GRAIL, LLR, and LOLA constraints on the interior structure of the Moon

The interior structure of the Moon is constrained by its mass, moment of inertia, and k2 and h2 tidal Love numbers. We infer the likely radius, density, and (elastic limit) rigidity of all interior layers by solving the inverse problem using these observational constraints assuming spherical symmetry. Our results do not favor the presence of a low rigidity transition layer between a liquid outer core and mantle. If a transition layer exists, its rigidity is constrained to 43−9+26 GPa, with a preference for the high rigidity values. Therefore, if a transition layer exists, it is more likely to have a rigidity similar to that of the mantle (∼70 GPa). The total (solid and liquid) core mass fraction relative to the lunar mass is constrained to 0.0098−0.0094+0.0066 and 0.0198−0.0049+0.0026 for interior structures with and without a transition layer, respectively, narrowing the range of possible giant impact formation scenarios.