Abstract

Basic Sessions

Day 1, May 15（Mon.）　10:00-10:18　Room B (Room 1202)

1B-O-1000（2P-40）　　PDF

Origin of the short-lived radionuclide ⁹²Nb and solar system formation

(¹Univ. Tokyo, ²QST)
^oYuki Hibiya¹, Tsuyoshi Iizuka¹, Hatsuki Enomoto¹, Takehito Hayakawa²

Meteorites have isotopic evidence that short-lived nuclides were present in the early solar system. Understanding the origin of SLRs has important implications for early solar system evolution. Among them, niobium-92 (⁹²Nb) has been used to infer the timing of supernova explosions and planetary differentiation, assuming a uniform distribution in the early solar system. Here, we present the niobium–zirconium (Nb–Zr) dating of Northwest Africa 6704, a meteorite thought to form in the outer protosolar disk, and demonstrated that the initial ⁹²Nb/⁹³Nb ratio of the solar system is enriched by about 80% in the outer disk compared to the inner. Our newly obtained initial ⁹²Nb/⁹³Nb value in the outer disk is higher than the expected galactic background produced solely by thermonuclear Type Ia supernovae, requiring that ⁹²Nb has a core-collapse supernovae (CCSNe) origin. Given that short-lived radionuclides inherited from the interstellar medium were homogeneously distributed in the protosolar disk, the ⁹²Nb heterogeneity suggests that a nearby CCSN contributed significantly to ⁹²Nb production. We envisage that the CCSN ejecta was injected into the core of the protosolar cloud shortly before it collapsed, consistent with the hypothesis that a supernova triggered the formation of our solar system.