Energetic electron precipitation in Jupiter's upper atmosphere

Abstract

Energy deposition by electrons having a Maxwellian energy distribution with characteristic energies 10, 30, and 100 keV, precipitating in the high-latitude upper atmosphere of Jupiter, has been studied using a continuous slowing down approximation. Electron fluxes, volume excitation, and ionization rates have been calculated. Chemical equilibrium equations have been solved for 24 ionic species using extensive hydrocarbon chemistry and incorporating diffusive transport for the ion H⁺. H₂ Lyman and Werner bands and H Ly α intensities are obtained considering pure absorption in hydrocarbons. Comparison with Voyager ultraviolet spectrometer data requires incident energy fluxes of about 10, 18, and 45 ergs cm^-2 s^-1 for characteristic energies 10, 30, and 100 keV, respectively, for polar model methane abundance. Numerical experiments have been performed to study the effect of changing atomic hydrogen and methane number density, three-body reaction rates, incident energy flux, and H₂(v≥4) vibrational temperature on plasma densities. Electrons with characteristic energy 30 keV or somewhat higher give good overall agreement with Voyager 2 electron densities and also simulate the low-altitude peak measured by Pioneer 11. The calculated bremsstrahlung X ray flux is smaller by 1 to 2 orders of magnitude than the observed low-energy (<2 keV) X ray flux. New observations of high-energy (>2 keV) bremsstrahlung X ray emissions are required to give a definite resolution of the identity and energy of the particles responsible for the aurora on Jupiter.