Parameters of the optical properties of the lunar surface powder in relation to solar-wind bombardment

The optical properties of the moon are quantitatively compared with those of powder samples bombarded by ions from a hydrogen discharge plasma. Deficiencies in the simulation of the solar-wind bombardment include contaminants deposited on, and injected into, the sample surfaces. Also an unknown fraction of the sputtered atoms returns to the lunar surface after flight in the gravity field. The variable albedo of the powder samples due to darkening by ion bombardment is studied in relation to parameters of color, photometric function, and polarization while holding composition, surface structure, or powder particle size fixed. Simulation of the solar wind was not adequate to permit identification of lunar compositions from lunar color. The lunar photometric function requires a rough macrostructure. A number of properties of the photometric function plus the polarization of earthshine, however, are shown to be incapable of presently proving whether the lunar surface is underdense or compacted. A polarization parameter indicates a lunar powder whose particles are mostly less than 0.1 mm in size. Effects expected from solar-wind bombardment include surface darkening and decoloration, erosion, preferential erosion of some substances, dust cementation, and alterations of surface layer composition.