A near-Earth supernova, on the other hand, would have devastating effects on our planet. It can change the Earth’s biosphere and cause mass extinctions. “If you look at the period since the formation of the solar system, which extends over billions of years, very close cosmic explosions cannot be ruled out,” emphasizes Wallner.
The search for the isotopes Fe-60 and Pu-244
During a supernova, radioactive atoms are also freshly formed. The researchers from Dresden and Urbana are primarily interested in the radioactive iron isotope Fe-60 and the plutonium isotope Pu-24.
After about 2.6 million years, about half of all Fe-60 atoms have transformed into a stable nickel isotope. “Fe-60 is extremely rare on Earth because it is not produced significantly naturally. However, it is produced in large quantities right before a supernova explosion,” explains Wallner.
All of the Fe-60 that was present when the Earth formed about 4.5 billion years ago has long since disappeared. If a sediment of this isotope appears in the deep sea or in the surface material of the moon today, it probably comes from a supernova that “should have occurred near Earth only a few million years ago.”
The situation is similar with Pu-244. After 80 million years, about half of this isotope has changed into other elements. It is probably caused by neutron star collisions rather than supernovae. “Plutonium-244 also requires explosive events and, according to the theory, is created in a similar way to the elements gold or platinum, which have always occurred naturally on Earth and which now consist of stable atoms,” explains the scientist.
A speck of dust through the galaxy
During cosmic explosions at a distance of ten to 150 parsecs, our solar system protects the intrusion of radioactive isotopes on Earth – according to current theories, mainly the solar wind and the magnetic field of the heliosphere.
Because the isotopes tend to accumulate in dust grains, Fe-60 and Pu-244 atoms can still end up on Earth. But very few atoms reach the earth’s surface in a year. In addition, even the most sensitive instruments only capture about every 5,000th particle. Only about a thousand Fe-60 atoms have been measured in the past 20 years. With Pu-244 there are even fewer.
Since Fe-60 atoms are mixed with other material in most samples, the samples undergo very complex chemical processing. However, this low concentration can only be detected by accelerator mass spectrometry systems. One of these facilities, Dreams (Dresden Accelerator Mass Spectrometry facility), is already located at the Helmholtz Center Dresden-Rossendorf. Hamster is said to be the next facility of this kind.