Circumstellar debris disks are the extrasolar analogues of the asteroid belt and the Kuiper belt. These disks consist of comets and leftover planetesimals that continuously collide to produce copious amounts of circumstellar dust that can be observed as infrared excess or in resolved imaging. As an obvious outcome of the planet formation process, debris disks can help us constrain planet formation theories and learn about the history of our own solar system. Structures in the disks such as gaps or warps can hint at the presence of planets. Thus, the study of debris disks is an important branch of exoplanetary science. In this thesis, some aspects of debris disks are considered in detail. A handful of debris disks show observable amounts of gas besides the dust. One such case is the edge-on debris disk around the young A-type star β Pictoris, where the gas is thought to be of secondary origin, i.e. derived from the dust itself. By observing this gas, we can thus learn something about the dust, and therefore about the building blocks of planets. In paper I, spectrally resolved observations of C II emission with Herschel/HIFI are presented. The line profile is used to constrain the spatial distribution of carbon gas in the disk, which helps understanding the gas producing mechanism. In paper II, we analyse C II and O I emission detected with Herschel/PACS and find that the oxygen must be located in a relatively dense region, possibly similar to the CO clump seen by ALMA. An upcoming analysis of our ALMA C I observations will give us a clearer picture of the system. Another famous debris disk is found around the nearby, 440 Myr old A-star Fomalhaut. Its morphology is that of an eccentric debris belt with sharp edges, suggesting shaping by a planet. However, gas-dust interactions may result in a similar morphology without the need to invoke planets. We test this possibility in paper III by analysing non-detections of C II and O I emission by Herschel/PACS. We find that there is not enough gas present to efficiently sustain gas-dust interactions, implying that the morphology of the Fomalhaut belt is due to a yet unseen planet or alternatively stellar encounters. One of the biggest challenges in exoplanetary research is to answer the question whether there are inhabited worlds other than the Earth. With the number of known rocky exoplanets in the habitable zone increasing rapidly, we might actually be able to answer this question in the coming decades. Different approaches exist to detect the presence of life remotely, for example by studying exoplanetary atmospheres or by analysing light reflected off the surface of an exoplanet. In paper IV, we study whether biosignatures (for example, certain minerals or microorganisms) ejected into a circumstellar debris disk by an impact event could be detected. We consider an impact similar to the Chicxulub event and model the collisional evolution of the ejected debris. Dust from such an event can potentially be detected by current telescopes, but analysis of the debris composition has to wait for future, advanced instruments. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Submitted. Paper 4: Submitted.</p>

Escherichia coli and Serratia liquefaciens, two common microbial spacecraft contaminants known to replicate under low atmospheric pressures of 25 mb, were tested for growth and survival in simulated martian conditions. Stressors of high salinity, low temperature, and low pressure were screened alone and in combination to determine how they might affect microbial activity. Growth and survival of E. coli and S. liquefaciens under low temperatures (30, 20, 10, or 5 °C) with increasing concentrations (0, 5, 10, or 20 %) of three salts believed to be present on the surface of Mars (MgCl2, MgSO4, NaCl) were monitored over 7 d. Results indicated higher growth rates for E. coli and S. liquefaciens at 30 and 20 °C and in solutions without salt or in 5 % concentrations. No increase in cell density occurred under the highest salt concentrations at any temperatures tested; however, survival rates were high, especially at 10 and 5 °C. Growth rates of E. coli and S. liquefaciens with and without salts at 1013, 100, or 25 mb of total atmospheric pressure were robust under all pressures. In a final experiment, E. coli was maintained in Mars-simulant soils in a Mars Simulation Chamber. Temperatures within the chamber were changed diurnally from -50 °C to 20 °C; UV light was present during daytime operation (8 hrs), and pressure was held at a constant 7.1 mb in a Mars atmosphere for 7 d. Results from the full-scale Mars simulation indicated that E. coli failed to increase its populations under simulated Mars conditions, but was not killed off by the low pressure, low temperature, or high salinity conditions. Escherichia coli, and potentially other bacteria from Earth, may be able to survive on Mars. Surviving bacteria may interfere with scientific studies or, if future conditions become more favorable for microbial growth, modify the martian atmosphere and biogeochemistry.

