Chinese-led team discovers nitrogen-bearing organics in lunar soil, shedding light on early solar system

An international research team led by Chinese scientists has identified, for the first time, multiple nitrogen-bearing organic compounds on the surfaces of lunar soil grains, offering new insights into the origin and evolution of early life in the solar system.

By analyzing lunar soil samples returned by China's Chang'e 5 and Chang'e 6 missions, scientists from the Institute of Geology and Geophysics at the Chinese Academy of Sciences, the University of New Mexico, and Changsha University of Science and Technology have uncovered the history of organic delivery from asteroids and comets to the inner solar system. Their findings were published in the journal Science Advances on Thursday.

Researchers believed that in the early solar system, asteroids and comets acted as "couriers", delivering organic matter and essential life elements like carbon, nitrogen, oxygen, phosphorus, and sulfur to terrestrial planets. These materials may have provided some of the chemical building blocks necessary for the origin and evolution of life on early Earth.

While Earth's frequent geological and biological processes have erased much of this early history, the moon, with its minimal geological activity, serves as a "time capsule", preserving evidence of these deliveries and helping scientists infer the early history of organic matter input on Earth.

Although previous studies of Apollo lunar soils detected organic matter containing carbon and hydrogen, the presence of nitrogen-bearing organics in lunar regolith remained unknown. This intermediate evidence has long been missing from the hypothesis that organics were delivered and transformed by asteroid impacts.

Using high-resolution microscopy, energy-dispersive spectroscopy, and spectroscopic techniques, researchers found that the organic matter on the lunar soil surface is primarily composed of carbon, nitrogen, and oxygen, and exhibits no fixed chemical structure.

"In some samples, we identified amide functional groups, which are important in biological molecules like proteins," said Dong Mingtan, first author of the study and a PhD candidate at the Institute of Geology and Geophysics. "This indicates that these organic materials are not simply graphitized carbon but have undergone complex chemical reorganization, bringing their structure closer to organic molecules potentially usable by life."

Further analysis revealed that the hydrogen, carbon, and nitrogen isotopic compositions of these lunar organics are generally lighter than those in carbonaceous chondrites and asteroid samples.

Dong noted that this isotopic signature aligns with processes induced by impact events, where high temperatures trigger the decomposition and volatilization of organic molecules from extraterrestrial bodies, causing lighter isotopes to preferentially condense and deposit onto lunar minerals.

The research also identified signatures of solar wind implantation in lunar organic matter for the first time. "We found distinct variations in hydrogen isotopic composition and hydrogen-to-carbon ratios near the grain surfaces, indicating prolonged exposure on the lunar surface and continuous irradiation by the solar wind," said Hao Jialong, corresponding author of the study and a senior engineer at the institute. "These features effectively rule out terrestrial contamination as the source of these organics."

"The results reveal a continuous evolutionary sequence of lunar organic matter — from exogenous delivery through impact-induced restructuring to space-weathering modification — offering new insights into the evolution of small-body materials and organic delivery history in the early solar system," Dong said.

He also emphasized that the techniques developed in this study can be applied to future deep-space sample return missions, such as China's Tianwen 2 mission, expected to return asteroid samples by the end of 2027, to identify microscale organic matter and interpret their evolutionary processes.