Matching Items (12)

132747-Thumbnail Image.png

Characterizing Diurnal Density and Temperature Variations in the Martian Atmosphere Using Data/Model Comparisons

Description

This project focuses on using Neutral Gas and Ion Mass Spectrometer (NGIMS) density data for carbon dioxide, oxygen, carbon monoxide, and nitrogen during deep dip campaigns 5, 6, and 8.

This project focuses on using Neutral Gas and Ion Mass Spectrometer (NGIMS) density data for carbon dioxide, oxygen, carbon monoxide, and nitrogen during deep dip campaigns 5, 6, and 8. Density profiles obtained from NGIMS were plotted against simulated density profiles from the Mars Global Ionosphere-Thermosphere Model (MGITM). Averaged temperature profiles were also plotted for the three deep dip campaigns, using NGIMS data and MGITM output. MGITM was also used as a tool to uncover potential heat balance terms needed to reproduce the mean density and temperature profiles measured by NGIMS.

This method of using NGIMS data as a validation tool for MGITM simulations has been tested previously using dayside data from deep dip campaigns 2 and 8. In those cases, MGITM was able to accurately reproduce the measured density and temperature profiles; however, in the deep dip 5 and 6 campaigns, the results are not quite the same, due to the highly variable nature of the nightside thermosphere. MGITM was able to fairly accurately reproduce the density and temperature profiles for deep dip 5, but the deep dip 6 model output showed unexpected significant variation. The deep dip 6 results reveal possible changes to be made to MGITM to more accurately reflect the observed structure of the nighttime thermosphere. In particular, upgrading the model to incorporate a suitable gravity wave parameterization should better capture the role of global winds in maintaining the nighttime thermospheric structure.

This project reveals that there still exist many unknowns about the structure and dynamics of the night side of the Martian atmosphere, as well as significant diurnal variations in density. Further study is needed to uncover these unknowns and their role in atmospheric mass loss.

Contributors

Created

Date Created
  • 2019-05

130873-Thumbnail Image.png

Close Encounters of the First Kind: On Cultural Representations of Extraterrestrials, First Contact, & the Mythology of the Alien Other

Description

Western culture has oversimplified and mythologized the possibility of first contact with extraterrestrial intelligence. Whether through anthropocentrism, lack of contextual literature and/or available knowledge, or simple misunderstanding, humanity has failed

Western culture has oversimplified and mythologized the possibility of first contact with extraterrestrial intelligence. Whether through anthropocentrism, lack of contextual literature and/or available knowledge, or simple misunderstanding, humanity has failed to fully consider the impacts of seeking out alien life. Instead, humanity’s cultural and political representations of extraterrestrials tell us a great deal about the people behind the stories—all of us stuck together on our pale blue dot. This thesis explores the mythological character that is ever-present in the extraterrestrial conversation, and how past and current cultural creators in the global West have perpetuated and changed that paradigm. This thesis is also an exploration of the ways we envision our ability to contact and interact with an unknown extraterrestrial other—in many ways mythological, and in some ways as powerful symbols for struggles against oppression. I argue for a more nuanced, creative, and scientifically driven representation and consideration of first contact with extraterrestrial intelligence.

Contributors

Agent

Created

Date Created
  • 2020-12

131992-Thumbnail Image.png

A History of Astrobiology: Social Network Structures of the Emerging Field

Description

Astrobiology, as it is known by official statements and agencies, is “the study of the origin, evolution, distribution, and future of life in the universe” (NASA Astrobiology Insitute , 2018).

Astrobiology, as it is known by official statements and agencies, is “the study of the origin, evolution, distribution, and future of life in the universe” (NASA Astrobiology Insitute , 2018). This definition should suit a dictionary, but it may not accurately describe the research and motivations of practicing astrobiologists. Furthermore, it does little to characterize the context in which astrobiologists work. The aim of this project is to explore various social network structures within a large body of astrobiological research, intending to both further define the current motivations of astrobiological research and to lend context to these motivations. In this effort, two Web of Science queries were assembled to search for two contrasting corpora related to astrobiological research. The first search, for astrobiology and its close synonym, exobiology, returned a corpus of 3,229 journal articles. The second search, which includes the first and supplements it with further search terms (see Table 1) returned a corpus of 19,017 journal articles. The metadata for these articles were then used to construct various networks. The resulting networks describe an astrobiology that is well entrenched in other related fields, showcasing the interdisciplinarity of astrobiology in its emergence. The networks also showcase the entrenchment of astrobiology in the sociological context in which it is conducted—namely, its relative dependence on the United States government, which should prompt further discussion amongst astrobiology researchers.