Tardigrades are microscopic animals that can survive exposure to multiple extreme conditions. This remarkable ability makes them suitable laboratory model organisms for conducting biological to astrobiological research. Whereas tardigrade extreme-tolerance research has been focused predominantly on their ability to endure extreme desiccation, responses to other extraordinary conditions (i.e. hypergravity, pH, radiation and low temperature) remain un-described. These extreme tolerance research areas, in addition to life history traits, were documented in our studies on the eutardigrade species Hypsibius dujardini. We found that specimens tolerated extreme g-equivalent forces (i.e., 16060g) and radiation levels (i.e. 5 kGy), with decreased survivorship at increased accelerations and radiation doses. Radiation induced bystander effects (RIBEs) manifested as a threshold response, with the threshold value between 3 and 5 kGy. Extreme acidic (pH 1 and 2) and alkaline (pH 11 to 14) conditions caused death instantaneously, while exposures to pH 4, 6, 8, 9, and 10 were tolerated. Tardigrade eggs reared at 0 °C for 4 days developed relatively slowly, diminishing their biological age relative to their chronological age. Extending cold exposure (0 °C) time (days = 10, 20 and 40) decreased incubation time (days = 3, 2 and 1, respectively) at 22 °C; lengthening cold exposure time led to decreased growth in juveniles and lowered survivorship in adults, suggesting that costs are associated with increasing incubation time at 0 °C. Tolerance to hypergravity, large radiation doses and a wide-range in pH conditions support the notion that tardigrades are suitable organisms for astrobiological research, particularly in exploring parameters associated with potential transfer and habitability in extreme environments. RIBEs in adult tardigrades and the ability for tardigrade embryos to alter their ‘biological clocks’ based on exposed cold temperature duration have applications in biological research. Characterizing molecules involved in bystander signaling and response and biological clock adjustments during development could have important implications for improving biological practices such as radiotherapy and cryopreservation. / Thesis / Doctor of Philosophy (PhD) / While interest in tardigrade extreme tolerance research has increased over the last decade, many research areas continue to be underrepresented or non- existent. And, while recognized tardigrade species have been increasing steadily in number, fundamental biological details, like individual life history traits, remain unknown for most. The main objectives in this thesis therefore were to survey the life history traits for the freshwater tardigrade species Hypsibius dujardini, increase knowledge about its extreme-tolerance abilities and describe its utility in astrobiological and biological studies. Research involved tardigrade tolerance to hypergravity, pH levels and radiation exposure (and associated radiation-induced bystander effects) as well as responses to temperature changes during development. Findings reported in this dissertation provide new data about H. dujardini, thereby narrowing the information gap that currently exists in the literature for this species.

The key to the RNA world hypothesis is the ribozyme, an information and catalytic agent that preceded proteins and DNA. Prior to ribozymes the sequences of RNA needed to build up to a length that could potentially be a ribozyme. This research focuses on computational modelling of hydrolysis, polymerization, and template-directed ligation to determine sequence patterns and characteristics that may have emerged due to these simple processes. A model containing L- and D-chirality monomers is used that incorporates the advantage of being a uniform chirality to achieve chiral symmetry breaking. Another chirality model is used where being uniform provides no advantage and a symmetry breaking still occurs. Beyond chirality we look at nucleobase models where we use a two letter alphabet containing adenine and uracil to determine symmetry breaking in sequence space. This results in self-complementary sequences dominating this model at all ligation rates but under certain initial conditions including high concentration, other types of sequences can be dominant. If a third base, guanine is added to this model a wobble base is created. In these models the self-complementary sequences containing uracil are the most prevalent due to uracil’s ability to pair with both adenine and guanine. Finally, upon adding a fourth base to the model guanine also becomes a wobble pair and the sequences containing uracil and guanine dominate the system for low ligation rates but at higher rates the uniform uracil and guanine sequences dominate. For each model a version is run with the templating reaction scaling linearly with the number of binding sites and without, where all templates are equally good. Generally, the scaling causes symmetry breakings at lower ligation values for each model. / Thesis / Master of Science (MSc) / The origin of life on Earth is a long-debated question that has been asked by nearly every civilization to have existed. This research addresses the origin of life in the context of the RNA World theory, which proposes that the first kind of replicating molecules were RNA strands, specifically, catalytic RNA sequences, called ribozymes. We carry out computer simulations of the formation and break-up of short RNA strands. Strands can grow by joining together randomly, or due to the action of template strands. We find that, if this process occurs repeatedly, the RNA strands in the mixture move towards states in which groups of sequences that are good templates for one another occur together at high concentrations. By studying the possible states that arise in this reaction mixture, we hope to learn about the first replicating RNA strands that lead to the origin of life.

