Mars: Components of infrared spectra and the composition of the dust cloud

Infrared spectra of Mars are made up of three separate components, each of which may dominate the spectrum under different Martian meteorological and observational conditions. By means of laboratory examples we show that both the shape and spectral contrast of the spectral curves change dramatically, depending on which component is dominant. Each experimental condition has been experienced during either the Mariner 69 or 71 observations. Comparing the preliminary Mariner 71 radiance data with laboratory transmission spectra, we suggest that the clay mineral montmorillonite could be the major component of the Martian dust cloud.