On October 19th Thursday 2021, the Chinese Academy of Sciences released the latest research results of the Chang’e-5 lunar scientific research samples. A number of breakthroughs have given a new understanding of the evolution of the moon. The research results of the lunar samples of Chang’e 5 show that magma activity still existed on the moon until 2 billion years ago. The lunar mantle source area of late magma activity is not rich in radioactive heat-generating elements and is very “dry”. This series of research is led by the Institute of Geology and Geophysics of the Chinese Academy of Sciences and the National Astronomical Observatory, and jointly carried out by a number of research institutions. The related results have formed 4 papers, one published in the “National Science Review”, and published in the international academic journal “Nature” 3 articles.
The duration and geochemical characteristics of the lunar basalt magma are the “keys” for understanding the thermal-chemical evolution of the moon. Previous studies have confirmed that magma activity on the moon lasted at least approximately 2.8 to 3 billion years ago. However, there has been controversy in the scientific community about the exact time when the lunar magma activity ceased. The study found that the lunar sample of Chang’e 5 is a new type of lunar basalt, which is different from the lunar samples collected and returned by the United States and the Soviet Union. Researchers analyzed more than 50 uranium-rich minerals in the basalt cuttings of the Chang’e 5 lunar sample and determined that the basalt formation age was 20.30±0.04 billion years, indicating that there was still magma activity on the moon until 2 billion years ago, which is more than the limit of previous lunar samples. Magma activity has been extended for about 800 million years.
10月19日，中国科学院发布嫦娥五号月球科研样品最新研究成果，多项突破性进展给出了对月球演化的全新认识。嫦娥五号月球样品研究结果显示，月球直到20亿年前仍存在岩浆活动，晚期岩浆活动的月幔源区并不富含放射性生热元素，而且非常“干”。该系列研究由中国科学院地质与地球物理研究所和国家天文台主导，联合多家研究机构共同开展，相关成果形成4篇论文，在《国家科学评论》发表1篇，在国际学术期刊《自然》发表3篇。
月海玄武岩浆的持续时间和地球化学特征是理解月球热-化学演化的“钥匙”。此前的研究已证实，月球岩浆活动至少持续到大约28亿至30亿年前。但对于月球岩浆活动停止的确切时间，科学界一直存在争议。研究发现，嫦娥五号月球样品为一类新的月海玄武岩，不同于美国和苏联采集返回的月球样品。科研人员对嫦娥五号月球样品玄武岩岩屑中50余颗富铀矿物进行分析，确定玄武岩形成年龄为20.30±0.04亿年，表明月球直到20亿年前仍存在岩浆活动，比以往月球样品限定的岩浆活动延长了约8亿年。
The cause of the most recent magmatic activity on the Moon has always been an unsolved mystery. At present, there are two possible explanations in the scientific community: the lunar mantle source is rich in radioactive elements to provide a heat source, or the lunar mantle is rich in water to lower its melting point. The latest study found that the lunar mantle source area of the basalt from the lunar sample of Chang’e 5 is not enriched in “Krip material.” Since the “Krip material” is rich in radioactive heat-generating elements, this result proves that the radioactive heat-generating elements of the lunar mantle are not the main reason for the formation of the basalt of the Chang’e-5 lunar sample. Regarding whether the magma source area is rich in water, the research team measured the water content and hydrogen isotopic composition in the basalt of the Chang’e 5 lunar sample, and found that the water content in the lunar mantle source area was only 1 to 5 micrograms/g, which means that the lunar mantle Very “dry”. This discovery also excludes the hypothesis that the lunar mantle is rich in water and has a low melting point, resulting in an abnormally prolonged duration of magma activity in this area.
月球最晚期岩浆活动的成因一直是未解之谜，目前科学界存在两种可能的解释：月幔源区富含放射性元素以提供热源，或月幔富含水从而降低其熔点。最新研究发现，嫦娥五号月球样品玄武岩的月幔源区并不富集“克里普物质”。由于“克里普物质”富含放射性生热元素，这一结果证明月幔放射性生热元素并不是形成嫦娥五号月球样品玄武岩的主要原因。对于岩浆源区是否富含水，科研团队测定了嫦娥五号月球样品玄武岩中的水含量和氢同位素组成，发现月幔源区的水含量仅为1至5微克/克，也就是说月幔非常“干”。这一发现也排除了月幔富水而具有低熔点，导致该区域岩浆活动持续时间异常延长的猜想。
(B), (c) and (d) are the partial images of the cuttings respectively.
(B) The figure shows the melt inclusion (MI) surrounded by ilmenite.
(C) and (d) show that apatite is mainly produced in the intergranular area and is euhedral or semi-automorphic
According to the hypothesis of the origin of the big impact, the original Earth collided with a planetary planet the size of Mars, forming a “disk” composed of high-temperature magma and gas around the earth. When the temperature begins to cool, materials such as silicate first gather to form the moon (Figure 1), and water is a highly volatile material that escapes into space in a gaseous form and is lost. Therefore, the moon born in this way contains almost no water and is a nearly dry planet. The research results of the lunar samples of Chang’e 5 further provided supporting evidence for the origin and evolution of the moon, raised new scientific questions for the study of the lunar thermal evolution history, and proposed new directions for future lunar exploration and research.
We welcome domestic and foreign scientists to join the ranks of the research on these data and samples. At present, research on lunar samples is mainly carried out by domestic scientific research institutions, and foreign scientists have joined the Chinese team to carry out joint research. In the follow-up, we will issue relevant policies, uphold the principles of “equality and mutual benefit, peaceful use, and inclusive development”, expand international exchanges and cooperation, and provide more Chinese wisdom, Chinese solutions, and Chinese power for the peaceful use of space and the promotion of a community with a shared future for mankind.
根据大撞击起源假说，原始地球与一个火星大小的星子碰撞，形成了一个围绕地球的、由高温岩浆和气体组成的“盘”。当温度开始冷却时，硅酸盐等物质首先聚集形成月球（图1），而水属于强挥发的物质，会以气态形式向太空逃逸而丢失。因此，这种方式诞生的月球，几乎不含水，是一个近乎干透了的星球。嫦娥五号月球样品的研究成果进一步为月球起源及演变提供了支撑证据，为月球热演化历史研究提出了新的科学问题，对未来的月球探测和研究提出了新的方向。
我们欢迎国内外科学家加入对这些数据和样品的研究行列。目前，月球样品研究主要由国内科研机构牵头开展，也有国外的科学家加入中国团队开展联合研究。后续，我们将出台相关政策，秉持“平等互利、和平利用、包容发展”的原则，扩大国际交流与合作，为人类和平利用太空、推动人类命运共同体提供更多中国智慧、中国方案、中国力量。
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