In a companion paper, Fields, Hochmuth, and Ellis (2004) we take the view that the new Knie et al results have now given heavy weight to the claim that a supernova exploded near the Earth 3 million years ago. In light of this revelation, we explore the implications of the new, precision iron-60 data for our understanding of supernova explosions--in effect, using the deep-ocean sediments as a telescope to probe the nuclear fires of massive stars! On the one hand, we found that our current understanding of iron-60 production in supernovae has uncertainties which are significant--enough so that they allow for a supernova distance anywhere from 30 to 300 light years away. Thus, the new iron-60 result now urgently demands a concerted effort to create better theoretical models for supernova synthesis of this (and other) radioactive species. On the other hand, the iron-60 detection offers the hope that other searches for deep-ocean radioactivity can shed light on the nature of supernovae. One can turn the argument around, and use the pattern of observed radioactivities to study the ashes of the supernova's nuclear burning. We predicted the signals from other radioactive species, several of which should be detectable with present techniques. We particularly encourage searches for the very rare and heavy radioactive species halfnium-182 and plutonium-244. These would give not only further confirmation of the supernova picture, but they would also provide that first direct evidence that the supernovae do produce the heaviest elements, in a mechanism known as the "r-process."
Searches for other live radioactive species are ongoing, and we eagerly await their results. Detection of one or more species, also 3 million years ago, would lend confidence to the supernova interpretation. This would open the door to new connections among astrophysics, biology, and geology.
It is intriguing to note that, at about the time of the iron-60 event, there was a larger than average rate of extinction of biological species (which may or may not be due to the explosion). In addition, the effect of the explosion on terrestrial life would bear more exploration. The beautiful new Knie et al results give impetus to pursue such speculations more seriously, in order to shed new light on this possible explosion in our own cosmic back yard.