Scientists have obtained new evidence that Earth is passing through an interstellar region containing radioactive material left over from an ancient supernova explosion. Traces of iron-60 detected in tens of thousands of years old ice samples taken from Antarctica show that the Solar System collected the remains of an exploded star during its journey in the Local Interstellar Cloud. Scientists detected the remains of supernova that reached the Earth.
The international research team led by Helmholtz-Zentrum Dresden-Rossendorf detected the rare radioactive iron-60 isotope in Antarctic ice. The study, published in Physical Review Letters, revealed that the Solar System is currently passing through the Local Interstellar Cloud, which consists of very sparse gas and dust between stars, and that the Earth is collecting iron-60 in the process. Iron-60 is formed inside massive stars and is scattered into space when these stars explode as supernovae.
Geological records show that the Solar System was exposed to iron-60-bearing supernova remnants twice millions of years ago. However, there has been no recent star explosion that could deliver this isotope directly to Earth. Therefore, the discovery of iron-60 in surface snow in Antarctica that was less than 20 years old a few years ago opened up a new question about the origin of the isotope. The explanation that the research team focused on was that iron-60 could be stored for a long time in the Local Interstellar Cloud and reached Earth as the Solar System passed through this cloud.
Traces of iron-60 have previously been found in seafloor sediments in samples dating back to 30,000 years ago. Despite this, alternative explanations for the source of the isotope were not completely excluded. The Antarctic ice samples examined in the new study date back to 40,000 to 80,000 years ago. This period coincides with the period during which the Solar System entered the Local Interstellar Cloud. The researchers compared the amount of iron-60 in these samples to previously examined surface snow and seafloor sediments.
The results showed that the amount of iron-60 reaching the Earth 40,000-80,000 years ago was lower than today and in more recent periods. This difference shows that the Solar System passed through an environment poorer in iron-60 in the past or that the Local Interstellar Cloud had density differences within itself. The change of the iron-60 signal in a short time interval on a cosmic scale, such as tens of thousands of years, also pushed into the background the explanation of a weakening flow from supernova explosions millions of years ago.
Samples taken from the European EPICA ice drilling project, in which the Alfred Wegener Institute was involved, were used for the research. The team transported approximately 300 kilograms of ice from Bremerhaven to Dresden and chemically processed it. At the end of this process, only a few hundred milligrams of powder remained. Researchers carried out a very sensitive preparation process to separate iron-60 from this powder without loss.
The prepared samples were checked with beryllium-10 and aluminum-26 isotopes in the DREsden Accelerator Mass Spectrometry laboratory within HZDR. Since the expected concentrations of these isotopes in Antarctic ice are known, the measurements were used to understand whether iron-60 was lost during the process. The team determined that there was no significant loss during the sample preparation process. The final measurement was made at the Heavy Ion Accelerator Facility at the Australian National University.
According to researchers, this facility is the only center in the world that can detect such low amounts of iron-60. Using electric and magnetic filters, unwanted atoms were separated by mass, and only a few iron-60 atoms were selected from the sample, which initially contained about 10 trillion atoms. The research team is now preparing to work on older Antarctic ice cores. The new goal is to study the ice that formed before the Solar System entered the Local Interstellar Cloud.
In this way, a clearer picture will be obtained about both the structure of the cloud and the past movement of the Solar System within the interstellar medium. The Beyond EPICA – Oldest Ice project, in which the Alfred Wegener Institute is involved, is among the studies carried out to reach older ice cores.
Comments
You can write your views about this story. Comments may be moderated according to site settings.