On the dust/gas tori of Phobos and Deimos

The dust and gas environment in the vicinity of the orbit of the Phobos moon is assessed using both theoretical methods and observations from previous missions to Mars. It is found that a stable ring of dust particles with radii ≈ 100 μm could exist with a normal optical depth close to the upper limit determined from the Viking Orbiter 1 mission. The presence of a gas ring with neutral number density substantially higher than the hot atomic oxygen background is possible only if the Phobos moon maintains a certain level of outgassing with Q_gas > 10²³ molec. s^-l. The narrow width (≈ 400 km) and the strong plasma perturbations sometimes observed by the Phobos 2 spacecraft at crossings of the orbit of the Phobos moon are still a puzzle to be investigated by further data analysis.