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Executive Summary

The NAI team led by the Carnegie Institution of Washington is studying the evolution of organic compounds from prebiotic molecular synthesis and organization to cellular evolution and diversification. Our program attempts to integrate the sweeping narrative of life’s history through a combination of bottom-up and top-down studies. On the one hand, we study processes related to chemical and physical evolution in plausible prebiotic environments — the interstellar medium, circumstellar disks, extrasolar planetary systems, the primitive Earth, and other Solar System objects. Complementary to these bottom-up investigations of life’s origin, we carry out field and experimental top-down efforts to document the nature of microbial life at extreme conditions and the characterization of organic matter in ancient fossils. Both types of efforts inform our development of biotechnological approaches to life detection on other worlds.

Our team’s research activities focuses on life’s chemical and physical evolution, from the interstellar medium, through planetary systems, to the emergence and detection of life, across seven integrated areas of research:

1. We are applying theory and observations to investigate chemical evolution in the interstellar medium, in circumstellar disks, during planetary formation, and on Solar System bodies.
2. We are carrying out analytical research on extraterrestrial samples, including meteorites and interplanetary dust particles, with an emphasis on organic molecules and evidence for water.
3. We are studying prebiotic chemical and isotopic evolution on Earth, with an emphasis on the sulfur cycle and the role of sulfur in prebiotic organic synthesis.
4. We are investigating possible mechanisms of prebiotic molecular selection and macromolecular organization, including the self-organization of amphiphiles and the selective adsorption of organic molecules onto mineral surfaces.
5. We are continuing to study life in extreme environments, with field studies of hydrothermal microbial communities and laboratory studies of stress adaptation of microbes in high-pressure and high-temperature environments.
6. We are examining ancient fossils and microbes fossilized in the laboratory with a variety of analytical techniques to assess preservation mechanisms of molecular and isotopic biosignatures, and we are studying modern geothermal systems to investigate preservation of biosignatures during silicification in these environments.
7. We are applying our enhanced understanding of life’s chemical and physical evolution to develop new techniques in astrobiotechnology — procedures that will be applied to the design and testing of instruments for life detection, initially in terrestrial settings and eventually on spacecraft to be sent to other Solar System bodies.

Fuller understanding of life’s origin, evolution, and distribution requires major advances on all these topics, as well as the extensive challenge of integrating these topics. During the past year we achieved significant progress in each of these research areas, and we devoted increased attention to the interfaces among these theoretical, experimental, and field approaches.

Among the highlights from the past year’s research in the area of the evolution from molecular clouds to habitable planetary systems were the following:

• New models for the oligarchic growth stage of planet formation predicts that terrestrial planet precursors and giant planet cores grow more rapidly (10⁵ and 10⁶ yr, respectively) than in some previous models, the result of disequilibrium between the processes that determine planetesimal velocities, collisional fragmentation, and capture of fragments by primordial atmospheres.
• Spectroscopic observations of the Beta Pictoris disk show it to be carbon rich, with a C/O ratio 18 times solar, the result either of impact disruption of carbon-rich planetesimals or outgassing of methane from large planetesimals at much higher rates than water and other oxygen-containing materials.
• The observation of silicate dust around the white dwarf GD 362 indicates that the dust around this old, post-main-sequence stellar remnant formed by the tidal disruption of a large asteroid.
• The disk around young star HR 4796A has an extremely red color that matches that of material made up of long organic chains and seen on outer Solar System bodies.
• Continued radial velocity measurements of the nearest 1,000 stars, now being made with a precision of 1 m/s, are sensitive to terrestrial-mass planets in small orbits and Saturn-mass planets orbiting beyond 5 AU.
• The thermal emission was measured from the transiting planet around bright star HD189733.
• Construction continued on the camera system for the Carnegie Astrometric Planet Search, to be dedicated to the long-term search for astrometric signatures of extrasolar planets around low-mass stars.

Highlights in the area of extraterrestrial materials and the origin and evolution of organic matter in the Solar System during the past year included the following:

• Chemical and isotopic analysis of high-purity samples of insoluble organic matter (IOM) from the CR and CM groups of chondritic meteorites indicate that these meteorites contain interstellar organic matter that resembles refractory organic matter in comets and interplanetary dust particles (IDPs). Little is known about how this complex and enigmatic material forms in the interstellar medium, but the relatively large amounts that can be isolated from CR chondrites will greatly facilitate its study.
• Raman spectra of high-purity samples of IOM from a range of primitive chondritic meteorites support the view that the chondrites all accreted similar IOM but have undergone different degrees of parent-body metamorphism.
• All of the microanalytical techniques developed for study of the IOM in meteorites and IDPs are being applied to the samples of comet Wild-2 returned by the Stardust mission as part of the efforts of NAI team members who are part of the Stardust Preliminary Examination Team.
• Documentation of a remarkable degree of carbon isotope heterogeneity in a partially differentiated meteorite has raised questions about the extent of planetary melting needed to achieve carbon isotope homogeneity, the origin of carbon isotopic heterogeneity on Earth, and the ultimate fate of carbon incorporated into the Earth prior to global differentiation and core formation.
• Mineralogical and textural relationships in alteration assemblies in Martian meteorites, together with information from stable isotope chemistry and secondary mineralization, have indicated that fluid alteration of the host rocks of Martian meteorites was not extensive and was probably limited in space and time.

Highlights in the area of prebiotic chemical and isotopic evolution on Earth during the past year included the following:

• The facile synthesis of succinate from citrate under hydrothermal conditions has been ruled out as an effective pathway. Instead succinate probably formed through dehydration and subsequent decarboxylation of citrate to yield itaconate; hydration of exomethylene carbon yields methylsuccinyl alcohol, and a retroaldol reaction of methysuccinyl alcohol yields succinate and formaldehyde.
• Sulfur isotope signatures of different sulfur metabolisms were determined for the first time, including those for sulfate-reducing, sulfite-disproportionating and sulfur-disproportionating bacteria, and these signatures permitted the calibration of global sulfur isotope models to constrain the relative proportions of sulfide burial and sulfide reoxidation in the sulfur cycle.
• Required sample sizes for the newly developed laser fluorination gas chromatograph mass spectrometer have been reduced from a few micromoles to approximately ten nanomoles. This tool is revealing micrometer-scale sulfur isotope heterogeneity in fresh drill core samples of Archean terrain, critical to mapping the microstructure of Archean microbial communities.
• A new suite of minerals was synthesized in order to explore their catalytic qualities, including tungstenite (WS₂), molybdenite (MoS₂), and awaruite (Ni₃Fe), all minerals found in aqueously altered mafic rocks. Preliminary results reveal substantial catalytic activity for carbonyl insertion chemistry.

Highlights in the area of prebiotic molecular selection and organization during the past year included the following:

• DNA microarray technologies continued to be applied to the combinatoric study of interactions between organic molecules and mineral surfaces that may mimic the selection of organic molecules from the prebiotic “soup.”
• A significant advance in the power of microarray identification was the recognition that specific mass fragments permit sugars and amino acids to be distinguished.
• Studies of the formation of RNA oligomers on the clay mineral sodium montmorillonite showed that rates of formation differ significantly among oligomers, implying that only a limited number of oligomers could have formed by this mechanism on the early Earth, rather than equal amounts of all possible oligomers.

