Measurement of the Abundance of CO₂ in the Martian Atmosphere

High-resolution measurements have been made of CO2 absorption on Mars, in the ~i + 2~2 + 3~'~ band at 1.05 ~. The instrument used was a PEPSIOS three-étalon, Fabry-Pérot spectrometer that ac- cepted light from a circle 0.447 times the diameter of the planetary image during the 1967 opposition. The results for the CO2 abundance a~ (in m atm) can be summarized by the relation ao = (84 ± 6) - O.2(T - 195) - 1.O(p - 7), where T is the effective average temperature in degrees Kelvin, and p is the surface pressure in rnillibars. The value 83 ± 8 m atm is believed to be the best estimate of CO2 abundance, corresponding to a partial surface pressure of CO2 of 6.1 mb. The composition of the Martian atmosphere is judged to be between 60 per cent and 100 per cent C02, corresponding to a range of 9-6 mb in surface pressure. No variation in the observed equivalent line widths with Martian longitude was ob- served. I. INTRODUCTIO