Elements essential to life, such as carbon, nitrogen, oxygen, phosphorus, and sulfur, were "delivered" to the Earth and Moon during the early stages of the Solar System via asteroids and comets impacting their surfaces. These exogenous materials may have provided the chemical building blocks necessary for the origin and early evolution of life on Earth. But extensive geological activity and biological processes on Earth have largely erased the direct records of these early inputs on our planet.

In contrast, the Moon, with its relatively limited geological activity, serves as a natural "time capsule," making it easier to unravel the history and evolution of extraterrestrial organic matter.

A recent study has for the first time systematically identified multiple nitrogen-bearing organic species on the surfaces of lunar soil grains returned by China's Chang'e-5 and Chang'e-6 missions. The research further reveals an evolutionary pathway defined by exogenous delivery, impact modification, and continuous solar wind processing.

The findings demonstrate that the Moon not only records the history of organic material delivery by asteroids and comets to the inner Solar System but also preserves evidence of how these materials were subsequently modified by impacts and irradiation on an airless celestial body.

The study was led by a research team from the Institute of Geology and Geophysics of the Chinese Academy of Sciences (IGGCAS), in collaboration with researchers from institutions including the University of New Mexico and Changsha University of Science and Technology. Their findings were published in Science Advances on April 8.

While carbon and nitrogen had previously been detected in Apollo lunar soils, the existence, morphology, origin, and preservation mechanisms of nitrogen-bearing organic matter in lunar regolith remained poorly understood prior to this research. For the study, the team selected lunar soil grains returned by the Chang'e-5 and Chang'e-6 missions for in-depth analysis. Using multiple microscopic and spectroscopic techniques, the researchers conducted integrated analyses to systematically characterize the morphology, chemical bonding, functional groups, and stable isotopic compositions of the organic matter.

The study revealed that organic matter on lunar soil surfaces primarily exists in three forms—particle-like, surface-adhered, and inclusion-like—at submicrometer to micrometer scales, and these materials often contains inorganic mineral particles typical of lunar soil. Chemically, these materials are dominated by carbon, nitrogen, and oxygen and are generally amorphous in structure; amide functional groups were also identified in some samples. These observations indicate that lunar organics are not merely carbon in graphite form—a highly ordered, nearly pure form of carbon—but have undergone more complex chemical reorganization.

Further analysis showed 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 triggered by impact events. Specifically, impacts by asteroids, comets, and other extraterrestrial bodies not only delivered organic materials to the lunar surface but also likely induced their decomposition, volatilization, migration, and subsequent condensation onto mineral surfaces—forming new nitrogen- and oxygen-bearing structures.

Additionally, the team identified signatures of solar wind implantation in lunar organic matter for the first time. NanoSIMS depth profiling revealed that some surface-associated organics exhibit distinct variations in hydrogen isotopic composition and H/C ratios near 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.

The researchers noted that such solar wind implantation signatures serve as a characteristic "fingerprint" of solar wind–material interactions, effectively ruling out terrestrial contamination as the source of these organics.

The study establishes an analytical framework for identifying and interpreting microscale organic matter and its evolutionary processes. Furthermore, the results reveal a continuous evolutionary sequence of lunar organic matter: from exogenous delivery, through impact-induced restructuring, to space-weathering modification. This sequence offers new insights into the evolution of small-body materials and the history of organic delivery in the early Solar System.

Representative organic matter in Chang'e-6 (A–B) and Chang'e-5 (C–D) lunar soils. Secondary electron images acquired by scanning electron microscopy overlaid with carbon elemental maps from energy-dispersive spectroscopy. (Image by HAO Jialong's Group)

Schematic illustration of the formation and evolution of organic matter in lunar soil. (Image by HAO Jialong's Group)