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2009 Annual Science Report

NASA Ames Research Center Reporting  |  JUL 2008 – AUG 2009

Executive Summary

This report summarizes the efforts of the current Ames Team during the first nine months of the CAN-5 performance period and the final efforts of the previous Ames Team under CAN-3. The Ames CAN-3 Team addressed the development of habitable planetary environments, the origins of biological functions, biosignatures created by microbial ecosystems fueled by light or by chemical energy, and the survival of life in space and in changing environments on Earth.

The current Ames Team addresses the cosmochemical, planet-forming, geochemical, and biological processes that combine to create habitable environments. We trace, spectroscopically, the cosmic evolution of organic molecules from the interstellar medium to protoplanetary disks, planetesimals and finally onto habitable bodies. We characterize the diversity of planetary systems emerging from protoplanetary disks, with a focus on the formation of planets that provide chemical raw materials, energy, and environments necessary to sustain prebiotic chemical evolution and complexity. We are developing and evaluating a more quantitative methodology for assessing the habitability of early planetary environments – particularly Mars – via capabilities that will be, or might be, deployed in situ. Finally, we are identifying critical requirements for the emergence of biological complexity in early habitable environments by examining key steps in the origins and early evolution of catalytic functionality and metabolic reaction networks. The direct involvement in multiple NASA missions provides context, motivation, and collaborative opportunities for our research and our education and public outreach efforts. Please visit http://www.amesteam.arc.nasa.gov/.

We have measured the spectra and chemistry of materials under simulated space conditions in the laboratory. We have incorporated our unique collection of polycyclic aromatic hydrocarbon (PAH) spectra into a user-friendly database.

We are finalizing for web launch the tools needed to query the database and analyze astronomical spectra. This database will revolutionize how astronomers analyze PAH spectra, helping them to understand how carbonaceous species evolve across the universe. We published five PAH-related papers. We have also published one paper and are working on several others describing reactions that produce prebiotic compounds, such as nucleobases, by UV irradiation of cosmic ices. These results will be used to interpret astronomical observations made with ground-based and orbiting telescopes. We conducted experiments on simulated extraterrestrial materials to analyze extraterrestrial samples returned by NASA missions and also those that fall to Earth in meteorites. We received an NAI DDF grant to investigate the modification of organic materials under interstellar conditions via UV-Visible spectroscopy, particularly PAH. We continue to be intimately involved with the extraction, distribution, and analysis of samples from Comet 81P/Wild 2 returned by the Stardust mission. We are participating in the Hayabusa asteroid sample return mission; this sample is due back to Earth in June 2010. An Ames Team member is a science team member with the O/OREOS (Organisms/ORganics Exposure to Orbital Stresses), which is NASA’s first Astrobiology Small Payloads mission. We are contributing specifically to the SEVO (Space Environment Viability of Organics) component of O/OREOS.

We examined the processes leading to the development of planets in circumstellar habitable zones. We extended previous models of the photodissociation region of the protoplanetary disk and included the freezing of species, simple grain surface chemistry and desorption of ices. Under certain conditions in the opaque cloud interiors, we find that gas-phase elemental oxygen freezes out as water ice and that the elemental C/O abundance ratio can exceed unity, leading to complex carbon chemistry. We studied viscously accreting protoplanetary disks that are irradiated by ultraviolet and X-ray photons from a solar-mass central star using static, thermo-chemical disk models and, more recently, time-dependent models. We followed disk evolution around stars of different masses and found that disk survival time is relatively independent of mass for stars with masses less than three solar masses. We also found that disks around higher mass stars are short-lived (~105 years). We continued our work on models of large-scale transport in protoplanetary disks. We have been developing numerical schemes to accurately describe turbulent diffusion and meridional advection along with chemical reactions. We reported new computations of the spatial distribution of oxygen isotopes in the protoplanetary nebula. We continued to develop the Systemic Console (SC), a flexible GUI-based computational tool for analyzing radial velocity and transit data for extrasolar planetary systems. SC users have already made several important discoveries, including the first characterizations of the low-mass planets Gl 581c, and 55 Cnc e and f. The new planet survey at Lick Observatory is using SC as the primary analysis tool. Our simulations of planet formation showed that large terrestrial planets can accrete in the inner 0.1 AU of the disks orbiting nascent red dwarf stars. A low-cost space mission such as TESS could readily detect such planets.

