Polycyclic aromatics in the Chang'E 5 lunar soils

Polycyclic aromatics are ubiquitous in the interstellar medium and meteorites, yet the search for lunar polycyclic aromatics remains a significant challenge. Here, we analyze Chang'E-5 lunar soil samples, revealing polycyclic aromatic concentrations of 5.0-9.2 µg/g (average: 7.4 ± 1.4 µg/g). Their aromatic structures are highly condensed, comparable to ~4 nm graphene sheets, and distinct from terrestrial analogs, such as wood char, soot and kerogen. While meteorite impacts are the most likely sources, the stable carbon isotope composition of polycyclic aromatics in Chang'E-5 lunar soil (δ¹³C: -5.0 ± 0.6‰ to +3.6 ± 1.3‰) is more enriched in ¹³C compared to that in meteorites. This enrichment suggests a de novo formation mechanism during meteorite impacts, involving the conversion of non-aromatic organic matter-which is more enriched in δ¹³C-into polycyclic aromatics. This process may play a significant role in carbon accretion in lunar regolith, as the resulting polycyclic aromatics are more stable and resistant to degradation compared to smaller organic molecules (e.g., amino acids), which are largely destroyed during impact events.