Nitrogen isotopic variations in the early Solar System recorded by pallasites

To gain new insights into nitrogen (N) isotopic variations in the early Solar System, N and noble gas (Ne, Ar) isotopes were measured in metal fragments and olivine separates from thirteen pallasites and five IIIAB iron meteorites. While δ15N values in olivine are affected by cosmogenic 15N, as demonstrated by cosmogenic 21Ne abundances, the δ15N values of metal phases reflect reservoir signatures rather than secondary processes. Non-carbonaceous (NC) pallasites have lower δ15N values (–88.86 ± 0.90 ‰ to –45.04 ± 0.91 ‰) than carbonaceous (CC) pallasites (–34.03 ± 0.69 ‰ to –26.12 ± 0.64 ‰), indicating their parent bodies accreted isotopically distinct N-bearing precursors in the inner and outer regions of the protoplanetary disk. The δ15N variations within each reservoir also suggest N isotopic heterogeneity at a smaller scale. While NC irons and NC pallasites exhibit overlapping δ15N values, CC pallasites are less 15N-rich than CC irons, implying that their parent bodies accreted in different locations and/or at different times within the outer disk.