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Martian oxygen density at the exobase deduced from O I 130.4‐nm observations by Spectroscopy for the Investigation of the Characteristics of the Atmosphere of Mars on Mars Express

2009; American Geophysical Union; Volume: 114; Issue: E2 Linguagem: Inglês

10.1029/2008je003130

2156-2202

J. Y. Chaufray, François Leblanc, Éric Quémerais, Jean‐Loup Bertaux,

Atmospheric and Environmental Gas Dynamics

Several observations of the O I 130.4‐nm triplet have been analyzed to determine the oxygen density in the Martian upper atmosphere using a three‐dimensional Monte Carlo radiative transfer model describing each line of the triplet. Solar resonant scattering is the dominant source of excitation of the O I 130.4‐nm triplet in the upper atmosphere of Mars. The atomic oxygen density at the exobase is found to be 1.2 −0.5 +1.2 × 10 7 cm −3 for solar zenith angles between 20° and 55° and to decrease by a factor of 2 for solar zenith angles between 55° and 90°. Although the major contribution to the observed brightness is produced above the exobase, it is possible to extrapolate the density profile below the exobase and to estimate the [O]/[CO 2 ] mixing ratio as 0.6–1.2% at 135 km. The major source of uncertainty comes from the uncertainty in the absolute calibration, as expected for an optically thick emission, and also, to a lesser degree, from the temperature at the exobase. The profiles are better reproduced by a large exospheric temperature (>300 K), which may suggest the presence of a hot oxygen population.