Precise initial abundance of Niobium-92 in the Solar System and implications for p-process nucleosynthesis

1,2Makiko K. Haba,1,3Yi-Jen Lai,1Jörn-Frederik Wotzlaw,4Akira Yamaguchi,5,6,7Maria Lugaro,1Maria Schönbächler
Proceedings of the National Academy of Sciences of teh United States of America (PNAS) (in Press) Link to Article [https://doi.org/10.1073/pnas.2017750118]
1Institute of Geochemistry and Petrology, ETH Zürich, 8092 Zürich, Switzerland;
2Department of Earth and Planetary Sciences, Tokyo Institute of Technology, Tokyo 152-8551, Japan;
3Macquarie GeoAnalytical, Department of Earth and Environmental Sciences, Macquarie University, Sydney, NSW 2109, Australia;
4Antarctic Meteorite Research Center, National Institute of Polar Research, 190-8518 Tokyo, Japan;
5 Observatory, Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network (ELKH), 1121 Budapest, Hungary;
6Institute of Physics, ELTE Eötvös Loránd University, 1117 Budapest, Hungary;
7Monash Centre for Astrophysics, School of Physics and Astronomy, Monash University, VIC 3800, Australia

The niobium-92–zirconium-92 (92Nb–92Zr) decay system with a half-life of 37 Ma has great potential to date the evolution of planetary materials in the early Solar System. Moreover, the initial abundance of the p-process isotope 92Nb in the Solar System is important for quantifying the contribution of p-process nucleosynthesis in astrophysical models. Current estimates of the initial 92Nb/93Nb ratios have large uncertainties compromising the use of the 92Nb–92Zr cosmochronometer and leaving nucleosynthetic models poorly constrained. Here, the initial 92Nb abundance is determined to high precision by combining the 92Nb–92Zr systematics of cogenetic rutiles and zircons from mesosiderites with U–Pb dating of the same zircons. The mineral pair indicates that the 92Nb/93Nb ratio of the Solar System started with (1.66 ± 0.10) × 10−5, and their 92Zr/90Zr ratios can be explained by a three-stage Nb–Zr evolution on the mesosiderite parent body. Because of the improvement by a factor of 6 of the precision of the initial Solar System 92Nb/93Nb, we can show that the presence of 92Nb in the early Solar System provides further evidence that both type Ia supernovae and core-collapse supernovae contributed to the light p-process nuclei.

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