Composition and Structure of the Martian Atmosphere: Preliminary Results from Viking 1

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Science  27 Aug 1976:
Vol. 193, Issue 4255, pp. 786-788
DOI: 10.1126/science.193.4255.786


Results from the aeroshell-mounted neutral mass spectrometer on Viking I indicate that the upper atmosphere of Mars is composed mainly of CO2 with trace quantities of N2, Ar, O, O2, and CO. The mixing ratios by volume relative to CO2 for N2, Ar, and O2 are about 0.06, 0.015, and 0.003, respectively, at an altitude near 135 kilometers. Molecular oxygen (O2+) is a major component of the ionosphere according to results from the retarding potential analyzer. The atmosphere between 140 and 200 kilometers has an average temperature of about 180° ± 20°K. Atmospheric pressure at the landing site for Viking 1 was 7.3 millibars at an air temperature of 241°K. The descent data are consistent with the view that CO2 should be the major constituent of the lower martian atmosphere.