Two sets of laboratory experiments were used to produce and characterize amorphous weathering products under probable conditions for the Martian surface, and one global spectral analysis using thermal-infrared (TIR) data from the Thermal Emission Spectrometer (TES) instrument was used to constrain variations in amorphous silicates across the Martian surface. The first set of experiments altered crystalline and glassy basalt samples in an open system under strong (pH 1) and moderate (pH 3) acidic conditions. The second set of experiments simulated a current-day Martian weathering scenario involving transient liquid water where basalt glass weathering solutions, formed in circumneutral (pH ~5.5 and 7) conditions, were rapidly evaporated, precipitating amorphous silicates. The samples were characterized using visible and near-infrared (VNIR) spectroscopy, TIR spectroscopy, scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray diffraction (XRD).
All experiments formed amorphous silicate phases that are new to spectral libraries. Moderately acidic alteration experiments produced no visible or spectral evidence of alteration products, whereas exposure of basalt glass to strongly acidic fluids produced silica-rich alteration layers that are spectrally consistent with VNIR and TIR spectra from the circum-polar region of Mars, indicating this region has undergone acidic weathering. Circum-netural pH basalt weathering solution precipitates are consistent with amorphous materials measured by rovers in soil and rock surface samples in Gale and Gusev Craters, suggesting transient water interactions over the last 3 billion years. Global spectral analyses determine that alteration conditions have varied across the Martian surface, and that alteration has been long lasting.
In this study, the influence of fluid mixing on temperature and geochemistry of hot spring fluids is investigated. Yellowstone National Park (YNP) is home to a diverse range of hot springs with varying temperature and chemistry. The mixing zone of interest in this paper, located in Geyser Creek, YNP, has been a point of interest since at least the 1960’s (Raymahashay, 1968). Two springs, one basic (~pH 7) and one acidic (~pH 3) mix together down an outflow channel. There are visual bands of different photosynthetic pigments which suggests the creation of temperature and chemical gradients due to the fluids mixing. In this study, to determine if fluid mixing is driving these changes of temperature and chemistry in the system, a model that factors in evaporation and cooling was developed and compared to measured temperature and chemical data collected downstream. Comparison of the modeled temperature and chemistry to the measured values at the downstream mixture shows that many of the ions, such as Cl⁻, F⁻, and Li⁺, behave conservatively with respect to mixing. This indicates that the influence of mixing accounts for a large proportion of variation in the chemical composition of the system. However, there are some chemical constituents like CH₄, H₂, and NO₃⁻, that were not conserved, and the concentrations were either depleted or increased in the downstream mixture. Some of these constituents are known to be used by microorganisms. The development of this mixing model can be used as a tool for predicting biological activity as well as building the framework for future geochemical and computational models that can be used to understand the energy availability and the microbial communities that are present.
Sulfur oxidation is a process that is seen a wide variety of places. One particular place is Yellowstone national park where an abundance of hot springs are present. These acidic and hot places are prime locations for sulfur oxidation to occur. At a very basic level this is thought of as Sulfur, oxygen, and water forming sulfate and hydrogen. Many other reactions occur when an organism performs these processes, and many enzymes are used for this. This paper aimed to create, balance, and analyze the reactions involved in the paper Sulfur Oxidation in the Acidophilic Autotrophic Acidithiobacillus spp. (Wang et al., 2019) Once these reactions were balanced thermodynamic properties were found to evaluate the Gibbs Free Energy of these reactions. This allowed for a unique energy-based view of how this web of reactions relate to each other.