Exploration of the lunar deep interior through global deformation modeling.

The Moon is the most well-known extraterrestrial planetary body thanks to observations from ground-based, space-borne instruments and lunar surface missions. Data from Lunar Laser Ranging (LLR), magnetic, gravity, surface observations and seismic Apollo ground stations help us to quantify the deformation undergone by the Moon due to body tides. These observations provide one of the most significant constraints that can be employed to unravel the deep interior. The Moon deforms in response to tidal forcing exerted by, to first order, the Earth, the Sun and, to a lesser extent, by other planetary bodies. We use the degree-2 tidal Love number as a tool for studying the inner structure of our satellite. Based on measurements of the tidal Love numbers k2 and h2 and quality factors from the GRAIL mission, LLR and Laser Altimetry on board the LRO spacecraft, we perform a random walk Monte Carlo samplings for combinations of thicknesses and viscosities for models of Moon with and without inner core. By comparing predicted and observed parameters of the lunar tidal deformations, we infer constraints on the outer core viscosity, for a Moon with a thin outer core and a thick inner core, and a Moon with a thicker outer core but a denser and thinner inner core. In addition, by deducing the temperature and assuming the chemical composition of the low-viscosity zone, we obtain stringent constraints on its radius, viscosity and density.