Uranium on the Moon: Global distribution and U/Th ratio

Abstract

The Kaguya Gamma‐Ray Spectrometer uniquely identified uranium gamma‐ray lines from the Moon with a superior energy resolution of ∼1%. A global lunar map of uranium distribution is derived for the first time. It was found that uranium abundances vary up to 2 ppm with an average of ∼0.3 ppm, while the average thorium abundance was ∼1.2 ppm. From these analyses, significant variation in U/Th ratio was found in the farside of the Moon that had not been reported by previous observations or in lunar materials. Our observations suggest that the lunar highland is not as uniform as has been long considered.