The unstable 92Nb atom, which has long since disappeared, provides information about the beginning of our solar system. Credit: Makiko K. Haba
Using the extinct niobium-92 atom, ETH researchers were able to date events in the early solar system with greater precision than before. The study concludes that the supernova explosions must have occurred in the environment where our sun was born.
If an atom in a chemical element has an excess of protons or neutrons, it becomes unstable. It will release these additional particles as gamma radiation until it becomes stable again. One of these unstable isotopes is niobium-92 (92Nb), which experts also call radionuclide. Its half-life of 37 million years is relatively short, so it was extinguished shortly after the formation of the solar system. Today, only its stable son isotope, zirconium-92 (92Zr), testifies to the existence of 92Nb.
However, scientists continued to make use of the extinct radionuclide in the form of 92Nb-92Zr chronometer, with which they can date events that occurred at the beginning of the solar system about 4.57 billion years ago.
Use of 92Nb-92The Zr timer has so far been limited by a lack of accurate information on the amount of 92Nb that was present at the birth of the solar system. This compromises its use to date and determine the production of these radionuclides in stellar environments.
Meteorites are the key to the distant past
Now, a research team from ETH Zurich and the Tokyo Institute of Technology (Tokyo Tech) has greatly improved this timer. The researchers achieved this improvement through a clever trick: they recovered zircon and rare rutilic minerals from meteorites that were fragments of the protoplanet Vesta. These minerals are considered the most suitable for determining 92Nb, because they provide accurate evidence of how common 92Nb was at the time of the meteorite formation. Then, with the uranium-lead dating technique (uranium atoms that decompose into lead), the team calculated how abundant 92Nb was at the time the formation of the solar system. By combining the two methods, the researchers were able to considerably improve the accuracy of the 92Nb-92Stopwatch Zr.
“This improved timer is therefore a powerful tool for providing accurate ages for the formation and development of asteroids and planets – events that happened in the first tens of millions of years after the formation of the solar system,” said Maria Schönbächler, Professor at the Institute of Geochemistry and Petrology at ETH Zurich, which led the study.
Supernovas released niobium-92
Now that researchers know more precisely how abundant 92Nb was at the beginning of our solar system, they can more accurately determine where these atoms were formed and where the material that makes up our sun and planets originated.
The new model of the research team suggests that the internal solar system, with the terrestrial planets Earth and Mars, is largely influenced by the material ejected by Type Ia supernovae in our Milky Way galaxy. In such stellar explosions, two orbiting stars interact with each other before exploding and releasing stellar material. In contrast, the outer solar system was powered mainly by a core collapsing supernova – probably in the stellar nursery where our sun was born – in which a massive star collapsed on itself and exploded violently.
Reference: “Initial abundance needs Niobium-92 in the Solar System and implications for the nucleosynthesis of the p process” by Makiko K. Haba, Yi-Jen Lai, Jörn-Frederik Wotzlaw, Akira Yamaguchi, Maria Lugaro and Maria Schönbächler, February 23 of 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2017750118