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2013 Annual Science Report

Astrobiology Roadmap Objective 3.2 Reports Reporting  |  SEP 2012 – AUG 2013

Project Reports

  • An Atomic Level Description of the Specific Interactions Between Nascent Peptide and Ribosome Exit Tunnel

    The ribosome exit tunnel is an ancient path that must be traveled by all peptides/proteins synthesized by the ribosome. We have synthesized peptolides and demonstrated their potential as probes to decipher the interaction between the nascent peptide and the exit tunnel. This study has furnished vital information about the path of travel of peptides attached to the flag-pole moiety of a ketolide. In continuation of our study, we have designed and synthesized a second generation of hybrid molecules taking inspiration from peptide sequences that are known to naturally stall translation. We will characterize the interactions of these stall peptolides with the ribosome exit tunnel using the tools we have developed during our investigation of the peptolides.

  • Task 1.1.1: Leaching of Radiogenic Potassium From Titan’s Core Into Its Ocean

    Working with graduate student Jason Hofgartner and NAI collaborator Christophe Sotin, we modeled the equilibrium chemistry of potassium at high pressure in the interior aqueous media in Saturn’s moon Titan to determine the extent of potassium leaching. This, in turn, allows us to test the hydrated silicate core model proposed by J. Castillo-Rogez and NAI Titan deputy PI Jonathan Lunine.

    ROADMAP OBJECTIVES: 1.1 2.1 2.2 3.2 7.1
  • Biosignatures in Ancient Rocks – Kasting Group

    The work by Ramirez concerned updating the absorption coefficients in our 1-D climate model. Harman’s work consisted of developing a 1-D code for modeling hydrodynamic escape of hydrogen from rocky planets.

    ROADMAP OBJECTIVES: 1.1 3.2 4.1 4.2 4.3 5.1 5.2 5.3 6.1 6.2 7.1 7.2
  • Cosmic Distribution of Chemical Complexity

    This project explores the connections between chemistry in space and the origin of life. It is comprised of three tightly interwoven tasks. We track the formation and evolution of chemical complexity in space starting with simple carbon-rich molecules such as formaldehyde and acetylene. We then move on to more complex species including amino acids, nucleic acids and polycyclic aromatic hydrocarbons. The work focuses on carbon-rich species that are interesting from a biogenic perspective and on understanding their possible roles in the origin of life on habitable worlds. We do this by measuring the spectra and chemistry of analog materials in the laboratory, by remote sensing with small spacecraft, and by analysis of extraterrestrial samples returned by spacecraft or that fall to Earth as meteorites. We then use these results to interpret astronomical observations made with ground-based and orbiting telescopes.

    ROADMAP OBJECTIVES: 2.1 2.2 3.1 3.2 3.4 4.3 7.1 7.2
  • Investigation 1: Habitability of Icy Worlds

    Habitability of Icy Worlds investigates the habitability of liquid water environments in icy worlds, with a focus on what processes may give rise to life, what processes may sustain life, and what processes may deliver that life to the surface. Habitability of Icy Worlds investigation has three major objectives. Objective 1, Seafloor Processes, explores conditions that might be conducive to originating and supporting life in icy world interiors. Objective 2, Ocean Processes, investigates the formation of prebiotic cell membranes under simulated deep-ocean conditions, and Objective 3, Ice Shell Processes, investigates astrobiological aspects of ice shell evolution.

    ROADMAP OBJECTIVES: 2.1 2.2 3.2 4.1 5.1 5.2 5.3 6.2 7.1 7.2
  • Advancing Techniques for in Situ Analysis of Complex Organics: Laser Mass Spectrometry of Planetary Materials

