After the Chang'e-6 mission brought home the world's first samples collected from the moon's far side on Tuesday, Chinese scientists eagerly look forward to conducting research on the samples to uncover more mysteries of the moon.

"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," said Yang Wei, a researcher at the Institute of Geology and Geophysics of the Chinese Academy of Sciences (CAS).

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

Lunar samples brought by the earlier Chang'e-5 mission have already drawn applications for access from international scholars, with the process 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, including lunar crust thickness, 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 of the moon, 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 (SPA) Basin on the far side of the moon.

The colossal SPA Basin was formed by a celestial impact over 4.3 billion years ago and has a diameter of 2,500 km, equivalent to the distance from Beijing to Hainan, and a depth of about 13 km. 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 Xianhua, an academician of the CAS.

However, prior to the Chang'e-6 mission, all ten 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 said.

For the first time in human history, samples were retrieved from the far side of the moon. The international scientific community has shown unprecedented interest in the samples returned by the Chang'e-6 mission, Li said.

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 SPA Basin before. The exact time of the impact that formed the SPA 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 have selected scientific 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 SPA 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.