Emmy Hughes PhD Defense

June 25th, 1 p.m., Ford ES&T L1205

Zoom link: https://gatech.zoom.us/j/96940711745

Dissertation title: Martian Salts and Surface Materials as Paleoclimate Indicators through Orbital, In Situ, and Analogue Analyses

Committee Members: James Wray (advisor), Frances Rivera-Hernández (co-advisor), Chris Carr, Suniti Karunatillake, Ben Tutolo.

Abstract

Mars—a cold, dry planet today—one was home to flowing, pooling, and concentrating liquid water. The aqueous processes that occurred billions of years ago on the surface of Mars left traces, often in the form of minerals. The composition, structure, and chemistry of these minerals records the environments in which they formed, including the temperature of fluids in an environment. Here, we investigate the paleoclimate of Mars in three distinct ways: through orbital data of a proposed ancient hydrothermal lake on Mars; in situ data of an ancient, habitable lake on Mars; and in situ study of a series of lakes on earth that serve as Mars analogues. We rely on spectroscopy—primarily, near-infrared, Raman, laser induced spectroscopy, and X-ray fluorescence—to determine the mineralogical and chemical makeup of climate indexing minerals, as proxies for their environments. We find that the proposed ancient hydrothermal system on Mars (Eridania Basin in the Mars southern highlands) has minimal definitive surface evidence for hydrothermalism, and the mineralogy and geochemistry is more consistent with low-temperature, minimal water-to-rock weathering of basaltic materials. This suggests a limited watershed and may fit into a broader history of a colder early Mars. Study of the Mars analogue Basque Lakes in British Columbia, Canada, reveals a suite of metastable minerals forming in brine pools and efflorescent crusts seasonally, and indicates that cold-temperature salts form from freezing brines, which might act as cold-climate indicators when preserved in the rock record. We identify a region of the near-infrared that is particularly useful for identifying warm- and cold-temperature salts on Mars and Earth. Finally within Gale crater, Mars (the landing site of the Mars Curiosity rover), we report on unusual geochemical signatures within dark-toned laminations in sulfate-bearing strata, suggesting that likely warm diagenetic fluids permeated bedding planes to form hydrated Na-Mg-sulfates and fluorine-bearing minerals. These fluids might be linked to major climate cycles forming the stratigraphy in this region