Deep‐Ocean Crusts as Telescopes: Using Live Radioisotopes to Probe Supernova Nucleosynthesis

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 of2.2 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 60Fedata with several supernova nucleosynthesis models to calculate the supernovadistance as a function of progenitor mass, finding an allowed range of 15-120pc. We also predict the signals expected for several other radioisotopes, whichare independent of the supernova distance. Species likely to be present near orabove background levels are 10Be, 26Al, 53Mn, 182Hf and 244Pu. Of these, 182Hfand 244Pu are nearly background-free, presenting the best opportunities toprovide strong confirmation of the supernova origin of the 60Fe signal, and todemonstrate that at least some supernovae are the source for the r-process. Theaccuracies of our predictions are hampered by large uncertainties in thepredicted 60Fe yields for supernovae of different masses, so the new crust datamotivate a redoubled theoretical attack on this problem.Comment: 13 pages, 2 figures, AASTeX. Comments welcom