Supernova Dust Evolution Probed by Deep-sea 60Fe Time History

There is a wealth of data on live, undecayed Fe-60 (t (1/2) = 2.6 Myr) in deep-sea deposits, the lunar regolith, cosmic rays, and Antarctic snow, which is interpreted as originating from the recent explosions of at least two near-Earth supernovae. We use the Fe-60 profiles in deep-sea sediments to estimate the timescale of supernova debris deposition beginning similar to 3 Myr ago. The available data admits a variety of different profile functions, but in all cases the best-fit Fe-60 pulse durations are >1.6 Myr when all the data is combined. This timescale far exceeds the less than or similar to 0.1 Myr pulse that would be expected if Fe-60 was entrained in the supernova blast wave plasma. We interpret the long signal duration as evidence that Fe-60 arrives in the form of supernova dust, whose dynamics are separate from but coupled to the evolution of the blast plasma. In this framework, the >1.6 Myr is that for dust stopping due to drag forces. This scenario is consistent with the simulations in Fry et al. (2020), where the dust is magnetically trapped in supernova remnants and thereby confined around regions of the remnant dominated by supernova ejects, where magnetic fields are low. This picture fits naturally with models of cosmic-ray injection of refractory elements as sputtered supernova dust grains and implies that the recent Fe-60 detections in cosmic rays complement the fragments of grains that survived to arrive on the Earth and Moon. Finally, we present possible tests for this scenario.

Automated summary

A variety of data sources provide evidence for the recent explosions of near-Earth supernovae, including live Fe-60 found in deep-sea deposits, the lunar regolith, cosmic rays, and Antarctic snow. The duration of Fe-60 pulses in deep-sea sediments is estimated to be more than 1.6 million years, suggesting that Fe-60 arrives in the form of supernova dust rather than being entrained in the supernova blast wave plasma. This scenario is consistent with simulations that propose magnetic trapping of dust in supernova remnants. It also implies that the recent Fe-60 detections in cosmic rays complement the fragments of grains that have survived to reach the Earth and Moon.