2011 Annual Science Report

Arizona State University Reporting  |  SEP 2010 – AUG 2011

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 seek to answer these questions through laboratory, field and computational research, and use them as the basis for much of our education and outreach. To this end, the project is organized around ... Continue reading.

Field Sites
29 Institutions
20 Project Reports
74 Publications
4 Field Sites

Project Reports

  • Astrophysical Controls on the Elements of Life, Task 7: Update Catalog of Elemental Ratios in Nearby Stars

    Future surveys like Kepler for habitable planets will likely be limited to select regions of the sky. In anticipation, we have created the first maps of what the solar neighborhood looks like in the “light” of bio-essential elements such as C, N, O, Si and Fe. To make these maps, we painstakingly compiled and analyzed 25 years’ worth of measured data on 44 chemical elements in 1224 stars that are within 500 light-years of the Sun and potentially host habitable exoplanets. Our new catalog “the Hypatia Catalog“ and the first maps produced from it suggest there are certain directions on the night sky that show enhanced abundances of bio-essential elements. These “habitability hotspots” or “habitability windows” may be of use in current and future searches for Earth-like planets.

  • Astrophysical Controls on the Elements of Life, Task 2: Model the Chemical and Dynamical Evolution of Massive Stars

    The elemental ratios in stars and their planets will differ because each star has a different contributions from sources of stellar nucleosynthesis. The dominant contributions of heavy elements to molecular clouds come from supernova explosions, which may also contribute material just prior to star formation. To quantify what elements might be contributed by supernovae, in this task we first perform numerical simulations of stellar evolution, predicting how stellar properties (e.g., luminosity, temperature, internal composition, stellar winds, etc.) change over time. These results are made available to the public. We then simulate the explosions of massive stars as supernovae, to determine what elements are ejected. As a complementary study, we are also using spectra of stars, obtained during radial velocity planet searches, to find the chemical abundances of hundreds of nearby, potentially habitable stars, to assess the variability of starting compositions, and we are also modeling how the habitable zones of stars with these starting compositions might vary over time.

  • Astrophysical Controls on the Elements of Life, Task 1: High-Precision Isotopic Studies of Meteorites

    The elemental abundances of planetary systems potentially are affected by contributions from nearby supernovae. Injection of supernova material can be studied by isotopic analyses of meteorites, especially calcium-rich, aluminum-rich inclusions (CAIs) within them, which reveal the presence in the forming Solar System of short-lived radionuclides. Initial abundances of these radionuclides not only signal contributions from a supernova but also provide a chronometer to date the injection and other formation events. Radionuclides, especially 26Al, also can affect the thermal evolution and volatile retention within planetary bodies. In this task we seek to measure initial abundances of radionuclides in meteorites, especially CAIs, and to constrain the timing of early Solar System events.

  • Stoichiometry of Life – Task 2d – Field Studies – Marine Hydrothermal Systems: Deep Hot Biosphere – Lead

    The deep hot biosphere beneath the seafloor remains one of the most extremely poorly understood ecosystems on Earth. Collaborator Hartnett participated in Leg 331 Deep Hot Biosphere of the Integrated Ocean Drilling Program and collected sediments drilled from hydrothermal mounds in the Okinawa Trough region. The organic geochemistry of the sediments will be assessed and related to the presence and activity of microorganisms beneath the seafloor. The scientific party included NAI scientists from three teams (ASU, Penn State, Hawaii) as well as astrobiologists from Japan; the main research objective was to document the existence of an active, metabolically diverse subvent biosphere associated with hydrothermal activity.

  • Stoichiometry of Life – Task 2c – Biological Soil Crusts: Metal Use and Acquisition

    Desert biological soil crusts (BSCs) are a complex consortia of microorganisms including cyanobacteria, algae, and fungi. BSCs are the primary colonizers of desert soils, supplying both carbon and nitrogen to these arid-land ecosystems. As such, they may represent an analog for soil development on the early Earth. BSCs occupy an extremely nutrient-poor niche, and meet their nutrient and metal requirements by manipulating their surroundings via the production of metal-binding ligands called siderophores. The soil crust’s metabolism affects the chemical composition of soil porewaters and soil solid phases; these alterations to soil metal contents may represent a biosignature for biological soil crusts that can be preserved over long time scales.

