Probing the Martian Atmosphere in the Ultraviolet

Several fundamental differences in atmospheric chemistry exist between Mars and the Earth. The martian atmosphere is primarily CO2 (95%), with strong vertical mixing, cold temperatures (typically 220K), low pressures (6 mb at the surface), high atmospheric dust and cloud particle content, and no man-made atmospheric constituents. Earlier difficulties in explaining why the atmosphere was not more decomposed into CO and O2 have been placated with models using updated reaction rates, 'moderate' eddy mixing of order 107 cm2s-1, and the odd hydrogen catalytic cycle (Shimazaki, 1989; Krasnopolsky, 1992). Odd nitrogen and sulfur catalytic cycles are of marginal importance, and other catalytic cycles shown to be important in the terrestrial atmosphere are unimportant on Mars (Yung et al., 1977; Krasnopolsky, 1992). Currently, much work is being undertaken to examine the importance of heterogeneous chemistry (e.g., Atreya and Blamont, 1990; Krasnopolsky, 1992), but uncertainties in particle properties make efficiencies difficult to evaluate. Also, atmospheric chemistry may significantly alter atmospheric composition on climatic timescales, particularly during periods of low obliquity (Lindner and Jakosky, 1985).