China’s Chang’e-6 mission returned lunar soil that shows solar wind particles reached greater depths on the Moon’s far side than on the near side. The difference stems from Earth’s magnetosphere, which slows incoming particles that strike the near side.
Researchers from the Institute of Geology and Geophysics at the Chinese Academy of Sciences analyzed 1.935 grams of regolith collected from the South Pole-Aitken Basin. They measured noble gases including neon, krypton, and xenon and found clear isotopic and depth differences compared with earlier near-side samples.
The Chang’e-6 material showed a neon isotope ratio of 20Ne/22Ne at 11.34 ± 0.22. This value indicates stronger fractionation caused by higher-energy particles. Stepwise heating experiments released xenon mainly at high temperatures, confirming deeper implantation on the far side.
Earth’s magnetosphere creates the contrast. When the Moon passes through the magnetosheath, solar wind speed drops from roughly 400 km/s to 200 km/s. This slower flow affects only the near side, which faces Earth. The far side remains exposed to the undisturbed wind.
The team estimates that about 25 percent of the solar wind recorded at the Chang’e-5 near-side site arrived at reduced speed. No similar effect appears in the Chang’e-6 data. The findings were published in Nature Geoscience.