Oxygen Isotope Constraints on the Importance of Photochemical Processing in Protoplanetary Disks

Abstract Observations have revealed evidence of photochemical processing in protoplanetary disks. This processing occurs in the photon-dominated layer, the optically thin regions of the disk high above the disk midplane. It remains unclear, however, how much this photochemical processing impacts the compositions of the planets and their building blocks within the disk. Here we use the oxygen isotopic compositions of solar system solids, which have been attributed to photochemistry in the solar nebula, to quantitatively evaluate whether this processing could have produced the conditions needed to provide the diversity of compositions seen in the solar system. We do this by modeling the chemical evolution while fine dust grows into the building blocks of the planets. We find that the oxygen isotopic evolution cannot be attributed to processing in the solar nebula and must instead be inherited from the parent molecular cloud. Further, our results indicate that the observed photochemical processing in protoplanetary disks does not significantly impact the compositions of planets that form within them.