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.
All Science Journal Classification (ASJC) codes
- Astronomy and Astrophysics
- Space and Planetary Science
- minor planets, asteroids: general
- nuclear reactions, nucleosynthesis, abundances
- protoplanetary disks