The Upper Atmosphere of Venus: A Review

The implications of recent data on Venus obtained by Mariner 5, Venera 4 and ground based observations for the aeronomy of Venus is received. The theoretical thermal structure model of McElroy based on a pure CO2 atmosphere is in good agreement with the temperature deduced from the hydrogen distribution obtained by Mariner 5. No credible mechanism has been devised to recombine CO and O to CO2 in the upper atmosphere. It is suggested that O2 is formed but that CO and O2 recombine to CO2 in the dense atmosphere far enough above the cloud tops to agree with abundance measurements. Serious difficulties exist for the H2 model of the upper atmosphere. It is suggested that deuterium can account for the anomalous Lyman α glow observed by Mariner 5 without implying a large D/H planetary ratio. Other problems such as the maintenance of the ionosphere at night and the escape of water are discussed.