In order ultimately to discern the habitability (potential to support life) of ancient Martian environments as part of the effort under CAN-5, we have begun to characterize analog field sites on Earth and to develop reaction-transport models that calculate cellular energy balance as a function of geochemical environment. We visited the Josephine Ophiolite Complex (JOC) of Northern California and collected samples from each type section of the exposed ocean crust that represent differing extents and styles of parent rock alteration.

We presented our preliminary observations of the site and its minerals at the 2009 annual meeting of the Geological Society of America. Measurements by Moessbauer and X-ray diffraction are currently underway. We developed a preliminary cell-scale reaction transport model for calculating “energetic habitability.” This model calculates methanogenic energy yields for a single spherical cell in an infinite medium of defined physics and chemistry (temperature, salinity, pH, and concentrations of H2 and ΣCO2). We used the model to examine the habitability of fluids affected by serpentinization (i.e., elevated H2 and pH, and potentially decreased ΣCO2) across a range of relevant parameter space. To conclude its efforts under CAN-3, team biogeochemists are preparing for publication a long-term incubation experiment that examined the effects of variable sulfate levels (e.g., Archaean ocean levels) on sulfide isotopes as signatures of sulfur cycling in photosynthetic microbial mats. This work characterized a broader range of sulfur isotopes and sulfur species at considerably finer spatial resolution than had been achieved previously.

We documented a substantial decline in the quantity of Ni in the Proterozoic oceans compared to the Archean oceans, as measured by the amount of Ni precipitated in Banded Iron Formations. With less Ni in oceans, methanogens are put at a competitive disadvantage with respect to other fermenters such as sulfate reducers. This development probably had important consequences for global climate and the oxidation state of the atmosphere.

Ames CAN-3 team members further refined their numerical model to link microbial mats to global biosphere processes in order to reflect more details of the carbon cycles. Changes in carbon cycling affect the organisms that depend on the breakdown of photosynthate by fermentation. For example, our novel fermentation algorithm indicates consequences for the timing of sulfate reducing bacteria metabolism in the mats.

Our investigations of protobiological systems during the CAN-3 performance period will continue through the CAN-5 period. We investigated whether enzymatic activity can arise from an inventory of protein polymers that have random sequences and that might have existed in habitable environments. We recently created de novo an enzyme from a non-catalytic protein structure (scaffold) based on two structural motifs called zinc fingers with randomized loop regions. Amino acid sequence analysis revealed that the new protein very likely adopts a different three-dimensional structure. To facilitate the analysis of the structure and function of this novel enzyme we have evolved in vitro new variants of it that have higher thermal stability and activity. The core of the protein appears to be highly structured while the termini are markedly more flexible. Mutants of our protein, in which 13 amino acids at either or both ends were deleted, retain enzymatic activity of at least 10% compared to the full-length enzyme. This indicates that proteins even simpler than the original one could have exhibited catalytic functions. In parallel, we initiated computational studies to redesign another simple protein that had been created previously through in vitro evolution. This protein binds adenosine triphosphate (ATP). The objective is to change its specificity such that it will instead bind guanosine triphosphate (GTP).

One candidate structure has already been developed. It involves five single-point mutations that allow amino-acid side chains to form three favorable hydrogen bonds with GTP and prevent water from penetrating the core of the protein. Other candidate structures are being designed. Once completed, these studies will provide the first evidence that simple proteins that might have existed at the time of life’s origin could evolve and diversify their functions and structures through a small number of point mutations.

Members of the CAN-3 team assessed the potential for life to move beyond Earth and survive in potentially lethal radiation environments. A short test flight with Stanford’s BioLaunch program was conducted with a tardigrade.
The entire Ames Team has pursued diverse education and public outreach (EPO) activities that included efforts in high-impact public venues. Team research efforts have contributed source material for the team’s EPO program. We implemented a graduate-level astrobiology course at the University of California at Santa Cruz and continued an undergraduate astrobiology and space exploration course at Stanford University. We gave numerous lab tours and demonstrations to students and educators, made presentations to K-12 classrooms, universities, museums, planetariums, national park visitor centers, scientific conferences, and the media. Team members also participated in National Public Radio interviews and were filmed for shows on the Discovery Channel and National Geographic.

