The abundance of 40Ar in lunar soils is significantly higher than the expected values from solar wind implantation and 40K decay, a phenomenon known as 40Ar excess. Traditionally, this excess is attributed to 40Ar generated by the decay of 40K within the Moon. This radiogenic 40Ar degasses to the lunar surface, where it is ionized by solar radiation and subsequently captured by lunar soils. However, stepwise heating (200 °C–1300 °C) and degassing analyses of noble gas isotopes in Chang'e-5 lunar soils samples reveal the presence of two types of 40Ar: one unrelated to 36Ar, likely originating from in situ 40K decay in the soils, and another correlated with 36Ar, which may primarily derive from Earth wind. Earth wind, an ion flux formed by the escape of Earth's atmosphere, is thought to be injected onto the lunar surface under the regulation of Earth's magnetosphere. The study proposes that the excess 40Ar in lunar soils may primarily stem from the continuous escape of Earth's atmosphere and be injected onto the lunar surface through both the inner and outer regions of Earth's magnetosphere, offering a new perspective for understanding volatile exchange between the Earth-Moon system.

https://doi.org/10.1016/j.icarus.2025.116803