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Assessment of the NASA Astrobiology Institute 2 Interdisciplinary Research This chapter evaluates the success of the NASA Astrobiology Institute (NAI) in achieving its stated goal of conducting, supporting, and catalyzing collaborative interdisciplinary research. NAI CONTRIBUTIONS The NAI has had considerable success in defining key scientific objectives and initiating interdisciplinary research. The NAI has also provided a mechanism for developing collaborations on both a national and an international scale. The NAI has been instrumental in keeping astrobiology a cutting-edge field and fully complements other Astrobiology program elements in NASA’s Science Mission Directorate. Although the enormous potential of the NAI for promoting collaborative, distributed, interdisciplinary research has not yet been fully realized, considerable progress has been made. The NAI has successfully established the infrastructure to promote interdisciplinary research by providing competitive proposal opportunities for major science teams (or nodes) with a geographically distributed membership. These nodes are further facilitated by a central coordinating office—NAI Central—whose small but highly professional staff provides oversight of NAI operations and develops the state-of-the-art Web tools necessary to operate a virtual institute. Strategic decisions are made by NAI leadership in partnership with NASA Headquarters as, for example, in the development of the Director’s Discretionary Fund and plans to have NAI Central develop an integrated Web presence for the Astrobiology program as a whole.1 Additional information on the organization of the NAI can be found in Chapter 1. The NAI has succeeded in managing proposal competitions that are not biased in favor of NASA centers, demonstrating high scientific standards and fairness. Unfortunately, the NAI’s success has been tempered by recent budget cuts that threaten the ability of the NAI to reach its full potential. Scientific Contributions Although the committee was not charged to undertake a review of the NAI’s scientific contributions, it is not possible to evaluate the NAI’s success in conducting, supporting, and catalyzing collaborative interdisciplinary research without some brief mention of the NAI’s scientific achievements. Fortunately for the committee, the NAI has compiled a list of what it believes to be its top research accomplishments. Starting with the early Earth and moving outward in time and space, these accomplishments include research aimed at elucidating the following:
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Assessment of the NASA Astrobiology Institute Early habitability of Earth. The NAI has supported Stephen Mojzsis (University of Colorado team) and others (e.g., Mark Harrison, University of California, Los Angeles, team) to investigate the oldest rocks and to use ancient zircons to characterize the environment of the young Earth. One result is evidence for an ocean and hydrological cycle in the Hadean Eon, the first 500 million years of Earth’s history.2,3 For additional details see Box 2.1. The rise of oxygen and Earth’s “middle age.” NAI support was critical in fostering a new interest in the Archean and Proterozoic Eons, the geological periods from approximately 3.9 billion to 2.5 billion and from 2.5 billion to 542 million years ago, respectively. The NAI sponsored collaborative deep-drilling projects and isotopic studies to document the co-evolution of Earth’s biota with the rise of atmospheric oxygen. Findings include new evidence of oxygen before the so-called Great Oxidation Event, improved understanding of the timing of this event, and evidence that this event led to a Proterozoic world unlike what came before or after.4-8 For additional details see Box 2.2. Snowball Earth. The NAI supported fieldwork by Paul Hoffman (Harvard University) and his students to provide high-resolution stratigraphic and geochemical data needed to refine the hypothesis that Earth was, at times, completely covered with ice during the period from 850 million to 630 million years ago. Snowball Earth and other extreme events are now considered a natural aspect of Earth’s evolution on long timescales. Other NAI investigators at the California Institute of Technology and Arizona State University have investigated the implications of this period for the evolution of life.9-12 For additional details see Box 2.3. Microbial mat ecology. In situ studies, led by the NAI team at NASA’s Ames Research Center, of the Guerrero Negro hypersaline microbial mats (modern representatives of one of Earth’s earliest and most pervasive BOX 2.1 EARLY HABITABILITY OF EARTH Direct information concerning the first 500 million years of Earth history—the Hadean Eon, approximately 4.0 billion to 4.5 billion years ago—is very limited, since practically no crustal rocks from that time have survived. Researchers do know that asteroids and comets collided with Earth much more frequently than they do today, and astronomers also tell us that the Sun was about 30 percent fainter then, so that Earth may have been cold, unless there was a large greenhouse effect to trap the Sun’s heat and raise surface temperatures above the freezing point. Also of special interest is the apparent fact that life arose on Earth either during or shortly after the Hadean Eon. Understanding the chemical state of the earliest atmosphere and ocean is critical to any theory of the origins of life on Earth. Stephen Mojzsis (University of Colorado team) and colleagues have been investigating the geological record, including the use of ancient zircons to determine the environment on the earliest Earth. The oldest rocks, found in Australia, Canada, and Greenland, are less than 4.0 billion years old. Some of the zircons they contain are much older; oxygen isotope dating places some of these zircons at ages up to 4.3 billion years. Mojzsis and colleagues conclude that these zircons were formed from magmas containing a significant component of reworked continental crust that formed in the presence of water at Earth’s surface. This result is consistent with the presence of a hydrosphere interacting with the crust within only 200 million years of Earth’s Moon-forming event. Bibliography C.E. Manning, S.J. Mojzsis, and T.M. Harrison, “Geology, Age and Origin of Supracrustal Rocks at Akilia, West Greenland,” American Journal of Science 306: 303-366, 2003. S.J. Mojzsis, T.M. Harrison, and R.T. Pidgeon, “Oxygen-isotope Evidence from Ancient Zircons for Liquid Water at the Earth’s Surface 4,300 Myr Ago,” Nature 409: 178-181, 2001.
