Date of Award

Fall 1-1-2025

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Geology and Geophysics

First Advisor

Karato, Shun-ichiro

Abstract

Volatile delivery of terrestrial planets within the snowline is one of the key issues in planetary science. The solar wind has been considered a significant contributor to the volatile acquired by dust within the snowline and of airless planetary bodies surfaces. This thesis explores the effects of solar wind implantation on planetary materials through a series of experimental and theoretical studies, focusing on three interrelated aspects: volatile acquisition, lattice damage mechanical weakening dust grains, and volatile isotopic evolution of the irradiated mineral grains. First, we performed hydrogen implantation experiments on olivine, orthopyroxene, and quartz to investigate the distribution and concentration of implanted hydrogen in silicates. We analyzed the hydrogen concentration depth profiles using Nuclear Resonance Reaction Analysis (NRRA). After implantation, hydrogen concentration in these minerals far exceeds the thermodynamic solubility limits and an upper limit of hydrogen concentration (i.e., saturation level) can be identified. Our results reveal a dependence of hydrogen penetration depth and saturation level on both implantation energy and mineral species. These findings offer explanations for the high surface water contents observed on planetary bodies such as the Moon and Itokawa. We further evaluate the potential of hydrogenated dust grains as carriers of water to the inner solar system, discussing their delivery via turbulent mixing mechanisms in the protoplanetary disk. Second, we conducted nano-indentation tests on hydrogen-implanted olivine crystals to investigate the impact of implantation on dust grain microstructures and sticking probabilities, which is a key factor in planetesimal formation. A significant mechanical weakening was shown in the near-surface region, with reductions of up to ~85% in hardness and ~74% in elastic modulus, due to the implantation damage revealed by TEM. We proposed that dust exposed to the solar wind may develop a mechanically weakened surface and thus the dust sticking probability could be enhanced, influencing dust aggregation in the protoplanetary disk. Finally, we developed a model to investigate the evolution isotopic ratios of volatile elements (H and N) in planetary materials exposed to the solar wind over time. Considering the mass and energy-dependent penetration depths of different isotopes, the saturation behavior of implanted particles and the history of solar wind evolution, we show that the irradiated materials will be enriched in heavy volatile isotopes and their isotopic ratios will deviate from original solar values as the exposure duration becomes longer.

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