ORCID

http://orcid.org/0000-0002-8555-9000

Date of Award

Spring 5-15-2022

Author's School

Graduate School of Arts and Sciences

Author's Department

Physics

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

This dissertation reports the results of laboratory studies of lunar soil samples, gas-to-solid filamentary enstatite grains from a likely-cometary interplanetary dust particle (IDP), and exogenous clasts in the CH3 chondrite Acfer 182 that likely originated from a differentiated basaltic planetesimal. These studies were performed using multi-instrument analyses involving high-resolution scanning and transmission electron microscopy (SEM/TEM) techniques, nanoscale secondary ion mass spectrometry (NanoSIMS), synchrotron infrared nanospectroscopy (SINS), electron probe microanalysis (EPMA), and Raman spectroscopy. The results of these analyses are used to examine space weathering phenomena, energetic processing and radial transport in the protoplanetary disk, and the origins of igneous inclusions in a chondritic meteorite.SINS measurements of vertical cross-section samples extracted from two mature lunar soils (10084 and 79221) were used to investigate the depth-dependent effects of space weathering in the mid-infrared, 1500–700cm−1 (6.7–14.3 µm). Space weathering induces reddening, darkening, and diminished contrast in the infrared spectra of lunar material. The physical and chemical changes hypothesized to be responsible for these optical effects occur on scales below the diffraction limit of traditional far-field spectroscopic techniques. The sub-micron resolution measurements reported here provide evidence that the effects of space weathering vary continuously as a function of distance from the space-exposed surface. These findings are broadly consistent theoretical models of space weathering and provide a direct spatial link between the physical/chemical changes in space-exposed grain surfaces and spectral changes of space-weathered bodies. Filamentary enstatite crystals, formed by gas-solid condensation in the solar nebula, are found in chondritic porous interplanetary dust particles of probable cometary origin. The oxygen isotopic composition of four filamentary enstatite grains from the giant cluster interplanetary dust particle U2-20 GCP are reported. These grains represent both the 16O-rich solar (∆17O ≈ −30 ‰) and 16O-poor planetary (∆17O ≈ 0 ‰) isotope reservoirs. These measurements provide evidence for very early vaporization of dust-poor and dust-rich regions of the solar nebula, followed by condensation and outward transport of crystalline dust to the comet-forming region very far from the Sun. A 100 µm × 50 µm grain of the rare titanium sulfide mineral heideite containing exsolution lamellae of calcium-rich titanium oxide was observed in the CH3 chondrite Acfer 182. Also observed were two phosphide spherules of schreibersite and barringerite with kamacite eutectic structures. Thin veins of shock-induced kamacite cross-cut the oxide lamellae, suggesting that it was ejected into the protoplanetary debris disk during an impact event before eventually being accreted by the CH chondrite parent body. This assemblage is distinct from heideite grains found in enstatite chondrites, aubrites, and the Kaidun meteorite and likely originated from a differentiated, highly-reduced planetesimal in the inner Solar System.

Language

English (en)

Chair and Committee

Ryan C. Ogliore

Committee Members

Erik A. Henriksen

Comments

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Available for download on Monday, October 24, 2022

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