Li Yang: What Did Chang'e Find from Its Lunar Exploration?

The observation of galaxies over ten thousand years brought us a close look at one gram of lunar soil. In 2004, China officially launched the "Chang'e" Lunar Exploration Programme. After completing the three steps of lunar exploration: orbiting, landing, and returning, the Chang'e 5 rover landed near Mons Rümker in the northwest of Oceanus Procellarum on 1 December 2020 and collected a total of 1,731 grams of "lunar specialities". It successfully returned to the Dorbod Banner landing site on 17 December 2020, completing China's first extra-terrestrial sample-returning mission, which marked significant progress and a breakthrough in China's Lunar Exploration Programme.

What scientific secrets are hidden in the Chang'e 5 lunar soil samples? What research results have Chinese scientists achieved? Li Yang, Deputy Director of the Centre for Lunar and Planetary Sciences of the Institute of Geochemistry, Chinese Academy of Sciences, unveiled the mystery of Chang'e's lunar exploration in an exclusive interview with East Meets West of the China News Service.

A summary of the interview is as follows:

CNS: What is the research value of lunar soil? How can it help us to improve our understanding of the formation and evolutionary history of the Moon?

Li Yang: Lunar soil is a fine powder formed by the breaking, melting, vaporising, depositing, cementing, and tumbling of rocks on the lunar surface under the impact of small celestial bodies and meteorites, solar wind radiation, solar flare particles, galactic cosmic rays, and temperature differences between day and night. The average thickness of lunar soil is about 5 metres in the lunar maria and about 10 metres in the highlands.

The lunar soil, which covers the majority of the lunar surface, is both a direct object for visual observation and remote sensing, as well as a major carrier and target for landing, roving, and sample-returning. The study of lunar soil not only provides us with a wealth of information on the formation and evolutionary history of the Moon, but its physical, chemical, and mechanical properties also provide important support for the implementation of scientific and engineering missions such as lunar landing and roving, as well as future lunar base construction and resource extraction and utilisation. The results of lunar research will also allow a new understanding of the formation and evolution of the Earth and other bodies in the solar system from a comparative planetary perspective. The relevant analytical techniques can be widely applied to studying samples from the Earth, Mars and meteorites.

A lunar sample was on display at the main event of the 2021 Space Day of China in Nanjing, Jiangsu province. China News Service. Photo by Yang Bo.

CNS: The Chang'e 5 rover landed near Mons Rümker in the north of the largest lunar mare Oceanus Procellarum on the near side of the Moon, a place never visited by landers from other countries. Will this also help us solve some of the major scientific questions that were previously unanswered?

Li Yang: The Chang'e 5 landing site is far from the previous sampling sites of lunar exploration missions, the US Apollo and Soviet Luna, and according to the results of previous impact crater statistical dating studies, there are relatively young lunar mare basalts exposed in the area. Studying the Chang'e 5 lunar soil will therefore allow us to reconnect with the formation and evolutionary history of the Moon in both space and time.

The major scientific questions involved include: how far back in time did the Moon's volcanism continue, what factors led to the continued eruption of basalt in the region, whether there are KREEP outcrops of late magmatic evolution in the region, and what are the specific differences in the evolutionary processes that the Chang'e 5 lunar soil has undergone compared to the Apollo and Luna lunar soils.

Based on the results of the current study, we know that the geological age of the lunar mare basalts in the Chang'e 5 landing area is about 2 billion years, which is 800 million years later than the previous study, refreshing the previous international understanding of the geological age of the lunar mare basalts. Further results have also shown that there are no KREEP outcrops in the area and that the radioelement content and water content of the basalts are not significantly high. Therefore, the exact factors responsible for the continued eruption of the luna mare basalts in this region are still being investigated.

The Chang'e 5 rover automatically sampled the Moon's surface. Photo by China National Space Administration.

CNS: What research work is currently being conducted on the Chang'e 5 lunar samples? What are the key research directions of the Institute of Geochemistry of the Chinese Academy of Sciences? What is the significance of this?

Li Yang: Three batches of Chang'e 5 lunar samples have been publicly applied for and released, covering a wide range of research topics. These include the determination of the geological age of the basalts mentioned above, as well as the mineral composition, elemental and isotopic composition, and weathering characteristics of the lunar soil. The Institute of Geochemistry of the Chinese Academy of Sciences has a good foundation in the study of extra-terrestrial samples such as lunar soil. The main research contents include the formation and evolution of the lunar crust, lunar volcanism and basaltic eruptions, lunar soil formation and spatial and temporal evolutionary history, dust environment of the lunar surface, interaction processes between lunar space environment and surface materials, water generated by the solar wind, etc. A series of innovative research results are expected to be achieved. The above research work will provide an essential basis and support for our understanding of the formation and evolutionary history of the Moon, the evolutionary history of the space environment of the lunar surface, and the development of lunar exploration projects.

CNS: Why do people have high expectations for Chang'e 5 lunar sample research?

Li Yang: First of all, the lunar and deep space exploration projects are a full manifestation of comprehensive national power and the high ground of scientific and technological competition among space powers. Chang'e 5 lunar soil is another lunar sample obtained by humanity in 44 years, and at the same time, China has become the third country in the world to complete the lunar landing and sample returning. Every Chinese is proud of the country's prosperity and the progress of science and technology. Secondly, as scientists, it is our honour and responsibility to be personally involved in the research of lunar samples, and it is an excellent opportunity to demonstrate the level of research by using our own lunar samples to achieve first-class research results. In addition, the lunar samples are of great value to science popularisation, as they can widely and deeply inspire the general public, especially primary and secondary school students, to learn about the Moon and the solar system, and thus nurture talents for the long-term development of China's planetary science and deep-space exploration projects.

Visitors visited Lunar Sample No. 001 on display at the National Museum of China.

Photo by Shi Chunyang, China News Service.

CNS: What are China's long-term plans for lunar exploration? What are the international plans?

Li Yang: The fourth phase of China's Lunar Exploration Programme has planned three lunar exploration missions of Chang'e 6, 7, and 8, and the manned lunar landing mission is also under active and in-depth discussion. The United States is planning to explore the lunar polar region and a lunar orbiting space station, while Russia is planning to verify the landing and working environment of the lunar polar region through three exploration programmes, namely Luna-25, 26, and 27, to lay the foundation for the future siting and construction of a lunar base. In addition, the UK, the European Space Agency, India, and Israel also have planned their own lunar exploration programmes. We are living in an era of prosperity, and as scientific researchers, it is our duty and responsibility to do our part in the fierce international competition.

The profile of the interviewee:

Li Yang, a Project Researcher, he graduated from the University of the Chinese Academy of Sciences in May 2013 with a PhD degree in science, specialising in astrochemistry, joined the Institute of Geochemistry, Chinese Academy of Sciences in September 2013, and is currently Deputy Director of the Centre for Lunar and Planetary Sciences and Sub-centre Director of the Public Technology Service Centre of the Institute of Geochemistry, Chinese Academy of Sciences. He is deeply involved in China's lunar and planetary exploration programme.

Editor: Yuan Jingjing