Investigating the Evolution of Surface Water on Mars through Spectroscopy of Secondary Minerals

Citation

Leask, Ellen Kathleen (2020) Investigating the Evolution of Surface Water on Mars through Spectroscopy of Secondary Minerals. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/TWR4-N128. https://resolver.caltech.edu/CaltechTHESIS:02192020-182835054

Abstract

Despite its current arid climate, Mars’ surface preserves a wide variety of morphologies and minerals that point to a water-rich past. However, the mechanisms and timing of this environmental change are not yet well understood. In this dissertation, we explore a variety of water-related minerals through visible-shortwave infrared (VSWIR) reflectance spectroscopy to better understand the environmental conditions at the time of their formation, and trace the evolution of surface water on Mars over time. We also demonstrate the capabilities of VSWIR spectroscopy at laboratory and field scales in a Mars analogue environment (Samail Ophiolite, Oman)—an emerging technique for use on future landed missions that enables us to differentiate between spectrally-similar minerals and spot rare minerals that help to constrain environmental conditions and better understand the geologic context of samples. On Mars, we use orbital datasets (predominantly CRISM, the Compact Reconnaissance Imaging Spectrometer for Mars) to investigate secondary minerals in the southern highlands of Mars, focusing on perchlorate, chloride, and sulphate minerals. We identify a previously unknown artifact in the CRISM dataset, which mimics perchlorate absorptions; previous orbital perchlorate detections (including those associated with recurring slope lineae) are not robust when data are reprocessed, suggesting that there may not be orbitally-detectable reservoirs of perchlorate on Mars, which would enable liquid brines to exist at the surface today. A detailed investigation of chloride deposits across the southern highlands of Mars points to an episodic surface-runoff water source rather than upwelling groundwater, a process which continued to create chloride deposits into the Amazonian era. Where chloride and sulphate deposits are in close proximity (Terra Sirenum, Mars), they do not appear to be genetically related as they often are on Earth; instead, they point to chemically distinct groundwater vs. surface water reservoirs in Terra Sirenum through the Hesperian and into the Amazonian. Together, these studies indicate that briny and/or acidic volumes of water at the surface capable of creating mineral deposits continued to exist — at least episodically — on Mars into the Amazonian, rather than ceasing much earlier in Mars’ history.

Thesis Files