Planned observation of Phobos/Deimos dust rings by PLANET-B

An imaging CCD camera and an impact dust detector carried by the Mars mission (PLANET-B of ISAS, Japan) are potential instruments to search for the Phobos/Deimos dust rings proposed by theoretical investigations. We have reexamined the structure of dust rings based on the numerical simulation for dynamical evolution of ejecta from satellites around Mars, taking into account the gravity forces by the Sun, Mars, and the parent satellite and the solar radiation pressure forces on the ejecta as well as the perturbations due to the oblateness of Mars. It is found that the particles ejected with the mass of nearly 10(-7)g from Phobos and 10(-8)g from Deimos have a relatively longer survival lifetime against the collisions with Mars and the parent satellite. Deimos ring has higher number density (10(-7)m(-3)) than Phobos ring (10(-8)m(-3)). During roughly 2 years of mission life of PLANET-B from October 1999, a few ten particles across the rings will be detected by the dust detector with an effective area of 0.01m(2) and a threshold mass of 10(-10)g. The imaging camera, on the other hand, will have a chance to look for the rings of the optical depth of roughly 10(-7) to 10(-9) from a favorable forward scattering angle of about 17(0). (C) 1997 COSPAR.