Juno Observations of Ion‐Inertial Scale Flux Ropes in the Jovian Magnetotail.

Two ion‐inertial scale magnetic flux ropes are identified in the Juno magnetic field measurements in the dawnside Jovian magnetotail. Previously reported plasmoids in this region had typical diameters of several Jovian radii (RJ). However, events reported here are only ∼0.15–0.19 RJ in diameter, assuming that they move at the local Alfven speed. Using the plasma density determined by the Juno Waves instrument, the diameters are calculated to be on the order of the local ion inertial length (∼0.6–1.6 di). Multiple reversals in the north‐south component are observed ∼30 min before one of these events, which suggests that plasmoid ejection in the dawnside magnetotail may proceed via multiple X‐line reconnection in a highly thinned cross‐tail current sheet in a manner similar to that observed at Mercury and Earth. Further studies will be required to determine the contribution of these small flux ropes to mass loss through plasmoid ejection. Plain Language Summary: Magnetized planets such as Earth, Mercury, and Jupiter interact with the solar wind and create magnetospheres. Within these magnetospheres, magnetic reconnection periodically reconfigures the magnetic field and in the process releases mass and energy. Frequently observed as part of magnetic reconnection are loop‐like or helical magnetic structures called magnetic flux ropes. At Earth and Mercury, these vary in diameter from hundreds to thousands of km. At Jupiter, however, magnetic reconnection operates differently than Earth or Mercury, primarily because of the Galilean moons which add significant plasma to the magnetosphere. Previously reported magnetic flux ropes at Jupiter were much larger when compared to their terrestrial counterparts. Using data from the Juno spacecraft, which has the capability to detect small structures, we found magnetic flux ropes which were much smaller than those previously observed. The presence of small‐scale flux ropes in Jupiter's magnetosphere could have far‐reaching implications for its magnetospheric dynamics, specifically on how mass is lost from the magnetosphere. Key Points: Magnetic structures on the ion inertial scales are identified in Juno's high temporal resolution data measured in Jupiter's magnetotailThese structures are shown to be quasi‐force‐free flux ropes using minimum variance analysis and force‐free model fittingMultiple reversals in the north‐south component are observed during a 30‐min interval, possibly due to sequential plasmoid release [ABSTRACT FROM AUTHOR]