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K. E. Cyr (NASA Johnson Space Center), C. M. Sharp (Steward Observatory, University of AZ), J. I. Lunine (Lunar and Planetary Lab, University of AZ)
Recent diffusive and advective nebular water vapor distributions suggest that while there is an overall drying of the inner nebula as the nebula ages, there is also a "wet" zone of local water vapor enhancement, which gradually decreases with time. We quantify the effects of these radial and temporal water distribution variations on solar nebula chemistry and the local nebular C/O ratio. The SOLGASMIX chemical equilibrium code was used to compute abundances of nebular elements and major molecular species, C, N, S etc., for a variety of water-depleted nebular settings produced by the water distribution models, and for low- and high-pressure (10-5 and 10-3 atm) nebulae. Results show that both the diffusive and advective water distributions cause relatively oxidizing and reducing nebular conditions to occur across 0.1-5 AU, varying over time. Abundances of organics and numbers of condensable species increase over what would be expected to form from a solar composition gas. Modest increases occur in a relatively oxidizing nebula assuming a solar C/O ratio of 0.42, while large increases, several orders of magnitude for gaseous organic species, occur in a more reducing nebula with solar C/O of 0.6. The radial and temporal variety of nebular conditions may help explain the variation in oxidation state of meteorites. Additionally, the increase in organics in the inner nebula could have allowed local accretion of organics to the terrestrial planets, and perhaps supplied organics to the Jovian planetesimal formation region and beyond via outward mixing processes. The increase in condensates itself could possibly increase the catalyzed production of organics through Fischer-Tropsch type reactions, though further study is required. Lastly, nebular water could have been directly supplied to Earth and the other terrestrial planets via icy planetesimal drift and scattering.