Convection in the Moon and the existence of a lunar core

The marked departure of the Moon from hydrostatic equilibrium is an important clue to its physical evolution. The ellipticity of the earthward bulge, determined statistically from the geometrical librations, is over twice that determined dynamically from Cassini's laws. The inference is drawn that the internal density varies with angle. This may arise through convection or because the Moon has a finite strength which enables original density anomalies to be retained. The latter explanation is untenable if creep rates in the interior exceed 10$^{-20}$ s$^{-1}$. The hypothesis of flow suggests a search for evidence of small movements in the surface. A satisfactory theory must explain why the mechanical ellipticity is neither $\frac{1}{4}$ nor 1.