Photometric modelling of the Martian dust rings

There are reasons to expect that Mars is surrounded by a region of dust, similar to rings, originating from the bombardment of Phobos and Deimos by meteroids. Using a simple radiative transfer model, we have investigated the angular distribution and the absolute values of the solar radiance scattered by such a dust region, to the purpose of assessing the possibilities and limitations of future photometric searches after the circummartian dust. Our model values of the number density of the dust grains in the space around Mars and of their size distribution have been derived from the results obtained by other authors. The single-scattering albedo of the dust grains has been deduced from the reflectance spectra of Phobos, taken by the spacecraft Phobos 2. Calculations, carried out for a few phenomenological phase functions, have shown that in the visible the radiance scattered by the rings is well within the detectability range of a modern sensible photometer, so that the prospectives for photometric search for the Martian dust rings are optimistic. Furthermore, our results confirm that the dust region could not be observed by the Viking cameras and this supports o our assumptions regarding the optical properties of the circummartian grains.