Understanding the distribution, abundances and metabolic activities of microbial life in the subsurface is fundamental to our understanding of the role microbes play in many areas of inquiry such as terrestrial biogeochemical cycling and the search for extraterrestrial life. The deep terrestrial subsurface is known to harbor microbial life at depths of up to several kilometers where, in some cases, organisms live independently from the photosphere and atmosphere. Ancient fracture fluids trapped within the crystalline basement of the Canadian Precambrian Shield have been shown to be preserved on geologic timescales (millions to billions of years). Significant challenges exist when probing the deep terrestrial subsurface including the low biomass abundance, heterogeneous distribution of biomass, and the potential for matrix effects during sampling and analysis. This Master’s thesis project has two main parts. The first study utilizes phospholipid fatty acid (PLFA) analysis to determine the extent of mineral matrices on the effectiveness of PLFA extraction and analysis from deep terrestrial subsurface samples. This was done by creating a bacterial dilution series of known concentration to inoculate one of two mineral matrices, granite or bentonite. This study revealed the presence of significant influence of mineral matrices on PLFA extraction and demonstrated the unreliability of PLFA-based biomass conversion factors with respect to complex microbial communities. The second study in this thesis combine PLFA analysis with stable carbon isotope analysis to characterize microbial communities associated with fracture fluids with mean residence times of ~1.4 Ga from boreholes located ~2.4km below the surface in Kidd Creek Mine, in Timmins, Ontario. Characterizing communities in subsurface systems has large implications for the search for life on other planets and moons, acting as an analogue environment. Large volumes of water from two boreholes, 12261 and 12299, were passively filtered for 6-12 months to collect microbial biomass. Borehole adjacent biofilms were also collected along with mine service water, which served as a control. All samples had significant biomass associated with them but were distinct in PLFA fingerprint and δ13C – PLFA signatures indicating the presence of three distinct microbial communities living in association with the fracture fluids and gases. These results have implications for the potential existence of ancient deep subsurface communities that have survived geologic time in isolation, in particular with relation to the subsurface of Mars, as well as give us insight into life on the early Earth. / Thesis / Master of Science (MSc)

No description available.