    This line of work within the Goddard Center for Astrobiology (GCA) seeks to connect key science objectives related to understanding organics in our solar system to specific techniques and protocols that may enable us to achieve those objectives with in situ investigations. In particular, laser mass spectrometry (MS) techniques are being developed for analysis of complex, nonvolatile organic molecules, such as those that might be found at Mars, Titan, comets, and other planetary bodies, with limited chemical sample manipulation, preparation, and processing (as may be required by flight missions). The GCA laser MS effort is complementary to both (i) instrument development work supported by NASA programs such as ASTID, PIDDP, and MatISSE, to forward the design and testing of new prototype spaceflight hardware, and (ii) ongoing research and development within Theme 4 of the GCA, concerning analytical chemical sample analysis as well as across GCA (particularly with Theme 3) to define combined analysis techniques that may affect future mission design. There are additionally aspects of this effort that relate to understanding synthetic pathways for certain complex organics in planetary environments. Areas of activity with GCA support during this period included: * Comparative study of prompt and two-step laser desorption MS (LDMS) analyses * Development of protocols for induced molecular dissociation and tandem mass spectrometry (MS/MS) * Mars analog analyses using laser TOF-MS, ion trap MS, and SAM-like protocols

    ROADMAP OBJECTIVES: 2.1 2.2 3.2 7.1
  • Habitability, Biosignatures, and Intelligence

    Understanding the nature and distribution of habitable environments in the Universe is one of the primary goals of astrobiology. Based on the only example of life we know, we have devel-oped various concepts to predict, detect, and investigate habitability, biosignatures and intelli-gence occurrence in the near-solar environment. In particular, we are searching for water vapor in atmospheres of extrasolar planets and protoplanets, developing techniques for remote detec-tion of photosynthetic organisms on other planets, have detected a possible bio-chemistry sig-nature in Martian clays contemporary with early life on Earth, developed a comprehensive methodology and an interactive website for calculating habitable zones in binary stellar systems, expanded on definitions of habitable zones in the Milky way Galaxy, and proposed a novel ap-proach for searching extraterrestrial intelligence.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 4.1 4.2 6.2 7.1 7.2
  • Culturing Microbial Communities in Controlled Stress Micro-Environments

    In NAI Theme 4B, our goal in Year 1 has been to initiate our understanding of how cells structure their genomes in response to specific environmental stresses and to determine whether or not such mechanisms have been a major force in directing the evolution of cells in natural environments over evolutionary time. Natural environments are typically rather heterogeneous at small scales, as established by sampling from geothermal hot spring communities, and so it is important to understand the generic impact on the evolution and structure of microbial communities. Our first step towards probing this phenomenon has been to culture living bacterial populations within a small specially constructed microfluidic device (called the GeoBioCell), where strong physical, chemical and biological gradients can be imposed under carefully controlled conditions.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.1 5.2 5.3 6.1
  • Project 2: Processing of Precometary Ices in the Early Solar System

    The discovery of numerous planetary systems still in the process of formation provides a unique opportunity to see how our own solar system may have formed 4.6 billion years ago. Our research group studies physical processes that determine thermal environments in and around young planetary systems in order to constrain the prebiotic chemistry which can occur there. In one study we have built a unique code which simulates the heating of dense molecular gas in chemically active outflows (CAOs) associated with protostars. Our code will be used to model the wealth of molecular observations of CAOs which will be obtained by SOFIA and other observatories. In another study we have discovered a new mechanism whereby asteroids in the solar nebula are heated by magnetohydrodynamical processes. The goal of the second study is to determine whether asteroids can be warm enough to support prebiotic chemistry in protoplanetary systems that were not innoculated by short-lived radionuclides such as aluminum-26.

    ROADMAP OBJECTIVES: 1.1 3.1 3.2
  • Investigation 2: Survivability on Icy Worlds

    Investigation 2 focuses on survivability. As part of our survivability investigation, we examine the similarities and differences between the abiotic chemistry of planetary ices irradiated with ultraviolet photons (UV), electrons, and ions, and the chemistry of biomolecules exposed to similar conditions. Can the chemical products resulting from these two scenarios be distinguished? Can viable microbes persist after exposure to such conditions? These are motivating questions for our investigation.

