Recent progress on interstellar radionuclides on Earth and the Moon

TL;DR

The paper synthesizes AMS-based efforts to detect interstellar radionuclides on Earth and the Moon, focusing on $^{60}$Fe, $^{244}$Pu, and related nuclides to probe stellar nucleosynthesis and Local Interstellar Medium dynamics. It reports evidence for a globally inhomogeneous deposition of $^{60}$Fe on Earth and evaluates a potential, energy-dependent survival of primary GCR $^{60}$Fe through Earth's atmosphere and lunar surface, suggesting a limited but non-negligible contribution under certain conditions. The work also details advances in chemical extraction and purification crucial for ultra-trace radionuclide measurements (e.g., Pu, Cm, Hf) and outlines future directions, including extended archival sampling and the deployment of new facilities such as HAMSTER. Overall, the study advances constraints on interstellar influx timing, origin, and deposition mechanisms, with implications for nucleosynthesis sites and ISM mixing on Myr timescales, and informs future searches for heavier r-process radionuclides on Earth and the Moon.

Abstract

The detection of interstellar radionuclides in geological archives provides insights into nucleosynthesis in stars and stellar explosions as well as interstellar medium dynamics in the Local Bubble and the Local Interstellar Cloud. In this work, current projects to detect interstellar radionuclides with accelerator mass spectrometry will be reviewed. These projects aim to address unsolved questions regarding the timing and the origin of the influxes and to establish new radionuclides for future searches. For the first time, experimental evidence for an inhomogeneous deposition of interstellar 60Fe onEarthwill be presented and another potential source for 60Fe on Earth and the Moon, primary galactic cosmic rays, will be introduced.

Figures (1)

• Figure 1: Schematic overview of interstellar radionuclides with their half-lives, potential detection timescales, geological samples and interstellar structures such as the complex of local interstellar clouds (CLIC) and the Local Bubble being investigated in past, current and future projects.