Energy mapping of Jupiter's auroral electrons from Juno/UVS data using a new H2 UV emission model

Abstract

Juno, which studies the Jovian system, continues to expand our knowledge of Jupiter's magnetosphere and its environment. Thanks to onboard instruments such as Jupiter Energetic Particle Detector Instrument (JEDI) and Jovian Auroral Distributions Experiment (JADE), in situ measurements have allowed us to derive a realistic representation of charged particle energy distributions precipitating in the auroral regions. Because of the distance between Juno's measurement location and the position of impact of the charged particles, where auroral emissions are produced, these energetic distributions of magnetospheric particles are likely to be affected by various phenomena such as wave-particle interactions on their way from Juno to the atmosphere. These processes can accelerate or decelerate the particles, changing their average energies. Hence, the energy distributions of particles measured at Juno's altitude are likely different from those at auroral altitudes. In this study we develop a UV emission model, combined with an electron transport model, that allows us to relate the auroral emission spectra of H$_ $ molecules with the energy distribution of impinging electrons. Thanks to observations of the Jovian aurora by the Ultraviolet Spectrograph (UVS) on board Juno, we determined the characteristic energies of electrons precipitating in auroral regions during perijove 32. We modeled the relationship between color ratio (CR) and the characteristic energy of precipitating electrons. Initially, we considered mono-energetic electron fluxes. In a second step, we considered fluxes governed by a kappa distribution. We derived characteristic energy maps for electrons precipitating in Jupiter's auroral regions. In comparison with similar previous studies based on Space Telescope Imaging Spectrograph on board Hubble Space Telescope (HST/STIS) observations, we find that modeling the CR with a mono-energetic distribution leads to a systematic underestimation of the average energy of electrons precipitating in the auroral regions by a factor of 3-5. In this study we show that it is possible to derive a more realistic estimate of electron energy flux distributions at auroral altitudes.