    ROADMAP OBJECTIVES: 1.1 2.2 3.2 5.1 5.3 6.1 6.2
  • Deconstruction of the Ribosome

    In this Project we are investigating the folding and interactions of a fragment of rRNA with a fragment of a ribosomal protein (rProtein), both derived from T. thermophilus. The goal is to examine the granularity of rRNA-rProtein recognition, to determine if small RNA and protein components of the ribosome can recapitulate interactions observed in the native ribosome. We have assayed the in vitro and in vivo folding and interactions of an isolated subdomain of rRNA with an rProtein and with a peptide fragment of the rProtein. Chemical mapping shows that a 199-nucleotide fragment of Domain III of the 23S rRNA (defined here as Domain IIIcore) folds to a near-native state. This rRNA fragment binds to ribosomal protein L23 in a yeast three-hybrid assay, as predicted from interactions in the native ribosome. A peptide was designed based on the segment of the rProtein that penetrates deep into the core of the native ribosome and associates primarily with Domain IIIcore. A spectroscopic assay shows that the peptide forms a 1:1 complex with both Domain III and Domain IIIcore. The results indicate that rRNA-rProtein recognition is fine-grained, and can be directed by specific interactions between small rRNA and rProtein fragments.

    ROADMAP OBJECTIVES: 3.2 4.1 4.2
  • Ice Chemistry: Radiation Induced Chemical Processing

    Prebiotic molecules such as amino acids, sugar, and sugar alcohols are thought to be delivered to the early Earth by meteorites and comets and may have played crucial role in the origin of life. However, there is no conclusive evidence of these molecules found in the interstellar medium. However, simple precursors such as formaldehyde, acetaldehyde, acetone, propanal, propenal, and acetic acid were observed in the interstellar medium such as toward the star forming region SgrB2. Extraterrestrial ices with abundant molecules like water, methane, carbon monoxide, carbon dioxide, ammonia, and methanol are exposed to ionizing radiation such as galactic cosmic radiation and UV radiation. Here, we have been investigating the effect of ionizing radiation on simple astrophysical ice representatives in the solid state using FTIR, UV-VIS, Raman spectroscopy as well as the products analyzed in the gas phase (fragment free reflectron time-of-flight mass spectroscopy combined with single photon ionization (ReTOF-PI)) while subliming to the gas phase after a controlled temperature desorption. Our laboratory simulation experiments provide clear evidence of the formation of large number of aldehydes, ketones such as acetaldehyde, acetone in methane-carbon monoxide ices, formation of simple sugar alcohols (glycerol) in methanol ices and possibly formation of amino acid (glycine) in mixed ices of water, carbon dioxide, methane, and ammonia.

  • Dynamics of Self-Programming Systems

    Living systems are unique in that they have the capacity to evolve. Evolving systems can reprogram themselves and so they are able to respond to perturbations by creating new functionality. This feature is something very different from physical systems, which obey a fixed or predetermined equation of motion. This project is a theoretical attempt to describe this state of affairs mathematically, and to construct computer programs that have the capacity to evolve and thus become more complex without this being “built in” by the original programmer.

    ROADMAP OBJECTIVES: 3.2 4.1 4.2 5.3 6.2
  • Project 4: Geochemical Steps Leading to the Origins of Life

    We investigate the geochemical steps that may have lead to the origin of life, focusing on identifying and characterizing mineral catalyzed organic reaction networks that lead from simple volatiles, e.g., CO2, NH3, and H2, up to greater molecular complexity. We continue to explore the role of minerals to enhance molecular selection, both isomeric and chiral selection, as well as molecular organization on mineral surfaces. We continue to refine our understanding of the evolution of mineralogical complexity in the context of planetary evolution.

  • Mining Archaeal Genomes for Signatures of Very Early Life

    Carl Woese proposed that life started as semi-autonomous subcellular forms named progenotes. The progenotes lacked cell membranes and readily exchanged information, suggesting that aspects of information processing had already been developed. Woese further hypothesized that certain early life processes crossed a Darwinian threshold, where incorporation of new components of a processes was not tolerated. We aim at determining whether translation, transcription, and replication have crossed the Darwinian threshold. To determine whether DNA replication has crossed the Darwinian Threshold, interchangeability of the DNA replication processivity factor known as the sliding clamp is being examined. It is only in the presence of the sliding clamp that DNA polymerases in extant organisms can gain the speed required to replicate their genomes. In Bacteria, the sliding clamp is the b-subunit of Pol-III and in Archaea and Eukarya the functional homolog is proliferating cell nuclear anti-gen (PCNA). We have, therefore, expressed and purified a sliding clamp from each of the three domains of life (E. coli beta-subunit, M. acetivorans PCNA, and human PCNA). Sliding clamps are loaded in a clamp loader dependent manner; therefore, we have cloned, expressed and purified an archaeal clamp loader from M. acetivorans. Our next step is to determine whether an archaeal clamp loader can interact with each of the sliding clamps from the three domains of life and whether any of the interactions leads to loading of the sliding clamps onto DNA to orchestrate processive DNA synthesis.

