Solar cycle variability of hot oxygen atoms at Mars

The population of hot oxygen atoms in the Martian exosphere is reexamined u sing newly calculated hot O production rates for both low and high solar cy cle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O-2(+) ions. These calculations take into account the calculated vibrational distribution of O-2(+) and the new meas ured branching ratios. Furthermore, these calculations also consider the va riation of the dissociative recombination cross section with the relative s peed of the participating ions and electrons, the rotational energy of the O-2(+) ions, and the spread of the ion and electron velocities. These produ ction rates were next used in a two-stream model to obtain the energy depen dent flux of the hot oxygen atoms as a function of altitude. Finally, the c alculated flux at the exobase was input into an exosphere model, based on L iouville's theorem, to calculate the hot oxygen densities as a function of altitude in the exosphere and the resulting escape flux. It was found that hot oxygen densities vary significantly over the solar cycle; the calculate d densities vary from about 2x10(3) to 6x10(3) cm(-3) at an altitude of 100 0 km. The escape flux also varies from about 3x10(6) to 9x10(6) cm(-2) s(-1 ).