Researchers report measurements of the supernova-derived isotope 60Fe in deep-sea sediments. The Solar System regularly passes through clouds of interstellar material, such as the present Local Interstellar Cloud (LIC), potentially affecting Earth's exposure to interstellar dust and cosmic rays. The origin of the clouds is uncertain. Anton Wallner and colleagues measured trace concentrations of the radioisotope 60Fe in five deep-sea sediment samples from Indian Ocean cores spanning the past 33,000 years. 60Fe is not naturally produced on Earth, and its presence in the geological record indicates exposure to supernova ejecta or passage through supernova remnants. The authors detected 60Fe levels significantly above the background that would be expected from purely terrestrial iron. Based on these measurements, the authors estimated an average 60Fe deposition rate of 3.5 atoms per square centimeter per year over the past 33,000 years, with no discernable trend over time. The findings indicate that the interstellar medium traversed by the Earth during the past 33,000 years contains 60Fe. However, the low estimated deposition rate and the lack of change in deposition during this time suggests that the LIC is not the isolated remnant of a recent supernova and that supernova-produced 60Fe permeates the interstellar medium, according to the authors.
Article #19-16769: "60Fe deposition during the late Pleistocene and the Holocene echoes past supernova activity," by Anton Wallner et al.
MEDIA CONTACT: Anton Wallner, Australian National University, Canberra, AUSTRALIA and Helmholtz-Zentrum Dresden-Rossendorf, GERMANY; tel: +49-1748283418; e-mail: anton.wallner@anu.edu.au
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Journal
Proceedings of the National Academy of Sciences