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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:

• Continued radial velocity measurements of the 2,000 Sun-like stars within 50 parsecs yielded a number of new extrasolar planet candidates, including the first Neptune-mass planet, the first terrestrial-planet analogue, and the second nearby bright transiting planet. Velocity measurement precision of 1 m/s has been achieved routinely at the Keck and Anglo-Australian Telescopes.
• Construction proceeded 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.
• High-contrast visible light imaging and novel spatially resolved spectra of the disk surrounding the young star TW Hydrae revealed a warp and smaller grains in the inner part of the disk. Both could result from collisions induced by a planet already formed within the disk.
• Far-ultraviolet spectroscopy of the disk around the 12-Myr-old M star AU Microscopii showed that most of the primordial gas has been removed from the disk. A giant planet orbiting this low-mass star, as others have suggested, would be difficult to form by traditional core-accretion. The low gas contents of AU Mic and its more massive cousin Beta Pictoris indicate that the gas dissipation mechanism is largely independent of the luminosity of the central star.
• A newly developed semi-analytical model for the oligarchic growth stage of planet formation predicts the formation of Earth-mass terrestrial planets in the habitable zone of a Sun-like star.
• Theoretical models of the diversity and signature of extrasolar planets led to the prediction of a new type of terrestrial planet with a substantial fraction of carbon.

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 group of chondritic meteorites indicate that these meteorites contain interstellar organic matter that resembles refractory organic matter in comets and interplanetary dust particles. 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.
• Chemical, isotopic, and nuclear magnetic resonance measurements on high-purity samples of IOM from other primitive chondritic meteorites have revealed complex but systematic trends attributable to parent body processing of a common precursor that resembled the insoluble organic matter in CR chondrites.
• The first confocal Raman images of IOM from primitive chondrites reveal variations in Raman band characteristics that correlate with the composition of the organic matter and with the extent of parent body metamorphism. Raman imaging may prove to be a useful non-destructive technique for analyzing organic matter in Stardust samples and classifying unequilibrated chondritic meteorites.
• The documentation of extreme isotopic heterogeneity of carbon in a partially differentiated meteorite raises questions concerning the extent of parent body melting needed to achieve carbon isotopic homogeneity and the origin of carbon heterogeneity on Earth.
• Trace element concentrations in clays and hydrous silicates in contact with carbonates and halites in Martian meteorites indicate that these samples were subjected to multiple episodes of aqueous alteration while on Mars.

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

• Experimental studies of metal-sulfide-promoted prebiotic chemistry showed that pyrite can reductively demethylate certain compounds formed by catalyzed hydroformylation reactions to yield succinic acid. That an abiotic pathway links the methylated intermediates with four-carbon dicarboxylic acids strengthens the hypothesis that metal sulfide catalysis provided a critical connection between environmental chemistry and the emergence of life.
• A newly developed laser fluorination gas chromatograph mass spectrometer permits measurements of multiple isotope ratios at nanomole levels of sulfur. This tool is being applied to refine the isotopic analysis of sulfide mineralogy in Archean drill cores.
• Measurements of multiple sulfur isotopes in experiments with sulfate-reducing, sulfur-disproportionating, and thisulfate-disproportionating bacteria progressed toward the goal of deconvolving mass-dependent sulfur fractionations associated with metabolic and biogeochemical networks. Analysis of four sulfur isotopes as a tracer of post-Archean biochemical cycles promises to decouple mass-dependent and mass-independent fractionation.
• A method was developed to conduct high-precision abundance measurements of organic nitrogen isotopes on nanomole-size samples. The method is being applied to organic inclusions in Archean rocks and meteorites.

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

• A “PAH world” model for life’s origins was developed by which self-organized stacks of PAH molecules provide a template for the first, RNA-like, self-replicating genetic polymer.
• DNA microarray technologies were applied for the first time 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 theoretical study of molecular adsorption onto mineral surfaces demonstrated that strong chiral adsorption requires three points of bonding between the molecule and mineral, a result that clarifies the contrasting behavior of the amino acids alanine and aspartic acid on calcite surfaces.
• Organic molecules, including amino acids and nucleobases, were shown to be rapidly removed from an acidic hot spring environment by adsorption on clay minerals, a phenomenon that may point to a mechanism for the prebiotic selection and organization of biomolecules.

Svalbard is the target of annual field excursions by the Arctic Mars Analog Svalbard Expedition (AMASE), which includes participation by several investigators from the Carnegie Institution.

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

• Subseafloor archaea related to the most abundant group of archaea in seawater were shown to have genes for nitrogen fixation. That these potential nitrogen-fixing archaea are found in deep seawater near mid-ocean ridges but not in deep seawater off axis suggests that this group of archaea circulates through the N-poor subseafloor as part of their life cycle.
• Characterization of a microbial community at the 3.5-Ma Baby Bare Seamount revealed a higher diversity of microorganisms than expected, including anaerobic hyperthermophiles and hydrogen-utilizing thermophiles. These diverse organisms must have novel metabolisms and physiologies that allow for growth in the absence of nutrients derived from photosynthesis.
• Study of microbial biofilms formed on minerals in subseafloor habitats at Axial Volcano on the Juan de Fuca Ridge yielded evidence for biofilm formation at temperatures considerably higher than 121°C, the highest growth temperature so far demonstrated for isolated microbes.
• Collection of new samples of Fe-oxidizing bacteria from the Loihi Seamount and new methods for obtaining and culturing DNA from these organisms led to their reclassification as a deeply branching group of proteobacteria.
• High-pressure, high-temperature experiments showed that methane readily forms by reduction of carbonate under conditions typical for terrestrial planetary mantles.
• In experiments designed to understand adaptations that allow microbial life to persist at high pressures, mRNA from E. coli cells subjected to pressures up to 2 GPa was isolated for DNA microarray analysis to identify genes turned off and on in response to pressure.

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.
• Raman spectroscopy, energy-dispersive X-ray microanalysis, and time-of-flight secondary ion mass spectrometry of mineralized bacterial sheaths produced by Fe-oxidizers within a modern iron seep demonstrate a complexity in the distribution of molecular species that points to the difficulty of identifying biosignatures in ancient samples that have suffered some level of modification.
• Stable C, N, O, and H isotope analyses of samples from the Mars analog site in Svalbard demonstrate a range of biogenic and abiogenic sources of carbon compounds that can potentially be sorted on the basis of coupled isotopic anomalies and geobiological context.
• New organic geochemical analyses of extracts from late Archean shale and carbonate rocks form Western Australia substantiate earlier documented relationships among lipid biomarkers, carbon isotopes, and rock types. These results support syngenicity between fossil lipids and their host rocks and indicate biological cycling of oxygen 400 My before the steep rise of atmospheric oxygen.
• Pyrolysis gas chromatography mass spectrometry and ¹³C solid-state nuclear resonance spectroscopy have illuminated the chemical transformations that accompany the conversion of modern organic matter into plant fossils.

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 has been tested in a Mars analog environment on Svalbard. Results were confirmed with other biotechnology tests including ATP measurements, DNA amplification using degenerate species and gene-specific primers, and an enzyme-based test for cell wall components.
• A proposal to test microarrays for radiation exposure in low Earth orbit on the European Space Agency Biopan series of missions was approved. A 2006 flight will carry both protein and DNA microarrays.
• In another application of similar technology, a hand-held device will be flown on 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.