Human lunar exploration projects in the past 60 years have revealed that the surface of the moon, that is, the lunar crust, is dominated by plagioclase minerals, while the mantle covered by the lunar crust may be more mafic (rich in iron and magnesium). However, it has been difficult for scientists to find out the detailed structure of the lunar mantle for many years.
In the early morning of May 16, Beijing time, the world's top academic journal Nature published an online article from Chinese scientists: China's chang'e-4 lunar probe is located in the von K & Aacute; RM & Aacute; The yutu-2 lunar rover was deployed to explore the South Pole Aitken basin. Based on the initial spectral observations of the visible near infrared imaging spectrometer (vins), scientists inferred that the low calcium pyroxene and olivine minerals on the lunar surface might originate from the lunar mantle. This is also the first preliminary evidence of mantle source material on the back of the moon.
Li Chunlai, deputy director of the National Astronomical Observatory of the Chinese Academy of Sciences and director of the lunar and deep space exploration research department, is the first author and corresponding author of the paper. Ren Xin and Liu Jianjun of the lunar and deep space exploration research department are the co corresponding authors. The research work is jointly completed by the National Astronomical Observatory of the Chinese Academy of Sciences, the Key Laboratory of space active optoelectronic technology of Shanghai Institute of Technical Physics of the Chinese Academy of Sciences, and the Institute of Geochemistry of the Chinese Academy of Sciences. Ouyang Ziyuan, the chief scientist of China's lunar exploration project and known as the father of Chang'e, is also one of the authors of the paper.
Like many other planets in the solar system, the moon is thought to have experienced a magma ocean stage, in which the moon is mostly or completely molten. According to the theory of the early evolution of the moon, the lunar crust was formed by the floating and crystallization of lighter plagioclase components in the magmatic ocean, while heavier minerals such as olivine and pyroxene sank to form the lunar mantle. However, this inference about the composition of the lunar mantle has not been well confirmed.
The characteristics of the lunar mantle, especially in its composition, structure and bedding, are still uncertain and lack of literature. Patrick Pinet, from the University of Toulouse, France CNRS and Irap, wrote in an interpretation article: surprisingly, the Apollo spacecraft of NASA and the lunar probe of the Soviet Union both landed near the moon, but neither of them brought back samples from the lunar mantle.
In order to explore the lunar mantle, scientists all over the world focus on the crater. It is generally believed that the objects leading to the crater formation may penetrate the lunar shell and reach the interior of the moon, causing part of the lunar mantle material to be brought to the lunar surface. The largest, deepest and oldest crater on the moon is the South Pole Aitken basin on the back of the moon, with a diameter of 2500 km and formed more than 4 billion years ago.
Data from NASA's previous grail mission, which was to accurately explore and map the moon's gravity field to determine its internal structure, indicate that the crater may have been caused by an impact that penetrated the moon's crust and interior. Therefore, the exploration of the Antarctic Aitken basin is always expected by international scientists.
The Chinese lunar exploration project (CLEP) is the world's first lunar backside soft landing and patrol exploration. In May 2018, China launched the magpie bridge relay satellite, which is an earth to moon communication satellite serving chang'e-4, paving the way for subsequent lunar backside exploration and sampling return.
On January 3, 2019, chang'e-4 landed in the Antarctic Aitken basin, becoming the first unmanned probe to land on the back of the moon in human history. In order to sample the lunar mantle as much as possible, the landing site is the von K & Aacute; RM & Aacute; in the relatively flat Antarctic Aitken basin; The yutu-2 lunar rover was deployed to explore the Antarctic Aitken basin.
The paper introduces that on the first day of chang'e-4 landing on the moon, the visible near infrared imaging spectrometer successfully obtained high-quality spectral data of two exploration points near the landing point. After analyzing the data, the researchers found that the spectral data they obtained were different from those of typical lunar surface materials. This means that the material detected near the landing site is significantly different from most samples taken from the lunar surface. In particular, these materials contain mafic components, mainly a mixture of olivine and low calcium pyroxene (LCP), while the content of high calcium pyroxene (HCP) is very low.
Based on this, the researchers infer that the minerals of hypocalcite and olivine on the lunar surface may come from the upper mantle of the moon.
In the paper, the researchers also suggested that these substances came from the impact event of the Finsen impact crater near the detection point. The fenson crater impact event further excavated the deeper materials in the Antarctic aitoken basin, and the sputtered materials were scattered in the 'plain' of the von & bull; Carmen crater in the form of radiation.
Fenson impact crater is a relatively young large impact crater in the south of the back of the moon. It is formed by small objects impacting the inner surface of the Antarctic aitoken basin, with a diameter of 72 km, and is located in the northeast of the landing site.
In addition to the above inference, the researchers wrote, their results also confirm the inference that the lunar mantle is rich in olivine. The prediction that the lunar mantle is rich in olivine can not be ruled out. The lunar mantle may be mainly composed of low augite and olivine, rather than low augite and few olivine.
Pinet also said: 'the results of Li Chunlai and his colleagues are exciting, which is of great significance in determining the composition of the lunar mantle. In a broader sense, our findings may also influence our understanding of the formation and evolution of the interior of the moon. '
The researchers mentioned that in the future, yutu-2 will continue to observe the lunar soil in Feng & bull; Carmen crater, and these valuable data will help us to study its geological origin and elemental composition. It is reported that subsequent exploration will try to send the samples back to earth.