Highlights in the area of life in extreme environments during the past year included the following:

• A deep subseafloor methanogen was shown to be capable of fixing nitrogen at 92°C, almost 30°C higher than has ever been observed for nitrogen fixation. This work expands the temperature of nitrogen fixation into the hyperthermophilic range.
• A single species of Archaea within biofilms inside carbonate chimneys in the Lost City Hydrothermal Field on the Mid-Atlantic Ridge was shown both to produce and to oxidize methane. The two metabolically diverse cells of the single species appear in obligatory, symbiotic association.
• Characterization of a microbial community at the 3.5-Ma Baby Bare Seamount point to a subsurface hydrothermal system that harbors a high diversity of archaea and bacteria, including hyperthermophiles and organisms that use carbon dioxide as their carbon source and hydrogen as their energy source.
• Characterization of Fe-oxidizing bacteria from the Loihi Seamount demonstrated that PV-1, a deeply branching member of the proteobacteria, forms a unique filamentous Fe-oxide with secondary minerals and other attributes not known to be produced by any abiological processes. These organisms are being studied as possible biomarkers.
• High-pressure, high-temperature experiments showed that novel compounds, such as H₂O-H₂ and CH₄(H₂)₄, are stable over wide ranges of pressure and temperature in the icy satellites of the outer Solar System.
• A set of expression arrays is being developed to identify novel proteins involved in the adaptation of S. oneidensis MR-1 and E. coli K-12 to pressures as high as 2-3 GPa.

Highlights in the area of molecular and isotopic biosignatures during the past year included the following:

• Carbonate globules in mantle xenoliths from a Mars analog site in Svalbard, morphologically similar to carbonate globules in Martian meteorite AL84001, include hematite and magnetite within distinct zones and carbon in conjunction with magnetite, zonation patterns most likely formed during the precipitation of carbonate from a CO₂-rich hydrothermal fluid percolating through the mantle.
• Sedimentary structures in Early Archean sandstones of the 3.2-Ga Moodies Group, South Africa, have been shown to have a biological origin on the basis of microstructural features and stable C isotope analyses together with comparative studies of similar tidal habitats throughout Earth history to the Recent. On the basis of this study, siliciclastic tidal flat settings have been the habitat of thriving microbial ecosystems for at least the last 3.2 billion years.
• Stable C isotope analyses of samples from the Murchison chondrite show non-terrestrial isotopic signatures in nucleobases and structurally related compounds. These data provide strong evidence that nucleobases, or their precursors, were delivered to the early Earth by meteorite infall.
• Laser fluorination mass spectrometry has been demonstrated to be capable of distinguishing kinetically controlled processes from equilibrium biochemical and geochemical processes on the basis of the slope of data points on oxygen isotope diagrams.
• X-ray absorption near-edge spectroscopic analysis of Archean kerogens from the 2-7-Ga Hammersley Basin, Australia, indicate that the kerogens retain considerable carbon, nitrogen, and oxygen functional group information that signifies their biological origins, despite significant geochemical transformation of the host rocks. These studies provide a basis of the examination of even more ancient kerogens whose origins are controversial.

Highlights in the area of astrobiotechnology during the past year included the following:

• Life-detection instrumentation utilizing microfluidics to prepare samples for inoculation onto DNA and protein microarrays was field tested in a Mars analog environment on Svalbard. The antibodies chosen monitored for the presence of contaminant bacteria associated with human handling and lipopolysaccharides and were used as a control for contamination during sampling of ice cores from carbonate caves that are sources for ALH84001-analog carbonate globules.
• A portable test system utilizing this technology was field tested in a lunar analog site to monitor how human expeditions bio-contaminate their environment during extra-vehicular activities on a lunar or planetary surface.
• In another application of similar technology, a hand-held device will be flown on Shuttle flight STS 116A to the International Space Station to detect and monitor potentially harmful bacteria and fungi in the cabin environment.

In summary, our team’s recent research, including discoveries and characterization of new planetary systems, investigation of the fates of carbon and water on planetary building blocks and other worlds, elucidation of robust pathways for prebiotic organic synthesis, documentation of novel microbial metabolic strategies, evaluation of possible biosignatures, and development of new technologies for astrobiological exploration, inform the central questions of astrobiology. Taken together, these discoveries are changing our views of life’s origin and its possible distribution in the universe.