Chang'e-6 far-side soil holds solar wind xenon deeper than near-side samples

September 14, 2026 at 11:00 AM2 min

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Solar-wind krypton and xenon in lunar soil from the far side of the Moon remained trapped through low-temperature heating steps, with most xenon released only at high temperatures. In near-side soil collected by Chang'e-5, xenon release appears bimodal, with a larger share coming off early. The difference suggests solar wind ions sit deeper inside grains on the far side.

Key Facts

Chang'e-6 returned 1,935 grams of regolith from the South Pole-Aitken basin, and the analyzed far-side sample CE6C0300YJFM001 weighed about 1,000 milligrams.
Seven aliquots were taken from the sample container, each weighed to better than one microgram precision.
Three aliquots were heated to complete fusion in a single shot, while four were heated in steps with a carbon dioxide laser.
The released gas was cleaned over getters, separated cryogenically, and measured on a noble gas mass spectrometer at the Institute of Geology and Geophysics in Beijing.
The average abundances of krypton and xenon were unremarkable compared with Apollo and Luna samples.

Depth Signature in Xenon Release

Solar-wind krypton and xenon in the far-side soil held on through the low-temperature steps of a laser heating run, and most of the xenon came off at the high end. In near-side soil collected by Chang'e-5, the equivalent xenon release seems to be bimodal, with a larger share coming off early. A team led from the Institute of Geology and Geophysics at the Chinese Academy of Sciences reports in Nature Geoscience that the difference reads as a depth signature: on the far side, solar wind ions sit further inside the grains.

Magnetosheath Shielding

Earth's magnetosphere carries a buffer region around it, the magnetosheath, and the Moon passes through that region twice in each orbit. Plasma inside the magnetosheath moves considerably more slowly than the undisturbed wind outside it, and slower ions stop nearer the surface of whatever they hit. By the paper's geometry, the near-side sampling site is exposed to that slowed plasma during those crossings and the far-side site is blocked from it.

Stepwise Laser Heating

Gas held near the surface of a mineral grain is easier to drive out than gas buried inside it, so a release curve read across rising temperature steps carries information about where the gas was sitting. Previous studies have shown no significant diffusion losses of krypton and xenon in lunar soil, which is why those two carry the argument, in contrast to hydrogen and helium, which the paper describes as readily disturbed by surface processes on the Moon. Each aliquot went into its own copper holder, sized to match the three-millimetre laser spot so the heating would be even, and the chamber was pumped down and baked before anything was fired.