Oxygen Isotopic Compositions of Chondrules as Probes of Solar Protoplanetary Disk Formation

TL;DR

This study uses simulations to explore how oxygen isotopic compositions of chondrules inform us about the formation and evolution of the solar protoplanetary disk, considering different infall scenarios and isotopic exchange processes.

Contribution

It introduces a one-dimensional disk evolution model incorporating isotope exchange, providing new insights into the origins of chondrule isotopic signatures and disk formation conditions.

Findings

Reproduces chondrule isotopic compositions with moderate or large infall extents.

Suggests bimodal isotopic trends result from H2O vapor escape during heating.

Challenges explaining ordinary-chondrite isotopes within the current model at low temperatures.

Abstract

Chondrules are thought to have formed during transient flash-heating events in dust-enriched regions of the solar protoplanetary disk. Although laboratory studies have characterized the oxygen isotopic compositions of chondritic materials, quantitative interpretations based on simulations of disk formation and evolution remain limited. Here, we perform one-dimensional simulations of disk formation and evolution by solving a diffusion--advection equation with mass infall from the parental cloud core. We compute the temporal evolution of oxygen isotopic compositions using an experimentally derived isotope-exchange model. We examine how the oxygen isotopic signatures of the disk depend on the radial distribution of infalling material and the composition of the parental cloud core. We find that the oxygen isotopic compositions of carbonaceous-chondrite chondrules can be reproduced if either (i) the radial extent of mass infall onto the disk is moderate ($\sim 10~{\rm au}$), or (ii) it is large ($> 10~{\rm au}$) and the parental cloud core was ice-depleted and/or experienced weaker CO self-shielding than is commonly assumed. We further suggest the scenario that the observed bimodal trends in oxygen isotopic composition and redox state reflect the partial escape of H$_{2}$O vapor from chondrule-forming regions during heating. In contrast, if ordinary-chondrite chondrules formed inside the snow line under background temperatures of $\lesssim 500~{\rm K}$, their oxygen isotopic compositions may be difficult to explain within the present disk-evolution model, because oxygen isotopic exchange between silicates and vapor species proceeds efficiently only in the inner disk at $T \gtrsim 500$--$600~{\rm K}$.