Existence of an 16O-Rich Gaseous Reservoir in the Solar Nebula

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Science  08 Feb 2002:
Vol. 295, Issue 5557, pp. 1051-1054
DOI: 10.1126/science.1068200

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Carbonaceous chondrite condensate olivine grains from two distinct petrographic settings, calcium-aluminum–rich inclusion (CAI) accretionary rims and amoeboid olivine aggregates (AOAs), are oxygen-16 (16O) enriched at the level previously observed inside CAIs. This requires that the gas in the nebular region where these grains condensed was 16O-rich. This contrasts with an16O-poor gas present during the formation of chondrules, suggesting that CAIs and AOAs formed in a spatially restricted region of the solar nebula containing 16O-rich gas. The16O-rich gas composition may have resulted either from mass-independent isotopic chemistry or from evaporation of regions with enhanced dust/gas ratios, possibly in an X-wind environment near the young Sun.

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