Properties of Ion-Inertial Scale Plasmoids Observed by the Juno
Spacecraft in the Jovian Magnetotail
Abstract
We expand on previous observations of magnetic reconnection in Jupiter’s
magnetosphere by constructing a survey of ion-inertial scale plasmoids
in the Jovian magnetotail. We developed an automated detection algorithm
to identify reversals in the component and performed the minimum
variance analysis for each identified plasmoid to characterize its
helical structure. The magnetic field observations were complemented by
data collected by the Juno Waves instrument, which is used to estimate
the total electron density, and the JEDI energetic particle detectors.
We identified 87 plasmoids with ‘peak-to-peak’ durations between 10 s
and 300 s. 31 plasmoids possessed a core field and were classified as
flux-ropes. The other 56 plasmoids had minimum field strength at their
centers and were termed O-lines. Out of the 87 plasmoids, 58 had in situ
signatures shorter than 60 s, despite the algorithm’s upper limit to be
300 s, suggesting that smaller plasmoids with shorter durations were
more likely to be detected by Juno. We estimate the diameter of these
plasmoids assuming a circular cross-section and a travel speed equal to
the Alfven speed in the surrounding lobes. Using the electron density
inferred by Waves, we contend that these plasmoid diameters were within
an order of the local ion-inertial length. Our results demonstrate that
magnetic reconnection in the Jovian magnetotail occurs at ion scales
like in other space environments. We show that ion-scale plasmoids would
need to be released every 0.1 s or less to match the canonical 1 ton/s
rate of plasma production due to Io.