The Ames Team continued to forge its strong partnership with Lassen Volcanic National Park by reinforcing the connections between microbiology and astrobiology. The hydrothermal features in this park are key research targets for NASA’s astrobiology research program and they illustrate compelling aspects of astrobiology education and outreach. Team members, high school students, educators and park rangers participated in fieldwork and collected data from thermal features for NASA astrobiologists, classroom lectures, and public talks. The students examined hydrothermal features in the park and generated a database of temperature, pH, GPS coordinates, photos, and geochemical analyses that will be hosted on the NASA Ames Team website.

We developed the first of ultimately four or more astrobiology-interpretive-trailside signs. These signs will be located at hydrothermal sites that best illustrate the most compelling aspects of astrobiology research in Lassen. The Ames Team supported the implementation by Lassen Park of a Junior Park Astrobiology program for 5th through 12th graders during the upcoming school year.

The Ames Team has partnered with the Choctaw Nation to provide Native American students and their teachers access to NASA astronomers, scientists and astrobiology curriculum via five interactive seminars using NASA’s Digital Learning Network. The lectures encompassed topics such as cosmochemistry and astrobiology. In addition, the team has begun to partner with teachers at the Choctaw Nation’s Jones Academy and to help them incorporate astrobiology, astrochemistry and other astronomical topics into their science curriculum.

The Ames Team maintained its substantial presence in current and upcoming NASA missions. The P.I. is a strategic planning lead for the Mars Exploration Rover mission. A team Co-I is also P.I. of the CheMin X-ray diffraction spectrometer for the MSL mission. Other team members participate in the following ongoing or future missions: Kepler, Stardust, Stratospheric Observer for Infrared Astronomy, Mars Reconnaissance Orbiter, MSL, James Webb Space Telescope, Spitzer Space Telescope, Herschel, O/OREOS, ABE/ASPIRE, LCROSS, LADEE, and Comet Coma Rendezvous Sample Return Mission.

Publications

  • (no authors found) (2008). Science Priorities for Mars Sample Return. Astrobiology, 8(3), 489–535. doi:10.1089/ast.2008.0759

  • (no authors found) (2009). Crystal ball – 2009. Environmental Microbiology Reports, 1(1), 3–26. doi:10.1111/j.1758-2229.2008.00010.x

  • Bajt, S., Sandford, S. A., Flynn, G. J., Matrajt, G., Snead, C. J., Westphal, A. J., & Bradley, J. P. (2009). Infrared spectroscopy of Wild 2 particle hypervelocity tracks in Stardust aerogel: Evidence for the presence of volatile organics in cometary dust. Meteoritics & Planetary Science, 44(4), 471–484. doi:10.1111/j.1945-5100.2009.tb00745.x

  • Batygin, K., Bodenheimer, P., & Laughlin, G. (2009). DETERMINATION OF THE INTERIOR STRUCTURE OF TRANSITING PLANETS IN MULTIPLE-PLANET SYSTEMS. The Astrophysical Journal, 704(1), L49–L53. doi:10.1088/0004-637x/704/1/l49

  • Bauschlicher, C. W., Peeters, E., & Allamandola, L. J. (2009). THE INFRARED SPECTRA OF VERY LARGE IRREGULAR POLYCYCLIC AROMATIC HYDROCARBONS (PAHs): OBSERVATIONAL PROBES OF ASTRONOMICAL PAH GEOMETRY, SIZE, AND CHARGE. The Astrophysical Journal, 697(1), 311–327. doi:10.1088/0004-637x/697/1/311

  • Blank, J. G., Green, S. J., Blake, D., Valley, J. W., Kita, N. T., Treiman, A., & Dobson, P. F. (2009). An alkaline spring system within the Del Puerto Ophiolite (California, USA): A Mars analog site. Planetary and Space Science, 57(5-6), 533–540. doi:10.1016/j.pss.2008.11.018

  • Blum, J. S., Han, S., Lanoil, B., Saltikov, C., Witte, B., Tabita, F. R., … Oremland, R. S. (2009). Ecophysiology of “Halarsenatibacter silvermanii” Strain SLAS-1T, gen. nov., sp. nov., a Facultative Chemoautotrophic Arsenate Respirer from Salt-Saturated Searles Lake, California. Applied and Environmental Microbiology, 75(7), 1950–1960. doi:10.1128/aem.02614-08

