Chang'e-6 samples provide evidence suggesting global "magma ocean" on early moon

BEIJING, Feb. 28 (Xinhua) -- A new study of the lunar samples collected by China's Chang'e-6 mission has verified the hypothesis that the moon was entirely covered by a molten "magma ocean" in the early stages after its birth, providing critical evidence for understanding the moon's origin and evolution.

This study, led by a joint research team organized by the China National Space Administration (CNSA), has been published in the latest issue of the journal Science.

The Chang'e-6 mission in 2024 accomplished humanity's first-ever sampling from the far side of the moon, successfully retrieving 1,935.3 grams of lunar materials from the Apollo Basin within the South Pole-Aitken (SPA) Basin.

The research team from the Institute of Geology, Chinese Academy of Geological Sciences, was granted two grams of these Chang'e-6 samples to conduct their research.

The study revealed that the composition of basalt, a type of volcanic rock, from both the far and near sides of the moon proved similar. The basalt present in the Chang'e-6 samples is primarily 2.823 billion years old, and its characteristics support the lunar magma ocean model. The research also suggests that the impact event that created the SPA Basin may have altered the moon's early mantle, according to Liu Dunyi, a senior researcher at the institute.

The lunar magma ocean model was previously established based on samples from the moon's near side. The model proposes that the newborn moon went through a global melting event, creating a vast magma ocean. As this ocean cooled and crystallized, less dense minerals floated to the surface to form the lunar crust, while denser minerals sank to form the mantle. The remaining melt, enriched with incompatible elements, formed the KREEP layer, with the name derived from the initials of the key components, namely potassium (K), rare earth elements (REE) and phosphorus (P), Liu explained.

However, for decades, all lunar samples came from the moon's near side, leaving the model incomplete. "Without samples from the far side, it was like solving a puzzle with half the pieces missing," said Liu, while adding that the far-side samples collected by Chang'e-6 had changed this scenario.

"Our analysis showed that the KREEP layer exists on the moon's far side as well. The similarity in basalt composition between the far and near sides indicates that a global magma ocean may have spanned the entire moon," said Che Xiaochao, an associate researcher at the institute.

The SPA Basin, where Chang'e-6 landed, is no ordinary crater. Stretching 2,500 km, which is comparable to the distance from Beijing to south China's Hainan, and plunging to a depth of 13 km, this colossal scar, formed by a cataclysmic asteroid impact 4.3 billion years ago, is the oldest and largest impact basin in the inner solar system, according to scientists.

Notably, the new study also reveals that the lead isotope evolution paths in basalt from the far and near sides are different. This suggests that different regions of the moon evolved differently after the magma ocean crystallized. Giant impact events, especially the one that created the SPA Basin, likely changed the physical and chemical properties of the moon's mantle, according to Long Tao, another senior researcher in the team.

"In other words, the moon was once covered by a global magma ocean, but later bombardments of asteroids caused different evolution processes on the near and far sides," Long explained.

The research team plans to delve deeper into the moon's early impact history. "The Chang'e-6 sampling site is in the largest and oldest impact basin in the inner solar system, so it may contain records useful for the study of early solar system impacts," Che said. "We also hope to find materials from the moon's mantle."

"Studying the moon's impact history helps us understand Earth's own past, which has been obscured by tectonic activities," Long added.

The CNSA emphasized its commitment to advancing lunar research and sharing scientific findings with the international community. ■