°), 30–1200 keV, upward electron beams were observed over Zone II of Jupiter's main aurora during Juno perijove‐1They can be connected simply (non‐uniquely) to previously reported >10–100 s of MeV electron populations observed over the same regionAssuming symmetry, they provided >1026/s of >30 keV electrons to Jupiter's vast magnetosphere, a possibly critical and dominant source [ABSTRACT FROM AUTHOR]