Ancient star explosions revealed in the deep sea.
The interstellar medium is shaped by nearby supernova explosions. Ejecta containing fresh nucleosynthetic products may travel through the solar system as a temporary passage, or the solar system may navigate local clouds that may be isolated leftovers of supernova explosions.
Such situations could change the intensity of the galactic cosmic-ray flux to which Earth is exposed.
The supernova leftovers discovered in deep-sea sediments are unfolding the mystery surrounding the solar system’s space.
According to a recent study from the Australian National University, Earth has been moving through a cloud of mildly radioactive dust for the last 33,000 years. For the last 33,000 years, space has been continuously seeding Earth with a rare isotope of iron formed in supernovae.
Scientists examined deep-sea sediments from two separate places dating back 33,000 years. They identified clear traces of the isotope iron-60 using the HIAF’s mass spectrometer’s exceptional sensitivity.
Iron-60 is thought to be generated when stars explode in supernova explosions. It is radioactive and will decay completely in 15 million years. Meanwhile, any iron-60 discovered on Earth must have originated far later than the rest of the 4.6-billion-year-old Earth and must have come from nearby supernovae before settling on the ocean floor.
This isn’t the first time the isotope iron-60 has dusted our planet. Professor Anton Wallner, an ANU nuclear physicist, previously discovered traces of iron-60 approximately 2.6 million years ago, and potentially another approximately 6 million years ago. It means that it adds to the growing body of evidence that such dusting is still ongoing- Earth is still travelling through an interstellar cloud of dust that could have formed millions of years ago from a supernova.
The solar system is passing through the local interstellar cloud, a denser cloud of gas and dust (LIC). If this cloud formed millions of years ago from a supernova, it would contain iron-60. That is why scientists chose to look for more recent sediment.
They discovered extremely low amounts of iron-60 in the sediment, equal to radiation levels in space well below the Earth’s natural background levels, and the distribution of the iron-60 matched Earth’s recent travel through the nearby interstellar cloud. However, the iron-60 dated back further and was spread across the full 33,000-year measuring period.
Professor Wallner said, “Recent papers are suggesting that iron-60 trapped in dust particles might bounce around in the interstellar medium. So the iron-60 could originate from even older supernovae explosions, and what we measure is some echo. More data is required to resolve these details.”
The study included researchers from ANU, the Australian Nuclear Science and Technology Organization, HZDR, the University of Vienna, and TU Berlin.
Professor Wallner conducted research at the Australian National University’s Heavy Ion Accelerator Facility (HIAF). He also holds joint appointments at Germany’s Helmholtz-Zentrum Dresden-Rossendorf (HZDR) and Technical University Dresden (TUD).