Temporal Variations of 222Rn Density Distributions in the Lunar Exosphere

Because of radiogenic processes, the lunar interior is a source of rare gases like helium (⁴He), argon (⁴⁰Ar), and radon (²²²Rn) that might be released continuously, or impulsively during moonquakes. The detection of radon is therefore important in the sense that it can help trace the crustal dynamics on the Moon. In this study, we will introduce a Monte Carlo–based model designed to investigate the time-dependent transient dynamics of the lunar ²²²Rn exosphere. Our model accounts for the background emission and transient ejection of gas molecules from the lunar surface, encompassing loss processes such as radioactive decay, photoionization, and the cold trapping in permanently shadowed regions near the poles. Additionally, it incorporates the diurnal temperature fluctuations of the lunar surface, which significantly influence the condensation duration of the radon atoms and their subsequent release near the sunrise. This model also can support future observations in missions such as Chang’E 6 or other lunar explorations.