    ROADMAP OBJECTIVES: 3.2 3.4 4.2
  • Origins of Functional Proteins and the Early Evolution of Metabolism

    The main goal of this project is to identify critical requirements for the emergence of biological complexity in early habitable environments by examining key steps in the origins and early evolution of functional proteins and metabolic reaction networks. Specifically, we investigate whether protein functionality can arise from an inventory of polypeptides that might have naturally existed in habitable environments; we attempt to demonstrate multiple origins of a single enzymatic function; we investigate how primordial proteins could evolve through the diversification of their structure and functions; and we determine how simple proteins could carry out seemingly complex functions.

  • Extremophile Ribosomes

    Many animals share a common response to environmental stresses. The responses include reorganization of cellular organelles and proteins. Similar stress responses between divergent species suggest that these protective mechanisms may have evolved early and been retained from the earliest eukaryotic ancestors. Many eukaryotic cells have the capacity to sequester proteins and mRNAs into transient stress granules (SGs) that protect most cellular mRNAs. Our observations extend the phylogenetic range of SGs from trypanosomatids, insects, yeast and mammalian cells, where they were first described, to a species of the lophotrochozoan animal phylum Rotifera. We focus on the distribution of three proteins known to be associated with both ribosomes and SG formation: eukaryotic initiation factors eIF3B, eIF4E and T-cell-restricted intracellular antigen 1. We found that these three proteins co-localize to SGs in rotifers in response to temperature stress, osmotic stress and nutrient deprivation as has been described in other eukaryotes. We have also found that the large ribosomal subunit fails to localize to the SGs in rotifers. Furthermore, the SGs in rotifers disperse once the environmental stress is removed as demonstrated in yeast and mammalian cells. These results are consistent with SG formation in trypanosomatids, insects, yeast and mammalian cells, further supporting the presence of this protective mechanism early in the evolution of eukaryotes.

    ROADMAP OBJECTIVES: 3.2 4.2 5.3
  • Task Shortwave Solar Flux at Titan’s Surface

    What can we learn about pre-biotic chemistry by studying Titan? The surface of Titan is a special place for the study of pre-biotic chemistry because that is where the organic haze sedimenting from the atmosphere can come in contact with liquid water (briefly, from cryovolcanic eruptions) to form amino acids and other molecules relevant to life. But an energy source is also needed, and this may come from short-wave (ultraviolet – blue) solar radiation that makes its way through Titan’s dense haze layer to the surface. In this study we calculated the amount of UV-blue solar flux at Titan’s surface based on measurements made by the Descent Imager/Spectral Radiometer (DISR) instrument on the Huygens Probe coupled with radiative transfer models that include haze optical properties.

    ROADMAP OBJECTIVES: 2.2 3.1 3.2 3.3
  • Project 1E: Metagenomic Analysis of Novel Chemolithoautotrophic Bacterial Cultures

    Metagenomic sequence information was obtained from two chemolithoautotrophic bacterial cultures: (1) an iron-oxidizing, nitrate-reducing culture that is capable of growth with either soluble or insoluble, mineral-bound (biotite, smectite) Fe(II) as the sole energy source; and (2) an aerobic iron/sulfur-oxidizing culture that grows with insoluble framboidal pyrite as the sole energy source. Both of these cultures carry-out novel neutral-pH lithotrophic microbial pathways, the discovery of which broadens our view of potential Fe/S based life on Earth (past and present) and other rocky planets. We hypothesize that genetic components of Fe/S oxidation identified in the metagenome of the cultures will bear resemblance to analogous components to be identified in other iron-oxidizing pure cultures being sequenced at JGI, together with existing published and unpublished information from other chemolithoautotrophic microorganisms. Identification of such genetic systems will enable comparative genomic analysis of mechanisms of extracellular phyllosilicate Fe/S redox metabolism, and facilitate development of techniques to detect the presence and expression of genes associated with chemolithotrophic Fe/S metabolism in various terrestrial environments.

