Oxygen isotopic evolution of silicate dust in the protosolar disk: 3D Monte Carlo simulation

Oxygen isotope compositions of Solar System materials including the Earth are distinct from that of Sun (McKeegan et al., 2011). This difference has been explained by oxygen isotope exchange between original silicate dust enriched in ¹⁶O and water vapor depleted in ¹⁶Oinside the snowline (e.g., Yurimoto & Kuramoto, 2004). In order to understand this isotopic exchange reaction in the protosolar disk, we recently discussed the effective reaction temperature of oxygen isotope exchange between water vapor and amorphous silicate dust moving in a steady accretion disk (Ishizaki et al., 2023) using the experimentally determined isotope exchange reaction kinetics (Yamamoto et al., 2018; 2020). We found that the oxygen isotope exchange reaction with water vapor occurs at 650-750 K for amorphous silicate dust with Mg₂SiO₄ composition (Ishizaki et al., 2023). However, our steady accretion disk model did not discuss the effects of (1) O isotope exchange between amorphous silicate dust and CO gas, which is the reservoir of ¹⁶O-rich component, and (2) enhanced abundance of H₂O inside the snowline. Both effects should be considered to examine the reaction timescale, the final O isotope composition of dust, and the spatial distribution of reacted dust, i.e., oxygen isotope exchange history of dust in the protosolar disk. In this presentation, we will present the results of our new model of oxygen isotope exchange of amorphous silicate dust in a steady accretion disk, including the exchange reaction kinetics with CO and the change of H₂O/CO/dust abundance ratio due to icy pebble accretion.