17:15 〜 19:15
[PCG21-P06] 円盤形成段階における原始太陽系星雲の酸素同位体組成の時空間進化
キーワード：原始太陽系星雲、酸素
Oxygen is the most fundamental element in solid materials. Meteorites and their components exhibit a diverse range of oxygen isotope compositions. This isotopic variation is generally interpreted as the result of mixing between isotopically distinct reservoirs in the solar nebula (e.g., Ushikubo et al. 2012; Kawasaki et al. 2018; Tenner et al. 2018; Yamamoto et al. 2022). These reservoirs are thought to have formed through self-shielding of CO gas in the protosolar molecular cloud (e.g., Yurimoto & Kuramoto 2004; Krot et al. 2020), resulting in three major oxygen reservoirs—H2O, CO, and silicate—each with distinct isotope compositions.
Within the framework of the self-shielding scenario, the oxygen isotopic composition of the parental molecular cloud core is assumed to be spatially homogeneous. The spatial heterogeneity of the oxygen isotopic composition observed in the solar nebula is thought to arise from the radial drift of icy dust aggregates and subsequent isotope exchange reactions between silicate dust and nebular gas (e.g., Yurimoto & Kuramoto 2004). The inward migration of icy dust aggregates could locally enhance the abundance of 16O-depleted H2O relative to 16O-enriched CO (e.g., Cuzzi & Zahnle 2004). Both H2O and CO vapors could then react with silicate grains in the inner region of the disk, where the temperature is high (e.g., Yamamoto et al. 2018, 2020, 2024; Ishizaki et al. 2023), leading to the depletion or enrichment of silicate grains in 16O. While this scenario qualitatively explains the origin of the spatial heterogeneity in oxygen isotopic compositions within the solar nebula, quantitative validation through numerical modeling is essential.
Here, we construct a model to investigate the spatiotemporal evolution of the oxygen isotopic composition of the solar nebula, incorporating the dynamics of gas and dust aggregates. We calculate the time evolution of gas and dust surface densities during the disk formation stage, when mass accretion from the parental molecular cloud core is active. Our model also accounts for key thermal processes, including crystallization, evaporation, and recondensation. In this presentation, we discuss how the physical properties of the solar nebula influence the spatial distribution of oxygen isotopic compositions at the end of the disk buildup stage.
Within the framework of the self-shielding scenario, the oxygen isotopic composition of the parental molecular cloud core is assumed to be spatially homogeneous. The spatial heterogeneity of the oxygen isotopic composition observed in the solar nebula is thought to arise from the radial drift of icy dust aggregates and subsequent isotope exchange reactions between silicate dust and nebular gas (e.g., Yurimoto & Kuramoto 2004). The inward migration of icy dust aggregates could locally enhance the abundance of 16O-depleted H2O relative to 16O-enriched CO (e.g., Cuzzi & Zahnle 2004). Both H2O and CO vapors could then react with silicate grains in the inner region of the disk, where the temperature is high (e.g., Yamamoto et al. 2018, 2020, 2024; Ishizaki et al. 2023), leading to the depletion or enrichment of silicate grains in 16O. While this scenario qualitatively explains the origin of the spatial heterogeneity in oxygen isotopic compositions within the solar nebula, quantitative validation through numerical modeling is essential.
Here, we construct a model to investigate the spatiotemporal evolution of the oxygen isotopic composition of the solar nebula, incorporating the dynamics of gas and dust aggregates. We calculate the time evolution of gas and dust surface densities during the disk formation stage, when mass accretion from the parental molecular cloud core is active. Our model also accounts for key thermal processes, including crystallization, evaporation, and recondensation. In this presentation, we discuss how the physical properties of the solar nebula influence the spatial distribution of oxygen isotopic compositions at the end of the disk buildup stage.