    ROADMAP OBJECTIVES: 4.1 5.3 6.1 6.2 7.1
  • Stoichiometry of Life, Task 2a: Field Studies – Yellowstone National Park

    Field work and subsequent laboratory analysis is an integral part of following the elements. One of our field areas is the hot spring ecosystems of Yellowstone, which are dominated by microbes, and where reactions between water and rock generate diverse chemical compositions. These natural laboratories provide numerous opportunities to test our ideas about how microbes respond to different geochemical supplies of elements. Summer field work and lab work the rest of the year includes characterizing the natural systems, and controlled experiments on the effects of changing nutrient and metal concentrations (done so as to not impact the natural features!).

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.2
  • Stoichiometry of Life, Task 3a: Ancient Records – Geologic

    We have generated and are interpreting a wide range of geochemical data from rocks that are over 1.5 billion years old. The data indicate that the ancient ocean was very different than today and had regions that were full of toxic hydrogen sulfide. These extreme conditions in the ocean were the backdrop against which early organisms appeared and evolved—and perhaps struggled.

  • Stoichiometry of Life, Task 4: Biogeochemical Impacts on Planetary Atmospheres

    Oxygenation of Earth’s early atmosphere must have involved an efficient mode of carbon burial. In the modern ocean, carbon export of primary production is dominated by fecal pellets and aggregates produced by the animal grazer community. But during most of Earth history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. In this task we experiment with the marine cyanobacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. We have found so far that aggregation and sinking of these minute cyanobacteria is influenced by the concentration of nutrients in the growth medium.

    ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2
  • Stoichiometry of Life, Task 2b: Field Studies – Cuatro Cienegas

    Cuatro Cienegas is a unique biological preserve in México (state of Coahuila) in which there is striking microbial diversity, potentially related to extreme scarcity of phosphorus. We aim to understand this relationship via field sampling of biological and chemical characteristics and a series of enclosure and whole-pond fertilization experiments.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2
  • Stoichiometry of Life, Task 3b: Ancient Records – Genomic

    The goal of Task 3b is to advance understanding of elemental cycling in ancient ecosystems. Team members are developing experimental and computational approaches aimed at genomic analysis of modern ecosystems, and extending these approaches in novel ways to infer the function and composition of ancient communities.

    ROADMAP OBJECTIVES: 5.1 5.2 5.3
  • Astrophysical Controls on the Elements of Life, Task 4: Model the Injection of Supernova Material Into Protoplanetary Disks

    Our Solar System is known to have contained short-lived radionuclides such as 26Al and 60Fe when it formed. These must have been created either during or just before Solar System formation. A supernova explosion is thought to be the most likely source. Depending on the manner of supernova injection, other elements relevant to life may accompany the radionuclides. In this task we study how a supernova might inject material into the protoplanetary disk from which the planets in the Solar System formed, after the formation of the protostar. This tests the hypothesis of supernova injection and quantifies its contributions to radionuclides and other elements.

  • Astrophysical Controls on the Elements of Life, Task 3: Model the Injection of Supernova Material Into Star-Forming Molecular Clouds

    Our Solar System is known to have contained short-lived radionuclides such as 26Al and 60Fe when it formed. These must have been created either during or just before Solar System formation. A supernova explosion is thought to be the most likely source. Depending on the manner of supernova injection, other elements relevant to life may accompany the radionuclides. In this task we study how a supernova might inject material into the molecular cloud from which the Solar System formed, before formation of the protostar. This tests the hypothesis of supernova injection and quantifies its contributions to radionuclides and other elements.

  • Habitability of Water-Rich Environments, Task 5: Evaluate the Habitability of Small Icy Satellites and Minor Planets

    We are investigating whether liquid can exist beneath the surface ice of small icy satellites and Kuiper belt objects (KBOs). We are also trying to predict whether this liquid can be brought to the surface in a “cryovolcanic” flow, or if there are other observational signatures of subsurface liquid. Numerical modeling has been performed to understand physical and chemical processes, fluid chemistry and mineralogy of low- and high-temperature aqueous processes on icy bodies in the outer solar system.

