Nucleosynthetic isotope variations as tracers for genetic relationships of meteorites and their parent bodies
EMBARGOED UNTIL 2028-11-20
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2025
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Doctoral Thesis
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EMBARGOED UNTIL 2028-11-20
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Abstract
Nucleosynthetic isotope variations are powerful tracers, revealing genetic relationships of planetary materials which help to unravel the complex chemical and dynamic history of the early solar system. Inherited from stellar sources, nucleosynthetic isotope variations reflect incomplete mixing of dust in the protoplanetary disk. They show a wide range of variability throughout the solar system, as observed in bulk meteorites. Planetary materials with similar nucleosynthetic isotope compositions are considered to be genetically linked and sourced from a similar region of the protoplanetary disk, perhaps even originating from the same meteorite parent body. Titanium and Cr isotope data clearly demonstrate this solar system isotope heterogeneity, both were instrumental in establishing the dichotomy between non-carbonaceous (NC) material, representative of the inner solar system, and carbonaceous (CC) material, representative of the outer solar system. This dichotomy is also reflected in distinct isotope compositions for other elements, including Ca, Ni, Zn and Mo. This thesis applies the nucleosynthetic Ti and Cr isotope systems on samples from the Almahata Sitta strewn field (Chapter 2) and presents Ti and Zr isotope analyses of a representative selection of enstatite meteorites (Chapter 3). Finally, mixing models based on multiple nucleosynthetic isotope systems are implemented to constrain the origin of Phobos in preparation of returned samples from the Martian Moon eXplorer mission (MMX) (Chapter 4).
This thesis presents high precision nucleosynthetic Ti isotope analysis on samples from the Almahata Sitta strewn field (Chapter 2). The Ti isotope data were combined with Cr isotope data obtained on the same sample aliquots. Samples from this field originate from the same parent body, asteroid 2008 TC3, but contain a range of compositionally diverse lithologies. The Ti and Cr isotope composition of eleven Almahata Sitta fragments constrain and confirm the presences of NC and CC material from a rubble-pile parent body, which is a product of multi-generation accretion. This sample set also includes three ureilite-related trachyandesites, including ALM-A, and the new data confirms that trachyandesites reflect parts of the ureilite parent body (UPB) crust. The dynamics in the early solar system within the asteroid belt are examined further based on the diverse samples from asteroid 2008 TC3. The presence of NC and CC material in a single body provides evidence that mixing processes took place between inner and outer solar system materials, likely influenced by nucleation and migration of Jupiter.
Nucleosynthetic isotope analysis of the two systems Ti and Zr were performed to constrain the parent bodies of enstatite meteorites (Chapter 3). Previous analysis of enstatite chondrites and aubrites have suggested the possibility of multiple parent bodies. To better understand their origins, eleven meteorites, including two EH4, three EH3, two EL3 and two EL6 chondrites, as well as two aubrites are analyzed for their nucleosynthetic Ti and Zr composition. Our data supports multiple parent bodies for enstatite meteorites, at least one for aubrites, one for EH4/5 chondrites and one for EL chondrites, with EH3 chondrites displaying two distinct Ti isotope populations, one overlapping with EL chondrites, and one overlapping with EH4/5 chondrites. Distinguishing the possible parent bodies of enstatite chondrites is particularly important because they are considered as potential building blocks of Earth. Aubrites and enstatite chondrites have distinct Ti and Zr isotope compositions compared to terrestrial samples. This suggests that enstatite meteorites cannot be the only building blocks of Earth. Additionally, we analyzed chondrite LAR 12247 for its Ti and Zr isotope composition, with results indicating that it is an ordinary chondrite, in contrast to its classification as a CR chondrite.
Finally, isotope mixing models are implemented based on multiple nucleosynthetic isotope systems to constrain the formation pathway of the Martian moon Phobos (Chapter 4). The composition of the Martian moon will be analyzed upon return of pristine samples from the MMX mission. The chemical analysis of these samples, including nucleosynthetic isotope analysis, will help to discriminate whether Phobos is a captured asteroid or the product of a giant impact. An isotope mixing model is implemented between two endmembers, Mars and thirteen different impactor compositions, for seven nucleosynthetic isotope compositions. The results show that at least two different isotope systems, such as Ti, Cr, Fe, and Ca, are needed to constrain the composition of the impactor in a giant impact scenario. Analysis of less abundant elements Ni, Mo, and Zr, are complimentary, and helpful for identifying an impactor with a more intermediate composition such as that observed for ordinary and enstatite chondrites, which is similar to the Martian composition.
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ETH Zurich
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Cosmochemistry; ISOTOPE GEOCHEMISTRY; Titanium; Zirconium; Chromium
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03946 - Schönbächler, Maria / Schönbächler, Maria