Mariner 6 and 7 Ultraviolet Spectrometer Experiment Analysis of Hydrogen LymanAlpha Data

Mariner 6 and 7 ultraviolet spectrometers that flew by Mars in 1969 observed the Lyman-, dayglow of atomic hydrogen. Data in the altitude range 200 to 24,000 km are analyzed to determine the structure of the Martian exosphere. The classical evaporative theory is applied to calculate a hydrogen density distribution. A spherical model of the dayglow Lyman-a emission, using radiative transfer theory, is used to produce theoretical intensities for comparison with the data in order to determine temperature and density in the exosphere. It is found that the exospheric temperature is 350 ø ___ 100øK and that the number density at 250 km is 3 ___ 1 X 10' cm '•. The existence of a Lyman-a corona implies a primary source of hydrogen on Mars, probably the photodissociation f water vapor.