Acceleration of Ions in Jovian Plasmoids: Does Turbulence Play a Role?

Abstract

The dissipation processes which transform electromagnetic energy into kinetic particle energy in space plasmas are still not fully understood. Of particular interest is the distribution of the dissipated energy among different species of charged particles. The Jovian magnetosphere is a unique laboratory to study this question because outflowing ions from the moon Io create a high diversity in ion species. In this work, we use multispecies ion observations and magnetic field measurements by the Galileo spacecraft. We limit our study to observations of plasmoids in the Jovian magnetotail, because there is strong ion acceleration in these structures. Our model predicts that electromagnetic turbulence in plasmoids plays an essential role in the acceleration of oxygen, sulfur, and hydrogen ions. The observations show a decrease of the oxygen and sulfur energy spectral index γ at ∼30 to ∼400 keV/nuc with the wave power indicating an energy transfer from electromagnetic waves to particles, in agreement with the model. The wave power threshold for effective acceleration is of the order of 10 nT2Hz−1, as in terrestrial plasmoids. However, this is not observed for hydrogen ions, implying that processes other than wave‐particle interaction are more important for the acceleration of these ions or that the time and energy resolution of the observations is too coarse. The results are expected to be confirmed by improved plasma measurements by the Juno spacecraft.

Energetic Oxygen and Sulfur Charge States in the Outer Jovian Magnetosphere: Insights From the Cassini Jupiter Flyby

“…Additionally, certain processes can lead to charge‐state‐dependent acceleration, which may contribute to observed differences in the Cassini and Juno observations. For example, wave‐particle interactions within Jovian plasmoids would further accelerate higher charge state species (Kronberg et al, ), while acceleration in reconnection exhausts is species dependent (e.g., Drake, Cassak, et al, ; Drake, Swisdak, et al, ; Vines et al, ). Future work is needed to better understand how these dynamical processes may shape the outer magnetospheric suprathermal ion composition.…”

The in-situ exploration of Jupiter's radiation belts

“…Theories that do not involve charge exchange and reionization and set no restrictions on heavy ion charge states, also exist. The energetic ion fluxes beyond Europa's orbit that seed the ion belts can be enhanced following tail reconnection events [Louarn et al 2014;Kronberg et al 2019], as at Saturn [Mitchell et al 2015]. An ion heating source at 20-25 Rj, the nature of which is not understood [Selesnick et al, 2001], may be relevant.…”

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

“…A similar dichotomy in flux rope size is seen at Mercury (DiBraccio et al., 2015; Slavin et al., 2009; J. Zhong et al., 2019), whose magnetosphere is closest to that of Earth with tail reconnection being driven by a Dungey‐type (Dungey, 1961) magnetic flux transfer cycles, but also possesses differences related to its proximity to the Sun and its lack of an ionosphere. Small‐scale flux ropes play an important role in energizing electrons and ions, which can undergo both, adiabatic acceleration due to the evolving flux rope structure (Drake et al., 2006a; Le et al., 2012; Z. H. Zhong et al., 2020) and nonadiabatic acceleration due to electromagnetic turbulence (Kronberg et al., 2019).…”