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mascons(mas -konz) Short for mass concentrations. Positive gravitational anomalies associated with the young circular lunar maria, where relatively dense disk-shaped masses are now known to be located close to the surface: because the gravitational attraction is somewhat higher over these regions, mascons perturb the orbits of lunar satellites. They were produced either by the mare basalt itself as it flooded the basins or by the uplifting of higher-density mantle material during basin excavation. Mascons imply the existence of a rigid lunar crust for at least 3000 million years. The removal of crust during crater formation may also produce negative gravitational anomalies; these are observed in the younger large craters and around the Orientale Basin, which is only partly lava-filled. Because the circular maria are topographic lows, mascons may be partially isostatically compensated, i.e. they may have sunk under their excess density until some sort of equilibrium depth was reached with relation to adjacent material.
Collins Dictionary of Astronomy © Market House Books Ltd, 2006