Photochemical self-shielding of CO has been proposed as a mechanism to produce solids observed in the modern,
16O-depleted solar system. This is distinct from the relatively
16O-enriched composition of the solar nebula, as demonstrated by the oxygen isotopic composition of the
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Photochemical self-shielding of CO has been proposed as a mechanism to produce solids observed in the modern,
16O-depleted solar system. This is distinct from the relatively
16O-enriched composition of the solar nebula, as demonstrated by the oxygen isotopic composition of the contemporary sun. While supporting the idea that self-shielding can produce local enhancements in
16O-depleted solids, we argue that complementary enhancements of
16O-enriched solids can also be produced via C
16O-based, Fischer-Tropsch type (FTT) catalytic processes that could produce much of the carbonaceous feedstock incorporated into accreting planetesimals. Local enhancements could explain observed
16O enrichment in calcium-aluminum-rich inclusions (CAIs), such as those from the meteorite, Isheyevo (CH/CHb), as well as in chondrules from the meteorite, Acfer 214 (CH3). CO self-shielding results in an overall increase in the
17O and
18O content of nebular solids only to the extent that there is a net loss of C
16O from the solar nebula. In contrast, if C
16O reacts in the nebula to produce organics and water then the net effect of the self-shielding process will be negligible for the average oxygen isotopic content of nebular solids and other mechanisms must be sought to produce the observed dichotomy between oxygen in the Sun and that in meteorites and the terrestrial planets. This illustrates that the formation and metamorphism of rocks and organics need to be considered in tandem rather than as isolated reaction networks.
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