The Production of Hot Oxygen at the Exobases of the Terrestrial Planets

Fast oxygen atoms are produced near the exobases of all the terrestrial planets in dissociative recombination of O ₂ ⁺ . The distribution of velocities of the O atoms is important for the morphology of the hot O coronas, and for the escape of O from Mars. The spectrum of the O atoms depends on the relative yields of the five energetically accessible channels in dissociative recombination, on the vibrational and rotational distribution of the O ₂ ⁺ , and on the ion and electron temperatures. We combine here our calculations of the distribution of vibrational levels of O ₂ ⁺ near the exobases of the earth, Venus and Mars, with measurements by Kella et al. (1997) of the yields of the combinations of electronic states of the product O atoms in dissociative recombination of O ₂ ⁺ to estimate the spectrum of the O atoms. Monte Carlo calculations are carried out to determine the details of the O atom velocity distribution, including the influence of electron and ion temperatures on the spread of velocities. We report spectra of energetic O atoms at the exobases of the earth, Venus and Mars.