Scientists investigating why the Moon's two sides look so different have uncovered new evidence that could help explain this long-standing mystery. A research team led by Professor Hejiu Hui of Nanjing University analyzed lunar rocks collected by China's Chang'e-6 (CE6) mission and found clues suggesting that enormous movements of molten rock shaped the Moon billions of years ago. The researchers examined the chemical compositions of three types of lunar rock: anorthosites, Mg-suite rocks, and mare basalts.
They compared these samples from the Moon's far side with material collected from the near side during the Apollo and Chang'e-5 missions. Their findings suggest that the Moon's striking differences emerged through large-scale heat-driven circulation within its ancient lunar magma ocean (LMO), after the Moon became tidally locked to Earth. Why the Moon's Two Sides Are So Different The side of the Moon facing Earth looks remarkably different from the hemisphere permanently turned away from us.
The near side features vast plains of dark volcanic basalt and relatively high concentrations of potassium, rare earth elements, and phosphorus (KREEP). In contrast, the far side is dominated by ancient, heavily cratered highlands, with a much thicker crust and relatively few volcanic plains. Scientists have debated the origins of this uneven structure for decades.
Proposed explanations have included differences in how the Moon's original magma ocean circulated, a massive collision, heating caused by gravitational tides, and uneven development of the lunar crust. However, none of these ideas has gained universal acceptance. Another important question has remained unanswered.
Although the contrasts between the two hemispheres are clearly visible at the surface and within the crust, scientists have been uncertain whether similar differences extend deep into the lunar mantle. Chang'e-6 Samples Reveal a Surprising Similarity A major opportunity to investigate this mystery arrived in 2024, when Chang'e-6 became the first mission to return samples from the Moon's far side. For the first time, scientists could directly compare rocks collected from both lunar hemispheres.
The analysis revealed an important similarity beneath the Moon's contrasting surfaces. Basalts collected by Chang'e-6 show chemical signatures indicating that they originated from depleted mantle material, much like the low-Ti basalts brought back by Apollo astronauts. This suggests that the mantle cumulates, minerals that accumulated as the Moon's magma ocean crystallized, do not differ substantially in composition between the two hemispheres.
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