Chang’e-6 Samples Reveal Moon Volcanic Activity
- Scientists analyzing rocks returned by China's Chang'e-6 mission have uncovered evidence that enormous movements of molten rock shaped the Moon's two contrasting hemispheres billions of years ago.
- The side of the Moon facing Earth features vast plains of dark volcanic basalt and high concentrations of potassium, rare earth elements, and phosphorus.
- A major research opportunity arrived in 2024 when the Chang'e-6 mission became the first to return samples from the Moon's far side.
Scientists analyzing rocks returned by China’s Chang’e-6 mission have uncovered evidence that enormous movements of molten rock shaped the Moon’s two contrasting hemispheres billions of years ago. Hejiu Hui of Nanjing University led the research team examining the chemical compositions of lunar samples to solve a long-standing planetary mystery.
Contrasting Hemispheres of the Moon
The side of the Moon facing Earth features vast plains of dark volcanic basalt and high concentrations of potassium, rare earth elements, and phosphorus. In contrast, the permanently turned-away 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 magma ocean circulation, a massive collision, gravitational tidal heating, and uneven crustal development.
Chang’e-6 Lunar Sample Analysis
A major research opportunity arrived in 2024 when the Chang’e-6 mission became the first to return samples from the Moon’s far side. The analysis revealed that basalts collected by Chang’e-6 share chemical signatures with low-Ti basalts brought back by Apollo astronauts. This indicates that mantle minerals accumulated from the original magma ocean do not differ substantially in composition between the two hemispheres. Magnesium-suite rocks from both missions also show similar magnesium number values.
Magnesium-Rich Far Side Crust
While the mantle appears relatively uniform, the lunar crust reveals a pronounced contrast. Anorthosite samples returned by the far-side mission contain higher peak magnesium numbers than comparable Apollo samples. Furthermore, these magnesium-suite samples contain extremely low concentrations of rare earth elements and lower thorium-to-samarium ratios than their Apollo counterparts.
Gravitational Tidal Forces and Magma Circulation
To explain these findings, the research team developed a model involving large-scale heat-driven circulation within the ancient lunar magma ocean. After the Moon became tidally locked to Earth, gravitational forces generated more heat on the near side than on the far side. This uneven heating created a temperature difference that drove hot magma and magnesium-rich anorthosite material from the near side toward the far side, producing a thicker crust there while concentrating late-stage materials on the near side.