Interpretation of the Mariner 5 Lyman Alpha Measurements

Abstract

The Mariner 5 Lyman alpha measurements can be fitted with the barometric-exospheric equation only if a two-component model atmosphere is used. Of the three possible hypotheses to explain such an atmosphere, the model containing a mixture of atomic hydrogen and molecular hydrogen is preferred over the atomic hydrogen-deuterium model or the atomic hydrogen two-temperature model. The source of molecular hydrogen in the upper atmosphere may be chemical reactions either in the hot, dense lower atmosphere or in the upper atmosphere. The photodissociation of molecular hydrogen produces atoms with excess kinetic energy which either escape from the planetary gravitational field or react with the molecules in the lower atmosphere. The presence of molecular hydrogen affects calculations of the temperature of the Venus upper atmosphere as well as its ionic and chemical structure.