A Chinese research team has published work explaining the stark difference between the Moon's near and far sides. The Earth-facing side is dominated by broad dark basalt plains known as maria, while the far side is covered by thicker crust and countless impact craters.

That asymmetry has been a signature unsolved problem in planetary science since the far side was first photographed in 1959. Crustal thickness, the distribution of volcanic activity and elemental composition all differ between the two hemispheres.

Analysing samples returned by lunar missions, the researchers present evidence of clear differences in the temperature and chemical composition of the mantle beneath each side. Values from far-side material differ systematically from near-side samples.

The contrast may originate in a large early impact or in the cooling of the lunar magma ocean. If the mantle on one side remained hot for longer, that would account for the concentration of volcanism there.

Direct returns of far-side material remain rare. The far side cannot communicate directly with Earth and requires a relay satellite, and landing and ascent control are correspondingly harder.

The findings were published in an international journal, and some material is reported to be earmarked for international collaborative study for further verification. The work is expected to inform resource prospecting and the selection of candidate sites for future crewed bases.