^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 the 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.

^1,2,3Benoit Côté et al. (>10)
Science 371, 945-948 Link to Article [DOI: 10.1126/science.aba1111]
¹Research Centre for Astronomy and Earth Sciences, Eötvös Loránd Research Network, Konkoly Observatory, 1121 Budapest, Hungary.
²Institute of Physics, Eötvös Loránd University, 1117 Budapest, Hungary.
³National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, MI 48824, USA.
Reprinted with permission from AAAS

The composition of the early Solar System can be inferred from meteorites. Many elements heavier than iron were formed by the rapid neutron capture process (r-process), but the astrophysical sources where this occurred remain poorly understood. We demonstrate that the near-identical half-lives (≃15.6 million years) of the radioactive r-process nuclei iodine-129 and curium-247 preserve their ratio, irrespective of the time between production and incorporation into the Solar System. We constrain the last r-process source by comparing the measured meteoritic ratio 129I/247Cm = 438 ± 184 with nucleosynthesis calculations based on neutron star merger and magneto-rotational supernova simulations. Moderately neutron-rich conditions, often found in merger disk ejecta simulations, are most consistent with the meteoritic value. Uncertain nuclear physics data limit our confidence in this conclusion.