  • Boersma, C., Bauschlicher, C. W., Allamandola, L. J., Ricca, A., Peeters, E., & Tielens, A. G. G. M. (2010). The 15–20  μ m PAH emission features: probes of individual PAHs?. A&A, 511, A32. doi:10.1051/0004-6361/200912714

  • Boersma, C., Mattioda, A. L., Bauschlicher, C. W., Peeters, E., Tielens, A. G. G. M., & Allamandola, L. J. (2008). THE 5.25 AND 5.7 μm ASTRONOMICAL POLYCYCLIC AROMATIC HYDROCARBON EMISSION FEATURES. The Astrophysical Journal, 690(2), 1208–1221. doi:10.1088/0004-637x/690/2/1208

  • Boersma, C., Mattioda, A. L., Bauschlicher, C. W., Peeters, E., Tielens, A. G. G. M., & Allamandola, L. J. (2009). ERRATUM: “THE 5.25 AND 5.7 μm ASTRONOMICAL POLYCYCLIC AROMATIC HYDROCARBON EMISSION FEATURES” (2009, ApJ, 690, 1208). The Astrophysical Journal, 694(1), 704–705. doi:10.1088/0004-637x/694/1/704

  • Bouwman, J., Paardekooper, D. M., Cuppen, H. M., Linnartz, H., & Allamandola, L. J. (2009). REAL-TIME OPTICAL SPECTROSCOPY OF VACUUM ULTRAVIOLET IRRADIATED PYRENE:H 2 O INTERSTELLAR ICE. The Astrophysical Journal, 700(1), 56–62. doi:10.1088/0004-637x/700/1/56

  • Davis, S. S. (2009). An analytical model for a transient vapor plume on the Moon. Icarus, 202(2), 383–392. doi:10.1016/j.icarus.2009.03.019

  • Des Marais, D. J., Allamandola, L. J., Benner, S. A., Boss, A. P., Deamer, D., Falkowski, P. G., … Yorke, H. W. (2003). The NASA Astrobiology Roadmap. Astrobiology, 3(2), 219–235. doi:10.1089/153110703769016299

  • Dupraz, C., Reid, R. P., Braissant, O., Decho, A. W., Norman, R. S., & Visscher, P. T. (2009). Processes of carbonate precipitation in modern microbial mats. Earth-Science Reviews, 96(3), 141–162. doi:10.1016/j.earscirev.2008.10.005

  • Fike, D. A., Finke, N., Zha, J., Blake, G., Hoehler, T. M., & Orphan, V. J. (2009). The effect of sulfate concentration on (sub)millimeter-scale sulfide δ34S in hypersaline cyanobacterial mats over the diurnal cycle. Geochimica et Cosmochimica Acta, 73(20), 6187–6204. doi:10.1016/j.gca.2009.07.006

  • Fike, D. A., Gammon, C. L., Ziebis, W., & Orphan, V. J. (2008). Micron-scale mapping of sulfur cycling across the oxycline of a cyanobacterial mat: a paired nanoSIMS and CARD-FISH approach. ISME J, 2(7), 749–759. doi:10.1038/ismej.2008.39

  • Glavin, D. P., Dworkin, J. P., & Sandford, S. A. (2008). Detection of cometary amines in samples returned by Stardust. Meteoritics & Planetary Science, 43(1-2), 399–413. doi:10.1111/j.1945-5100.2008.tb00629.x

  • Gorti, U., & Hollenbach, D. (2008). PHOTOEVAPORATION OF CIRCUMSTELLAR DISKS BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET AND X-RAY RADIATION FROM THE CENTRAL STAR. The Astrophysical Journal, 690(2), 1539–1552. doi:10.1088/0004-637x/690/2/1539

  • Gorti, U., Dullemond, C. P., & Hollenbach, D. (2009). TIME EVOLUTION OF VISCOUS CIRCUMSTELLAR DISKS DUE TO PHOTOEVAPORATION BY FAR-ULTRAVIOLET, EXTREME-ULTRAVIOLET, AND X-RAY RADIATION FROM THE CENTRAL STAR. The Astrophysical Journal, 705(2), 1237–1251. doi:10.1088/0004-637x/705/2/1237

