Live ~(60)Fe has recently been detected in a deep-ocean ferromanganese crust, isolated in layers dating from about 3 Myr ago. Since ~(60)Fe has a mean life of 2.2 Myr, a near-Earth supernova is the only likely source for such a signal, and we explore here the consequences of a supernova origin. We combine the ~(60)Fe data with several supernova nucleosynthesis models to calculate the supernova distance as a function of progenitor mass, finding an allowed range of 15-120 pc. We also predict the signals expected for several other radioisotopes, which are independent of the supernova distance. Species likely to be present near or above background levels are ~(10)Be, ~(26)Al, ~(53)Mn, ~(182)Hf, and ~(244)Pu. Of these, ~(182)Hf and ~(244)Pu are nearly background-free, presenting the best opportunities to provide strong confirmation of the supernova origin of the ~(60)Fe signal and to demonstrate that at least some supernovae are sources for the r-process. The accuracies of our predictions are hampered by large uncertainties in the predicted ~(60)Fe yields for supernovae of different masses, so the new crust data motivate a redoubled theoretical attack on this problem.
展开▼
