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Executive Summary

The Ames Research Center Team conducted investigations to understand how habitable planetary systems and environments develop, how biological systems arise and affect their planetary environment, and how changing environments might affect our biosphere. These investigations broadly address NASA’s current Astrobiology Roadmap and strengthen NAI participation in flight missions, NASA’s new vision for exploration, and education and public outreach. The Team’s strong involvement in several NASA missions provides context, motivation, and resource-sharing opportunities for the research, education and public outreach efforts. The Ames Team research and education and public outreach activities are highlighted in their website at http://www.amesteam.arc.nasa.gov .

We investigated the processes that influence the formation of planetary systems and the evolution of planetary atmospheres. Photoevaporation processes in protoplanetary disks around young stars can clear a disk and thus affect the likelihood that habitable planets might form. We extended our model of these processes to explore optically thick disks that are the birthplaces of planets. Our model predicted distributions of the molecule HDO (deuterated water) that were corroborated by observations by the Spitzer Space Telescope. The extreme UV, far UV, and X ray radiation from the central star each exert different important effects upon the size, density and composition of various regions within the evolving disk. We published papers documenting the effects of photoevaporation as a function of stellar mass in order to determine which mass star has the longest-lived disks and the highest probability of forming planets. A new book chapter presents theoretical models of the thermal and density structure of disks and compares their predictions with observations. We modeled in two dimensions the condensation/ sublimation front in the early solar nebula to determine the phase state (gas or ice) of important species relating to organic chemical processes. Water ice is a ubiquitous part of the protoplanetary disk. Ice forms as close as 1 AU from stars that are generally similar to our Sun and it exhibits complex vertical phase structures in planet-forming regions. We studied the chemical evolution of disks, focusing on H₂O, CO, OCS, CH₃OH and CH₃OCH₃ as examples of simple molecules related to more complex ones. Small sets of reactions (2 to 5) dominate locally and account for more than 90% of the cycling of a given chemical compound. We will study the evolution and movement of organic species in the nebula and their presence in habitable planet regions. We completed “Systemic,” a public-domain radial velocity data analysis package that performs detailed analyses of 100,000 radial velocity data sets that mimic a wide distribution of planetary systems. We completed a collaborative web-based environment (c.f. http://www.oklo.org/php/login.php) wherein users can submit fits, discuss their properties, and participate in further analyses. We simulated the late stages of terrestrial planet formation around binary stars. Tight binary stars with maximum separations of less than 0.2 AU and small eccentricity had little effect on the accreting bodies. Binary stars with maximum separation of 0.3 AU perturb the accreting disk such that the formation of Earth-like planets near 1 AU is unlikely. The passage of the solar system through dense interstellar dust clouds was shown likely to cause particles to build up in the stratosphere, block sunlight, plunge Earth into a snow- and ice-covered state, and destroy ozone. We determined that Martian gullies are likely to form by water under present conditions. We used data from the Arctic to develop a numerical model for flows under sub-freezing conditions.

Figure 1. Illustration of how processes act to determine planet habitability. These processes are, of course, a subset of all processes that have to be ultimately considered, but they are critical ones.

Our investigations of prebiotic organic matter from space advanced on three fronts. We published data and a new model that help to explain how infrared emission features can arise from polycyclic aromatic hydrocarbons (PAH) even in interstellar regions where UV radiation is relatively low. We demonstrated in another publication that nitrogen is an abundant and ubiquitous component in cosmic PAH. In yet another study, we demonstrated that PAH ions are important constituents in ices, even at temperatures exceeding 50 K. Accordingly, such ions might play important roles in the chemistry, spectroscopy and physics of icy bodies, both in the Solar System and in the interstellar medium. We collaborated with the Goddard NAI team to study quinoline, amino acids, and other biomolecule-like compounds that are formed during our simulations of interstellar chemistry. We examined model lipid membranes and monolayers that might simulate key chemical and structural constituents during prebiotic evolution. We employed Langmuir compression algorithms and Nuclear Magnetic Resonance measurements to examine the effects of PAH constituents in these structures. PAH tend to increase the size of lipid vesicles as well as shield their contents from potentially destructive UV radiation. Our involvement with NASA’s Stardust mission aims to extract and analyze organic constituents from those samples in order to provide additional insights into the organic chemistry of the early Solar System.

