Precipitating electron properties of Ganymede’s aurora retrieved from Juno/UVS observations during PJ34

Context . Ganymede’s UV aurorae, observed by HST and Juno/UVS, trace interactions between its atmosphere and Jupiter’s magneto-sphere. These emissions, dominated by O I lines at 130.4 and 135.6 nm, are driven by electron impact on species such as H 2 O, O, and O 2 , and yet the properties of the precipitating electrons remain poorly constrained. Aims . Our aim was to retrieve the energy and flux of precipitating electrons using UV observations from Juno/UVS during PJ34 and to assess the dominant atmospheric species producing the observed emissions. Methods . Using the TransPlanet electron transport model and a non-local thermodynamic equilibrium (non-LTE) radiative transfer module, we simulated O I emissions for 17 auroral subregions, testing both monoenergetic and kappa-type electron distributions. The I (135.6 nm)/ I (130.4 nm) line ratio was used as a diagnostic, with values varying by target species. Results . Monoenergetic distributions fit most regions better, with mean energies of 17–300 eV and fluxes up to 2 mW m −2 . Kappa and Maxwellian distributions yielded higher fluxes, but poorer spectral fits. Poor fits in some regions reflect low S/N or non-ideal electron populations. Conclusions . Our results suggest that Ganymede’s UV aurorae are mainly driven by low- to intermediate-energy electrons. Upcoming high-resolution observations and in situ data from Juice and Europa Clipper will be key to refining these diagnostics.