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2014 Annual Science Report

Arizona State University Reporting  |  SEP 2013 – DEC 2014

Executive Summary

The “Follow the Elements” NAI Team at ASU carries out research, education and outreach activities centered on the chemical elements of life. Our activities are motivated by a simple observation: that life-as-we-know-it uses a non-random selection of the chemical elements. This observation prompts many questions:

  • What are the rules that govern the selection of these “bioessential” elements?
  • How might these elements differ in extreme environments on Earth or beyond?
  • How common are the bioessential elements in the extraterrestrial environments that might harbor life?
  • How are the distributions of these elements in the cosmos shaped by astrophysical processes?

The answers to these questions will shape the future exploration for life on other worlds. We sought to address these questions through laboratory, field and computational research, and use them as the basis for much of our education and outreach. To this end, our project is organized around three major research themes: The Stoichiometry of Life; The Habitability of Water-Rich Environments; and Astrophysical Controls on the Elements of Life. We pursue each theme by way of a number of focused research tasks.

During the final year of our project, the Astrobiology Program at Arizona State University brought to closure the major research tasks described in our CAN5 proposal, as well as associated projects begun during this time. Much of this work had already been accomplished and published in prior project years; in this final reporting period the efforts resulted in 45 additional peer-reviewed publications that appeared in print during the reporting period, including several publications in high-profile journals. Collectively, this ongoing research advanced our goal of integrating life science, geoscience, planetary science and astrophysics to understand how the distribution of chemical elements shapes the distribution of life in space and time, and to guide the search for life beyond Earth. This work is comprehensively described in the main report. Key outcomes are highlighted here.

1. The Stoichiometry of Life

This theme includes several tasks aimed at elucidating relationships between the availability of bioessential elements and prokaryotic ecosystems. In this final project year, these tasks involved: various experimental studies in the laboratory (Task 1); field studies (Tasks 2a, b, and c); evolutionary studies in the geologic and genomic records (Tasks 3a and 3b, respectively); and an experimental l project to understand key controls on the carbon cycle in prokaryote-dominated oceans (Task 4).

Notable milestones and outcomes in Year 6:

  • In Task 1, we prepared two manuscripts reporting on a study of metabolomics of the cyanobacterium Synechocystis sp. PCC6803 under different nutrient conditions in the laboratory, carried out in prior years in collaboration with Autonomous University of Barcelona. A host of elemental, biological macromolecule, metabolomic, and transcriptomic changes were observed, including unexpected increases in metal:C ratios under phosphorous limitation.
  • Task 2a encompasses many basic research projects arising from fieldwork at Yellowstone National Park (YNP). Work in this final year focused primarily on driving results into publications, particularly a submitted paper outlining “Principles of Geobiochemistry”. Specific notable advances included the suggestion from new experiments that heterotrophy is a major metabolic strategy for archea in hot springs, and the finding that major (C, N, P) and trace element composition (Ni, Cu, Zn, Mo) in biomass extracted from YNP hotsprings is in the ranges measured in microbes living in more moderate settings.
  • Task 2b centers on fieldwork in Cuatro Cienegas. In Year 6, results of fieldwork and experiments from preceding years were worked into a number of publications, and new sequencing data from field fertilization experiments were analyzed. Overall, we saw a strong response of the water column aquatic microbial community to all fertilizer treatments, but responses of sediment microbes were muted.
  • Task 2c evolved from DDF funding to study microbial colonization of freshly erupted pumice. This year, NDA and biogeochemical analyses were completed and papers published and submitted, providing among the first-ever data characterizing the ecology of microbes that colonize sterile, floating pumice in the wake of a volcanic eruption.
  • Task 3a, investigations into element availability and redox in the geologic record, largely wound down in previous years. However, this final year saw an innovative new exploration and application of iodine:calcium ratios as a unique proxy for oxygen content in shallow seawater.
  • Task 3b analyses of the (meta)genomic diversity in the hotsprings of Yellowstone National Park, and the correlations of this diversity with variations in geochemical variables and geography, were reported in a series of publications.
  • Task 4 saw the completion and publication of a study to assess the effects of clays at different concentrations on the formation of microbial aggregates that can promote carbon export from the ocean surface.

