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The Oxygen Isotopic Composition of Water in the Inner Solar System

  • Author(s): Nunn, Morgan
  • Advisor(s): Thiemens, Mark H
  • et al.

Where there is water, there can be life. Improving our understanding of how life, as we know it, arose uniquely in our solar system on Earth depends critically on our understanding of the history of water in the solar system. Better characterizing the sources of water to the Earth-Moon system is crucial in constraining this history and motivated the experiments described in this dissertation.

The oxygen isotopic composition of water in lunar samples in addition to meteorites from Mars and several asteroids, which have delivered significant material to the Earth-Moon system, were characterized. The ordinary chondrite (OC) samples, Bjurböle matrix, Bjurböle chondrules, and ALHA77216, contain 17O-enriched water with, Δ17O up to 1.5‰, released by high temperature heating. Water liberated from the carbonaceous chondrite (CC), Murchison, by heating to high temperatures (≤ 1000˚C) possess Δ17O approaching -1.5‰. Low-temperature fractions of water from these OC and CC samples is mass-dependently fractionated (Δ17O ≅ 0‰). The eucrite, PCA 91006 releases water upon heating to 50-350˚C with Δ17O ≅ 1‰ and 600-1000˚C with as low as -11‰. The martian meteorite, NWA 7034, contains water with an average Δ17O = 0.32‰. The lunar samples analyzed (10049, 10057, 10060, 12021, 12039, 14163, 14305, 79035) possess water with average Δ17O = 0.18‰. The oxygen isotopic composition of a whole rock sample of a carbonaceous chondrite (CC) meteorite, Sutter’s Mill, was also measured, and possesses Δ17O = -1.8‰. The 1σ error on these Δ17O values is 0.011‰. These results reveal that delivery of water by OCs and CCs could account for almost all of the lunar water isotopic compositions measured.

Complementary studies measuring the isotopic composition of ozone (O3), an important precursor to water, formed in experiments performed under analogous conditions to those that existed early in the formation of the solar system were also conducted. Additionally, experiments characterizing the isotopic composition of O2 involved in ion-molecule reactions which dominate molecule-formation processes occurring in cold regions of interstellar molecular clouds were also conducted. These complementary studies help define and explain the isotopic composition of oxygen-bearing reservoirs, especially water, in the present-day inner solar system.

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