Scientists say they may have solved one of lunar science’s longest running puzzles, thanks to the first physical samples ever returned from the Moon’s far side. New chemical analysis of lunar dust collected by China’s Chang’e-6 mission suggests that a colossal ancient impact fundamentally altered the Moon’s interior, helping explain why its near and far hemispheres look strikingly different.
For decades, scientists have been puzzled by the Moon’s uneven appearance. The near side, which always faces Earth, is dominated by broad volcanic plains, while the far side is rugged, heavily cratered, and largely lacking in lava flows. Since the Soviet Luna 3 probe first photographed the far side in 1959, theories have ranged from differences in crust thickness to variations in internal heat, but direct evidence was missing.
That gap closed in 2024 when Chang’e-6 successfully returned dust from the Moon’s far side. The samples were collected from the South Pole Aitken Basin, a massive impact structure nearly 2,500 kilometers wide and believed to be the largest known crater in the solar system.
A research team led by Heng-Ci Tian at the Chinese Academy of Sciences analyzed isotopes of potassium and iron in the samples. When compared with near side material gathered during the Apollo missions and China’s Chang’e-5 mission, the differences were stark. Far side samples were enriched in heavier isotopes, particularly potassium, while lighter isotopes were depleted. According to the study published in the Proceedings of the National Academy of Sciences, these values were compared with samples from the Moon’s near side, previously gathered during the Apollo missions and by China’s Chang’e-5 spacecraft.
According to the researchers, this pattern cannot be explained by typical volcanic processes. Instead, they argue it points to extreme heating during the South Pole Aitken impact. The collision likely vaporized lighter isotopes, allowing them to escape, while heavier isotopes remained behind, permanently altering the Moon’s chemical makeup.
More significantly, the data suggest the effects of the impact reached deep into the lunar mantle. Isotopic signatures indicate that the far side mantle may have been chemically reworked, possibly through large scale melting and redistribution of material triggered by the collision.
The findings support a growing view that massive impacts do more than scar planetary surfaces. They can reshape internal structures, influence long term geological evolution, and create hemispheric differences that persist for billions of years.
With far side samples now available for detailed study, researchers finally have direct evidence from a region once completely inaccessible. As analysis continues, the Moon’s asymmetry is shifting from an unsolved curiosity to a case study in how violent beginnings can leave lasting planetary fingerprints.