  • Hausrath, E. M., Treiman, A. H., Vicenzi, E., Bish, D. L., Blake, D., Sarrazin, P., … Brantley, S. L. (2008). Short- and Long-Term Olivine Weathering in Svalbard: Implications for Mars. Astrobiology, 8(6), 1079–1092. doi:10.1089/ast.2007.0195

  • Hollenbach, D., & Gorti, U. (2009). DIAGNOSTIC LINE EMISSION FROM EXTREME ULTRAVIOLET AND X-RAY-ILLUMINATED DISKS AND SHOCKS AROUND LOW-MASS STARS. The Astrophysical Journal, 703(2), 1203–1223. doi:10.1088/0004-637x/703/2/1203

  • Hollenbach, D., Kaufman, M. J., Bergin, E. A., & Melnick, G. J. (2008). WATER, O 2 , AND ICE IN MOLECULAR CLOUDS. The Astrophysical Journal, 690(2), 1497–1521. doi:10.1088/0004-637x/690/2/1497

  • Jahnke, L. L., Orphan, V. J., Embaye, T., Turk, K. A., Kubo, M. D., Summons, R. E., & Des Marais, D. J. (2008). Lipid biomarker and phylogenetic analyses to reveal archaeal biodiversity and distribution in hypersaline microbial mat and underlying sediment. Geobiology, 6(4), 394–410. doi:10.1111/j.1472-4669.2008.00165.x

  • Kane, S. R., Mahadevan, S., von Braun, K., Laughlin, G., & Ciardi, D. R. (2009). Refining Exoplanet Ephemerides and Transit Observing Strategies. Publications of the Astronomical Society of the Pacific, 121(886), 1386–1394. doi:10.1086/648564

  • Konhauser, K. O., Pecoits, E., Lalonde, S. V., Papineau, D., Nisbet, E. G., Barley, M. E., … Kamber, B. S. (2009). Oceanic nickel depletion and a methanogen famine before the Great Oxidation Event. Nature, 458(7239), 750–753. doi:10.1038/nature07858

  • Mattioda, A. L., Ricca, A., Tucker, J., Bauschlicher, C. W., & Allamandola, L. J. (2009). FAR-INFRARED SPECTROSCOPY OF NEUTRAL CORONENE, OVALENE, AND DICORONYLENE. The Astronomical Journal, 137(4), 4054–4060. doi:10.1088/0004-6256/137/4/4054

  • Meschiari, S., Wolf, A. S., Rivera, E., Laughlin, G., Vogt, S., & Butler, P. (2009). Systemic: A Testbed for Characterizing the Detection of Extrasolar Planets. I. The Systemic Console Package. Publications of the Astronomical Society of the Pacific, 121(883), 1016–1027. doi:10.1086/605730

  • Montgomery, R., & Laughlin, G. (2009). Formation and detection of Earth mass planets around low mass stars. Icarus, 202(1), 1–11. doi:10.1016/j.icarus.2009.02.035

  • Nuevo, M., Milam, S. N., Sandford, S. A., Elsila, J. E., & Dworkin, J. P. (2009). Formation of Uracil from the Ultraviolet Photo-Irradiation of Pyrimidine in Pure H 2 O Ices. Astrobiology, 9(7), 683–695. doi:10.1089/ast.2008.0324

  • Orphan, V. J., & House, C. H. (2009). Geobiological investigations using secondary ion mass spectrometry: microanalysis of extant and paleo-microbial processes. Geobiology, 7(3), 360–372. doi:10.1111/j.1472-4669.2009.00201.x

  • Orphan, V. J., Jahnke, L. L., Embaye, T., Turk, K. A., Pernthaler, A., Summons, R. E., & Des Marais, D. J. (2008). Characterization and spatial distribution of methanogens and methanogenic biosignatures in hypersaline microbial mats of Baja California. Geobiology, 6(4), 376–393. doi:10.1111/j.1472-4669.2008.00166.x

  • Parenteau, M. N., & Cady, S. L. (2010). MICROBIAL BIOSIGNATURES IN IRON-MINERALIZED PHOTOTROPHIC MATS AT CHOCOLATE POTS HOT SPRINGS, YELLOWSTONE NATIONAL PARK, UNITED STATES. PALAIOS, 25(2), 97–111. doi:10.2110/palo.2008.p08-133r

  • Pohorille, A., & Deamer, D. (2009). Self-assembly and function of primitive cell membranes. Research in Microbiology, 160(7), 449–456. doi:10.1016/j.resmic.2009.06.004

