⁶⁰ Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity

Abstract

Nuclides synthesized in massive stars are ejected into space via stellar winds and supernova explosions. The solar system (SS) moves through the interstellar medium and collects these nucleosynthesis products. One such product is 60Fe, a radionuclide with a half-life of 2.6 My that is predominantly produced in massive stars and ejected in supernova explosions. Extraterrestrial 60Fe has been found on Earth, suggesting close-by supernova explosions ∼2 to 3 and ∼6 Ma. Here, we report on the detection of a continuous interstellar 60Fe influx on Earth over the past ∼33,000 y. This time period coincides with passage of our SS through such interstellar clouds, which have a significantly larger particle density compared to the local average interstellar medium embedding our SS for the past few million years. The interstellar 60Fe was extracted from five deep-sea sediment samples and accelerator mass spectrometry was used for single-atom counting. The low number of 19 detected atoms indicates a continued but low influx of interstellar 60Fe. The measured 60Fe time profile over the 33 ky, obtained with a time resolution of about ±9 ky, does not seem to reflect any large changes in the interstellar particle density during Earth’s passage through local interstellar clouds, which could be expected if the local cloud represented an isolated remnant of the most recent supernova ejecta that traversed the Earth ∼2 to 3 Ma. The identified 60Fe influx may signal a late echo of some million-year-old supernovae with the 60Fe-bearing dust particles still permeating the interstellar medium.

Future radioisotope measurements to clarify the origin of deep-ocean 244Pu

“…We consider first the data of Wallner et al [18] on the 60 Fe pulse from ∼ 3 Mya. The timing of this signal is consistent with that measured previously in 60 Fe deposits in deep-ocean sediments and crusts [4][5][6][7][8][9], though this peak is somewhat broader. A model in which 60 Fe from a SN 100 Mpc away is transported to Earth in dust via 'pinball' trajectories that are deflected and trapped by a magnetic field within the SN remnant is compatible with a pulse of the observed size and duration ∼ 1 Myr [28], and the pulse width indicated by the Wallner et al [18] measurements could also reflect smearing in the crust they study.…”

“…Measurements of live radioactive isotopes can provide insights into recent astrophysical explosions such as corecollapse supernovae (SNe) within O(100) pc of Earth [1] that are expected to occur every few million years, clarifying the possibility of rarer events within O (10) pc that might have caused mass extinctions in the past [2,3]. Many experiments over the past two decades have detected pulses of live 60 Fe in deep-ocean deposits [4][5][6][7][8][9] from between 2 and 3 My ago (Mya), very likely due to a nearby core-collapse SN. There have also been hints of earlier deep-ocean 60 Fe deposition, as well as measurements of 60 Fe in the lunar regolith [10], in cosmic rays [11] and in Antarctic snow [12].…”

The Radioactive Nuclei $^{\textbf{26}}$Al and $^{\textbf{60}}$Fe in the Cosmos and in the Solar System

“…Indeed, accelerator mass spectrometry was successfully applied in pioneering work at Munich, where live 60 Fe was discovered for the first time in a ferromanganese crust from the ocean floor (Knie et al, 1999). Since then, this method has been further developed at TU Munich and later at the Australian National University, searching for interstellar 60 Fe in terrestrial archives as well as in lunar samples (Knie et al, 2004;Wallner et al, 2016;Fimiani et al, 2016;Ludwig et al, 2016;Koll et al, 2019;Wallner et al, 2020Wallner et al, , 2021. Measurement backgrounds of 60 Fe/Fe as low as 3 × 10 −17 , equivalent to one identified background event over one day of measurement, can be handled (Wallner et al, 2015c).…”

“…Time-resolved depth profiles were generated for a number of archives by studying individual layers that represent specific time periods in the past. Up to now, the 60 Fe contents of three different deep-sea archives (6 sediment cores, 7 FeMn-crusts and two FeMn-nodules), recovered from the Indian, Pacific and Atlantic Oceans respectively, were determined (Knie et al, 2004;Wallner et al, 2016;Ludwig et al, 2016;Wallner et al, 2020Wallner et al, , 2021. Moreover, 60 Fe was found in Antarctic snow (Koll et al, 2019), and in lunar soil (Fimiani et al, 2016).…”

Studying the low-energy excess in cosmic-ray iron: a possible evidence of a massive supernova activity in the solar neighborhood via primary 60Fe

“…The Local Bubble is a low density region of the size of ∼200 pc around the Sun filled with hot H i gas that itself was formed in a series of SN explosions [29,35,45,48,50,54]. There are multiple reports of an excess of radioactive 60 Fe found in the deep ocean sediments [31,34,41,42,44,46,52,53], in lunar regolith samples [27,32,33], and more recently in the Antarctic snow [43]. Such deposits can be made by SN explosions in the solar neighborhood.…”