Document Type


Publication Date



The population of hot oxygen atoms in the Martian exosphere is reexamined using newly calculated hot O production rates for both low and high solar cycle conditions. The hot oxygen production rates are assumed to result from the dissociative recombination of O2+ ions. These calculations take into account the calculated vibrational distribution of O2+ and the new measured branching ratios. Furthermore, these calculations also consider the variation of the dissociative recombination cross section with the relative speed of the participating ions and electrons, the rotational energy of the O2+ ions, and the spread of the ion and electron velocities. These production rates were next used in a two-stream model to obtain the energy dependent flux of the hot oxygen atoms as a function of altitude. Finally, the calculated flux at the exobase was input into an exosphere model, based on Liouville'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 calculated densities vary from about 2×103 to 6×103 cm−3 at an altitude of 1000 km. The escape flux also varies from about 3×106 to 9×106 cm−2s−1.


Copyright © 1998 by the American Geophysical Union.

The following article appeared in the Journal of Geophysical Research: Space Physics 103(A12), and may be found at

Permission to Deposit an Article in an Institutional Repository:

Adopted by Council 13 December 2009.

AGU allows authors to deposit their journal articles if the version is the final published citable version of record, the AGU copyright statement is clearly visible on the posting, and the posting is made 6 months after official publication by the AGU.