China’s Chang’e-6 mission has found a new form of iron in Moon dust, and it does not match anything in the Apollo samples from the Moon’s near side.The mineral, called gamma-Fe, is a rare form of metallic iron found as round nanoparticles. It was recovered from the mission’s two-kilogram sample of far-side soil.Writing in Nature Communications, the team says the grains were shaped by billions of years of micrometeorite impacts. Apollo dust, in contrast, is rich in alpha-Fe, a different form made by solar wind.The difference comes down to shielding.

Gamma-Fe appears to form only where the Moon’s surface is protected by Earth’s magnetic tail, which points away from the Sun toward the Moon’s far side.The find is a geological fingerprint. It shows the far side weathers in a fundamentally different way, and gives scientists a new marker for reading space-weathering history on other worlds. The nanoparticles formed over billions of years of micrometeorite impacts.

Scientists see gamma-Fe as a new marker for reading space-weathering history.