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The Moon is slightly asymmetrical.

The Moon is slightly asymmetrical in bulk form, possibly as a consequence of its evolution under Earth's gravitational influence. Its crust is thicker on the far side, while most volcanic basins -- and unusual mass concentrations -- occur on the near side.

Mass is not distributed uniformly inside the Moon. Large mass concentrations ("Mascons") lie beneath the surface of many large lunar basins and probably represent thick accumulations of dense lava. Relative to its geometric center, the Moon's center of mass is displaced toward Earth by several kilometers.