Contributors

Created

Date Created
  • 2019-12

158553-Thumbnail Image.png

Universal Biochemistry Within and Across Biological Domains and Levels of Organization on Earth

Description

Universal biology is an important astrobiological concept, specifically for the search for life beyond Earth. Over 1.2 million species have been identified on Earth, yet all life partakes in certain

Universal biology is an important astrobiological concept, specifically for the search for life beyond Earth. Over 1.2 million species have been identified on Earth, yet all life partakes in certain processes, such as homeostasis and replication. Furthermore, several aspects of biochemistry on Earth are thought to be universal, such as the use of organic macromolecules like proteins and nucleic acids. The presence of many biochemical features in empirical data, however, has never been thoroughly investigated. Moreover, the ability to generalize universal features of Earth biology to other worlds suffers from the epistemic problem of induction. Systems biology approaches offer means to quantify abstract patterns in living systems which can more readily be extended beyond Earth’s familiar planetary context. In particular, scaling laws, which characterize how a system responds to changes in size, have met with prior success in investigating universal biology.

This thesis rigorously tests the hypothesis that biochemistry is universal across life on Earth. The study collects enzyme data for annotated archaeal, bacterial, and eukaryotic genomes, in addition to metagenomes. This approach allows one to quantitatively define a biochemical system and sample across known biochemical diversity, while simultaneously exploring enzyme class scaling at both the level of both individual organisms and ecosystems. Using the Kyoto Encyclopedia of Genes and Genomes (KEGG) and the Joint Genome Institute’s Integrated Microbial Genomes and Microbiomes (JGI IMG/M) database, this thesis performs the largest comparative analysis of microbial enzyme content and biochemistry to date. In doing so, this thesis quantitatively explores the distribution of enzyme classes on Earth and adds constraints to notions of universal biochemistry on Earth.

Contributors

Agent

Created

Date Created
  • 2020

156916-Thumbnail Image.png

Biochemical Networks Across Planets and Scales

Description

Biochemical reactions underlie all living processes. Their complex web of interactions is difficult to fully capture and quantify with simple mathematical objects. Applying network science to biology has advanced our

Biochemical reactions underlie all living processes. Their complex web of interactions is difficult to fully capture and quantify with simple mathematical objects. Applying network science to biology has advanced our understanding of the metabolisms of individual organisms and the organization of ecosystems, but has scarcely been applied to life at a planetary scale. To characterize planetary-scale biochemistry, I constructed biochemical networks using global databases of annotated genomes and metagenomes, and biochemical reactions. I uncover scaling laws governing biochemical diversity and network structure shared across levels of organization from individuals to ecosystems, to the biosphere as a whole. Comparing real biochemical reaction networks to random reaction networks reveals the observed biological scaling is not a product of chemistry alone, but instead emerges due to the particular structure of selected reactions commonly participating in living processes. I perform distinguishability tests across properties of individual and ecosystem-level biochemical networks to determine whether or not they share common structure, indicative of common generative mechanisms across levels. My results indicate there is no sharp transition in the organization of biochemistry across distinct levels of the biological hierarchy—a result that holds across different network projections.

Finally, I leverage these large biochemical datasets, in conjunction with planetary observations and computational tools, to provide a methodological foundation for the quantitative assessment of biology’s viability amongst other geospheres. Investigating a case study of alkaliphilic prokaryotes in the context of Enceladus, I find that the chemical compounds observed on Enceladus thus far would be insufficient to allow even these extremophiles to produce the compounds necessary to sustain a viable metabolism. The environmental precursors required by these organisms provides a reference for the compounds which should be prioritized for detection in future planetary exploration missions. The results of this framework have further consequences in the context of planetary protection, and hint that forward contamination may prove infeasible without meticulous intent. Taken together these results point to a deeper level of organization in biochemical networks than what has been understood so far, and suggests the existence of common organizing principles operating across different levels of biology and planetary chemistry.

