Driver of Energetic Electron Precipitation in the Vicinity of Ganymede

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.