Abstract The stable isotope composition of carbonates records the environmental formation conditions and can indicate potential biosignatures if formed biologically. Martian meteorite carbonates display unusually high δ 13 C values, not explained using known terrestrial processes. Carbonates have been detected across the martian surface, including observations by the Perseverance Rover in Jezero Crater. However, the stable isotope effects of surface irradiation in carbonate minerals remain poorly constrained. We investigated the influence of ultraviolet (UV) and non‐UV radiation on δ 13 C and δ 18 O values of carbonates under both Low Earth Orbit (LEO) and laboratory conditions. Three natural carbonates, two calcites (Iceland spar, Bolivian stromatolite) and one aragonite (French microbialite), were exposed to LEO UV and non‐UV radiation for 29 ± 4 hr. Laboratory experiments employed reagent‐grade calcite and natural aragonite exposed to UV under N 2 atmospheres at 6 mbar (4.5 torr) or 1.73 mbar (1.3 torr) for 24–70 hr in the McMaster Planetary Simulator (MPS). Most carbonates showed no significant radiation‐induced changes in their δ 13 C and δ 18 O values. However, three cases exhibited minor stable isotope shifts, including carbon and oxygen isotope effects in LEO and MPS carbonates, an oxygen isotope effect in the LEO‐UV‐exposed French microbialite, and carbon isotope effects in two UV‐exposed MPS calcites. These results suggest that short‐term radiation cannot explain the 13 C enrichment in martian meteorites but may initiate subtle stable isotope effects. This study establishes a baseline for radiation‐induced stable isotope effects in carbonates, informing interpretations of martian carbonate isotopes, biosignature preservation potential, and analyses planned for Mars Sample Return.
Plain Language Summary Carbonates form when carbon combines with oxygen and other elements, often in water‐rich environments. On Earth, their chemical “fingerprints,” measured as carbon and oxygen stable isotope compositions, tell us about the conditions in which they formed, such as temperature, water chemistry, and biological activity. On Mars, carbonates have been found in many places, including by the Perseverance Rover in Jezero Crater. Some martian meteorites contain carbonates with unusual carbon isotope compositions that cannot be explained using the processes observed on Earth. One explanation is that radiation from the Sun and space, which constantly bombards the martian surface, might change carbonate isotope compositions over time. To test this, we exposed different carbonate samples to radiation both in space (LEO) and in a Mars simulation chamber in the laboratory. Most samples did not show changes, but a few showed small shifts in their stable isotope compositions. Our results suggest that short‐term radiation is unlikely to cause the extreme carbon isotope compositions seen in martian meteorites. However, subtle changes could build up over long periods. This work helps scientists interpret martian carbonate data and assess how well these minerals might preserve signs of past life for future Mars Sample Return missions.
Key Points Carbonates were exposed to ultraviolet (UV) and/or non‐UV radiation in Low Earth Orbit (LEO) and Mars simulations to test the effects on their carbon and oxygen isotope compositions Most carbonate samples showed no changes in their δ 13 C and δ 18 O values after 24–70 hr of UV and/or non‐UV radiation exposure Results provide baseline data for interpreting Martian carbonates and assessing biosignature preservation for Mars Sample Return