Contributors

Agent

Created

Date Created
  • 2018

156605-Thumbnail Image.png

On the origin of the living state

Description

The origin of Life on Earth is the greatest unsolved mystery in the history of science. In spite of progress in almost every scientific endeavor, we still have no clear

The origin of Life on Earth is the greatest unsolved mystery in the history of science. In spite of progress in almost every scientific endeavor, we still have no clear theory, model, or framework to understand the processes that led to the emergence of life on Earth. Understanding such a processes would provide key insights into astrobiology, planetary science, geochemistry, evolutionary biology, physics, and philosophy. To date, most research on the origin of life has focused on characterizing and synthesizing the molecular building blocks of living systems. This bottom-up approach assumes that living systems are characterized by their component parts, however many of the essential features of life are system level properties which only manifest in the collective behavior of many components. In order to make progress towards solving the origin of life new modeling techniques are needed. In this dissertation I review historical approaches to modeling the origin of life. I proceed to elaborate on new approaches to understanding biology that are derived from statistical physics and prioritize the collective properties of living systems rather than the component parts. In order to study these collective properties of living systems, I develop computational models of chemical systems. Using these computational models I characterize several system level processes which have important implications for understanding the origin of life on Earth. First, I investigate a model of molecular replicators and demonstrate the existence of a phase transition which occurs dynamically in replicating systems. I characterize the properties of the phase transition and argue that living systems can be understood as a non-equilibrium state of matter with unique dynamical properties. Then I develop a model of molecular assembly based on a ribonucleic acid (RNA) system, which has been characterized in laboratory experiments. Using this model I demonstrate how the energetic properties of hydrogen bonding dictate the population level dynamics of that RNA system. Finally I return to a model of replication in which replicators are strongly coupled to their environment. I demonstrate that this dynamic coupling results in qualitatively different evolutionary dynamics than those expected in static environments. A key difference is that when environmental coupling is included, evolutionary processes do not select a single replicating species but rather a dynamically stable community which consists of many species. Finally, I conclude with a discussion of how these computational models can inform future research on the origins of life.

Contributors

Agent

Created

Date Created
  • 2018

154046-Thumbnail Image.png

Hydrothermal habitats: measurements of bulk microbial elemental composition, and models of hydrothermal influences on the evolution of dwarf planets

Description

Finding habitable worlds is a key driver of solar system exploration. Many solar

system missions seek environments providing liquid water, energy, and nutrients, the three ingredients necessary to sustain life.

Such environments

Finding habitable worlds is a key driver of solar system exploration. Many solar

system missions seek environments providing liquid water, energy, and nutrients, the three ingredients necessary to sustain life.

Such environments include hydrothermal systems, spatially-confined systems where hot aqueous fluid circulates through rock by convection. I sought to characterize hydrothermal microbial communities, collected in hot spring sediments and mats at Yellowstone National Park, USA, by measuring their bulk elemental composition. To do so, one must minimize the contribution of non-biological material to the samples analyzed. I demonstrate that this can be achieved using a separation method that takes advantage of the density contrast between cells and sediment and preserves cellular elemental contents. Using this method, I show that in spite of the tremendous physical, chemical, and taxonomic diversity of Yellowstone hot springs, the composition of microorganisms there is surprisingly ordinary. This suggests the existence of a stoichiometric envelope common to all life as we know it. Thus, future planetary investigations could use elemental fingerprints to assess the astrobiological potential of hydrothermal settings beyond Earth.

Indeed, hydrothermal activity may be widespread in the solar system. Most solar system worlds larger than 200 km in radius are dwarf planets, likely composed of an icy, cometary mantle surrounding a rocky, chondritic core. I enhance a dwarf planet evolution code, including the effects of core fracturing and hydrothermal circulation, to demonstrate that dwarf planets likely have undergone extensive water-rock interaction. This supports observations of aqueous products on their surfaces. I simulate the alteration of chondritic rock by pure water or cometary fluid to show that aqueous alteration feeds back on geophysical evolution: it modifies the fluid antifreeze content, affecting its persistence over geological timescales; and the distribution of radionuclides, whose decay is a chief heat source on dwarf planets. Interaction products can be observed if transported to the surface. I simulate numerically how cryovolcanic transport is enabled by primordial and hydrothermal volatile exsolution. Cryovolcanism seems plausible on dwarf planets in light of images recently returned by spacecrafts. Thus, these coupled geophysical-geochemical models provide a comprehensive picture of dwarf planet evolution, processes, and habitability.

Contributors

Agent

Created

Date Created
  • 2015

155766-Thumbnail Image.png

The Diversity of Chemical Composition and the Effects on Stellar Evolution and Planetary Habitability

Description

I present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially

I present a catalog of 1,794 stellar evolution models for solar-type and low-mass stars, which is intended to help characterize real host-stars of interest during the ongoing search for potentially habitable exoplanets. The main grid is composed of 904 tracks, for 0.5-1.2 M_sol at scaled metallicity values of 0.1-1.5 Z_sol and specific elemental abundance ratio values of 0.44-2.28 O/Fe_sol, 0.58-1.72 C/Fe_sol, 0.54-1.84 Mg/Fe_sol, and 0.5-2.0 Ne/Fe_sol. The catalog includes a small grid of late stage evolutionary tracks (25 models), as well as a grid of M-dwarf stars for 0.1-0.45 M_sol (856 models). The time-dependent habitable zone evolution is calculated for each track, and is strongly dependent on stellar mass, effective temperature, and luminosity parameterizations. I have also developed a subroutine for the stellar evolution code TYCHO that implements a minimalist coupled model for estimating changes in the stellar X-ray luminosity, mass loss, rotational velocity, and magnetic activity over time; to test the utility of the updated code, I created a small grid (9 models) for solar-mass stars, with variations in rotational velocity and scaled metallicity. Including this kind of information in the catalog will ultimately allow for a more robust consideration of the long-term conditions that orbiting planets may experience.

In order to gauge the true habitability potential of a given planetary system, it is extremely important to characterize the host-star's mass, specific chemical composition, and thus the timescale over which the star will evolve. It is also necessary to assess the likelihood that a planet found in the "instantaneous" habitable zone has actually had sufficient time to become "detectably" habitable. This catalog provides accurate stellar evolution predictions for a large collection of theoretical host-stars; the models are of particular utility in that they represent the real variation in stellar parameters that have been observed in nearby stars.

Contributors

Agent

Created

Date Created
  • 2017

155890-Thumbnail Image.png

Investigation into the geodynamics of planetary ice-ocean systems: application to Jupiter's icy moon Europa

Description

The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with

The Jovian moon Europa's putative subsurface ocean offers one of the closest astrobiological targets for future exploration. It’s geologically young surface with a wide array of surface features aligned with distinct surface composition suggests past/present geophysical activity with implications for habitability. In this body of work, I propose a hypothesis for material transport from the ocean towards the surface via a convecting ice-shell. Geodynamical modeling is used to perform numerical experiments on a two-phase water-ice system to test the hypotheses. From these models, I conclude that it is possible for trace oceanic chemistry, entrapped into the newly forming ice at the ice-ocean phase interface, to reach near-surface. This new ice is advected across the ice-shell and towards the surface affirming a dynamical possibility for material transport across the ice-ocean system, of significance to astrobiological prospecting. Next, I use these self-consistent ice-ocean models to study the thickening of ice-shell over time. Europa is subject to the immense gravity field of Jupiter that generates tidal heating within the moon. Analysis of cases with uniform and localized internal tidal heating reveal that as the ice-shell grows from a warm initial ocean, there is an increase in the size of convection cells which causes a dramatic increase in the growth rate of the ice-shell. Addition of sufficient amount of heat also results in an ice-shell at an equilibrium thickness. Localization of tidal heating as a function of viscosity controls the equilibrium thickness. These models are then used to understand how compositional heterogeneity can be created in a growing ice-shell. Impurities (e.g. salts on the surface) that enter the ice-shell get trapped in the thickening ice-shell by freezing. I show the distribution pattern of heterogeneities that can form within the ice-shell at different times. This may be of potential application in identifying the longevity and mobility of brine pockets in Europa's ice-shell which are thought to be potential habitable niches.

Contributors

Agent

Created

Date Created
  • 2017

152707-Thumbnail Image.png

Variability of elemental abundances in the local neighborhood and its effect on planetary systems

Description

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

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 τ Ceti. τ 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. τ 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.

Contributors

Agent

Created

Date Created
  • 2014