The study, conducted by a collaborative team under the China National Space Administration (CNSA), has been published in the latest issue of the journal Science.
Chang'e 6, which in 2024 became the first mission to collect samples from the moon's far side, successfully returned with 1,935.3 grams of lunar material from the Apollo Basin within the South Pole-Aitken (SPA) Basin. Researchers from the Institute of Geology at the Chinese Academy of Geological Sciences received two grams of these samples for in-depth examination.
Their findings reveal a striking similarity in the composition of basalt, a volcanic rock, between the moon's far and near sides. The basalt from the Chang'e 6 samples dates back approximately 2.823 billion years and reinforces the lunar magma ocean model. Senior researcher Liu Dunyi explained that the study suggests the impact event that formed the SPA Basin may have altered the moon's early mantle.
The lunar magma ocean hypothesis was previously constructed based on samples exclusively collected from the near side. This model theorizes that the moon underwent a period of global melting shortly after its formation, creating a vast magma ocean. As it cooled and crystallized, lighter minerals surfaced to form the crust while denser materials sank, shaping the mantle. The residual melt, enriched with incompatible elements, formed the KREEP layer-an acronym denoting potassium, rare earth elements, and phosphorus.
However, without samples from the far side, the model remained incomplete. "Without samples from the far side, it was like solving a puzzle with half the pieces missing," Liu remarked. The far-side specimens retrieved by Chang'e 6 have now filled this gap.
"Our analysis confirmed that the KREEP layer is present on the moon's far side. The comparable basalt compositions on both sides strongly indicate that a global magma ocean once covered the entire moon," noted Che Xiaochao, an associate researcher at the institute.
The SPA Basin, the Chang'e 6 landing site, is a unique lunar feature. Spanning 2,500 km-roughly the distance between Beijing and Hainan province-and reaching depths of 13 km, this vast crater was created by an asteroid impact 4.3 billion years ago. Scientists regard it as the oldest and largest impact basin in the inner solar system.
Interestingly, the study also uncovered distinct lead isotope evolution paths in basalt samples from the moon's near and far sides, suggesting that different regions underwent unique evolutionary processes after the magma ocean solidified. Senior researcher Long Tao attributed these differences to massive asteroid impacts, particularly the one that created the SPA Basin, which may have altered the moon's mantle both physically and chemically.
"In other words, while the moon was once covered by a global magma ocean, subsequent asteroid bombardments led to divergent evolutionary paths for the near and far sides," Long explained.
Looking ahead, the research team intends to investigate the moon's early impact history further. "The Chang'e 6 site, situated in the largest and oldest impact basin in the inner solar system, may hold valuable records for studying early solar system collisions," Che stated. "We also hope to uncover materials originating from the moon's mantle."
Long emphasized that exploring the moon's impact history is crucial for understanding Earth's own past, much of which has been erased by tectonic activity.
The CNSA reaffirmed its dedication to advancing lunar research and sharing scientific discoveries with the global community.
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