Scientists have found iron-60 with interstellar origins in Antarctica, likely a distant supernova that occurred millions of years ago.
The samples came from 1,100 pounds of snow gathered from Antarctica where the high altitude of the sample kept it free of dust contamination. The snow was melted in a German lab and analyzed with an accelerator mass spectrometer, where the rare nuclear iron-60 isotope was detected.
How did they do it? Irradiated space dust can hold iron-60 but exposure to cosmic radiation also creates manganese-53. By comparing ratios of iron-60 and manganese-53 in the grains from the Antarctic snow, they found that the quantity of manganese was much lower than it would have been if the dust had traveled locally.
An illustration of the solar neighborhood and nearby clouds within a distance of about 10 pc. Our Solar System is located inside the Local Interstellar Cloud and near the G-Cloud, which are embedded in the larger Local Bubble with a diameter of about 100 pc. The relative motion of the clouds (blue) and the general motion of the Solar System (yellow) are indicated. Figure adapted from NASA/Goddard/Adler/U. Chicago/Wesleyan.
Iron-60 here from so long ago has since decayed. Even all atomic bomb tests could not have produced the amounts of iron-60 found in the snow sample. Iron-60 is produced in terrestrial nuclear reactors too but the amount that reactors generate is insignificant and confined to where it is made. Rare accidents such as the Fukushima Daiichi nuclear power plant in 2011 didn't introduce iron-60 to the environment in measurable quantities.
