Abstract
Atomic oxygen (O) and hydrogen (H) have been identified in the spectra of the upper atmosphere of Mars by the Mariner 6 and 7 Ultraviolet (UV) Spectrometer Experiment. In addition, the presence of carbon monoxide (CO) is inferred by self-absorption in the fourth positive emission of CO. We review the current status of our quantitative knowledge of the O densities derived from an analysis of the OI 1356 and 1304 Å emissions. Emphasizing the uncertainties in the quantitative description of the excitation sources of these lines, we present the preliminary results from a study now in progress of an atomic oxygen density profile which best fits the Mariner 1304 Å data. This model predicts the correct 1356 Å emission within a factor of 2. Upper and lower limits are placed on the CO density from an analysis of the (1,0) band of the (A-X) system of CO. We describe the results in terms of a percentage composition of O and CO at the ionospheric peak at 135 km. The O concentration is ∼3% and the CO concentration ∼0.3% of the CO2 density at this level. Below the level where the O:CO ratio is unity, the atmosphere is expected to be nearly uniformly mixed, with a decreasing mixing ratio of CO with decreasing height. This level in the atmosphere, identified as the turbopause, is near the 100-km level, but may be as high as 120 km.
