^1,2Haolan Tang, ¹Nicolas Dauphas
¹Origins Lab, Department of the Geophysical Sciences and Enrico Fermi Institute, The University of Chicago, 5734 South Ellis Avenue, Chicago IL 60637, USA
²Ion Probe Group, Department of earth and Space Sciences, University of California, Los Angeles, 595 Charles E. Young Drive East, Los Angeles, CA 90095, US

Iron-60 (t1/2 = 2.62 Myr) is a short-lived nuclide that can help constrain the astrophysical context of Solar System formation and date early Solar System events. A high abundance of 60Fe(60Fe/56Fe ≈ 4 × 10−7) was reported by in situ techniques in some chondrules from the LL3.00 Semarkona meteorite, which was taken as evidence that a supernova exploded in the vicinity of the birthplace of the Sun. However, our previous multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) measurements of a wide range of meteoritic materials, including chondrules, showed that 60Fe was present in the early Solar System at a much lower level (60Fe/56Fe ≈ 10−8). The reason for the discrepancy is unknown but only two Semarkona chondrules were measured by MC-ICPMS and these had Fe/Ni ratios below ~2× chondritic. Here, we show that the initial 60Fe/56Fe ratio in Semarkona chondrules with Fe/Ni ratios up to ~24× chondritic is (5.39 ± 3.27) × 10−9. We also establish the initial 60Fe/56Fe ratio at the time of crystallization of the Sahara 99555 angrite, a chronological anchor, to be (1.97 ± 0.77) × 10−9. These results demonstrate that the initial abundance of 60Fe at Solar System birth was low, corresponding to an initial 60Fe/56Fe ratio of (1.01 ± 0.27) × 10−8.

Reference
Tang H, Dauphas N (2015) Low 60Fe Abundance in Semarkona and Sahara 99555. Astrophysical Journal 802 22.
Link to Article [doi:10.1088/0004-637X/802/1/22]