Modeling Sodium Abundance Variations in the Lunar Crust: A Likely Proxy of Past Solar System History and a Potential Guide to Close-In Rocky Exoplanets

While the Moon and Earth are generally similar in terms of composition, there exist variations in the abundance of certain elements among the two bodies. These differences are a likely consequence of differing physical evolution of the two bodies over the solar system's history. We describe how our past and current modeling efforts indicate that a significant fraction of the initial sodium budget of the Moon may have been depleted and transported from the lunar surface since the Moon's formation. Using profiles of sodium abundances from lunar crustal samples may thus serve as a powerful tool towards exploring conditions on the Moon's surface throughout solar system history. Additionally, conditions on the Moon immediately after formation may still be recorded in the lunar crust and may provide a window towards interpreting observations from some of the first rocky exoplanets that will be most amenable to characterization.