Proton energy deposition and EUV emission in the Jovian and the Saturnian atmospheres

Abstract

A model of the interaction of energetic protons with the atmospheres of Jupiter and Saturn is developed to examine the possibility that the high latitude ultraviolet aurorae observed on both planets are at least partly excited by proton precipitation. The method is based on the continuous slowing down approximation and takes into account the partial conversion of protons into hydrogen atoms and the contributions of secondary electrons. Comparison with previous models of auroral electron degradation in hydrogen atmospheres indicated that the efficiency of both types of particles is fairly similar. However, the relative contribution of secondary electrons in the excitation of the ultraviolet H₂ band is found to depend on the energy of the primary protons. The H<i><i>_{_{<img src='/image/spc_char/alpha.gif' border=0>}}</i></i>/H<i><i>_{_{<img src='/image/spc_char/beta.gif' border=0>}}</i></i> intensity ratio is also different for proton and electron precipitations and roughly independent of the proton energy. The range of proton energies compatible with the spectral composition of the ultraviolet auroral spectra of Jupiter and Saturn is found to be ~ 1-1000 keV. It is suggested that ~ 1 MeV protons are viable candidates to explain the secondary peak observed in the longitudinal distribution of the Jovian auroral intensity. It is also shown that the H₂ bands/H<i><i>_{_{<img src='/image/spc_char/beta.gif' border=0>}}</i></i> ratio calculated in the model is compatible with the intensity of the visible arcs observed at Jupiter’s high latitude limb with the voyager camera.