2. The Habitability of Water-Rich Environments

This goal of this theme is to improve our ability to infer the availability of bioessential elements in aqueous environments on Mars, in the outer Solar System, and on water-rich exoplanets. It includes tasks involving: Improving computational codes to model water-rock interactions (Task 1); application of modern geodynamics codes to ice dynamics on Europa and other icy bodies (Task 2); integration of these and other computational models with observational data to better assess the habitability Europa (Task 3), Mars (Task 4), and other small icy bodies (Task 5).

  • Task 1 saw completion of a codes to model chemical alteration of rocks by migrating fluids across a range of permeabilities, for application to weathering on Earth, Mars, and other rocky bodies. Applications of these codes were reported in two LPSC abstracts.
  • Task 2, saw publication of a geodynamic framework for understanding transport of material from Europa’s ocean to its surface through its ice shell.
  • Task 3 saw the development of a novel argument that the possible presence of Mg salts on the surface of Europa can be used to infer that the ocean is rich in sulfate. This new finding, and investigation of Mg chemistry on the surface of Ceres, are being developed into publications.
  • Mars research under Task 4 focused on analysis of data from the Mars Exploration Rovers, Mars Science Laboratory (Curiosity), compared with terrestrial analog sites. A series of papers emerged in this final year making the case for specific past habitable settings on Mars, with the potential to preserve biosignatures.
  • Task 5 wound down with two theoretical studies. One suggested that the recent detection of silica nanoparticles emanating from Enceladus points to aqueous processes but not necessarily to high temperature environments. The other attempts to understand the chemical evolution of Ceres.

3. Astrophysical Controls on the Elements of Life

This theme aims to elucidate the influence of supernovae and other nucleosynthetic processes on the formation of solar systems, their composition, and evolution, with an emphasis on factors crucial to the formation of Earth-like planets. The theme includes tasks involving: High-precision isotopic studies of meteorites to quantify the timescales of the injection of supernova-derived materials (Task 1); computational modeling of the physical and chemical evolution of massive stars (Task 2); quantification of the injection of supernova ejecta to star-forming molecular clouds (Task 3) and protoplanetary disks (Task 4); modeling the chemical evolution of star-forming regions (Task 5); determining what elements might be used as observational proxies in stellar spectra for elements and isotopes not amenable to direct observation (Task 6); and incorporate element abundance data in the “HabCat” of nearby stars that could support life (Task 7).

  • Task 1 work was completed in Year 4.
  • In Task 2, we created a grid of stellar models for 0.5 – 1.2 solar masses, 0.1 to 1.5 times solar metallicity, and O/Fe ratios of 0.5 to 2 times solar with the TYCHO stellar evolution code. These models include predicted habitable zone locations as a function of time for each stellar model for a range of assumptions. The work feeds into Task 7.
  • Task 3 was completed in prior project years. Two follow-up projects resulted in new publications this year, one assessing the the production of the short-lived radionuclide 135Cs in a nearby supernova and the other synthesizing prior work in a review paper.
  • Task 4 was largely completed in prior years, but follow-on work on volatile transport was carried out and presented at conferences by two Ph.D. students.
  • In Task 5, we published two studies that examined the mixing of heavy elements generated by stars into the surrounding cluster environments
  • Task 6 was completed in Year 5, but new 3D supernova simulations were carried out in a follow-on study. The results will be added to the existing suite of models produced by this project used to study nucleosynthetic yields and structure formation in core collapse supernovae.
  • In Task 7, research culminated in two important publications. First, we published a pilot study of the element abundances in the nearby star τ Ceti and speculated on the potential rheological differences from Earth arising from differences in Mg/Si ratios. Second, the Hypatia Catalog of stellar abundance determinations was published and made available to the community. This catalog serves as a foundation for future work characterizing exoplanetary systems.

Other Institute Objectives

In addition to our research tasks, the team carried out many EPO activities supporting non-research objectives of the NAI, reported separately.

The team continued its weekly “coffee seminars”, drawing a regular group of ~ 25 students and faculty for informal seminars. This seminar series continues to be fully organized by program students.

The ideas and products developed in Years 1 – 5 were instrumental in formulating new research plans proposed to NASA that have become the foundation of a new ASU-based “Exoplanet Ecosystems” project as part of NASA’s new NExSS initiative.

Finally, the “Stellar Stoichiometry” workshop sponsored in Year 5 generated two publications in the reporting period, and a third in progress. One was a survey of the topic (Young et al., 2014). A second was a report on the innovative features of the workshop (Desch et al., 2014). A third publication is in preparation, based on a collaboration with five other research groups to determine why measurements of element abundances for a given star by different research groups often differ by more than the quoted observational errors.