Figure 2. This year our team expanded our knowledge of PAHs by demonstrating, among other things, that N-containing PAHs are widespread and that ionized PAHs persist to higher temperatures in ices and thus probably influence reactions more extensively than previously thought.

To understand the evolutionary origins of functional biological macromolecules, we have evolved, for the first time, a new enzyme with a catalytic activity that has not been observed in nature. We conducted molecular evolution experiments to select for and protein sequences capable of catalyzing the template-directed ligation of two RNA oligonucleotides. Proteins from the final experiment exhibited a ligation reaction whose chemistry is the same as that catalyzed by protein polymerases, and our newly evolved enzyme conferred a rate enhancement of at least a million fold. We continued investigations of an ATP (adenosine triphosphate)-binding protein that we had developed previously. We determined how the sequence and structure of this protein affect its stability, strength and selectivity of binding ATP, and we determined its evolutionary potential towards performing new functions. The ability to evolve novel enzymatic activities from relatively small libraries of randomized sequences suggests that the evolution of functional proteins may not have been a difficult or slow stage in the early evolution of life. Using a model chemistry that takes into account realistic thermodynamic and kinetic constraints, we have shown a possibility of self-organization of simple metabolism into pathways and cycles that persist in the population (i.e. are “collectively inherited”) even though they are not inherited at the level of individual protocells. Our results support a view that the formation of protocellular metabolism was largely deterministic and strongly constrained by laws of chemistry even though this formation might have been driven by non-genomic, highly stochastic processes.

Figure 3. Schematic diagram of the newly-evolved enzyme developed by selection in vitro. Two cysteine-x-x-cysteine sequence motifs (from the a-helix (green) and the N-terminal loop region) bind a zinc atom (gray sphere in the lower left corner), which stabilizes the structure of the protein. ADP fits into a hydrophobic binding pocket, formed by the loop region between the second b-strand and the a-helix, and is stabilized by hydrogen bonding of the adenosine NH2 to the protein backbone.

We continued our studies of microbial ecosystems and biosignatures. Our work with chemosynthetic microbial ecosystems has led to publications that establish energetic boundary conditions on subsurface life and that assess the life-supporting potential in actively serpentinizing ultramafic rocks — a potential analog for past and modern activity on Mars. By quantitatively addressing the potential of both biological and abiological source terms, this work will help to interpret the potential origin of methane in the Martian atmosphere. We developed an energy-balance model for photosynthetic microbial mats that offers a novel approach for quantifying and predicting chemical partitioning and volatile efflux. We quantified how fermentation in microbial mats during the night is related to volatile efflux (including potential biomarkers) and to anaerobic populations, with particular emphasis on the importance for chemical cycling on the Archaean Earth. We have also completed preliminary studies to document the degradation of potential biomarker compounds in hypersaline evaporitic systems. We initiated a detailed study to characterize the sulfur cycle in microbial mats over a range of sulfate concentrations representing modern to Archaean seawater. These efforts are relevant not only to interpreting Earth’s rock record but also to understanding the origins of organics and sulfur species that might be found in the extensive Martian evaporitic deposits. Team members serve as instrument PIs and interdisciplinary scientists on several missions, including Mars Exploration Rovers, Mars Reconnaissance Orbiter, and Mars Science Laboratory. The environments to be studied with these missions include potentially serpentinizing ultramafic rocks and evaporitic systems and thus have direct analogs in the focal environments of our ongoing research.

Figure 4. Cross-section of an actively growing gypsum crystal from a hypersaline pond in Guerrero Negro, Baja California Sur, Mexico. The vibrant colors are imparted by a suite of photosynthetic microorganisms that, along with a variety of accessory organisms, live embedded within the crystals. Our team is studying biomarker production and degradation in these sulfate-rich, evaporitic systems, which represent possible chemical analogs for what appear to have been the last vestiges of surface water on Mars. (Image Credit: Niko Finke, Ames Research Center)

We published our numerical model to link microbial ecosystems to global biosphere processes. We made further refinements to model the effects of competition between methanogens and sulfate-reducing bacteria on metabolism and gas flux in microbial mats. To prepare for future inclusion in the Virtual Planetary Laboratory model of the Caltech NAI Team, we developed algorithms to model the diffusion boundary layer, eddy flux and total flux across the water-air interface. We incorporated salinity responses by key microbiota into the model and found that community composition, gas flux, and chemical profiles within the mat are highly sensitive to changes in salinity.