    ROADMAP OBJECTIVES: 3.2 5.1 5.3 6.2
  • Genetic Evolution and the Origin of Life

    In this task biologists and chemists use field and laboratory work to better understand the environmental effects on growth rates for freshwater stromatolites and the mechanisms that govern their adaptation to their environment. Stromatolites are microbial mat communities that have the ability to calcify under certain conditions. They are believed to be an ancient form of life, that may have dominated the planet’s biosphere more than 2 billion years ago. Our work focuses on understanding these communities as a means of understanding environmental impacts on evolution, and characterizing their metabolisms and gas outputs, for use in planetary models of ancient environments. This year we also started a new project looking at the chemical affinities of the building blocks of life, as a way to understand how life might have initially formed from these chemical precursors.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 5.2 5.3 6.1 6.2
  • Task 3.1.1: Stimulated Pre-Biotic Reactions on Titan Surfaces

    The program at Georgia Tech. involves Dr. Claire Pirim (postdoctoral researcher) and Dr. Thomas Orlando (PI). It focuses on understanding the reactions occurring on Titan’s surface with an emphasis on determining whether mineral deposits from meteoritic impacts can catalyze the formation of more complex molecules possessing a prebiotic character.

  • Resurrection of an Ancestral Peptidyl Transferase

    Ancient components of the ribosome, inferred from a consensus of previous work, were constructed in silico, in vitro, and in vivo. The resulting model of the ancestral ribosome incorporates about 20% of the extant 23S rRNA and fragments of four ribosomal proteins. We confirmed that the ancestral rRNA can: (i) assume canonical 23S rRNA-like secondary structure, (ii) assume canonical tertiary structure, and (iii) form native complexes with ribosomal protein fragments. We call the assembled a-RNA and rPeptide fragments the aPTC. We are currently focusing on characterizing the catalytic activity of the a-PTC.

  • Project 7: Prebiotic Chemical Catalysis on Early Earth and Mars

    The “RNA World” hypothesis is the current paradigm for the origins of terrestrial life. Our research is aimed at testing a key component of this paradigm: the efficiency with which RNA molecules form and grow under realistic conditions. We are studying abiotic production and polymerization of RNA by catalysis on montmorillonite clays. The catalytic efficiency of different montmorillonites are determined and compared, with the goal of determining which properties distinguish good catalysts from poor catalysts. We are also investigating the origin of montmorillonites, to test their probable availability on the early Earth and Mars, and the nature of catalytic activity that could have led to chiral selectivity on Earth.

  • Project 8: Microenvironmental Influences on Prebiotic Synthesis

    Before biotic, i.e., “biologically-derived” pathways for the formation of essential biological molecules such as RNA, DNA and proteins could commence, abiotic pathways were needed to form the molecules that were the basis for the earliest life. Much research has been done on possible non-biological routes to synthesis of RNA, thought by many to be the best candidate or model for the emergence of life. Our work focuses on possible physicochemical microenvironments and processes on early earth that could have influenced and even directed or templated the formation of RNA or its predecessors.

  • Fischer-Tropsch-Type Reactions in the Solar Nebula

    We are studying Fischer-Tropsch-Type reactions in order to investigate the formation of complex hydrocarbons by surface-mediated reactions using simple gases (CO, N2, and H2) found in the early Solar Nebula. Although several theories exist as to how hydrocarbons are formed in the early Solar System, the compelling nature of this type of reaction is that it is passive and generates a wide variety of complex hydrocarbons using commonly available components (gases/grains) without invoking a complex set of conditions for formation. This method for generating hydrocarbons is important because it provides insight or potential as to how comets, meteorites, and the early Earth may have obtained their first hydrocarbon inventory. From this study, we have expanded the FTT experiments into several related areas of interest, of which the formation of amino acids and the trapping of noble gases are two examples.

    ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2
  • Task 3.2: Longer Wavelength Photochemistry of Condensates and Aerosols in Titan’s Lower Atmosphere and on the Surface.

    This study focuses on the condensed phase photochemistry on Titan. In particular, we focus on understanding longer wavelength photochemistry of solid hydrocarbons to simulate photochemistry that could occur based on the UV penetration through the atmosphere and on the evolution of complex organic species in astrobiologically significant regions on Titan’s surface. Here we investigate the oxygenation chemistry involving the condensed Titan’s organic aerosols with water-ice on Titan’s surface – induced by high energy photons simulating the cosmic ray induced chemistry on Titan’s surface.

    ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2 3.3
  • RiboVision: Visualization and Analysis of Ribosomes

    Ribosomes present special problems and opportunities related to visualization and analysis because they are exceeding complex and information-rich. Many structures have determined at near-atomic resolution, a large number of rRNAs have been sequenced, and each is a large macromolecular assembly with many components and highly complex function. We are devising visualization and analysis methods in analogy with Google Maps, but applied to the ribosome. We have used these tools to make important discoveries relevant to ribosomal structure, function and origins.

  • Task 3.3.1: Solubility of Organics in Simulated Titan Lake Solutions

    Widespread lakes of liquid methane and ethane were discovered on Titan by the Cassini mission in 2006, which naturally motivates questions about the solubility of surface materials in the liquid. Our goal is to measure the solubilities of Titan surface and atmospheric species in cryogenic liquid hydrocarbons, in order to constrain the composition of the hydrocarbon lakes, and provide an understanding into the nature of erosion and sedimentation on Titan. To date, we have measured the solubilities of argon and krypton in liquid methane and ethane, and the solubilities of benzene, naphthalene, and biphenyl in liquid ethane. Relatively high organic solubilities suggest that liquid hydrocarbon based weathering and sorting of surface organics should be occurring on Titan.

    ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2
  • Ribosome Palentology

    The origins of the translation machinery remain imprinted in the extant ribosome. The conformations of ribosomal RNA and protein components can be seen to change over time indicating clear molecular fossils. We are establishing methodology to determine chronologies of ancient ribosomal evolution. It is hypothesized that substantial, though necessarily incomplete evidence, relating to the origins and early development of the translation machinery and its relation to other core cellular processes continues to exist in the primary sequences, three-dimensional folding and functional interactions of the various macromolecules involved in the modern versions of these processes. To this end, we are using ribosomal paleontology to determine the relative age of various ribosomal components and subsystems and thereby develop timelines for the history of the ribosome as a whole as well as various sub processes such as initiation, termination, translocation etc. The results of these studies will interface ribosomal history with other key relating to the origin of life including the emergence of the genetic code, the origin of chirality, and the nature of the last common ancestor. We have also been developing new tools of ribosomal paleontology, to visualize the changes, and to determine timelines for ribosomal origins.

  • The Long Wavelength Limit of Oxygenic Photosynthesis

    Oxygenic photosynthesis (OP) produces the strongest biosignatures at the planetary scale on Earth: atmospheric oxygen and the spectral reflectance of vegetation. Both are controlled by the properties of Chlorophyll a, its ability to perform the water-splitting to produce oxygen, and its spectral absorbance that is limited to red and shorter wavelength photons. We seek to answer what is the long wavelength limit at which OP might remain viable, and how. This would clarify whether and how to look for OP adapted to the light from red dwarfs or M stars, which emit little visible light but abundant far-red and near-infrared. Very recently discovered cyanobacteria have been found to harbor alternative chlorophylls adapted to spectral light environments very much like that of M stars. This projects uses field, lab, and modeling studies to study these far-red adapted cyanobacteria as analogues for extrasolar oxygenic photosynthesis pushing the long wavelength limit.

