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Exoplanetary research is a key component in the search for life outside of Earth and the Solar System. It provides people with a sense of wonder about their role in the evolution of the Universe and helps scientists understand life's potential throughout a seemingly infinite number of unique exoplanetary environments. The purpose of this research project is to identify the most plausible biosignature gases that would indicate life's existence in the context of hyperarid exoplanetary atmospheres. This analysis first defines hyperarid environments based on known analogues for Earth and Mars and discusses the methods that researchers use to determine whether or not an exoplanet is hyperarid. It then identifies the most relevant biosignatures to focus on based on the scientific literature on analogous hyperarid environments and ranks them in order from greatest to least biological plausibility within extreme hyperarid conditions. The research found that methane (CH4) and nitrous oxide (N2O) are the most helpful biosignature gases for these particular exoplanetary scenarios based on reviews of the literature. The research also found that oxygen (O2), hydrogen sulfide (H2S) and ammonia (NH3) are the biosignatures with the least likely biological origin and the highest likelihood of false positive detection. This analysis also found that carbon dioxide (CO2) is a useful companion biosignature within these environments when paired with either CH4 or the pairing of hydrogen (H2) and carbon monoxide (CO). This information will provide a useful road map for dealing with the detection of biosignatures within hyperarid exoplanetary atmospheres during future astrobiology research missions.
ContributorsBrown, Kyle William (Author) / Cadillo-Quiroz, Hinsby (Thesis director) / Finn, Damien (Committee member) / Hartnett, Hilairy (Committee member) / School of International Letters and Cultures (Contributor) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2018-05
Description
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.
ContributorsOrrill, Brianna Isabel (Author) / Shock, Everett (Thesis director) / Howells, Alta (Committee member) / School of Life Sciences (Contributor) / School of Earth and Space Exploration (Contributor) / Barrett, The Honors College (Contributor)
Created2021-05
Description
The James Webb Space Telescope (JWST) is expected to revolutionize the current understanding of Jovian worlds over the coming decade. However, as the field pushes towards characterizing cooler, smaller, “terrestrial-like” planets, dedicated next-generation facilities will be required to tease out the small spectral signatures indicative of biological activity. Here, the feasibility of determining atmospheric properties, from near to mid-infrared transmission spectra, of transiting temperate terrestrial M-dwarf companions, has been evaluated. Specifically, atmospheric retrievals were utilized to explore the trade space between spectral resolution, wavelength coverage, and signal-to-noise on the ability to both detect molecular species and constrain their abundances. Increasing spectral resolution beyond R=100 for near-infrared wavelengths, shorter than 5um, proves to reduce the degeneracy between spectral features of different molecules and thus greatly benefits the abundance constraints. However, this benefit is greatly diminished beyond 5um as any overlap between broad features in the mid-infrared does not deconvolve with higher resolutions. Additionally, the inclusion of features beyond 11um did not meaningfully improve the detection significance nor abundance constraints results. The findings of this study indicate that an instrument with continuous wavelength coverage from approximately 2-11um and with a resolution of R~50-300, would be capable of detecting H2O, CO2, CH4, O3, and N2O in the atmosphere of an Earth-analog transiting an M-dwarf (magK=8.0) within 50 transits, and obtain better than an order-of-magnitude constraint on each of their abundances.
The Origins Space Telescope (Origins) is one of four flagship mission concepts, under review by the 2020 Decadal Survey, that may take the mantle of the next-generation space-based observatory. In conjunction with this research, a secondary trade space study was performed on behalf of the Origins Exoplanets Working Group. The primary purpose of this collaboration was to provide a scientific basis to the technical specifications for the mid-infrared detectors onboard the Mid-Infrared Spectrometer Camera Transit Spectrometer (MISC-T) instrument. The results of this work directly contributed to the alteration of the official technical specifications of the instrument design concept.
The Origins Space Telescope (Origins) is one of four flagship mission concepts, under review by the 2020 Decadal Survey, that may take the mantle of the next-generation space-based observatory. In conjunction with this research, a secondary trade space study was performed on behalf of the Origins Exoplanets Working Group. The primary purpose of this collaboration was to provide a scientific basis to the technical specifications for the mid-infrared detectors onboard the Mid-Infrared Spectrometer Camera Transit Spectrometer (MISC-T) instrument. The results of this work directly contributed to the alteration of the official technical specifications of the instrument design concept.
