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The niobium-92-zirconium-92 ( 92 Nb- 92 Zr) 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 92 Nb in the Solar System is important for quantifying the contribution of p -process nucleosynthesis in astrophysical models. Current estimates of the initial 92 Nb/ 93 Nb ratios have large uncertainties compromising the use of the 92 Nb- 92 Zr cosmochronometer and leaving nucleosynthetic models poorly constrained. Here, the initial 92 Nb abundance is determined to high precision by combining the 92 Nb- 92 Zr systematics of cogenetic rutiles and zircons from mesosiderites with U-Pb dating of the same zircons. The mineral pair indicates that the 92 Nb/ 93 Nb ratio of the Solar System started with (1.66 ± 0.10) × 10 -5 , and their 92 Zr/ 90 Zr 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 92 Nb/ 93 Nb, we can show that the presence of 92 Nb in the early Solar System provides further evidence that both type Ia supernovae and core-collapse supernovae contributed to the light p -process nuclei., Competing Interests: The authors declare no competing interest.