The distribution of hot hydrogen atoms produced by electron and proton precipitation in the Jovian aurora

Abstract

The energy distribution functions of nonthermal thermospheric hydrogen atoms are calculated for electron and proton precipitation in the Jovian aurora. A numerical model taking into account the production, elastic and inelastic relaxation and transport processes for hot H atoms is developed. This model is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot H atoms produced by electron and proton impact on H and H2 and exothermic chemical reactions. The distribution functions show a much higher energy tail for proton than electron precipitation. It is shown that the steady state flux of hot atoms (E ≥ 2 eV) is essentially isotropic. The peak and column hot H densities are about 3 × 105 cm−3 and 1 × 1014 cm−3 for a 100 erg cm−2 s−1 precipitation combining hard (22 keV) and soft (0.2 keV) electrons mixed with a 10 erg cm−2 s−1 flux of soft (0.3 keV) protons. These column densities, coupled with the wide range of hot H atom energies, may play an important role in the formation of the Lyman α line profile. Multiple scattering in the wings of the Ly α line by the fast H atoms is shown to partly account for the broad Ly α profile observed in the Jovian aurora with the Hubble space telescope.