2005ApJ...621..902F

Live ⁶⁰Fe has recently been detected in a deep-ocean ferromanganese crust, isolated in layers dating from about 3 Myr ago. Since ⁶⁰Fe 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 ⁶⁰Fe 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 ¹⁰Be, ²⁶Al, ⁵³Mn, ¹⁸²Hf, and ²⁴⁴Pu. Of these, ¹⁸²Hf and ²⁴⁴Pu are nearly background-free, presenting the best opportunities to provide strong confirmation of the supernova origin of the ⁶⁰Fe 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 ⁶⁰Fe yields for supernovae of different masses, so the new crust data motivate a redoubled theoretical attack on this problem.