The Moon has no atmosphere to shield its surface from the harsh space environment. Consequently, its soil is constantly exposed to streams of charged particles from the Sun, known as the solar wind. Over long periods, these particles gradually damage the uppermost surface of minerals, leaving microscopic traces that scientists can analyze.
In this study, scientists examined lunar soil grains returned by China’s Chang’e-5 and Chang’e-6 missions, which collected samples from different regions of the Moon. Using advanced microscopic and chemical analysis methods, the team investigated tiny structural changes in the minerals caused by prolonged exposure to solar wind particles.
They discovered that some grains preserve irradiation signatures accumulated over hundreds of thousands to millions of years. These signatures are seen as thin damaged rims in the grain’s uppermost surface, and tracks in the deeper part of the grain. By measuring these features, researchers can estimate how long each grain was exposed on the lunar surface.
The study also identified differences between samples collected from the Moon’s near side (Chang’e-5) and far side (Chang’e-6). Because the Moon periodically passes through Earth’s magnetic field, some regions may experience slightly different solar wind conditions. Comparing samples from the two Chang’e missions provides new insights into how space weathering varies across the lunar surface.
These findings demonstrate that lunar soil functions as a natural archive of the Sun’s activity over long timescales. By studying these tiny mineral records, scientists can gain a better understanding of how solar radiation gradually alters the surfaces of the Moon and other airless bodies, such as asteroids and Mercury.
R. Liu et al., “Million-year solar wind irradiation recorded in Chang’E-5 and Chang’E-6 samples,” Nature Communications, vol. 16, 2025, doi: 10.1038/s41467-025-64239-8