Este trabalho apresenta o estudo de algumas moléculas do meio interestelar úteis para o levantamento do conteúdo de matéria orgânica do universo e para as condições pré-bióticas na Terra e em outros ambientes no universo. Utilizamos como objeto-teste a Nebulosa Cabeça de Cavalo, devido à sua geometria simples, à sua distância moderada até nós, ao seu campo de radiação ultravioleta bem conhecido resultante da iluminação por uma estrela próxima, $\\sigma$ Orionis, e por ter sido extensivamente estudada por diversos trabalhos. Desse modo, podemos investigar com segurança diversos processos físicos e químicos no meio interestelar. O principal instrumento utilizado neste trabalho foi o código PDR Meudon devido ao fato de que é amplamente utilizado por ser um dos programas de análise de dados de projetos recentes de astronomia, como o projeto Herschel, e por ser público. O código pode ser utilizado para modelizar com confiabilidade a Nebulosa Cabeça de Cavalo, visto que ela mesma é uma PDR (região de fotodissociação) prototípica. Atualizamos o setor de química do código para testar diversos cenários de formação de moléculas. Consideramos o impacto nas abundâncias derivadas das moléculas de várias suposições em relação ao estado do gás (modelos isocórico, isotérmico e isobárico), decidindo em favor de um modelo isobárico. Verificou-se o papel dos raios cósmicos e de vários conjuntos de dados das reações químicas. Obtivemos as abundâncias de várias moléculas, incluindo algumas de potencial importância pré-biótica: CN e seus íons, HCN, HNC, nitrilas e seus íons, hidretos de nitrogênio, benzeno. Investigamos o papel dos ânions e dos PAHs. Finalmente, exploramos canais de produção para heterocíclicos nitrogenados com relevância em astrobiologia: pirrol e piridina. As presentes simulações apresentaram como a exploração de uma pequena gama de possíveis canais de produção de heterocíclicos já resultou em abundâncias significativas para ao menos uma espécie de heterocíclicos nitrogenados, a piridina. Dessa forma, excursões sistemáticas pelos diversos canais de produção deverão revelar mais espécies para serem alvos de buscas. / This work presents the study of some molecules of the interstellar medium that are useful for the bookkeeping of the molecular content of the universe and for prebiotic conditions on Earth and in other environments in the universe. The Horsehead Nebula was chosen as test object, due to its simple geometry, its moderate distance to us, its well-known ultraviolet radiation field resulting from the star $\\sigma$ Orionis, and due the fact that it has been extensively studied in several works. In this way, we can safely investigate several physical and chemical processes on the interstellar medium. The main tool used in the present work was the Meudon PDR code due the fact that it is widely used as one of the legacy data analysis programs of current astronomy projects, e.g. the Herschel project, and it is public. The code can reliably model the Horsehead Nebula, since this nebula is a prototypic PDR (photodissociation region). We updated the chemical sector of the code in order to test several scenarios for molecule production. We considered the impact on the derived molecule abundances of several assumptions relative to the gas state (isochoric, isothermal and isobaric models), and the isobaric model was found to be the most plausible. We checked the role of cosmic rays and several datasets of chemical reactions. We derived the abundances of several molecules, including some of potential prebiotic importance: CN and their ions, HCN, HNC, nitriles and their ions, nitrogen hydrides, and benzene. We investigated the role of anions and PAHs. Finally, we explored production channels for astrobiologically relevant nitrogenated heterocycles: pyrrole and pyridine. This presents simulations show us how the exploration of a small quantities of possibles path of prodution of heterocycles resulted already in significants abundances at least one n-heterocycle specie, the pyridine. Thereby, systemact tours for the many productions paths should show more species to be targe of searches.

The majority of adults in the US and in Europe appear to be scientifically illiterate. This has not changed in more than half a century. It is unknown whether the Australian public is also scientifically illiterate because no similar testing is done here. Public scientific illiteracy remains in spite of improvements in science education, innovative approaches to public outreach, the encouraging of science communication via the mass media, and the advent of the Internet. Why is it that there has been so little change? Is school science education inadequate? Does something happen between leaving high school education and becoming an adult? Does Australia suffer from the same apparent malady? The pilot study at the heart of this thesis tests a total of 692 Year Ten (16-year-old) Australian students across ten high schools and a first year university class in 2005 and 2006, using measures applied to adults. Twenty-six percent of those tested participated in a related scientific literacy project utilising in-person visits to Macquarie University in both years. A small group of the students (64) tested in 2005 were considered the best science students in seven of the ten high schools. Results indicate that no more than 20% of even the best high school science students - on the point of being able to end their formal science education - are scientifically literate if measured by adult standards. Another pilot test among 150 first year university students supports that indication. This compares to a scientific literacy rate of 28% for the US public. This thesis finds that the scientific literacy enterprise ?? in all its forms ?? fails scrutiny. Either we believe our best science students are leaving high school scientifically illiterate or there is something fundamentally wrong in our perceptions of public scientific illiteracy. This pilot study ?? probably the first of its kind ?? indicates we cannot rely on our current perceptions of a scientifically illiterate public. It demonstrates that a paradigm shift in our thinking is required about what scientific literacy is and in our expectations of a scientifically literate adult public. In the worst case scenario, governments are pouring millions of dollars into science education and public outreach with little or no basis for understanding whether either is effective. That is illogical, even irresponsible. It also impacts on the way astrobiology ?? or any science ?? is communicated in public.