ContributorsTremblay, Luke (Author) / Line, Michael R (Thesis advisor) / Schkolnik, Evgenya (Committee member) / Walker, Sarah (Committee member) / Arizona State University (Publisher)
Created2019
Description
The ability to find evidence of life on early Earth and other planets is constrained by the current understanding of biosignatures and our ability to differentiate fossils from abiotic mimics. When organisms transition from the living realm to the fossil record, their morphological and chemical characteristics are modified, usually resulting in the loss of information. These modifications can happen during early and late diagenesis and differ depending on local geochemical properties. These post-depositional modifications need to be understood to better interpret the fossil record. Siliceous hot spring deposits (sinters) are of particular interest for biosignature research as they are early Earth analog environments and targets for investigating the presence of fossil life on Mars. As silica-supersaturated fluids flow from the vent to the distal apron, they precipitate non-crystalline opal-A that fossilizes microbial communities at a range in scales (μm-cm). Therefore, many studies have documented the ties between the active microbial communities and the morphological and chemical biosignatures in hot springs. However, far less attention has been placed on understanding preservation in systems with complex mineralogy or how post-depositional alteration affects the retention of biosignatures. Without this context, it can be challenging to recognize biosignatures in ancient rocks. This dissertation research aims to refine our current understanding of biosignature preservation and retention in sinters. Biosignatures of interest include organic matter, microfossils, and biofabrics. The complex nature of hot springs requires a comprehensive understanding of biosignature preservation that is representative of variable chemistries and post-depositional alterations. For this reason, this dissertation research chapters are field site-based. Chapter 2 investigates biosignature preservation in an unusual spring with mixed opal-A-calcite mineralogy at Lýsuhóll, Iceland. Chapter 3 tracks how silica diagenesis modifies microfossil morphology and associated organic matter at Puchuldiza, Chile. Chapter 4 studies the effects of acid fumarolic overprinting on biosignatures in Gunnuhver, Iceland. To accomplish this, traditional geologic methods (mapping, petrography, X-ray diffraction, bulk elemental analyses) were combined with high-spatial-resolution elemental mapping to better understand diagenetic effects in these systems. Preservation models were developed to predict the types and styles of biosignatures that can be present depending on the depositional and geochemical context. Recommendations are also made for the types of deposits that are most likely to preserve biosignatures.
ContributorsJuarez Rivera, Marisol (Author) / Farmer, Jack D (Thesis advisor) / Hartnett, Hilairy E (Committee member) / Shock, Everett (Committee member) / Garcia-Pichel, Ferran (Committee member) / Trembath-Reichert, Elizabeth (Committee member) / Arizona State University (Publisher)
Created2021
Description
With the ability to observe the atmospheres of terrestrial exoplanets via transit spectroscopy on the near-term horizon, the possibility of atmospheric biosignatures has received considerable attention in astrobiology. While traditionally exoplanet scientists looking for life focused on biologically relevant trace gases such as O2 and CH4, this approach has raised the spectre of false positives. Therefore, to address these shortcomings, a new set of methods is required to provide higher confidence in life detection. One possible approach is measuring the topology of atmospheric chemical reaction networks (CRNs). To investigate and assess this approach, the ability of network-theoretic metrics to distinguish the distance from thermochemical equilibrium in the atmosphere of hot jupiters was tested. After modeling the atmospheres of hot jupiters over a range of initial conditions using the VULCAN modeling package, atmospheric CRNs were constructed from the converged models and their topology measured using the Python package NetworkX. I found that network metrics were able to predict the distance from thermochemical equilibrium better than atmospheric species abundances alone. Building on this success, I modeled 30,000 terrestrial worlds. These models divided into two categories: Anoxic Archean Earth-like planets that varied in terms of CH4 surface flux (modeled as either biotic or abiotic in origin), and modern Earth-like planets with and without a surface flux of CCl2F2 (to represent the presence of industrial civilizations). I constructed atmospheric CRNs from the converged models, and analyzed their topology. I found that network metrics could distinguish between atmospheres with and without the presence of life or technology. In particular, mean degree and average shortest path length consistently performed better at distinguishing between abiotic and biotic Archean-like atmospheres than CH4 abundance.
ContributorsFisher, Theresa Mason (Author) / Walker, Sara I (Thesis advisor) / Hartnett, Hilairy (Committee member) / Line, Michael (Committee member) / Shkolnik, Evgenya (Committee member) / Okie, Jordan (Committee member) / Arizona State University (Publisher)
Created2023