Radiation transfer modelling of the dust torus of phobos in view of the Mars9496 mission

Several interesting events of solar wind perturbation have been detected by the Phobos-2 spacecraft when it crossed the orbit of the Martian moon Phobos. These events have been interpreted as indirect evidence for a ring (torus) of gas and particulate material surrounding Mars and originating from internal outgassing and meteorite impacts on the satellites. The goal of one of the experiments onboard the spacecraft Mars9496 is the detection of the presumed ring by measuring the visible solar radiation scattered by dust particles orbiting around Mars. In order to estimate the possibility of detecting the torus, we have used a simple radiative transfer model assuming that single scattering of solar radiation from a plane-parallel homogeneous layer of dust approximates well the real physical situation. On the basis of these assumptions, we have computed the intensity of the solar radiation scattered in different directions by the grains. The results of these calculations, which represent a first attempt of an accurate quantitative estimate, confirm the observability of the ring by the photometer planned for the Mars9496 mission.