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Challenges 2014, 5(1), 152-158; doi:10.3390/challe5010152
Article

CO Self-Shielding as a Mechanism to Make 16O-Enriched Solids in the Solar Nebula

1,* , 2
 and 3
Received: 1 April 2014; in revised form: 8 May 2014 / Accepted: 13 May 2014 / Published: 21 May 2014
(This article belongs to the Special Issue Challenges in Astrobiology)
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Abstract: 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 C16O-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 C16O from the solar nebula. In contrast, if C16O 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.
Keywords: Fischer-Tropsch reaction; oxygen isotopic fractionation; nebular chemistry; protostellar nebulae; primitive solar nebula Fischer-Tropsch reaction; oxygen isotopic fractionation; nebular chemistry; protostellar nebulae; primitive solar nebula
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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MDPI and ACS Style

Nuth, III, J.A.; Johnson, N.M.; Hill, H.G.M. CO Self-Shielding as a Mechanism to Make 16O-Enriched Solids in the Solar Nebula. Challenges 2014, 5, 152-158.

AMA Style

Nuth, III JA, Johnson NM, Hill HGM. CO Self-Shielding as a Mechanism to Make 16O-Enriched Solids in the Solar Nebula. Challenges. 2014; 5(1):152-158.

Chicago/Turabian Style

Nuth, III, Joseph A.; Johnson, Natasha M.; Hill, Hugh G.M. 2014. "CO Self-Shielding as a Mechanism to Make 16O-Enriched Solids in the Solar Nebula." Challenges 5, no. 1: 152-158.

Challenges EISSN 2078-1547 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert