Energetic Ion Precipitation in Jupiter’s Polar Auroral Region Observed by Juno/JEDI

<p>Remote observations clearly show that soft X-ray emissions at Jupiter concentrate poleward of the main oval forming a so-called “hot spot” (Gladstone et al., 2002; Dunn et al., 2016). One hypothesis proposes that the X-rays are likely produced from precipitating energetic heavy ions that become fully stripped via interactions in Jupiter’s upper atmosphere; however, the details regarding the ion source and acceleration mechanism(s) of the soft X-ray (~2 keV) component is still an active area of research. NASA’s Juno mission – a Jupiter polar orbiting spacecraft – is shedding light onto this mystery with in situ observations of the energetic particle environment over the poles, and coordinated observing campaigns with Earth-orbiting X-ray observatories, e.g., Chandra and XMM-Newton. Recent ideas supported by Juno data include: 1) pitch angle scattering of energetic ions via electromagnetic ion cyclotron waves in the outer magnetosphere (Yao et al., 2021); and 2) acceleration of ions to several MeV over Jupiter’s poles via field-aligned electric potentials (Clark et al., 2017; Haggerty et al., 2017; Clark et al., 2020; Yao et al., 2021). New techniques have been recently developed to push the capabilities of Juno’s Jupiter Energetic particle Detector Instrument (JEDI) to measure the > 10 MeV ions (Westlake et al., 2019; Kollmann et al., 2020). In this presentation, we utilize these techniques to characterize the precipitating fluxes of > 10 MeV ions over Jupiter’s polar region with the goal of better understanding the sources of Jupiter’s X-ray auroral emissions.</p>

Revealing the source of Jupiter’s x-ray auroral flares

Jupiter’s rapidly rotating, strong magnetic field provides a natural laboratory that is key to understanding the dynamics of high-energy plasmas. Spectacular auroral x-ray flares are diagnostic of the most energetic processes governing magnetospheres but seemingly unique to Jupiter. Since their discovery 40 years ago, the processes that produce Jupiter’s x-ray flares have remained unknown. Here, we report simultaneous in situ satellite and space-based telescope observations that reveal the processes that produce Jupiter’s x-ray flares, showing surprising similarities to terrestrial ion aurora. Planetary-scale electromagnetic waves are observed to modulate electromagnetic ion cyclotron waves, periodically causing heavy ions to precipitate and produce Jupiter’s x-ray pulses. Our findings show that ion aurorae share common mechanisms across planetary systems, despite temporal, spatial, and energetic scales varying by orders of magnitude.

Direct Observational Evidence of the Simultaneous Excitation of Electromagnetic Ion Cyclotron Waves and Magnetosonic Waves by an Anisotropic Proton Ring Distribution

<p>Magnetosonic (MS) waves and electromagnetic ion cyclotron (EMIC) waves are two important plasma wave modes in the magnetosphere. Previous simulations have shown that both waves could be generated by a ring-like proton distribution, while direct observational evidence has yet to be reported. Here, we present simultaneous observations of MS and EMIC waves and a detailed case analysis. The linear growth rates estimated for both waves are in good agreement with the observed wave frequency spectra. The measured proton distribution evolution is also compared with the simulation results, providing direct observational evidence for the previous theoretical prediction that anisotropic ring-like proton distributions could excite MS and EMIC waves simultaneously. Our findings are crucial for understanding the generation mechanisms of and relation between MS and EMIC waves and for evaluating their combined effects on energetic electron and ion dynamics. </p>