An explanation for the light curve of Jupiter's and Saturn's satellites

Several satellites of Jupiter and Saturn show an asymmetric reflectance between the 'leading' hemisphere (which is generally brighter for the inner satellites of both systems) and the 'trailing' one (which is brighter for the outer satellites Callisto and Iapetus). In order to seek a unified explanation of these observational data it was assumed that, during the final phase of the satellite accumulation process, the surfaces were subjected to a heavy meteoroidal bombardment by the residual bodies in the circumplanetary protosatellite swarms. With suitable hypotheses about the orbital elements of these bodies, the resulting collision rate is anisotropic in an opposite way for inner and outer satellites, with a difference between the two hemispheres of the order of 10-20 percent for all satellites except Iapetus (for which the anisotropy is larger). It is concluded that the model can qualitatively account for the observed effect, even if it is diffcult to propose a detailed mechanism for changing the albedo properties of the satellite surfaces by means of meteoroidal collisions.