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Project Reports

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

  We carried out studies of self-enrichment of the earliest star clusters, building on the turbulence simulations in Pan & Scannapieco (2010) and Pan et al. (2011), and developing a method to track the formation of metal free stars.

  ROADMAP OBJECTIVES: 1.1 3.1

• Stoichiometry of Life, Task 3b: Ancient Records – Genomic

  Task 3b team members are involved in deciphering genomic records of modern organisms as a way to understand how life on Earth evolved. At its core, this couples the integrated measurement and modeling of evolutionary mechanisms that drove the differences between extant genomes (and metagenomes), with experimental data on how environmental dynamics might have shaped these differences across geological timescales. This goal draws from team members’ expertise encompassing theoretical and computational biology, microbial evolution, and studying life in both extreme and dynamic environments across the planet.

  ROADMAP OBJECTIVES: 5.1 5.2 5.3

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

  Abundances of both common and trace elements can have substantial effects on the habitability of stellar systems. We study the formation and composition of structures in supernova explosions that deliver isotopes that influence habitability to material that will form new stars and planets. We examine ratios of elements that have substantial effects of the mineralogy and interiors of planets. The relative abundances of common elements vary substantially among nearby stars, and we find that the impact of this on a star’s evolution can change the amount of time its planets are habitable by large factors.

  ROADMAP OBJECTIVES: 1.1 3.1

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

  Stars create the chemical elements heavier than hydrogen and helium, with the majority arising from the lives and violent deaths of massive stars in supernova explosions. The starting chemical composition of stars also affects their evolution and that of their associated planets. We have performed computational simulations for a large range of stellar masses to provide predictions for important stellar characteristics (i.e. brightness, temperature, stellar winds, composition) over the stars’ lifetimes and made the data available to the public. We have also simulated the explosions of massive stars to predict the chemical abundances of material ejected from the dying stars and how that material is distributed in the surrounding universe. As a complement, we are modeling how the habitable zones and planets of stars with different abundances evolve.

  ROADMAP OBJECTIVES: 1.1 3.1

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

  Dr. Mikhail Mironenko collaborated with colleagues and completed a code to compute chemical equilibria in low-temperature aqueous systems with salts, CO₂ hydrates, and liquid CO₂. The code could be used to calculate changes in phase composition during freezing or melting in icy cold environments on Mars, large asteroids, icy moons, comets, and trans-neptunian objects. Dr. C. Glein and Dr. E. Shock have published a model to calculate phase chemical equilibria between several hydrocarbons and N₂. The model can be used to explore gas-liquid-solid phase equilibria on Saturn’s moon Titan. Another model has been developed by Dr. Mironenko to calculate condensation of gases in ices and clathrates in the outer solar nebula.

  ROADMAP OBJECTIVES: 2.1 2.2

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

  The goal of this task is to see if material ejected from a star that has exploded as a supernova can make its way into the gas as it is forming new solar systems. It has been expected that this material, because it is moving so fast (> 2000 km/s) when it hits the cold, dense molecular cloud in which stars are forming, would shock, heat up, and then “bounce” off of the cloud boundary.

  ROADMAP OBJECTIVES: 1.1 3.1

• Stoichiometry of Life, Task 2a: Field Studies – Yellowstone National Park

  Yellowstone National Park harbors an array of hydrothermal ecosystems with widely varying geochemical characteristics and microbial communities. Our research aims to understand how the geochemistry of these hot springs shapes their constituent microbial communities including their composition and function. To accomplish this aim, we measure (1) physical and geochemical properties of hot spring fluids and sediments, (2) the rates of biogeochemical processes (i.e., methane oxidation, nitrogen fixation, microbial Fe cycling, photosynthesis, de-nitrification, etc.), and (3) markers for microbial community diversity (i.e., SSU rRNA, metabolic genes, lipids, proteins).

  ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2 7.2

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

  This project component involves a set of studies of 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 or nitrogen or iron? Is this change similar for different 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.

  ROADMAP OBJECTIVES: 5.2 5.3 6.1 6.2

• 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. We performed two studies to evaluate ecological impacts of nitrogen and/or phosphorus fertilization in a P-deficient and hyperdiverse shallow pond in the valley of Cuatro Cienegas, Mexico.

  ROADMAP OBJECTIVES: 5.1 5.2 5.3 6.1 6.2

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

  Co-I Farmer explored for past habitable environments on Mars as part of the MSL (Curiosity) team. He also participated in efforts to develop new life detection instruments for in situ astro-biological exploration of Mars, and documented lipid bio-signature preservation in siliceous hydrothermal deposits.

  Co-I Zolotov developed chemical weathering models for Mars. He argued that formation of salts and phyllo-silicates in the Noachian epoch was followed by aqueous mobilization and deposition of neutral salts in the Hesperian epoch. This hypothesis implies the occurrence of sulfate-saturated subsurface waters during a prolonged time after the formation of phyllo-silicates.

  ROADMAP OBJECTIVES: 2.1

• Stoichiometry of Life, Task 3a: Ancient Records – Geologic

  Fossil and chemical fingerprints of animal life first appear in the geologic record around 600 million years ago. The four billion years of Earth history before this milestone were marked by dramatic changes that we take for granted today but that set the stage for our existence. Our work is exploring the evolving compositions of the early atmosphere and ocean and their cause-and-effect relationships with the evolution of life—spanning the middle 50% of Earth history from the first production of oxygen via photosynthesis to the first appearance of animals—using established and novel geochemical tracers. This work is changing our view of the early environmental conditions that facilitated, and just as often throttled, the rise of life.

