Characterizing Habitable Environments on Mars Using Infrared Spectroscopy from Orbit

Abstract

Until recently, the search for habitable environments on Mars has mostly been driven by the motto “follow the water”, as water is thought to be one of the fundamental requirements for life. Over the last several decades, there has been abundant geomorphic and mineralogical evidence for surface and near-surface liquid water early in Mars’ history, increasing the potential for past habitable environments. However, it has becoming progressively clear that there are several more requirements, in addition to liquid water, that make an environment habitable including a source of energy for biochemical processes, major and trace elements to form macromolecules (e.g., CHNOPS), as well as clement physicochemical conditions (e.g., pH, salinity, temperature). The search for habitable environments on Mars has now become more refined, searching for locales that show evidence for not only liquid water, but these other important constraints. This dissertation first focuses on the Nili Fossae region of Mars, an area that shows extensive evidence for aqueous alteration with a diverse range of hydrated minerals. This work views the region through the lens of both bulk surface composition and secondary alteration minerals, in particular with respect to minerals that would indicate not only liquid water but an energy source and a means for creating organic materials, such as with serpentinization. The study ultimately uses what is learned in Nili Fossae to better understand the global distribution of mineralogical evidence for serpentinizing systems detectable from available orbital data. The studies presented here rely on near-infrared (~1.0-3.0 µm) reflectance and thermal-infrared (~5-50 µm) emissivity measurements of both the martian surface and terrestrial analog materials to best describe the composition of surfaces exposed in Nili Fossae. Chapter Two uses a complementary approach for looking at near- and thermal-infrared measurements of the surfaces in Nili Fossae to identify elevated bulk-silica exposures that imply increased aqueous alteration of a capping unit that was previously considered unaltered. This extends aqueous alteration to all three major stratigraphic units in the area. Chapter Three uses near- and thermal-infrared laboratory measurements of rocks from the Lost City Hydrothermal Field on Earth to better constrain the geochemical and astrobiological environment that formed similar minerals in Nili Fossae, Mars. This work identified a suite of spectral types and minerals (serpentine, Mg-carbonate, and talc/saponite) associated with low-temperature serpentinizing systems on Earth and compared them to what was observed in Nili Fossae. This resulted in an additional identification of serpentine within the region, and additional evidence for a sustained habitable serpentinizing system in Nili Fossae. This framework was used to search for similar sites across Mars in Chapter Four. This produced a global map of the distribution of spectral types associated with low-temperature serpentinizing systems. This study resulted in new identifications of serpentine across the southern highlands, predominately in isolated exposures in crater and valley walls, crater ejecta and ancient knobby terrains. Additionally, it found that serpentine was much more pervasive in the Nili Fossae region than previously thought, making it an increasingly compelling site for future detailed surface investigations with respect to habitability.