9:00 AM - 9:30 AM
[PPS07-06] Novel approaches based on correlated short-lived and stable isotope variations for dating nucleosyntheses and early solar system events
★Invited Papers
Keywords:supernova, short-lived radionuclide, nucleosynthesis, isotope dichotomy
Short-lived radionuclides (SLRs) present in the early solar system can be used to constrain the birth environment of our sun and serve as chronometers for nucleosyntheses and early solar system events. Their use as chronometers commonly rests on the assumption that they were uniformly distributed in the early solar system. However, this assumption has been challenged by the report of the heterogeneous distribution of the SLR 26Al (e.g., Bollard et al., 2019 GCA). Such SLR heterogeneity is compatible to the results of high-precision isotope analyses of meteorites, showing that carbonaceous chondrites (CC) and non-carbonaceous (NC) meteorites exhibit fundamentally different nucleosynthetic anomalies with respect to stable isotopes, such as Ti isotopes (e.g., Kruijer et al., 2019 Nature Astronomy). In addition, we have recently found that the SLR 92Nb was ~80% more abundant in CC than in NC reservoirs (Hibiya et al., 2019 LPSC). Because 92Nb exclusively originates from supernovae, 92Nb enrichment requires a biased distribution of ejecta from a supernova in the protoplanetary disk. These results call for establishment of new methodology for chronology of nucleosyntheses and early solar system events without assuming the homogeneous distribution of supernova-derived SLRs.
Here, we present novel chronological approaches coupling the SLR and nucleosynthetic stable isotope heterogeneities. In the chronology of early solar system events, the SLR heterogeneity leads to erroneous relative ages, which can be calibrated if the initial SLR abundance difference is known. We show that the 26Al and 92Nb clocks can be calibrated using the correlation with the nucleosynthetic Ti isotope heterogeneity, considering that these isotope variations are attributed to biased distribution of ejecta from a core-collapse supernova (CCSN) across the protoplanetary disk. Coupling the SLR and Ti isotope variations further allows us to estimate the timing of the CCSN. In the context of the heterogeneous distribution of CCSN ejecta, a difference in the initial abundance of a CCSN-derived SLR between two disk reservoirs is a function of two parameters: (i) the time interval from the CCSN to solar system formation and (ii) the difference in dilution factors of the ejecta in the disk reservoirs. Importantly, the latter can be independently estimated from the variation in the nucleosynthetic stable isotope heterogeneity, which in turn allows to date the CCSN. We combine the 26Al and Ti isotope heterogeneities and estimate the timing of the CCSN explosion to be 0.4–1.5 Myr before the CAI formation. In addition, assuming that CAIs record the isotope composition of the molecular cloud core in which the CCSN ejecta were most efficiently trapped, we estimate the distance between the CCSN and cloud core to be ~1 parsec. These results imply that our sun was born in a stellar cluster containing massive stars and a nearby CCSN triggered the formation of the solar system. We will extend the cosmochronological approach proposed here to other nuclides, in particular proton-rich SLR 98Tc and long-lived radionuclide 138La. Because 98Tc and 138La as well as 92Nb are produced by the same processes in CCSNe, combining these p-nuclides would potentially allows us to determine the timing of the last CCSN event more accurately than the combined 26Al–Ti chronometer.
Here, we present novel chronological approaches coupling the SLR and nucleosynthetic stable isotope heterogeneities. In the chronology of early solar system events, the SLR heterogeneity leads to erroneous relative ages, which can be calibrated if the initial SLR abundance difference is known. We show that the 26Al and 92Nb clocks can be calibrated using the correlation with the nucleosynthetic Ti isotope heterogeneity, considering that these isotope variations are attributed to biased distribution of ejecta from a core-collapse supernova (CCSN) across the protoplanetary disk. Coupling the SLR and Ti isotope variations further allows us to estimate the timing of the CCSN. In the context of the heterogeneous distribution of CCSN ejecta, a difference in the initial abundance of a CCSN-derived SLR between two disk reservoirs is a function of two parameters: (i) the time interval from the CCSN to solar system formation and (ii) the difference in dilution factors of the ejecta in the disk reservoirs. Importantly, the latter can be independently estimated from the variation in the nucleosynthetic stable isotope heterogeneity, which in turn allows to date the CCSN. We combine the 26Al and Ti isotope heterogeneities and estimate the timing of the CCSN explosion to be 0.4–1.5 Myr before the CAI formation. In addition, assuming that CAIs record the isotope composition of the molecular cloud core in which the CCSN ejecta were most efficiently trapped, we estimate the distance between the CCSN and cloud core to be ~1 parsec. These results imply that our sun was born in a stellar cluster containing massive stars and a nearby CCSN triggered the formation of the solar system. We will extend the cosmochronological approach proposed here to other nuclides, in particular proton-rich SLR 98Tc and long-lived radionuclide 138La. Because 98Tc and 138La as well as 92Nb are produced by the same processes in CCSNe, combining these p-nuclides would potentially allows us to determine the timing of the last CCSN event more accurately than the combined 26Al–Ti chronometer.