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Abstract There is a wealth of data on live, undecayed60Fe (t1/2= 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 the60Fe profiles in deep-sea sediments to estimate the timescale of supernova debris deposition beginning ∼3 Myr ago. The available data admits a variety of different profile functions, but in all cases the best-fit60Fe pulse durations are >1.6 Myr when all the data is combined. This timescale far exceeds the ≲0.1 Myr pulse that would be expected if60Fe was entrained in the supernova blast wave plasma. We interpret the long signal duration as evidence that60Fe 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 recent60Fe 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.
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The 59 Fe (n,γ) 60 Fe Cross Section from the Surrogate Ratio Method and Its Effect on the 60 Fe Nucleosynthesis
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Abstract Near-Earth supernova blasts which engulf the solar system have left traces of their ejecta in the geological and lunar records. There is now a wealth of data on live radioactive60Fe pointing to a supernova at 3 Myr ago, as well as the recent discovery of an event at 7 Myr ago. We use the available measurements to evaluate the distances to these events. For the better analyzed supernova at 3 Myr, samples include deep-sea sediments, ferromanganese crusts, and lunar regolith; we explore the consistency among and across these measurements, which depends sensitively on the uptake of iron in the samples as well as possible anisotropies in the60Fe fallout. There is also significant uncertainty in the astronomical parameters needed for these calculations. We take the opportunity to perform a parameter study on the effects that the ejected60Fe mass from a core-collapse supernova and the fraction of dust that survives the remnant have on the resulting distance. We find that with an ejected60Fe mass of 3 × 10−5M⊙and a dust fraction of 10%, the distance range for the supernova 3 Myr ago isD∼ 20–140 pc, with the most likely range between 50 and 65 pc. Using the same astrophysical parameters, the distance for the supernova at 7 Myr ago isD∼ 110 pc. We close with a brief discussion of geological and astronomical measurements that can improve these results.more » « less
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Abstract While modeling the galactic chemical evolution (GCE) of stable elements provides insights to the formation history of the Galaxy and the relative contributions of nucleosynthesis sites, modeling the evolution of short-lived radioisotopes (SLRs) can provide supplementary timing information on recent nucleosynthesis. To study the evolution of SLRs, we need to understand their spatial distribution. Using a three-dimensional GCE model, we investigated the evolution of four SLRs:53Mn,60Fe,182Hf, and244Pu with the aim of explaining detections of recent (within the last ≈1–20 Myr) deposition of live53Mn,60Fe, and244Pu of extrasolar origin into deep-sea reservoirs. We find that core-collapse supernovae are the dominant propagation mechanism of SLRs in the Galaxy. This results in the simultaneous arrival of these four SLRs on Earth, although they could have been produced in different astrophysical sites, which can explain why live extrasolar53Mn,60Fe, and244Pu are found within the same, or similar, layers of deep-sea sediments. We predict that182Hf should also be found in such sediments at similar depths.more » « less
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3847/1538-4357/ac12ce
