ORCID
0000-0001-6832-8190
Date of Award
4-26-2024
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Martian surfaces processes often result in changes in mineralogy and chemical perturbations in surface materials. Trace elements can serve as geochemical indicators of past aqueous and volcanic activity, and the mineralogy of the surface can offer evidence of specific mineral transformation pathways and therefore past conditions on Mars. Constraining past surface environments is critical to assessing the potential habitability of Mars in its past. Further, the composition of the Martian surface informs the availability of bioessential elements. Acquiring data from Mars to investigate its composition requires immense resources to plan, develop, and operate missions. Utilization of Mars rover payload instruments is regularly impacted by power, time, data, and thermal constraints. Martian meteorites are the only samples from Mars available on Earth at present and are limited in geologic context and lithologic diversity. Thus, data from Mars are limited. In this work, we employ a range of approaches to maximize the science return of Mars data sets acquired by the Mars Exploration Rovers (MER) Spirit and Opportunity, the Mars Science Laboratory Curiosity rover, and the Mars 2020 Perseverance rover. In Chapter 2, we investigate potential mineral transformation pathways to gray, coarse-grained hematite identified by Curiosity at the Vera Rubin ridge (VRR) in Gale crater through laboratory experiments. Several iron(III) minerals were subjected to fluids with variable acidity, background salts, background salt concentrations, and temperatures to assess their potential for transformation or coarsening to gray hematite. Of all conditions explored, only experiments using the iron hydroxysulfate jarosite resulted in gray hematite. Red, fine-grained hematite did not coarsen substantially and therefore is an unlikely precursor to gray hematite. The results of these experiments highlight the role of jarosite and acidic fluids in the formation of gray hematite at Vera Rubin ridge and indicate that gray hematite can be produced without generating new chemical energy for life. The MER Alpha Particle X-ray Spectrometers (APXS) regularly acquired spectra of rock, soil, and regolith targets on the Martian surface from which the elemental composition of these materials was determined. In Chapter 3, we provide quantifications of additional trace elements (Ga and Ge) from past MER APXS data through the creation of composite spectra to improve the statistical signal-to-noise ratio. Germanium enrichments of more than an order of magnitude relative to Martian meteorites and estimates for the bulk Martian crust and mantle provide further evidence for global volcanic outgassing of volatile elements. In contrast, the ratios of gallium to aluminum are consistent between the formations at Meridiani Planum and similar across locations at Gusev crater, implying gallium is not outgassed with germanium. In Chapter 4, we investigate the composition and volume of dust on the Planetary Instrument for X-ray Lithochemistry (PIXL) calibration target. Results indicate that dust on the calibration target is basaltic with enrichments in sulfur, similar to previous assessments of Martian dust in the literature. We provide the first quantification of phosphorus and titanium in dust on a homogeneous substrate and find that phosphorus is substantially enriched in dust relative to typical Martian soils or basaltic sands and may be sourced from volcanic degassing. The modeled composition of the dust at Jezero crater provides further evidence that dust is a well-mixed, global unit and is a component of Martian soils. Dust is likely adhered to the vertically mounted calibration target due to electrostatic effects. In Chapter 5, we discuss the obstacles associated with the quantification of rubidium from PIXL spectra due to overlapping iron pile-up peaks. The Fe Kα-Kα, Fe Kα-Kβ, and Fe Kα-Ca Kα pile-up peak centroids appear to be shifted tens of eV to slightly lower energies than expected in energy-corrected PIXL spectra. The mechanism for this apparent pile-up peak shifting is unclear. Shifting of the Fe Kα-Kβ pile-up peak to a lower energy increases the overlap with the Rb Kα and further inhibits the quantification of rubidium; therefore, caution is encouraged when interpreting rubidium concentrations from PIXL’s quantification software PIQUANT.
Language
English (en)
Chair and Committee
Jeffrey Catalano
Recommended Citation
Knight, Abigail Leigh, "Geochemical Processes on the Martian Surface: An Investigation of Dust, Mineral Transformations, and Trace Elements Along Rover Traverses" (2024). Arts & Sciences Electronic Theses and Dissertations. 3032.
https://openscholarship.wustl.edu/art_sci_etds/3032