  • Habitability of Water-Rich Environments, Task 2: Model the Dynamics of Icy Mantles

    Jupiter’s moon Europa provides a combination of physical and chemical conditions that may be among the most suitable in the solar system for sustaining life. Europa almost certainly has a liquid ocean. This ocean may have the ingredients necessary for life, but it is shielded from observation by a thick overlying ice layer. Under certain conditions this ice layer may undergo convection that can transport chemical species from the ocean to the surface, where they may be detected. Our computer modeling of convection in this ice layer aims to quantify how much ocean material may be brought to the surface. This work provides guidance for future missions to Europa.

  • Astrophysical Controls on the Elements of Life, Task 6: Determine Which Elemental or Isotopic Ratios Correlate With Key Elements

    In this task we explore how key elements and radioactive isotopes are created by nucleosynthesis during the explosions of massive stars. We also study the formation and composition of structures in supernova explosions that may be relevant to delivery of bioessential elements to forming solar systems. In particular, we have investigated how the bioessential elements Ca and Fe are produced during supernovae. We have discovered that they are produced by 6 distinct nucleosynthetic pathways, and that their relative abundances can be probed by observations of the gamma-ray radiation from the radioactive decay of the isotopes 44Ti and 56Ni into 44Ca and 56Fe. We also have investigated the co-production of O isotopic anomalies with the short-lived radionuclide 26Al. We find that delivery of 26Al to the early solar system would not necessarily have altered significantly its O isotopic composition.

  • Astrophysical Controls on the Elements of Life, Task 5: Model the Variability of Elemental Ratios Within Clusters

    In Tasks 3 and 4 we study how supernovae may enrich indvidual solar systems at the peripheries of high-mass star-forming regions. In this task we study in a statistical sense how stars of a variety of masses at the ends of their lives enrich star-forming molecular clouds and stellar clusters. Through detailed numerical hydrodynamic simulations we are studying the mixing of heavy elements into the surrounding medium and comparing our predictions to variable abundance ratios in present-day clusters. We also apply this research to star formation in the early universe, studying the transition between pristine (very low metallicity) and enriched star formation.

  • Habitability of Water-Rich Environments, Task 1: Improve and Test Codes to Model Water-Rock Interactions

    The goal of this task is to develop computer codes to model the chemistry and mineralogy of water-rock interactions on present and early Earth, and on extraterrestrial bodies with liquid water (ancient Mars, icy moons, early asteroids, and extrasolar planets). This year we developed and tested codes to model temporal changes in aqueous chemistry and mineralogy during vertical percolation of fluids through layered rocky materials. In particular, we were able to model neutralization of acidic fluids along with percolation together with changes in mineralogy of altered basalts. The model results closely match many observations.

  • Habitability of Water-Rich Environments, Task 3: Evaluate the Habitability of Europa’s Subsurface Ocean

    Europa is of keen interest to astrobiologists and planetary geologists because of indications that it may possess a sub-surface ocean. In this task we seek to understand the global distribution and timing of Europan geologic units, to identify regions of recent activity. We also seek to map chemical signatures on its surface. Simultaneously we are numerically modeling the convection in the icy shell overlying the subsurface ocean, with a particular aim of determining whether chemical species from the ocean can be brought to the surface. Through this combined approach we seek to understand Europa’s ocean’s pH and composition, and evaluate the habitability of this icy moon.

  • Habitability of Water-Rich Environments, Task 4: Evaluate the Habitability of Ancient Aqueous Solutions on Mars

    Field, laboratory, and numerical modeling studies have been performed to understand the chemical processes and mineralogy relevant to low- and high-temperature aqueous alteration processes on ancient Mars. Results show that significant amounts of aqueous solutions could have been involved in the formation of secondary minerals (silica, clays) observed on Mars, with important implications for its past habitability.

  • Stoichiometry of Life – Task 1 – Laboratory Studies in Biological Stoichiometry

    This project component involves a diverse set of studies of various microorganisms with which we are trying to better understand how living things use chemical elements (nitrogen, phosphorus, iron, etc) and how they cope, in a physiological sense, with shortages of such elements. For example, how does the “elemental recipe of life” change when an organism is starved for phosphorus? Is this change similar for diverse species of microorganisms? Are the changes the same if the organism is limited by a different key nutrient? Furthermore, how does an organism shift its patterns of gene expression when it is starved by various nutrients? This will help in interpreting studies of gene expression in natural environments. At an even more profound level: can an organism substitute an element that is similar to the one that is limiting, as in the case of arsenic for phosphorus?

    ROADMAP OBJECTIVES: 5.2 5.3 6.1 6.2