The majority of adults in the US and in Europe appear to be scientifically illiterate. This has not changed in more than half a century. It is unknown whether the Australian public is also scientifically illiterate because no similar testing is done here. Public scientific illiteracy remains in spite of improvements in science education, innovative approaches to public outreach, the encouraging of science communication via the mass media, and the advent of the Internet. Why is it that there has been so little change? Is school science education inadequate? Does something happen between leaving high school education and becoming an adult? Does Australia suffer from the same apparent malady? The pilot study at the heart of this thesis tests a total of 692 Year Ten (16-year-old) Australian students across ten high schools and a first year university class in 2005 and 2006, using measures applied to adults. Twenty-six percent of those tested participated in a related scientific literacy project utilising in-person visits to Macquarie University in both years. A small group of the students (64) tested in 2005 were considered the best science students in seven of the ten high schools. Results indicate that no more than 20% of even the best high school science students - on the point of being able to end their formal science education - are scientifically literate if measured by adult standards. Another pilot test among 150 first year university students supports that indication. This compares to a scientific literacy rate of 28% for the US public. This thesis finds that the scientific literacy enterprise ?? in all its forms ?? fails scrutiny. Either we believe our best science students are leaving high school scientifically illiterate or there is something fundamentally wrong in our perceptions of public scientific illiteracy. This pilot study ?? probably the first of its kind ?? indicates we cannot rely on our current perceptions of a scientifically illiterate public. It demonstrates that a paradigm shift in our thinking is required about what scientific literacy is and in our expectations of a scientifically literate adult public. In the worst case scenario, governments are pouring millions of dollars into science education and public outreach with little or no basis for understanding whether either is effective. That is illogical, even irresponsible. It also impacts on the way astrobiology ?? or any science ?? is communicated in public.

abstract: As the detection of planets become commonplace around our neighboring stars, scientists can now begin exploring their possible properties and habitability. Using statistical analysis I determine a true range of elemental compositions amongst local stars and how this variation could affect possible planetary systems. Through calculating and analyzing the variation in elemental abundances of nearby stars, the actual range in stellar abundances can be determined using statistical methods. This research emphasizes the diversity of stellar elemental abundances and how that could affect the environment from which planets form. An intrinsic variation has been found to exist for almost all of the elements studied by most abundance-finding groups. Specifically, this research determines abundances for a set of 458 F, G, and K stars from spectroscopic planet hunting surveys for 27 elements, including: C, O, Na, Mg, Al, Si, S, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, La, Ce, Nd, Eu, and Hf. Abundances of the elements in many known exosolar planet host stars are calculated for the purpose investigating new ways to visualize how stellar abundances could affect planetary systems, planetary formation, and mineralogy. I explore the Mg/Si and C/O ratios as well as place these abundances on ternary diagrams with Fe. Lastly, I emphasize the unusual stellar abundance of &tau; Ceti. &tau; Ceti is measured to have 5 planets of Super-Earth masses orbiting in near habitable zone distances. Spectroscopic analysis finds that the Mg/Si ratio is extremely high (~2) for this star, which could lead to alterations in planetary properties. &tau; Ceti's low metallicity and oxygen abundance account for a change in the location of the traditional habitable zone, which helps clarify a new definition of habitable planets. / Dissertation/Thesis / Ph.D. Astrophysics 2014