Estimation of the Size and Composition of the Lunar Core Based on the Gravity Field Model GL1500E and LLR Physical Libration Parameters

The lunar core is stratified into an outer core and an inner core. They can be estimated according to the second degree of gravity field model and selenophysical libration parameters from lunar laser ranging (LLR). We use the high-resolution lunar gravity field model GL1500E to evaluate the size and density of lunar core, which are inversed through a nonlinear particle swarm optimization. A large number of inversion indicates that, the outer diameter of the outer core is about 469 km with a corresponding density of 4 613 kg/m³, the radius of the inner core is around 303 km with a corresponding density of 7 004 kg/m³ and the density of mantle surrounds 3 340 kg/m³, which is quite close to the geological value of 3 360 kg/m³. The radii of inner core and outer core are quite close to other recent studies as well. The size and density of the lunar core found here can be therefore meaningful. If the lunar core is composed of pure iron and ferrous sulfide, our study shows that the inner core is mainly composed of pure iron whereas the outer core is largely composed of ferrous sulfide.