Earth Slows the Solar Wind As It Hits the Visible Side of the Moon

This is indicated by the first regolith samples taken from the hidden side by Chang'e-6. The Earth's 'magnetic shield' slows down the solar wind that hits the visible side of the Moon: this can be seen from the analyzes of the first lunar regolith samples taken from the hidden side of our natural satellite by the Chinese Chang'e-6 mission. The results are published in Nature Geoscience by a research team led by the Institute of Geology and Geophysics of the Chinese Academy of Sciences. The solar wind, with its continuous stream of charged particles at high speed, has been hitting the lunar surface for billions of years.

The lunar regolith has preserved traces of this bombardment, acting as a natural archive of volatile substances derived from the solar wind, including noble gases. Before this study, however, the lack of samples from the far side of the Moon prevented direct experiments demonstrating differences in the penetration of solar wind particles into the regolith between the two sides of our natural satellite. The turning point came with the Chinese Chang'e-6 mission, which in 2024 brought back to Earth 1,935 grams of regolith taken from the South Pole-Aitken basin on the far side of the Moon.

Isotopic analysis of the noble gases present in the samples demonstrates that ions from the solar wind penetrated deeper into the far side of the Moon than the visible side, meaning the hidden surface was exposed to higher energy particles. The study authors attribute this difference to a buffer zone found around Earth's magnetosphere, where the solar wind is slowed from its typical speed of 400 kilometers per second to about 200 kilometers per second.