Ultraviolet Reflectivity of Mars

Abstract

Ultraviolet spectrograms of Mars (2400 to 3500 angstroms, ~50-Å resolution) have been obtained with an objective grating spectrograph on an Aerobee rocket. The data indicate a reflectivity of 0.04 to 0.08 in the ultraviolet, increasing toward shorter wavelength according to a Rayleigh Law. The data can be represented by a model having an atmosphere of nitrogen, carbon dioxide, and argon, and a surface pressure of about 5 to 20 millibars. The photographic appearance of the planet in the blue is interpreted as a loss of surface contrast and reflectivity rather than an absorption in the atmosphere by the "blue haze." The model permits prediction of the general appearance of the planet in the photographic ultraviolet, blue, visible, and red. There are serious biological implications since the model suggests that ultraviolet radiation (2000 to 3000 Å) will reach the surface.