Hydrogen is the main constituent of stars, and thus dominates the protoplanetary disc from which planets are born. Many planets may at some point in their growth have a high-pressure interface between refractory planetary materials and ahydrogen-dominated atmosphere. However, little experimental data for these materials at the relevant pressure-temperature conditions exists. I have experimentally explored the interactions between planetary materials and hydrogen at high P-T conditions utilizing the pulsed laser-heated diamond-anvil cell. First, I found that ferric/ferrous iron (as Fe2O3 hematite and (Mg,Fe)O ferropericlase) are reduced to metal by hydrogen: Fe2O3 + 4H2 → 2FeO + H2O + 3H2 → 2FeH + 3H2O and (Mg1−xFex) O + 3/2 xH2 → xFeH + (1 − x) MgO + xH2O respectively. This reduction of iron by hydrogen is important because it produces iron metal and water from iron oxide. This can partition H into the core (as FeH) or mantle (as H2O/OH−) of a growing planet. Next, I expanded my starting materials to silicates. I conducted experiments on San Carlos Olivine at pressures of 5-42 GPa. In the presence hydrogen, I observed the breakdown of molten magnesium silicate and the reduction of both iron and silicon to metal, forming alloys of both Fe-H and Fe-Si: Mg2SiO4 + 2H2 + 3Fe → 2MgO + FeSi + 2FeH + 2H2O. Similar experiments using natural fayalite (Fe2SiO4) as a starting material at pressures of 5-21 GPa yielded similar results. Hydrogen reduced iron to metal as it did in experiments with iron oxides. Unlike with San Carlos olivine, above 10 GPa silicon remained oxidized, implying the following reaction: Fe2SiO4 + 3H2 → 2FeH+2H2O +SiO2. However, below 7 GPa, silicon reduces and alloys with iron. The formation of Fe-Si alloys from silicates facilitated by hydrogen could have important effects for core composition in growing planets. I also observed at low pressures (<10 GPa), quenched iron melt can trap more hydrogen than previously thought (H/Fe nearly 2 instead of 1). This may have important effects for the chemical sequestration of a hydrogen atmosphere at shallow depths in an early magma ocean. All of the experimental work presented herein show that the composition, chemical partitioning, and phase stability of the condensed portion of growing planets can be modified via interaction with overlaying or ingassed volatile species.

We model the self-compression of homogeneous, undifferentiated, Ceres-like bodies composed of various minerals and mineral-composites: antigorite, brucite, dolomite, lizardite and magnesite, plus mixtures which were the above minerals mixed with ice Ih. All of the modeled clay/ice bodies had a final radius within 1% of RCeres, an average final density of ~2083 kg m-3 and central pressures of ~133 MPa. The smallest radius was from magnesite, which had a final compressed radius of ~0.88 RCeres, central pressure of ~212 MPa and final density of ~2955 kg m-3. The most significant change in radius was due to the zero-pressure density as the highest densities created the highest force of gravity and produced the smallest radii, yet zero-pressure densities that matched Ceres produced 0.99 RCeres bodies. It was found that the addition of ice, anywhere from 9.1-19.1%, did not affect the body a measurable amount as the inclusion of ice resulted in a lower density creating a lower force of gravity, decreased central pressure and less overall compression. Models that closely resembled Ceres had internal pressures of 133 MPa, which is not enough pressure to induce pore collapse or produce drastic changes due to K and K'. Porosity and the addition of ice in Ceres-like bodies is possible and cannot be ignored when using more complicated modeling techniques. Each mineral and mineral-composite produced unique overall results which allowed us to compare each mineral to Ceres, understand how it has compressed over time and how objects of such a size are affected by compression. Due to the small size, low force of gravity and high bulk moduli of the given minerals, Ceres-like bodies do not compress a considerable amount if they are in fact composed of hydrated silicates.

The search for life on Mars is a major NASA priority. A Mars Sample Return

(MSR) mission, Mars 2020, will be NASA's next step towards this goal, carrying an instrument suite that can identify samples containing potential biosignatures. Those samples will be later returned to Earth for detailed analysis. This dissertation is intended to inform strategies for fossil biosignature detection in Mars analog samples targeted for their high biosignature preservation potential (BPP) using in situ rover-based instruments. In chapter 2, I assessed the diagenesis and BPP of one relevant analog habitable Martian environment: a playa evaporite sequence within the Verde Formation, Arizona. Coupling outcrop-scale observations with laboratory analyses, results revealed four diagenetic pathways, each with distinct impacts on BPP. When MSR occurs, the sample mass returned will be restricted, highlighting the importance of developing instruments that can select the most promising samples for MSR. Raman spectroscopy is one favored technique for this purpose. Three Raman instruments will be sent onboard two upcoming Mars rover missions for the first time. In chapters 3-4, I investigated the challenges of Raman to identify samples for MSR. I examined two Raman systems, each optimized in a different way to mitigate a major problem commonly suffered by Raman instruments: background fluorescence. In Chapter 3, I focused on visible laser excitation wavelength (532 nm) gated (or time-resolved Raman, TRR) spectroscopy. Results showed occasional improvement over conventional Raman for mitigating fluorescence in samples. It was hypothesized that results were wavelength-dependent and that greater fluorescence reduction was possible with UV laser excitation. In Chapter 4, I tested this hypothesis with a time-resolved UV (266 nm) gated Raman and UV fluorescence spectroscopy capability. I acquired Raman and fluorescence data sets on samples and showed that the UV system enabled identifications of minerals and biosignatures in samples with high confidence. The results obtained in this dissertation may inform approaches for MSR by: (1) refining models for biosignature preservation in habitable Mars environments; (2) improving sample selection and caching strategies, which may increase the success of Earth-based biogenicity studies; and (3) informing the development of Raman instruments for upcoming rover-based missions.