  Our efforts over the last year included continued analysis of mid-Proterozoic samples from Australia—emphasizing sulfur isotope systematics, trace metal geochemistry, and organic biomarkers.

  ROADMAP OBJECTIVES: 4.1 4.2

• 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’s history the oceans were dominated by unicellular, bacteria-like organisms (prokaryotes) causing a substantially altered biogeochemistry. In this task, we experiment with the marine cyano-bacterium Synechococcus sp. as a model organism and test its aggregation and sinking speed as a function of nutrient (nitrogen, phosphorus, iron) limitation. So far, we have found that these minute cyanobacteria form aggregates in conditions that mimic the open ocean and can sink gravitationally in the water column. Experiments with added clay minerals (bentonite and kaolinite) that might have been present in the Proterozoic ocean show, that these can accelerate aggregate sinking.

  ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2

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

  The initial Solar System abundances of the short-lived radionuclides (SLRs) ²⁶Al (half life ~0.73 Ma) and ⁶⁰Fe (half life ~2.6 Ma) are important to constrain since, if present in sufficient abundance, these SLRs served as heat sources for dehydration and differentiation processes on planetary bodies. The implications for this work include the astrophysical environment in which the Sun formed, and the abundance of water on the terrestrial planets.

  Research on this task was completed in Year 4.

  ROADMAP OBJECTIVES: 1.1 3.1

• Astrophysical Controls on the Elements of Life, Task 4: Model the Injection of Supernova Material Into Protoplanetary Disks

  The goal of this project has been to determine whether supernova material could be injected into a proto-planetary disk, the disk of gas and dust from which planets form. A secondary issue is whether these materials would be mixed within the disk efficiently, and whether such an injection into our own proto-planetary disk can explain the isotopic evidence from meteorites that the solar system contained short-lived radionuclides like ²⁶Al.

  ROADMAP OBJECTIVES: 1.1 3.1

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

  Abundances of both common and trace elements can have substantial effects on the habitability of stellar systems. Elemental ratios can change the stellar evolution and mineralogy, geophysics, and surface processes of planets. We study the abundances of large samples of nearby stars and individual systems and the extent of their variation. We examine ratios of elements that have substantial effects on the mineralogy and interiors of planets. The relative abundances of common elements vary substantially among nearby stars. Extremely non-solar abundance ratios at the level that can produce substantial changes in planetary and stellar properties are present in interesting numbers.

  ROADMAP OBJECTIVES: 1.1 7.2

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

  One of Jupiter’s moons, Europa, is one of the few places in the solar system in which the physical and chemical conditions may be suitable for sustaining life. Europa is composed on an outer H₂O layer, comprised of rigid ice overlying a liquid water ocean. It is this liquid water ocean which has been hypothesized as having the ingredients necessary for life, but it is shielded from our observation by the thick ice layer. However, under certain conditions, the ice layer is expected to undergo convection, possibly transporting chemicals from the liquid ocean to the surface, where we may be able to detect them. We perform computer modeling of ice/ocean convection to investigate how ocean material is carried up through the ice layer and whether it is expected to reach Europa’s surface. This work provides guidance for future missions which may probe the chemistry of the ice surface.

  ROADMAP OBJECTIVES: 1.1 2.2

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

  Mikhail Zolotov, Co-Investigator (Co-I) has provided arguments and performed numerical modeling to explain the presence of sulfates on Europa’s ocean and carbonaceous asteroids (chondrites), which could have been the building block of Galilean satellites. Sulfates could have formed through sulfide oxidation by O₂ and H₂O₂ accreted with ices irradiated in the solar nebula.

  ROADMAP OBJECTIVES: 1.1 2.2

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

  The first goal of this project is to determine the internal structure of small icy bodies. Co-I Steve Desch is especially considering Pluto and its moon Charon, which are Kuiper Belt Objects (KBOs). The possibility exists that these icy bodies may contain liquid water at great depths, despite their frigid surface temperatures and small sizes, because radioactive isotopes heat them and their ices might contain antifreezes like ammonia. These models are also extended to the dwarf planet Ceres. Pluto and Ceres are both targets of two NASA missions in 2015: New Horizons and DAWN.

  The second goal of this project is to evaluate the chemical composition of aqueous solutions that could have formed shortly after formation of asteroids, KBOs, and moons of giant planets. Co-I Mikhail Zolotov has considered stability of aqueous minerals on the surface of dwarf planet Ceres and suggested formation of the minerals through impacts of ice-rich surface rocks. If correct, this hypothesis implies water-rock differentiation of Ceres by ~3.9 Ga. Zolotov also argued for formation of asteroidal and Europa’s sulfates through low-temperature aqueous oxidation of sulfides by strong oxidants (O₂, H₂O₂) formed through radiolysis of water ice. Desch, in collaboration with JPL scientist Julie Castillo-Rogez, through ASU graduate student Marc Neveu, is considering the geochemistry of subsurface water on Ceres.

  Another of our tasks is to estimate chemical composition of methane-rich liquids that are present at the surface of Titan at extremely low temperatures. We are also helping to develop a concept for a mission to return samples from the plumes of Enceladus.

  ROADMAP OBJECTIVES: 2.2

• Stoichiometry of Life – Task 2c – Field Studies – Other

  We performed biogeochemical and microbiological studies of novel aquatic habitats, floating pumice in lakes of northern Patagonia that were derived from the 2011 eruption of the Puyehue / Cordon Caulle volcano in Chile.

  ROADMAP OBJECTIVES: 4.1 5.2 5.3 6.1