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Isotopic records of solar nebula evolution and controls on planetary compositions

Final Report Summary - ISONEB (Isotopic records of solar nebula evolution and controls on planetary compositions)

Isotopic Records of Solar Nebula Evolution and Controls on Planetary Composition
Although well mixed, the solar system is not homogenous. Endemic variability in the ‘mass independent’ isotopic compositions of different meteorites reflect an imperfect blending of a pre-solar component. Does this heterogeneity reflect a first order chemical variability or is it just distinctive flavouring that informs on processes in the early solar system? Fundamental to answering this question is an understanding of the origin of the isotope anomalies. Of prime concern is identifying the stellar source of the exotic component and the nature of the carrier grains. To address these specific goals we have built, in collaboration with the instrument manufacturer Thermo Fisher Scientific, a novel mass-spectrometer (a tribrid mass-filter,collision-cell,multi-collector inductively coupled plasma mass-spectrometer) which we dub Proteus. The successful development of this cutting edge instrument allowed us to make new analyses that robustly linked the isotopic anomalies in Ca to a Type Ia supernova, which implies a highly unusual astrophysical setting for the proto stellar nebula. We also found, for the first time, <2µm carriers of associated 50Ti anomalies in the matrix of a primitive meteorite. We were further able to demonstrate that the short-lived nuclide 26Al, was largely homogenously distributed within the accessible solar system, consistent with late injection of material from a Type Ia but not an astrophysically more likely Type II supernova. While the mass-independent isotopic signatures provide compelling testimony of nucleosynethic heritage, the variability of this component not the prime influence on planetary composition. Using subtle differences in the mass-dependent isotopic compositions of planetary bodies relative to primitive meteorites, we were able to show that vapour loss during energetic collisional accretion can dramatically change the chemistry of a growing planet. We estimate that the Earth lost ~40% by mass during such vapour loss, which markedly changed the abundances of its major elements relative to primitive meteorite building blocks. Moreover, we were able to show that this vapour loss occurred with the first ~1million years of accretion, when planetary bodies were still small with insufficient gravity to quantitatively retain vapour during collisionally induced melting.