Optical Properties of the Atmosphere and Surface of the Planet Mars

Abstract

O ALL the planets of the solar system, Mars attracts the most attention. The study of the surface and atmosphere of Mars is important. Observations of Mars show vastly different details in all parts of the spectrum, excluding the violet part. Besides that, it is known that extinction in the terrestrial atmosphere in the visible spectral range is practically caused only by scattering, because true absorption, concentrated in the comparatively few and shallow telluric bands, plays an insignificant role in reducing the total light flux. In the visual range of Mars' spectrum, in general, no absorption bands caused by the atmosphere of this planet have been detected. Hence, it is considered that the role of absorption in the atmosphere of Mars is still smaller than in the terrestrial. Good visibility of details on Mars, assuming that it has a scattering atmosphere, makes it possible to consider that the optical thickness of its atmosphere in the visible part of the spectrum is small. Many published calculations of the optical thickness and density of the atmosphere of Mars were based on this assumption (1-4). At the same time, in certain articles devoted to interpreting photometric observations of Mars, the opinion is stated that the atmosphere of this planet differs from the terrestrial in that true absorption plays a noticeable part in it. And so, neglecting scattering, attempts were made to interpret the observational data and in particular the coloration of Mars (5). Such a difference of opinions concerning the optical properties of Mars' atmosphere, compels us, in determination of quantities characterizing optical properties of the planet's atmosphere, to abandon the assumption that Mars has either a scattering or an absorbing atmosphere. Both effects must be considered. Only a subsequent comparison of theoretical calculations with the observational data makes it possible to explain the correlation between scattering and absorption in the atmosphere of Mars. Sharonov (6) has studied the role of true absorption in the atmosphere of Mars. He showed that observations of the distribution of brightness across the disk of Mars can be explained on the assumption of a purely scattering atmosphere. However, he took into account scattering of light of the first order only. It is very important to analyze that same problem, while taking into account scattering of all orders. In this work, an attempt is made to interpret the observational data by taking into account multiple scattering.