    ROADMAP OBJECTIVES: 3.2 4.2 5.1 5.3 6.2 7.2
  • Infrared Detections of Hypervolatiles in Distant Comets – Implications for Chemical Taxonomy

    Most IR taxonomic databases of comets concentrate on objects at heliocentric distances within 2 AU, where water (the main volatile species in comets) is active. In 2012, we found that we could quantify hypervolatiles (such as carbon monoxide and methane) using infrared facilities in comets at distances even beyond Jupiter, where water ice cannot sublime efficiently. This project has focused on a new approach to understand the activity of distant comets using infrared facilities, as well as on the role of hypervolatiles in the onset of activity and the implications for current taxonomic databases of primary volatiles.

    ROADMAP OBJECTIVES: 1.1 3.1 3.2 7.1
  • Molecular Biosignatures: Hopanoid Sources in Modern Systems

    Molecular fossils preserved in sedimentary rocks provide a record of Earth’s early biosphere and its associated carbon cycle. Among the earliest and most abundant molecular fossils are the hopanoids. Derived primarily from bacteria, their diagenetic products, the hopanes, are detectable over timescales of billions of years and have been proposed to be among the most abundantly preserved molecules on Earth. However, an overall picture of their environmental, physiological, and taxonomic origins remains elusive. Are they primarily remnants of primary producers or of heterotrophic consumers? Do they primarily come from free-living marine communities, or from shallow mats, tidal zone communities, or even terrigenous runoff? Here we aim to obtain compound-specific carbon isotope data for hopanoids to infer their sources in modern systems, as proxies for understanding ancient environments.

    ROADMAP OBJECTIVES: 3.2 5.1 5.3 6.1
  • Task 3.3.2: Trapping of Methane and Ethane in Titan Surface Materials

    We demonstrate that solid benzene can trap significant amounts of ethane and methane within its crystal structure at Titan surface temperatures. Experiments also suggest that liquid ethane can diffuse into solid benzene, resulting in the formation of a co-crystalline structure. This implies that lake edges and evaporite basins on Titan may hold important quantities of ethane. These results can help explain the release of methane observed at the Huygens landing site, and point toward a large possible reservoir of methane and ethane hidden within Titan’s surface organics.

    ROADMAP OBJECTIVES: 1.1 2.2 3.1 3.2
  • Task 3.4.1: Nuclear Magnetic Resonance Spectroscopy Studies of Titan Organic Analogues: Analytical Potential

    Nuclear magnetic resonance spectroscopy (NMR) has tremendous potential for the quantitative identification of solar system organic molecules of simple to complex nature with absolute structural identification. We have investigated its potential for the elucidation of very complex mixtures of Titan aerosol haze analogues (Tholins) with identification of the major components of modest complexity using 1, 2 and 3 dimensional spectral techniques. We have also performed studies of the utility of low resolution NMR on low temperature liquid hydrocarbon mixtures analogous to Titan lake liquids towards the development of multidimensional NMR instrumentation capable of future flight missions to solar system bodies of organic composition.

    ROADMAP OBJECTIVES: 2.2 3.1 3.2
  • Molecular Biosignatures: Reconstructing Events by Comparative Genomics

    Reconstructing ancient events in genome evolution provides a valuable narrative for planetary history. Phylogenetic analysis of protein families within microbial lineages can be used to detect horizontal gene transfers and the evolution of new metabolic pathways and physiologies, many of which are significant in reconstructing ancient ecologies and biogeochemical events. These gene transfers can also be used to constrain molecular clock models for early life evolution, applying principles of stratigraphy and date calibration. A better understanding of gene evolution, including partial horizontal gene transfer, is needed to improve these inferences and avoid systematic errors.

    ROADMAP OBJECTIVES: 3.2 3.4 4.1 4.2 4.3 5.1 5.2 6.1
  • Task 3.5.1: Titan as a Prebiotic Chemical System

