Detecting and unveiling remnants from 2-3 Myr old supernovae on Earth
A two million year old signal of 60Fe was detected in several terrestrial deep-sea archives and in lunar samples. This long-lived isotope is not produced on Earth, however, it is generated in massive stars and ejected during supernova explosions. The recent injection of 60Fe into the solar system coincides with the formation of the Local Bubble - a large cavity in the interstellar medium produced by multiple supernovae - into which our solar system is embedded. The most likely sources are stellar explosions within a moving group that passed the solar neighbourhood, and whose surviving members are now in the Scorpius-Centaurus stellar association.
We have traced the trajectories of the member stars back in time and calculated the most probable explosion sites of the perished stars. By determining their masses and explosion times, we found a sequence of supernovae starting 13 Myr ago. With analytical and numerical methods we modelled the Local Bubble and, as a consequence of its formation, the terrestrial 60Fe signature.
Similar calculations with another long-lived radionuclide, 26Al, show that a supernova-signal may be hidden behind a large terrestrial concentration.
Accelerator mass spectrometry measurements of 26Al within samples of four deep-sea sediment cores from the Indian Ocean confirm this result.