Figure 5. Results of a computational simulation of microbial mat development at a salinity of 50 parts per thousand, showing the inferred abundances of key microbial populations as a function of depth below the surface of the mat. The populations are as follows: PSB – purple sulfur bacteria; CSB – colorless sulfur bacteria; SRB – sulfate reducing bacteria; MET – methanogens; and CYA – cyanobacteria.

As part of our studies of microbial survival in space and other high-radiation environments, we participated in field trips to the Bolivian Andes as part of the SETI Institute NAI team effort led by Dr. Nathalie Cabrol. We isolated and cultured a psychrophilic halophilic bacterium and we currently are assaying both its response to desiccation and its resistance to UV radiation. We documented that other isolates shown to be resistant to UV radiation are also resistant to hard radiation at the accelerator facility at Idaho State University. We developed a faster, high-throughput method that utilizes fluorescent antibodies to detect direct and indirect DNA damage. We have begun efforts to assay the survival of microbes within rocks in space. We are assaying internal rock fracture volumes and developing methods for inserting microorganisms into fractures and then retrieving them.

Figure 6. Microorganisms from a dark green microbial mat in the Bolivian Andes. These microorganisms experience harsh UV light in their natural environment. Therefore, they are prime candidates for test to determine their resistance to other forms of radiation.

We continue to develop an analog model of South American land ecosystems in order to assess their biogeochemical cycles in the past (“hind-casting” these cycles). We completed databases for the following key model parameters: Length of Growing Season, Potential Evapo-Transpiration, soil nitrogen, Volcanic, Orbital and Solar factors, and other proxies of past biological activity and climate. Using satellite remote sensing data, we measured the spectral changes in South American plant cover linked to “El Niño” Southern Oscillation over the period of 1982-2000. We calibrated the model by creating 160 calibration stations, each with 20-year data and monthly resolution in order to capture maximum variation. Thus we improved our reconstruction of past Sea Surface Temperatures at 1-year resolution for the last 750 years and are extending it to 2,500 years to help predict past NDVI (vegetation “density”). To move beyond the relatively short time span of the tree-ring record, we conducted pollen analyses that are yielding further detail and larger time windows [present to 9300 years ago] for our research in Patagonia and in Tierra del Fuego [present to 10,000 years ago].

Figure 7. Correlation between SST and NDVI in South America. (Insert) Measuring and Calibration Stations.

The Ames Team’s Education and Public Outreach Project sustained its partnerships with California Academy of Sciences (CAS) and Yellowstone National Park (YNP) but also pursued other significant activities. The team authored the chapter on thermophiles and astrobiology in the new 2006 edition of the Yellowstone Resources and Issues guide. All nine permanent large “way side” (trail) ceramic signs that interpret thermophilic microorganisms and astrobiology have been installed in YNP. The team submitted extensive recommendations on astrobiology and microbiology content in exhibits for the new Old Faithful Visitors Center. A new astrobiology-themed exhibit, “Xtreme Life” was opened at the California Academy of Sciences. The exhibit, for which every phase of design and review involved Ames team members, will be viewed by potentially hundreds of thousands of visitors during its two-year run. The project now enters an initial design phase for a permanent astrobiology exhibit for the new CAS facility, to open in 2008. Team members were actively involved in the past year’s Jason Project, “Mysteries of Earth and Mars,” which prominently featured our work with hypersaline microbial mats as an analog activity. Team members participated in an intensive weeklong workshop, “Life at the Limits: Earth, Mars and Beyond”. This Lunar Planetary Institute-organized workshop enriched the teaching of science at the secondary school level by exposing teachers to astrobiology-related field and classroom experiences. The Ames team education and public outreach lead continues to work with curriculum developers at TERC Corporation to create new astrobiology products. The Ames team designed and launched a new website which features education and public outreach, and research efforts and accomplishments (http://www.amesteam.arc.nasa.gov).

Figure 8. This sign installed this year at Excelsior Crater in Midway Geyser Basin, is one of nine signs that were funded by NAI and that present astrobiology content contributed by the Ames team.

The Ames team maintained its ongoing substantial presence on NASA missions. The P.I. is a science operations planning lead for the Mars Exploration Rover mission. A team Co-I is also P.I. of the CheMin XRD spectrometer for the Mars Science Laboratory mission. Another Co-I serves as a Co-I with NASA’s Kepler mission. Several team members contribute to the SOFIA mission and others are involved with missions that are either scheduled or planned.