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2008 Annual Science Report

Carnegie Institution of Washington Reporting  |  JUL 2007 – JUN 2008

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 possible 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 planetesimal fragmentation and planet migration show that fragmentation increases the growth rates of planets, whereas migration impedes planet formation except under a limited range of circumstances, typically when the protoplanetary disk accretion rate is high.
  • 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, routinely detect new Neptune-mass planets and are beginning to probe the terrestrial planet mass regime.
  • The acquisition of new near-infrared filters is enabling the spectrophotometry of faint, distant Solar System objects, such as Kuiper Belt Objects, to identify water and methane ices on their surfaces.
  • New models for the transport of dust in the early solar nebula can account for the delivery of high-temperature materials to the formation region of comets, consistent with findings from the Stardust mission

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

  • Correlated structural and chemical analysis of ultra-thin samples of isotopically characterized insoluble organic matter (IOM) from two CR chondrites has revealed a wide range of microstructures and functional-group chemistry that is not related in a simple way to isotopic composition.
  • From analyses on extremely D- and 15N-rich matter in meteorites and highly primitive interplanetary dust particles (IDPs), carbonaceous nanoglobules appear to be present in carbonaceous chondrites, ordinary chondrites, IDPs, and samples of comet dust.
  • Continued analysis of comet Wild-2 samples returned by the Stardust mission has shown that cometary organic particles display a wide range of aromatic and aliphatic contents; atomic N/C and O/C ratios reveal a wide range in heteroatom content and are in all cases higher than those of primitive meteoritic IOM.
  • From C-XANES analysis, a robust spectral feature has been identified whose intensity correlates with the thermal history of the asteroidal parent bodies from which chondritic organic matter originated; this relation permits a precise determination of the effective temperature of metamorphism of a given chondritic meteorite from laboratory kinetic studies.
  • The characterization of graphite whiskers within high-temperature inclusions in CV3 chondrites, identified with Raman spectroscopy, raises the possibility that such material may be a significant component of interstellar space that could impact cosmological observations.
  • Analysis of kaersutite in melt inclusions from the Chassigny meteorite indicates that ancient Martian magmatic water contents were much higher than current estimates.
  • Sulfur isotope measurements on sulfate and sulfide phases in the Martian meteorites Nakhla and MIL 03346 indicate the presence of strong surface sulfur signals, implying assimilation of surface material, possibly via a salt or brine phase.

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 Gy, a result implying that those 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 predated 4 Ga.
  • As part of a larger study of abiotic nucleobase synthesis, laboratory experiments have demonstrated that, in the presence of ammonia and pyrite, significant quantities of succinic acid are generated from the aquathermolytic reaction of citrate and citramalate.
  • In early experiments testing the idea that specific minerals promote oxidation of saturated acids to olefinic acids, rapid synthesis of both orotic acid and uracil was demonstrated from fumaric acid under aqueous conditions, but the ultimate yield was low; a substantial increase in yield at elevated pressure (e.g., 300 MPa), however, is prompting a new look at this pathway.

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

  • A theoretical model for the attachment of the amino acid glutamate to iron oxide surfaces in aqueous environments, anchored by available experimental observations, predicts that at high concentrations of the elongate amino acid glutamate molecules attach by one end and “stand up” on the surface; this alignment could provide a mechanism for chiral selection and peptide bond formation.
  • Studies of the adsorption of nucleic acid components on rutile surfaces in water show that adsorption affinity varies greatly with molecular structure and with the base substituent, suggesting an interaction between the two-position substituent of the heterocyclic rings and the mineral surface.
  • In an ongoing study of chiral selection on mineral surfaces, the development of a field-amplified sample stacking strategy together with use of a bubble capillary and detection at low wavelengths permitted the determination of an enantiomeric excess of 3-carboxy adipic acid adsorbed on calcite and feldspar at concentration levels as low as a few nanomoles of compound.
  • A new framework was developed for mineral evolution on Solar System bodies, beginning with those minerals in the pre-solar nebula; progressing through those enabled by the activities of water, carbon dioxide, and oxygen; and culminating in those generated under conditions far from equilibrium by living systems.

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

  • An examination of subseafloor microbial community diversity from diffuse-flow hydrothermal vent sites on the Juan de Fuca Ridge, using terminal restriction fragment length polymorphism and 16S rRNA gene sequence analysis, showed that individual vents harbored distinct community structures, pointing to biogeographic barriers or environmental selection effects.
  • In a study of microbial colonization of newly formed hydrothermal vent sulfide chimneys on the Juan de Fuca Ridge, phylogenic analyses indicate that microbial assemblages in chimney interiors are dominated by a few archaeal phylotypes, implying that microbial diversity is low and dominated by iron-reducing and methane-producing Archaea, perhaps colonists originating from subseafloor diffuse-flow fluids.
  • Genomic analysis of Arctic microbial communities during AMASE expeditions to Svalbard indicates that field analysis yields a richer diversity of microorganisms than do parallel investigations conducted on samples returned to the laboratory, emphasizing the importance of in situ analysis in such studies.
  • In continued studies of the response of microbial life to elevated hydrostatic pressure, archaeal halophiles have been shown to be surprisingly barotolerant; mechanisms for protection against oxidative damage, including sequestration of chlorides for scavenging of free radicals, are currently under study.
  • 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.

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.
  • Study of microbially induced sedimentary structures in fossil tidal flats from the 2.9-Ga-old Pongola Supergroup in South Africa reveal a wide range of structures similar to those found in modern settings; and optical, chemical, and isotopic analyses support biogenicity of textures and carbon of biological origin.
  • Analyses of samples collected from ultrabasic reducing springs flowing through serpentine and peridotite rocks in northern California indicate that hydrocarbons can form through abiogenic processes at sites of active serpentinization.
  • A combination of scanning transmission X-ray microscopy and micro-Raman imaging of a series of kerogens spanning a range of depths in Neogene sediments of the Shinjo Basin, Japan, have permitted a documentation of the evolution in biosignatures accompanying transformation of biopolymers to geopolymers.

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

  • The 2007 Arctic Mars Analog Svalbard Expedition (AMASE) included successful deployments of two instrument prototypes for the Mars Science Laboratory, four prototype instruments for the ESA ExoMars mission, a “cliffbot” rover, and several other instruments in development for planetary missions in the more distant future.
  • Life-detection instrumentation targeting a variety of biological and chemical molecular species continued to operate on the International Space Station (ISS); these instruments address crew health during flight and contribute toward the development of technology and procedures necessary to monitor and document biological contamination during future human and robotic missions.
  • Protein microarrays containing several antibodies, fluorescent dyes, and nucleotide sequences were successfully flown in low-Earth orbit on the ESA Biopan 6 research platform aboard the Russian FOTON-M3 mission to assess the utility of microarrays in space flight missions.
  • 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.