Oxygen isotopic heterogeneity in the early Solar System inherited from the protosolar molecular cloud.
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- Record sourced from PubMed, PMID 33067241.
- Also identified by DOI 10.1126/sciadv.aay2724 and PMC identifier 7567603.
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Abstract
The Sun is <sup>16</sup>O-enriched (Δ<sup>17</sup>O = -28.4 ± 3.6‰) relative to the terrestrial planets, asteroids, and chondrules (-7‰ < Δ<sup>17</sup>O < 3‰). Ca,Al-rich inclusions (CAIs), the oldest Solar System solids, approach the Sun's Δ<sup>17</sup>O. Ultraviolet CO self-shielding resulting in formation of <sup>16</sup>O-rich CO and <sup>17,18</sup>O-enriched water is the currently favored mechanism invoked to explain the observed range of Δ<sup>17</sup>O. However, the location of CO self-shielding (molecular cloud or protoplanetary disk) remains unknown. Here we show that CAIs with predominantly low (<sup>26</sup>Al/<sup>27</sup>Al)<sub>0</sub>, <5 × 10<sup>-6</sup>, exhibit a large inter-CAI range of Δ<sup>17</sup>O, from -40‰ to -5‰. In contrast, CAIs with the canonical (<sup>26</sup>Al/<sup>27</sup>Al)<sub>0</sub> of ~5 × 10<sup>-5</sup> from unmetamorphosed carbonaceous chondrites have a limited range of Δ<sup>17</sup>O, -24 ± 2‰. Because CAIs with low (<sup>26</sup>Al/<sup>27</sup>Al)<sub>0</sub> are thought to have predated the canonical CAIs and formed within first 10,000-20,000 years of the Solar System evolution, these observations suggest oxygen isotopic heterogeneity in the early solar system was inherited from the protosolar molecular cloud.