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

Abstract

There is a wealth of data on live, undecayed 60Fe (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 60Fe 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-fit 60Fe 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 if 60Fe was entrained in the supernova blast wave plasma. We interpret the long signal duration as evidence that 60Fe 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 60Fe 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.

Proposed Lunar Measurements of r-Process Radioisotopes to Distinguish the Origin of Deep-sea 244Pu

“…The timing of this signal is consistent with that measured previously in 60 Fe deposits in deep-sea sediments and crusts (Knie et al 1999(Knie et al , 2004Fitoussi et al 2008;Ludwig et al 2016;Wallner et al 2016Wallner et al , 2020, though this peak is somewhat broader. The observed amplitude of the pulse and its duration of 1 Myr are consistent with a model in which 60 Fe from an SN 100 pc away is transported to Earth in dust grains via "pinball" trajectories that are deflected and trapped by a magnetic field within the SN remnant (Fry et al 2020;Ertel et al 2023). The pulse width indicated by the Wallner et al (2021) measurements could also reflect smearing in the crust they study.…”

“…Further, the second 60 Fe pulse shows that there were multiple explosions, as one would expect from massive stars that are highly clustered (Zinnecker & Yorke 2007). We thus follow Ertel et al (2023) in referring to the event around 3 Mya as the Pliocene event (SN Plio) and the event around 7 Mya as the Miocene event (SN Mio). In this paper, we study the interpretation and potential implications of these new experimental results, focusing on the information to be gained from lunar measurements of r-process radioisotopes.…”

Could a Kilonova Kill: A Threat Assessment

“…Live 60 Fe signals have been measured by many groups in deep-ocean deposits (Knie et al 2004;Fitoussi et al 2008;Ludwig et al 2016;Wallner et al 2016Wallner et al , 2021, Antarctic snow (Koll et al 2019), and in lunar regolith (Fimiani et al 2016). These signals take the form of two pulses, one ∼3 Myr ago and another ∼7-8 Myr ago, pointing to at least two recent nearby SN explosions (Ertel et al 2023). Moreover, Wallner et al (2021) detected live 244 Pu in deep-ocean samples with high significance, confirming earlier hints (Paul et al 2001;Wallner et al 2004;Raisbeck et al 2007;Wallner et al 2015).…”

Cosmic Contributions to the Deposition of Petroleum Source Rocks: Review and Analysis

“…Samples of undecayed 60 Fe in Antarctic snow confirm the global distribution, probes in lunar regolith and cosmic rays a source in the Milky Way galaxy. Recent explosions of at least two near-Earth supernovae have been identified as source of the mentioned radioactive isotopes [21].…”

“…This timescale exceeds the ≲0.1 Myr pulse by far that would be expected if 60 Fe was embedded in the supernova blast wave plasma. Apparently the long signal duration can be used as evidence that 60 Fe arrives in the form of supernova dust, whose dynamics are separated from but coupled to the evolution of the blast plasma [21].…”