Nickel isotopes reveal micrometeorite accretion on the lunar farside dominated by inner Solar System materials

Abstract Space weathering driven by meteoritic and micrometeoritic impacts plays a fundamental role in modifying the planetary surfaces. However, the sources of impactors and the effects of impact-induced evaporation on micrometeorite accretion remain unconstrained. Here, we analyzed the nickel isotopic compositions of regolith and lithic clasts collected by the Chang’e-6 (CE6) mission. Our results show that CE6 regolith and some lithic clasts exhibit systematically enriched heavy nickel isotopic compositions (δ 60 Ni = 1.07‰ to 1.25‰), consistent with cumulative evaporation during repeated micrometeoritic bombardment under quasi-saturated conditions. In addition, a subset of CE6 basaltic clasts records unusually light nickel isotopic compositions (δ 60 Ni = −0.95‰ to −0.48‰), beyond the range previously reported for lunar materials and indicative of post-evaporation recondensation. Further, the nickel isotopic anomalies of the CE6 regolith (μ 60 Ni = 7 ± 3 and μ 62 Ni = −6 ± 9) suggest that the long-term average accreting materials to the lunar surface were dominantly sourced from the inner Solar System.