BEIJING, April 11 (Xinhua) -- An international research team has made new discoveries from lunar soil samples returned by China's Chang'e-5 and Chang'e-6 missions. These new findings reveal the evolutionary history of organic matter in the solar system, according to a report by China Science Daily.
The study, led by the Institute of Geology and Geophysics at the Chinese Academy of Sciences in collaboration with researchers from the University of New Mexico, Changsha University of Science and Technology and other institutions, has, for the first time, systematically identified multiple nitrogen-bearing organic species on the surfaces of lunar soil grains.
The results demonstrate that the Moon not only records the history of organic delivery from asteroids and comets to the inner solar system, but also preserves evidence of subsequent modification of these materials by impacts and irradiation on an airless body.
In the early solar system, asteroids and comets acted as "couriers," continuously delivering organic matter, along with key bioessential elements such as carbon, nitrogen, oxygen, phosphorus, and sulfur, to terrestrial planets. These exogenous materials may have supplied some of the chemical ingredients necessary for the origin and early evolution of life on Earth.
However, due to extensive geological activity and biological processes, direct records of these early inputs have largely been erased on Earth. In contrast, the Moon, with its relatively limited geological activity, serves as a natural "time capsule" that is more likely to preserve evidence of the delivery and subsequent evolution of extraterrestrial organic matter.
Although carbon and nitrogen had previously been detected in Apollo lunar soils, the presence, morphology, origin and preservation mechanisms of nitrogen-bearing organic matter in lunar regolith remained poorly constrained. In this study, lunar soil grains returned by the Chang'e-5 and Chang'e-6 missions were selected for analysis.
The researchers conducted correlative investigations using multiple microscopic and spectroscopic techniques to systematically characterize the morphology, chemical bonding and functional groups, and stable isotopic compositions of the organic matter.
The researchers discovered that the hydrogen, carbon, and nitrogen isotopic compositions of these lunar organics are generally lighter than those reported for organic matter in carbonaceous chondrites and asteroid samples. This isotopic signature is consistent with evaporation-condensation and redeposition processes induced by impact events.
Specifically, impacts by asteroids, comets, and other extraterrestrial bodies not only delivered organic materials to the lunar surface but also likely triggered their decomposition, volatilization, migration, and subsequent condensation onto mineral surfaces, forming new nitrogen- and oxygen-bearing structures.
They also identified signatures of solar wind implantation in lunar organic matter for the first time. They discovered that some surface-associated organics exhibit distinct variations in hydrogen isotopic composition and H/C ratios near the grain surfaces. These features indicate prolonged exposure on the lunar surface after formation or deposition, during which the materials were continuously irradiated by the solar wind.
Hao Jialong, corresponding author of the study, said that such solar wind implantation signatures represent a characteristic "fingerprint" of solar wind-material interactions and effectively rule out the possibility of terrestrial contamination as the source of these organics.
The researchers noted that this work provides important technical and scientific support for future deep-space sample-return missions in China. From a technical perspective, the study establishes a robust analytical framework for the identification and interpretation of microscale organic matter, as well as its evolutionary processes. This framework can be directly applied to the analysis of organic matter and volatiles in samples returned by the Tianwen-2 mission.
From a scientific perspective, the results reveal a continuous evolutionary sequence of lunar organic matter -- from exogenous delivery through impact-induced restructuring, to space-weathering modification -- thereby offering new insights into the evolution of small-body materials and the history of organic delivery in the early solar system.
The related study was published on Thursday in Science Advances. ■