  • Rothschild, L. J. (2008). The evolution of photosynthesis…again?. Philosophical Transactions of the Royal Society B: Biological Sciences, 363(1504), 2787–2801. doi:10.1098/rstb.2008.0056

  • Sandford, S. A. (2008). Terrestrial Analysis of the Organic Component of Comet Dust*. Annual Review of Analytical Chemistry, 1(1), 549–578. doi:10.1146/annurev.anchem.1.031207.113108

  • Vogel, M. B., Des Marais, D. J., Parenteau, M. N., Jahnke, L. L., Turk, K. A., & Kubo, M. D. Y. (2010). Biological influences on modern sulfates: Textures and composition of gypsum deposits from Guerrero Negro, Baja California Sur, Mexico. Sedimentary Geology, 223(3-4), 265–280. doi:10.1016/j.sedgeo.2009.11.013

  • Vogel, M. B., Des Marais, D. J., Turk, K. A., Parenteau, M. N., Jahnke, L. L., & Kubo, M. D. Y. (2009). The Role of Biofilms in the Sedimentology of Actively Forming Gypsum Deposits at Guerrero Negro, Mexico. Astrobiology, 9(9), 875–893. doi:10.1089/ast.2008.0325

  • Wei, C., & Pohorille, A. (2009). Permeation of Membranes by Ribose and Its Diastereomers. Journal of the American Chemical Society, 131(29), 10237–10245. doi:10.1021/ja902531k