    Six years ago, NASA sponsored a National Academies report that asked whether life might exist in environments outside of the traditional habitable zone, where “weird” genetic molecules, metabolic processes, and bio‐structures might avoid the water‐based biochemistry that is found across the terran biosphere. In pursuit of this “big picture” question, we turned to Titan, which has exotic solvents both on its surface (methane‐hydrocarbon) and sub‐surface (perhaps super‐cooled ammonia‐rich water). This work sought genetic molecules that might support Darwinian evolution in both environments, including non‐ionic polyether molecules in the first and biopolymers linked by exotic oxyanions (such as phosphite, arsenate, arsenite, germanate) in the second. Further, we asked about the possibility that Titan might inform our understanding of prebiotic chemical processes, including those on “warm Titans”. Our experimental activities found few possibilities for non‐phosphate-based genetics in subsurface aqueous environments, even if they are rich in ammonia at very low temperatures. Further, we showed that polyethers are insufficiently soluble in hydrocarbons at very low temperatures, such as the 90‐100 K found on Titan’s surface. However, we did show that “warm Titans” could exploit propane as a biosolvent for certain of these “weird” alternative genetic biopolymers; propane has a huge liquid range (far larger than water). Further, we integrated this work with other work that allows reduced molecules to appear as precursors for more standard genetic biomolecules, especially through interaction with various mineral species.

    ROADMAP OBJECTIVES: 1.1 1.2 2.2 3.1 3.2 4.1 4.2 5.3 6.2 7.1 7.2
  • Remote Sensing of Organic Volatiles on Mars and Modeling of Cometary Atmospheres

    Using our newly developed analytical routines, Villanueva reported the most comprehensive search for trace species on Mars (Villanueva et al. 2013b, Icarus) and described in detail the chemical taxonomy of comets C/2001 Q4 and C/2002 T7 (de Val-Borro et al. 2013). He expanded our already comprehensive high-resolution spectroscopic database to include billions of spectral lines of ammonia (NH3, Villanueva et al. 2013a), hydrogen cyanide (HCN, Villanueva et al. 2013a, Lippi et al. 2013), hydrogen isocyanide (HNC, Villanueva et al. 2013a), cyanoacetylene (HC3N, Villanueva et al. 2013a), monodeuterated methane (CH3D, Gibb et al. 2013), and methanol (CH3OH, DiSanti et al. 2013). For each species, he developed improved or new fluorescence models using the new spectral models. These permit unprecedented improvement in models of absorption spectra in planetary atmospheres (Earth, Mars), and in computing fluorescence cascades for emission spectra of cometary gases pumped by solar radiation. Villanueva utilized these new models in analyzing spectra of comets that enabled record observations of CO in comet 29P/Schwassmann-Wachmann-1 (see report by Paganini), revealed the unusual organic composition of comet 2P/Encke (see report by Mumma), developed new fluorescence models for the ν2 band of methanol and for the ν3 band of CH3D in comets (see reports by DiSanti and by Bonev), and discovered two modes of water release in comet 103P/Hartley-2 (see report by Bonev).

    ROADMAP OBJECTIVES: 1.1 2.1 3.1 3.2 4.1 7.1
  • Volatile Composition of Comets: Emphasis on Oxidized Carbon

    DiSanti’s research emphasizes the chemistry of volatile oxidized carbon in comets, in particular the efficiency of converting CO to H2CO and CH3OH through reduction reactions on the surfaces of icy grains prior to their incorporation into the cometary nucleus. Additionally, oxidation reactions on grains can play a significant role, particularly for CO-enriched, C2H2-depleted comets such as C/2009 P1 (Garradd; see item 2 under Section 3 below). Such processes produce precursor molecules that (if delivered to Earth through impact of comet nuclei) could have enabled the emergence of life, and so are highly relevant to Astrobiology.

  • The Astrobiology Walk

    The Goddard Center for Astrobiology (GCA) has completed the development and installation of a permanent outdoor exhibit at the Goddard Space Flight Center (GSFC) Visitor Center as a major public outreach effort. The “Astrobiology Walk” is designed to showcase the latest scientific discoveries from the GCA research theme “Search for the Origin and Evolution of Organics” in the context of a timeline for the evolution of the Universe and the Solar System. The exhibit consists of ten outdoor stations situated on the circular pathway around the Visi-tor Center’s “Rocket Garden”, each with a memorable iconic 3D object to convey the main scientific message. QR codes link each placard to web sites relevant to that topic.

    ROADMAP OBJECTIVES: 1.1 1.2 2.1 2.2 3.1 3.2 4.1 4.3 7.1 7.2