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The driver of energetic electron precipitation into Ganymede's atmosphere has been an outstanding open problem. During the Juno flyby of Ganymede on 7 June 2021, Juno observed significant downward‐going electron fluxes inside the bounce loss cone of Ganymede's polar magnetosphere. Concurrently, Juno detected intense whistler‐mode waves, both in the quasi‐parallel and highly oblique directions with respect to the magnetic field line. We use quasi‐linear model to quantify energetic electron precipitation driven by quasi‐parallel and very oblique whistler‐mode waves, respectively, in the vicinity of Ganymede. The data‐model comparison indicates that in Ganymede's lower‐latitude (higher‐latitude) polar region, quasi‐parallel whistler‐mode waves play a dominant role in precipitating higher‐energy electrons above ∼100s eV (∼1 keV), whereas highly oblique waves are important for precipitating lower‐energy electrons below 100s eV (∼1 keV). Our result provides new evidence of whistler‐mode waves as a potential primary driver of precipitating energetic electrons into Ganymede's atmosphere. Plain Language Summary: During the Juno flyby of Ganymede on 7 June 2021, the Juno spacecraft detected energetic electrons precipitating into Ganymede's atmosphere. Simultaneously, Juno detected intense electromagnetic whistler‐mode waves in the vicinity of Ganymede. We use a physics‐based model to quantify the role of the observed whistler‐mode waves in energetic electron precipitation. The comparison between the Juno observation and modeling results reveals that whistler‐mode waves potentially play a dominant role in precipitating energetic electrons into Ganymede's atmosphere over a broad energy range from tens of eV to several hundred keV. Our findings are potentially important for understanding the loss process of energetic electrons in Ganymede's magnetosphere, as well as the generation of Ganymede's diffuse aurora. Key Points: We provide new evidence of whistler‐mode waves as a potential primary driver of precipitating energetic electrons into Ganymede's atmosphereThis finding is potentially important for the generation of aurora and the loss of energetic electrons in the vicinity of GanymedeJuno observations and quasi‐linear modeling are used to quantify energetic electron precipitation driven by whistler‐mode waves [ABSTRACT FROM AUTHOR]

Abstract The driver of energetic electron precipitation into Ganymede's atmosphere has been an outstanding open problem. During the Juno flyby of Ganymede on 7 June 2021, Juno observed significant downward‐going electron fluxes inside the bounce loss cone of Ganymede's polar magnetosphere. Concurrently, Juno detected intense whistler‐mode waves, both in the quasi‐parallel and highly oblique directions with respect to the magnetic field line. We use quasi‐linear model to quantify energetic electron precipitation driven by quasi‐parallel and very oblique whistler‐mode waves, respectively, in the vicinity of Ganymede. The data‐model comparison indicates that in Ganymede's lower‐latitude (higher‐latitude) polar region, quasi‐parallel whistler‐mode waves play a dominant role in precipitating higher‐energy electrons above ∼100s eV (∼1 keV), whereas highly oblique waves are important for precipitating lower‐energy electrons below 100s eV (∼1 keV). Our result provides new evidence of whistler‐mode waves as a potential primary driver of precipitating energetic electrons into Ganymede's atmosphere.

While previous studies suggested whistler mode waves as a potential driver of Jupiter's diffuse aurora, their quantitative contribution to generate diffuse aurora remains unclear. We perform an in‐depth analysis of an intriguing diffuse auroral electron precipitation event using coordinated observations of precipitating electrons and whistler mode waves from the Juno satellite. A physics‐based technique is used to quantify energetic electron precipitation driven by whistler mode waves. We find that the modeled electron precipitation features are consistent with the electron measurements from several keV to several hundred keV over M‐shells of 8–18, while additional mechanisms are needed to explain the observed electron precipitation at lower energies (

Abstract: The Juno spacecraft's Jupiter Energetic‐particle Detector Instrument has observed field‐aligned, unidirectional (upgoing) electron beams throughout most of Jupiter's entire polar cap region. The Waves instrument detected intense broadband whistler mode emissions occurring in the same region. In this paper, we investigate the pitch angle scattering of the upgoing electron beams due to interactions with the whistler mode waves. Profiles of intensity versus pitch angle for electron beams ranging from 2.53 to 7.22 Jovian radii show inconsistencies with the expected adiabatic invariant motion of the electrons. It is believed that the observed whistler mode waves perturb the electron motion and scatter them away from the magnetic field line. The diffusion equation has been solved by using diffusion coefficients which depend on the magnetic intensity of the whistler mode waves. [ABSTRACT FROM AUTHOR]

Juno observed the low-altitude polar region during perijove 1 on 27 August 2016 for the first time. Auroral intensity and false-color maps from the Ultraviolet Spectrograph (UVS) instrument show extensive diffuse aurora observed equatorward of the main auroral oval. Juno passed over the diffuse auroral region near the System III longitude of 120°-150° (90°-120°) in the northern (southern) hemisphere. In the region where these diffuse auroral emissions were observed, the Jupiter Energetic Particle Detector Instrument (JEDI) and Jovian Auroral Distributions Experiment (JADE) instruments measured nearly full loss cone distributions for the downward going electrons over energies of 0.1-700 keV but very few upward going electrons. The false-color maps from UVS indicate more energetic electron precipitation at lower latitudes than less energetic electron precipitation, consistent with observations of precipitating electrons measured by JEDI and JADE. The comparison between particle and aurora measurements provides first direct evidence that these precipitating energetic electrons are mainly responsible for the diffuse auroral emissions at Jupiter. [ABSTRACT FROM AUTHOR]