The returner of the Chang'e-6 lunar probe is opened during a ceremony at the China Academy of Space Technology under the China Aerospace Science and Technology Corporation in Beijing, capital of China, June 26, 2024. /CFP

Chinese scientists are eager to unravel the mysteries of the moon after the successful collection of the world's first samples from the moon's far side by the Chang'e-6 mission.

Yang Wei, a researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences (CAS), emphasized the significance of the Chang'e-6 mission in the history of lunar exploration. "The Chang'e-6 mission represents a significant milestone in the history of human lunar exploration, and it will contribute to a more comprehensive understanding of lunar evolution."

"New samples will inevitably lead to new discoveries. Fascination with the moon is rooted in Chinese culture. Chinese scientists are eagerly anticipating the opportunity to contribute to lunar research," Yang added.

First time in history

For the first time in human history, samples have been collected from the far side of the moon. The international scientific community has shown unprecedented interest in the samples brought by the Chang'e-6 mission, said Li Xianhua, an academician at the CAS.

The Chang'e-6 samples will be of great significance in studying the two-faced moon, which is crucial for understanding this celestial body, according to Li.

"We have never conducted a detailed study of the South Pole–Aitken Basin before. The exact time of the impact that formed the basin and the consequences of the impact are subject to investigation. Scientists have numerous theoretical speculations, but need analysis of the samples to test these hypotheses," Li said.

The impact was so huge that materials from the lunar lower crust or even upper mantle deep beneath the surface might have been brought up, which were usually difficult to obtain. "The Chang'e-6 samples are of great significance for our understanding of the formation and early evolution of the moon," Li noted.

In addition, the landing site of the Chang'e-6 mission was on a basalt formed by volcanic activity. Volcanic activities on the far side of the moon were relatively rare compared with the near side, and it would be intriguing to study and compare the volcanic activities on both sides of the moon, Li said.

"We have long anticipated the samples from the far side of the moon. Since the beginning of this year, our institute has organized a team for the research on the Chang'e-6 samples. We held seminars every week to discuss the related scientific questions and plan our research in advance," Li added.

"We recently also invited experts from other institutions who specialize in lunar studies to join us for discussions. The venue, which can accommodate 200 people, was packed, with many enthusiastic participants standing," Li said.

Scientists selected problems they deemed most important, such as the origin of lunar asymmetry, the composition of the lunar deep crust or mantle, the formation time of the South Pole–Aitken Basin and the Apollo Basin, the volcanic history of the lunar far side, the water content, and discovery of new minerals or rocks on the moon.

Lunar samples

Lunar samples brought by the earlier Chang'e-5 mission have already drawn applications for access from international scholars, and the process is well underway. The Chang'e-6 lunar probe carried four international payloads that were developed jointly by Chinese and foreign scientists. It is conceivable that the openness of Chinese lunar exploration activities will be mirrored in the study of Chang'e-6 lunar samples, Yang said.

As the moon's revolution cycle is the same as its rotation cycle, the same side always faces Earth. The other face, most of which cannot be seen from Earth, is called the far side or "dark side" of the moon. This term doesn't refer to visible darkness, but rather the mystery shrouding the moon's largely unexplored terrain.

Remote-sensing images show the moon's two sides are very different in terms of the thickness of lunar crust, magma activities and compositions.

The reason why the near side and the far side of the moon are so different remains one of the greatest mysteries, said Lin Yangting, another scientist from the CAS Institute of Geology and Geophysics.

"Through the analysis and research of the Chang'e-6 samples, we could have a comprehensive understanding of the moon, filling many gaps in our knowledge and addressing significant scientific questions," Lin said.

The Chang'e-6 probe landed and collected samples in an impact crater known as the Apollo Basin, located within the South Pole-Aitken Basin on the far side of the moon.

The colossal South Pole-Aitken Basin was formed by a celestial impact over 4.3 billion years ago and has a diameter of 2,500 kilometers, equivalent to the distance from Beijing to Hainan Province, and a depth of about 13 kilometers. It is believed to be the largest impact crater found in the inner solar system so far.

Compared to Chang'e-5, the landing and sampling site of Chang'e-6 has a complex geological structure, and the samples collected are likely to be mixtures, including in-situ basalt as well as materials ejected from surrounding areas due to the impact of small celestial bodies, Lin said.

"China's Chang'e-5 mission in 2020 initiated a new phase of in-depth studies on lunar samples after a 44-year hiatus, advancing our understanding of the moon's evolution," said Li.

However, prior to the Chang'e-6 mission, all 10 lunar sampling missions in human history, including the Chang'e-5 mission, took place on the near side of the moon.

"Our current knowledge of the moon primarily comes from research on samples collected from its near side, which does not represent a comprehensive scientific understanding of the whole moon," Li added. (CGTN)