Lunar soil 'time capsule' reveals organic evolution in solar system

Scientists have identified multiple nitrogen-containing organic compounds on the surfaces of lunar soil samples returned by China's Chang'e-5 and Chang'e-6 missions, providing new insights into the evolution of organic matter in the solar system.

The findings, released by a research team led by the Institute of Geology and Geophysics at the Chinese Academy of Sciences, along with international collaborators, reveal that the moon preserves a detailed record of how organic materials were delivered and transformed in space.

In the early solar system, asteroids and comets acted like "cosmic couriers," continuously delivering organic matter and life-related elements such as carbon, nitrogen, oxygen, phosphorus, and sulfur to terrestrial planets. While such materials may have helped start life on Earth, the planet's active geology and biological processes have mostly erased these early records.

In contrast, the moon, with its relatively inactive geology, acts as a "time capsule," preserving evidence of both the delivery of extraterrestrial organic matter and its subsequent evolution.

Previous studies of Apollo samples confirmed the presence of carbon and nitrogen in lunar soil, but the existence, composition, and origin of nitrogen-bearing organic compounds remained unclear. In this study, researchers conducted systematic analyses of lunar soil particles using advanced microscopy and spectroscopy techniques to examine their structure, chemical bonds, functional groups, and isotopic composition.

The results show that organic matter in lunar soil exists in three main forms: granular, attached, and encapsulated. These forms range from submicron to micron scale and are often mixed with common lunar minerals. Chemically, the materials primarily consist of carbon, nitrogen, and oxygen, with mostly amorphous structures. Some samples also show amide functional groups, suggesting that the organics have undergone complex chemical reprocessing rather than simple graphitization.

Isotopic analysis showed that hydrogen, carbon, and nitrogen in these lunar organics are generally "lighter" than those found in carbonaceous chondrites and asteroid samples. This pattern aligns with impact-driven processes like evaporation, condensation, and redeposition. The findings imply that when asteroids and comets strike the lunar surface, they not only deposit organic materials but also cause their decomposition, migration, and recombination into new nitrogen- and oxygen-bearing compounds.

The team also discovered, for the first time, signatures of solar wind implantation in lunar organic matter. Some surface-bound organics show distinct variations in hydrogen isotopes and hydrogen-to-carbon ratios near exposed areas, indicating long-term exposure to solar radiation. These "fingerprint-like" signals further rule out terrestrial contamination.

The study describes a continuous evolutionary pathway of lunar organic matter, from extraterrestrial delivery to impact-driven transformation and space weathering, providing new evidence for the history of organic transport in the early solar system. It also provides valuable scientific and technical support for China's upcoming deep-space sample-return missions.