Mariner 6 flew by Mars on July 31, 1969 at a distance of 3,431 km above the surface. Mariner 7 flew by on August 5, 1969 at a similar miss distance. These were the first spacecraft to carry spectroscopic instruments for observations of the atmosphere and surface. The University of Colorado instrument was an ultraviolet spectrometer. The most important results of the ultraviolet observations were the Discovery of the ultraviolet airglow of Mars and the First observations of atomic hydrogen escaping from the Mars upper atmosphere.