The elusive ⁶⁰Fe in the solar nebula

No ⁶⁰Ni or ⁶¹Ni anomalies have been detected in troilite inclusions from Muonionalusta, a 4565.3 0.1 Ma old IVA iron meteorite, to the level of the analytical precision of 10 ppm. Because Muonionalusta troilite is very old, has a high Fe/Ni ratio, and is free of ⁶¹Ni anomalies, it is the ideal material in which to search for potential excesses of ⁶⁰Ni produced by the decay of ⁶⁰Fe (t _1/2 = 2.62 Ma). The ⁶⁰Ni/⁵⁸Ni and Fe/Ni ratios (up to 1680) measured here imply an upper limit for the initial ⁶⁰Fe/ ⁵⁶Fe for the Muonionalusta troilite of 3 × 10^-9. Assuming that ⁶⁰Fe was homogeneously distributed across the nebula, this result suggests that the solar system initial ⁶⁰Fe/ ⁵⁶Fe ratio was less than 5 × 10^-9, which is lower than previously measured by at least a factor of 50.