Moon rocks offer clues to its two faces

A team led by Professor Hejiu Hui of Nanjing University examined rocks collected by China’s Chang’e-6 mission, which returned the first samples from the lunar far side in 2024. Researchers compared their chemistry with material brought back by Apollo and Chang’e-5 missions.

The Moon’s Earth-facing side contains extensive dark volcanic plains, while its far side has a thicker crust dominated by ancient, heavily cratered highlands.

The analysis found that rocks originating from the mantle beneath both hemispheres had broadly similar chemical characteristics. Far-side crustal rocks, however, were richer in magnesium, while other samples contained less material enriched in potassium, rare earth elements and phosphorus.

The researchers propose that these differences developed as the Moon’s ancient ocean of molten rock cooled and solidified.

After the Moon became tidally locked, keeping the same hemisphere facing Earth, stronger tidal heating on the near side may have driven vast currents beneath the developing crust. These flows could have carried early magnesium-rich crust toward the far side, thickening it while concentrating remaining molten material on the near side.

“This systematic geochemical comparison … indicates that the mantle displays no clear compositional dichotomy,” the authors wrote.

The proposed mechanism offers an explanation for how similar underlying mantle materials produced such different lunar landscapes. However, the researchers acknowledge that the samples may not represent the entire far side and that their model is not the only possible explanation. Further geochemical evidence will be needed to test the findings.

Earlier, Qazinform News Agency reported that October’s skywatching highlights include Saturn at opposition, the Orionid meteor shower and the Moon appearing near the Pleiades star cluster.