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Cook et al. (2021) found that iron meteorites have an initial abundance ratioof the short-lived isotope $^{60}$Fe to the stable isotope $^{56}$Fe of$^{60}$Fe/$^{56}$Fe $\sim$ $(6.4 \pm 2.0) \times 10^{-7}$. This appears torequire the injection of live $^{60}$Fe from a Type II supernova (SN II) intothe presolar molecular cloud core, as the observed ratio is over a factor often times higher than would be expected to be found in the ambient interstellarmedium (ISM) as a result of galactic chemical evolution. The supernovatriggering and injection scenario offers a ready explanation for an elevatedinitial $^{60}$Fe level, and in addition provides a physical mechanism forexplaining the non-carbonaceous -- carbonaceous (NC-CC) dichotomy ofmeteorites. The NC-CC scenario hypothesizes the solar nebula first accretedmaterial that was enriched in supernova-derived nuclides, and then lateraccreted material depleted in supernova-derived nuclides. While the NC-CCdichotomy refers to stable nuclides, not short-lived isotopes like $^{60}$Fe,the SN II triggering hypothesis provides an explanation for the otherwiseunexplained change in nuclides being accreted by the solar nebula. Threedimensional hydrodynamical models of SN II shock-triggered collapse show thatafter triggering collapse of the presolar cloud core, the shock front sweepsaway the local ISM while accelerating the resulting protostar/disk to a speedof several km/s, sufficient for the protostar/disk system to encounter within$\sim$ 1 Myr the more distant regions of a giant molecular cloud complex thatmight be expected to have a depleted inventory of supernova-derived nuclides.

astrophysical journal/the astrophysical journal

Possible Implications of Relatively High Levels of Initial $^{60}$Fe in  Iron Meteorites for the Non-Carbonaceous -- Carbonaceous Meteorite Dichotomy  and Solar Nebula Formation