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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 continued to make 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 planet formation that include the effects of planet migration and the acquisition of gaseous envelopes by solid planetary cores show that planets can survive the effects of migration and that the likelihood of planet formation and survival is greater in low-mass protoplanetary disks.
• Spectroscopic observations of reflected light from circumstellar disks show that disks typically display red spectra, whereas common materials of the interstellar medium such as silicates should scatter neutrally, a result that favors the presence of organic-rich materials such as tholins and suggests that building blocks of life are common in the later stages of planet formation.
• The Carnegie Astrometric Planet Search Camera (CAPSCam) was completed and mounted on the 2.5-m du Pont telescope at the Las Campanas Observatory and has begun astrometric searches for extrasolar planets.
• Continued radial velocity measurements of the nearest stars, now being made with a precision of 1 m/s, led to the discovery of 24 new extrasolar planets over the past year, 60% of the new planets announced during that period.
• The first (mid-infrared) spectrum of an extrasolar planet showed that no water vapor absorption features were present but detected a possible silicate emission feature.
• Photometric observations revealed the hottest planet yet known, indicating a planet with a stratosphere, and the first thermal emission from a Neptune-mass extrasolar planet.

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:

• The preparation of high-purity samples of insoluble organic matter (IOM) from the most primitive chondritic meteorites has continued and has provided a basis for selection of samples for more detailed analysis by a broad range of methods; this program has identified CR chondrites as hosts of the most primitive IOM and a particular CR2 meteorite (EET92042) with an elemental composition similar to that of comet Halley CHON particles.
• The highest abundances of amino acids ever measured in a meteorite were found in two primitive CR chondrites; these abundances are presumably much closer to the original amino acid contents of the parent bodies prior to any aqueous alteration and will aid in understanding how these astrobiologically important molecules formed in the interstellar medium or the early Solar System.
• Ion imaging of IOM from the most primitive chondrites has shown that such samples contain the same isotopic hotspots (enriched in D and/or 15N) as interplanetary dust particles, evidence that such IOM formed in the interstellar medium.
• All of the microanalytical techniques developed for study of the IOM in meteorites and IDPs were applied to the samples of comet Wild-2 returned by the Stardust mission as part of the efforts of NAI team members who were members of the Stardust Preliminary Examination Team.
• The first observation of hydrous ferric iron sulfate (jarosite) in a Martian meteorite (MIL 03346) provides sample context for remote sensing observations of sulfate deposits by the Mars Express orbiter and the identification of jarosite in sulfate-rich sediments on the Martian surface by the Opportunity rover.

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

• Oxygen isotope analysis of early Archean rocks and minerals, as well as of Proterozoic and more recent samples, shows no evidence for variations in isotope systematics over the past 4.1 Gy, a result that constrains 4.1 Ga as the minimum age of the events (e.g., accretion, magma ocean formation, core formation, Moon-forming giant impact) that exchanged and equilibrated Earth’s oxygen throughout the crust and mantle.
• High-resolution sulfur measurements of Astrobiology Drilling Program Core 9 show clear correlations with other drill cores obtained from the same basin and point to a correlation between isotope systematics and stratigraphic position that will be a focus for future studies.
• A new sample loading method has enabled a range of experimental studies of kinetic isotope fractionation associated with carbon fixation via hydrocarboxylation, a metal-sulfide-catalyzed reaction that mimics the action of acetyl CoA synthase; experiments to date verify that such surface-catalyzed reactions have high yields and provide credibility to the idea that transition-metal sulfides may have provided important catalytic functionality to the early Earth.
• 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:

• Microarray technologies, coupled with analysis procedures using time-of-flight secondary ion mass spectrometry, continued to be refined for use in the combinatoric study of interactions between organic molecules and mineral surfaces that may mimic organic molecular selection on the prebiotic Earth.
• Experiments in aqueous media at elevated temperature and confining pressure demonstrated that abiotic synthesis and subsequent condensation reactions of aliphatic lipid compounds are possible under hydrothermal conditions and that such molecules have robust properties of self-assembly into membranous structures that would be suitable boundary structure for primitive cellular life.
• 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:

• Ongoing study of microbial diversity and physiology at diffuse-flow vents in active hydrothermal vent environments and in ancient oceanic seeps show that microbial diversity varies among vent sites and changes with time at any given site and that fluid temperature and mixing of hydrothermal vent fluid with seawater are key factors affecting microbial community composition.
• 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.
• 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.
• Characterization of Fe-oxidizing bacteria from the Loihi Seamount demonstrated that the proteobacterium Mariprofundis ferrooxydans can form iron-oxide nanofibrils by cell excretion in directions influenced by gradients in Fe(II) and oxygen, suggesting a form of mechanotaxis not previously described in prokaryotes and possibly related to structures with similar preferred orientations documented in the fossil record.
• To extend studies of the response of microbial life to elevated hydrostatic pressure, incorporation of large-volume apparatus is underway in order to permit the collection of bulk material for nucleic acid microarray analysis as well as the initiation of studies of long-term adaptation to high pressure.
• High-pressure, high-temperature experiments showed that novel compounds, such as H2O-H2 and CH44, are stable over wide ranges of pressure and temperature in the icy satellites of the outer Solar System.

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

• Carbon analyses of Paleoproterozoic stromatolitic phosphorite deposits from the Aravilli Supergroup, India, reveal distinct biosignatures and point to a high degree of primary production during sedimentation.
• Laboratory experiments run at pressures and temperatures appropriate to the deep crust reveal that strictly abiotic carbon fixation exhibits 13C fractionation indistinguishable from biological fixation; in contrast, D/H fractionation differentiates between abiological and biological fractionation.

• 14C dating of organic compounds from hydrothermal hot springs in Kamchatka reveal that these molecules were derived from hydrothermal alteration of algal and bacterial mat detritus buried by volcanic ash.
• A combination of scanning transmission X-ray microscopy and micro-Raman imaging of a series of kerogens spanning a range of depths reveals the evolution in biosignatures accompanying transformation of biopolymers to geopolymers.

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

• Life-detection instrumentation targeting a variety of biological and chemical molecular species was flown for the first time on the International Space Station (ISS) during May-April 2007; an extended array of application is planned as new cartridges are launched to the ISS.
• Protein microarrays containing several antibodies, fluorescent dyes, and nucleotide sequences will be flown in low-Earth orbit on Biopan 6 to assess the utility of microarrays in space flight missions.
• The 2006 Arctic Mars Analogue Svalbard Expedition (AMASE) included successful deployments of a Cliffbot rover, two instrument prototypes for the Mars Science Laboratory, and several other instruments in development for planetary missions.

Figure 1. Microbes at a thermal spring, Bockfjord, Svalbard, AMASE 2006.

Figure 2. Postdoctoral Fellow Jennifer Eigenbrode taking an ice core at Friedrichbreen, Svalbard, AMASE 2006.

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.