The unstable atom 92Nb, which has long since disappeared, provides information about the beginnings of our solar system. Credit: Makiko K. Haba
Use the extinct niobium- 92 atom, ETH researchers were able to date the events in the early solar system with greater precision than before. The study concludes that supernova explosions must have occurred in the birth environment of our sun.
When an atom of a chemical element has an excess of protons or neutrons, it becomes unstable. It will shed these additional particles as gamma radiation until it becomes stable again. One such unstable isotope is niobium- 92 (92Nb), after which experts also name a radionuclide. The half-life of 37 million years is relatively short, and it therefore became extinct shortly after the formation of the solar system. Today, only its stable daughter isotope, zircon 92 (92Zr), testifies to the existence of 92Nb.
Yet scientists have continued to use the extinct radionuclide in the form of the 92Nb-92Zr chronometer with which they can date events that took place about 4.57 billion years ago in the early solar system.
Use of the 92Nb-92Zr chronometer has so far been limited by a lack of precise information regarding the quantity 92NB which was present during the birth of the solar system. This is detrimental to its use for dating and to determine the production of these radionuclides in stellar environments.
Meteorites hold the key to the distant past
Now a research team from ETH Zurich and the Tokyo Institute of Technology (Tokyo Tech) have significantly improved this chronometer. The researchers achieved this improvement by means of a clever trick: they recovered rare zircon and rutile minerals from meteorites that were fragments of the protoplanet Vesta. These minerals are considered the most suitable for determining 92Nb, because they provide exact evidence of how common 92Nb was during the formation of the meteorite. Then the team with the uranium-lead dating technique (uranium atoms that decay into lead) calculated how abundant 92NB was at the time when the solar system originated. By combining the two methods, the researchers succeeded in determining the accuracy of the 92Nb-92Zr chronometer.
“This improved chronometer is therefore a powerful tool for giving precise ages for the formation and development of asteroids and planets – events that occurred in the first ten million years after the formation of the solar system,” says Maria Schönbächler, professor at the Institute of Geochemistry and Petrology at ETH Zurich, who led the study.
Supernovae released niobium 92
Now that the researchers know more precisely how abundant it is 92NB was at the beginning of our solar system. They can more accurately determine where these atoms were formed and where the material that made up our sun and the planets came from.
The new model of the research team indicates that the inner solar system, with the Earth planets Earth and March, is largely influenced by material produced by Type Ia supernovae in our Milky Way galaxy. In such stellar explosions, two stars are in orbit with each other before exploding and releasing stellar material. In contrast, the outer solar system was fed primarily by a nuclear-falling supernova – probably in the star nursery where our sun was born – in which a massive star collapsed on itself and exploded violently.
Reference: “Exact Initial Abundance of Niobium-92 in the Solar System and Implications for P-Process Nucleosynthesis” by Makiko K. Haba, Yi-Jen Lai, Jörn-Frederik Wotzlaw, Akira Yamaguchi, Maria Lugaro and Maria Schönbächler, 23 February 2021 , Proceedings of the National Academy of Sciences.
DOI: 10.1073 / pnas.2017750118