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Project Reports

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

  Goals are to constrain conditions of Mars habitability and preservation potential through in situ studies with MER rover data, the MSL Curiosity rover operating at Gale Crater, and terrestrial analog studies.

  ROADMAP OBJECTIVES: 2.1

• Stoichiometry of Life – Task 2b – Field Studies in Cuatro Cienegas

  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

• Task: 3a: Ancient Records – Geologic

  Among the fundamental questions in Earth history is when and where O2 first accumulated in the shallow ocean. These settings could have been ideal local ‘oases’ for initial O2 accumulation and for early eukaryotic life. Iodine geochemistry has emerged as an exciting possibility for exploring such settings characterized by carbonate deposition, but the proxy remains only rudimentarily known because of the lack of validation and calibration in modern shallow carbonate environments. Our work over the past year sought to remedy that situation while simultaneously exploring the proxy’s potential in deep time.

  ROADMAP OBJECTIVES: 4.1 4.2

• 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 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 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. In addition we find that Synechococcus could potentially export carbon 2–3 times of that contained in their cells via aggregation, likely due to the scavenging of transparent exopolymer particles and dissolved organic matter. Thus, aggregation and sinking by these small cyanobacteria could have constituted an important mode of carbon export in the Proterozoic ocean.

  ROADMAP OBJECTIVES: 4.1 4.2 5.2 6.1 7.2

• 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 protoplanetary 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 protoplanetary 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 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), we examined the mixing of heavy elements generated by stars into the surrounding cluster environments.

  ROADMAP OBJECTIVES: 1.1 3.1

• Task 3: Evaluate the Habitability of Europa’s Subsurface Ocean

  We developed models for oceanic composition on Europa and provided arguments for a sulfate-rich oceanic water chemistry.

  ROADMAP OBJECTIVES: None Selected

• Astrophysical Controls – 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 1: High-Precision Isotopic Studies of Meteorites

  ROADMAP OBJECTIVES: 1.1 3.1

• Astrophysical Controls – 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 processed 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 of 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 1 – Improve and Test Codes to Model Water-Rock Interactions

  Numerical codes have been developed to model chemical alteration of rocks by migrating fluids. One code is for alteration of permeable rocks by percolating fluids. Another code is for alteration of low-permeability rocks disrupted through hydro-fracturing by forming overpressured fluids. The codes could be used to model chemical weathering on Mars and Earth, and metasomatism on asteroids, moons, and planets.

  ROADMAP OBJECTIVES: 2.1 2.2

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

  We constrained conditions of formation of silica phases in putative aqueous systems within the Saturn’s icy moon Enceladus, and evaluated the composition of aqueous fluids formed during thermal evolution and rock dehydration of the dwarf planet Ceres.

  ROADMAP OBJECTIVES: 2.2

• 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 aimed to understand how the geochemistry of these hot springs shapes their constituent microbial communities including their composition and function. To accomplish this aim, we measured (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

• Astrophysical Controls – Task 2 – Model the Chemical & 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: None Selected

• 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

• 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 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

• 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