Earthshine on a Young Moon: Explaining the Lunar Farside Highlands

摘要

The lunar farside highlands problem refers to the curious and unexplainedfact that the farside lunar crust is thicker, on average, than the nearsidecrust. Here we recognize the crucial influence of Earthshine, and propose thatit naturally explains this hemispheric dichotomy. Since the accreting Moonrapidly achieved synchronous rotation, a surface and atmospheric thermalgradient was imposed by the proximity of the hot, post-Giant-Impact Earth. Thisgradient guided condensation of atmospheric and accreting material,preferentially depositing crust-forming refractories on the cooler farside,resulting in a primordial bulk chemical inhomogeneity that seeded the crustalasymmetry. Our model provides a causal solution to the lunar highlands problem:the thermal gradient created by Earthshine produced the chemical gradientresponsible for the crust thickness dichotomy that defines the lunar highlands.