Biology
Scientific paper
Dec 2010
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010agufm.v31b2317d&link_type=abstract
American Geophysical Union, Fall Meeting 2010, abstract #V31B-2317
Biology
[1027] Geochemistry / Composition Of The Planets, [1041] Geochemistry / Stable Isotope Geochemistry, [5205] Planetary Sciences: Astrobiology / Formation Of Stars And Planets, [6299] Planetary Sciences: Solar System Objects / General Or Miscellaneous
Scientific paper
One of the longest standing problems in planetary science is the origin of the mass-independently fractionated oxygen isotopic reservoirs in the solar system. The oldest minerals formed in the solar system, calcium-aluminum-rich inclusions (CAIs), are 16O enriched compared to the terrestrial bodies (Earth, Mars, asteroids, and comets). In contrast to most terrestrial solids, whose enrichment-depletion patterns in 18O/16O and 17O/16O are well understood to result from mass-dependent processes, the oxygen isotopic distribution of the solar system requires one (or more) physical processes that produced distinct 16O enriched and 16O depleted reservoirs. Several mechanism have been proposed to date including: I) The injection of pure 16O by a supernova II) isotope selective photo-dissociation of CO and, III) symmetry-dependent chemical fractionation processes in the pre-solar nebula. Mechanism I has been ruled out, while recent experimental tests of mechanism II have cast doubt on the basic assumptions that underlie self-shielding models. Recently it was proposed that the 16O-rich and 16O-poor reservoirs present in the early solar system were produced by the heterogeneous chemical processes that produce H2O on the surface of interstellar dust grains in dense molecular clouds, the astrophysical setting where star formation is observed to occur (1). The production of mass-independently fractionated H2O is expected because its major precursors in these environments, O3(surf.) and HO2 (surf.) are well-known carriers of mass-independently fractionated oxygen isotopic anomalies in Earth’s atmosphere. The formation of complex molecular species in molecular clouds is widely believed to be dominated by chemical reactions that occur on the surfaces of cold interstellar dust grains. This talk will review how these heterogeneous chemical reactions, which in many ways mimic the photo-chemistry present in Earth’s atmosphere, leads to the formation of molecular species such as O2, O3, CO, CO2, and H2O on the surfaces of interstellar dust grains. If the formation of O3 on cold dust grains is mass-independently fractionated with a Δ17O ~ 25-35‰, as it is in Earth’s atmosphere, then the triple-oxygen isotopic composition of water inherited from the parent molecular cloud would be consistent with constraints provided by studies of the oxygen isotopic composition of primitive meteorites, cometary water, and the preliminary measurements of the solar wind by Genesis. In this talk, we present the first triple-oxygen isotopic measurements of O3 formed in molecular cloud conditions and will discuss the implications for planetary system formation. (1)Dominguez, Gerardo, A Heterogeneous Chemical Origin for the 17O-enriched and O-depleted Reservoirs of the Early Solar System. The Astrophysical Journal Letters 713, L59 (2010).
Chakraborty Subhasish
Dominguez Gerardo
Jackson Trachette L.
Thiemens Mark H.
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