  • Blake, D., Treiman, A.H. & Robinson, K.L.  (2009, in preparation).  CheMin detectability of carbonate and clay minerals in altered ultramafic rocks (tentative title).  Lunar and Planetary Science Conference, 41.
  • Blake, D.F., Vaniman, D., Anderson, R., Bish, D.L., Chipera, S., Chemtob, S., Crisp, J., Des Marais, D.J., Downs, R., Farmer, J.D., Gailhanou, M., Ming, D., Morris, D., Stolper, E., Sarrazin, P., Treiman, A. & Yen, A.  (2009).  The CHEMIN Mineralogical Instrument on the Mars Science Laboratory Mission. 40th Lunar and Planetary Science Conference, March 23-27, 2009, The Woodlands, TX. Abstract No. 1484.
  • Cardace, D. & Hoehler, T.M.  (2009).  Serpentinizing Fluids Craft Microbial Habitat.  In: Favolise-Stanton, A. (Eds.).  Soil and Biota of Serpentine: A World View. Proceedings of the Sixth International Conference of Serpentine Ecology.  Vol. 5.  Northeastern Naturalist (Steuben, Maine) Special Issue.
  • Cody, G.,.D., Ade, H., Alexander, C.M.O.D., Araki, T., Butterworth, A., Fleckenstein, H., Flynn, G., Gilles, M.K., Jacobsen, C., Kilcoyne, A.L.D., Messenger, K., Sandford, S.A., Tyliszczak, T., Westphal, A.J., Wirick, S. & Yabuta, H.  (2008).  Quantitative Organic and Light-Element Analysis of Comet 81P/Wild 2 Particles using C-, N-, and O- µ-XANES.  Meteoritics and Planetary Science, 43: 353-365.
  • Davis, S.S. & Young, E.D.  (2008).  The Distribution of Oxygen Isotopes in a Protoplanetary Nebula. Astrobiology Science Conference.
  • Des Marais, D.J. & Vogel, M.B.  (2008).  Interpreting biosignatures in the context of marine evaporitic environments. AGU Meeting, San Francisco, CA, December 2008. Abstract No. P53D-08.
  • Des Marais, D.J.  (2008).  Assessing the nature, distribution and duration of Noachian habitable environments. AGU Meeting, San Francisco, CA, December 2008. Abstract No. P43D-08.
  • Des Marais, D.J.  (2009).  Hints of habitable environments on Mars challenge our studies of Mars-Analog sites on Earth [Abstract], Goldschmidt Conference 2009.  Geochimica et Cosmochimica Acta, 73(13, Supp. 1 (June 2009)): A285.
  • Des Marais, D.J.  (2009).  Origins and Cycling of CO2 on Earth during the Archean and Proterozoic Eons [Abstract]. AAPG Conference, June 7-10, 2009, Denver, CO.
  • Des Marais, D.J.  (2009).  Potential lifestyles in ancient environments characterized by the Mars Exploration Rovers. The New Martian Chemistry Workshop (LPI), July 27-28, 2009, Medford, MA. Abstract No. 8031.
  • Des Marais, D.J.  (2009, in press).  Marine hypersaline Microcoleus-dominated cyanobacterial mats in the saltern at Guerrero Negro, Baja California Sur, Mexico. Cellular Origins, Life in Extreme Habitats and Astrobiology (COLE) Series.  In: Seckbach, J. (Eds.).  In Microbial Mats.  Springer.
  • Des Marais, D.J., Jakosky, B.M. & Hynek, B.M.  (2008).  Astrobiological implications of Mars surface composition and properties.  In: Bell, J.A. (Eds.).  In The Martian Surface: Composition, Mineralogy and Physical Properties.  Vol. 9, Chapter 26.  Cambridge Planetary Science.
  • Green, S.J. & Jahnke, L.L.  (2009, in press).  Microbial Mats.  In: Oren, A. & Seckbach, J. (Eds.).  Springer-Verlag.
  • Hoehler, T.M.  (2008).  Energy as a constraint on habitability in the subsurface. [ABSTRACT] (Invited).  EOS Trans. AGU, 89(53), Fall Meet. Suppl: B52B-01.
  • Hoehler, T.M., Alperin, M.J., McCollom, T.M. & Rogers, K.L.  (2008).  Habitability of serpentinizing systems for methanogenic microorganisms: an energy balance model. [ABSTRACT].  Geochimica et Cosmochimica Acta, 72(12), Supplement 1: 383.
  • Kwok, S. & Sandford, S.  (2008).  Organic Matter in Space.  Proceedings of IAU.  Vol. Proc. Of IAU Symposium 251.  Cambridge University Press: Cambridge.
  • Matrajt, G., Ito, M., Wirick, S., Messenger, S., Brownlee, D.E., Joswiak, D., Flynn, G., Sandford, S., Snead, C. & Westphal, A.  (2008).  Carbon Investigation of Two Stardust Particles: A TEM, NanoSIMS, and XANES Study.  Meteoritics and Planetary Science, 43: 315-334.
  • Parenteau, M.N., Jahnke, L.L., Boomer, S.M., Cady, S.L. & Pierson, B.K.  (2009).  Do cyanobacteria use Fe2+ as an electron donor for photosynthesis.  Abstr. Ann. Mtg. Am. Soc. Microbiology.
  • Pilcher, C.B. & Lissauer, J.J.  (2009).  The Quest for Habitable Worlds and Life Beyond the Solar System. Exploring the Origin, Extent and Future of Life.  In: Bertka, C.M. (Eds.).  Cambridge University Press.
  • Pohorille, A.  (2009, to be published).  Contingency vs. determinism in the origin of life.  Orig. Life Evol. Biosphere.
  • Pohorille, A.  (2009, to be published).  Emerging properties in the origins of life and Darwinian evolution.  Orig. Life Evol. Biosphere.
  • Pohorille, A., Wilson, M.A. & Wei, C.  (2009, in press).  The Earliest Ion Channels.  Bioastronomy.
  • Pohorille, A., Wilson, M.A. & Wei, C.  (2009, in press).  The Earliest Ion Channels.  In: Meech, K., Keane, J., Mumma, M., Siefert, J. & Werthimer, D. (Eds.).  Proceedings of the Bioastronomy 2007 Conference.  Astronomical Society of the Pacific.
  • Richard , D.T. & Davis, S.S.  (2008).  Polarimetric signature of dust and aggregates of silicates and organics. Astrobiology Science Conference.
  • Richard, D.T. & Davis, S.S.  (2008).  Lunar Dust Characterization by Polarimetric Signature: I Negative Polarization Branch of Sphere Aggregates of various Porosities.  Astronomy & Astrophysics, 483: 643-649.
  • Richard, D.T., Glenar, D.A., Stubbs, T.J., Davis, S.S. & Colaprete, A.  (2009).  “But still, like dust, I’ll rise” Modeling the Scattering Signature of Lunar Dust for the Lunar Atmosphere and Dust Environment Explorer. [Abstract]. NASA Lunar Science Institute Forum, July 2009.
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