Local Interstellar Cloud Structure Imprinted in Antarctic Ice by Supernova ^{60}Fe.

The solar system currently traverses the Local Interstellar Cloud (LIC), one of several warm cloudlets of the Complex of Local Interstellar Clouds (CLIC) in the solar neighborhood. The origin of these cloudlets is unknown and could be related to supernova shock wave dynamics. If supernovae are the source of these cloudlets or influence their properties, the CLIC may act as a cosmic archive for the supernova-produced radionuclide ^{60}Fe. We detected minuscule traces of interstellar ^{60}Fe in 295 kg of the European Project for Ice Coring in Antarctica Dronning Maud Land ice core, covering the time period 40-81 kyr ago. We find an ^{60}Fe/^{53}Mn ratio of (8±5)×10^{-4}, slightly above the expected cosmogenic production, corresponding to an interstellar deposition rate of (0.22_{-0.12}^{+0.14}) ^{60}Fe at/cm^{2}/yr. This influx is significantly lower than that observed in recent Antarctic snow and marine sediment records during the last 40 kyr. These results suggest that the LIC is a cosmic archive for supernova-produced ^{60}Fe. The imprinted ^{60}Fe time profile is evidence for a changing local interstellar environment over the last 80 kyr.