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Assessment of the NASA Astrobiology Institute BOX 2.2 THE RISE OF OXYGEN AND EARTH’S “MIDDLE AGE” High-precision studies of sulfur-isotope fractionation reveal that some photochemical reactions can produce isotope variations that do not scale simply with mass. These mass-independent fractionation (MIF) reactions require ultraviolet radiation that is blocked by O3, and the preservation of their fractionated reaction products requires low atmospheric O2. Sulfur-MIF studies indicate that Earth’s atmosphere became oxygenated (the “Great Oxidation Event”) in the early Proterozoic, about 2.3 billion years ago. One possible cause is the development of oxygenic photosynthesis at that epoch; alternatively, the rise of atmospheric O2 may have been mediated by geological processes. Access to unweathered and uncontaminated samples of the oldest and least-altered sedimentary rocks is essential for understanding the early history of life on Earth and the environments in which it may have existed. The NAI initiated the Astrobiology Drilling Program (ADP), an outgrowth of the Mission to Early Earth Focus Group, which funded drilling (primarily in Western Australia) to access fresh subsurface samples that are made available to a broad scientific community. Initial analyses reveal that at least trace amounts of O2 may have been present hundreds of millions of years before the Great Oxidation Event. Whereas it was once thought that the Proterozoic was a mildly oxygenated version of the modern, it is increasingly believed that the rise of oxygen led, paradoxically, to intensification of anoxia in large parts of the deep ocean. The NAI was instrumental in catalyzing research that tested the broad strokes of this hypothesis as well as research into the possible evolutionary consequences of a billion years of ocean redox stratification. Bibliography A.D. Anbar and A.H. Knoll, “Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge?” Science 297: 1137-1142, 2002. A.D. Anbar, Y. Duan, T.W. Lyons, G.L. Arnold, B. Kendall, R.A. Creaser, A.J. Kaufman, G. Gordon, C. Scott, J. Garvin, and R. Buick, “A Whiff of Oxygen Before the Great Oxidation Event?” Science 317: 1903-1906, 2007. H. Ohmoto, Y. Watanabe, H. Ikemi, S.R. Poulson, and B.E. Taylor, “Sulphur Isotope Evidence for an Oxic Archaean Atmosphere,” Nature 442: 908-911, 2006. S. Ono, B. Wing, D. Johnston, D. Rumble, and J. Farquhar, “Mass-dependent Fractionation of Quadruple Stable Sulfur Isotope System as a New Tracer of Sulfur Biogeochemical Cycles,” Geochimica et Cosmochimica Acta 70: 2238-2252, 2006. Y. Shen, A.H. Knoll, and M.R. Walter, “Evidence for Low Sulphate and Anoxia in a Mid-Proterozoic Marine Basin, Nature 423: 632-635, 2003. ecosystems), combined with greenhouse cultures, reveal a complex layered symbiotic ecology with more than 1,000 species and substantial diurnal fluxes of nutrients and of both reduced and oxidized gases. Ancient mats may have been a significant contributor to long-term atmospheric oxygenation.13-16 For additional details see Box 2.4. Discovery of the “rare biosphere.” Using novel biotechnology that permits detection of almost all members in a microbial community, the NAI team at the Marine Biological Laboratory have discovered that the microbial diversity in the deep ocean is up to 100 times greater than expected within a population that is more than a million-fold depleted relative to the primary microbiota. This “rare biosphere” gene pool could serve as reserve of genetic diversity for repopulation of a habitat should conditions change dramatically.17-20 For additional details see Box 2.5. Sub-seafloor life. NAI investigators from the University of Rhode Island, Woods Hole Oceanographic Institution, and the University of North Carolina led the first ocean-drilling expedition focused on exploration of subsurface life and habitability. Their results demonstrated that deep sub-seafloor communities are metabolically
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Assessment of the NASA Astrobiology Institute BOX 2.3 SNOWBALL EARTH During Snowball Earth events, biological productivity in the oceans collapsed for millions of years due to extensive freezing. The NAI supported much of the fieldwork by Paul Hoffman (Harvard University team) and his students—in Namibia, Spitsbergen, and northwestern Canada—that provided the high-resolution stratigraphic and geochemical data needed to test and refine the snowball hypothesis.The NAI also supported Samuel Bowring’s fieldwork that determined strong geochronometric constraints on the timing of Neoproterozoic ice ages. The Snowball Earth topic was an integral part of Harvard University’s 1998 NAI proposal, and much of that team’s efforts went into developing the concept into a truly multidisciplinary topic of great astrobiological importance. Although the severity of the historical glaciations is debated, theoretical Snowball conditions are associated with the nearly complete shutdown of the hydrological cycle. A recent result by Joseph Kirschvink and colleagues suggests that, during such long and severe glacial intervals, photochemical reactions would give rise to the sustained production of hydrogen peroxide, which is stored in the ice. The peroxide would then be released directly into the ocean and the atmosphere upon melting and could mediate global oxidation events in the aftermath of the Snowball. Low levels of peroxides and molecular oxygen generated during Archean and earliest Proterozoic non-Snowball glacial intervals could have driven the evolution of oxygen-using enzymes and thereby paved the way for the eventual appearance of oxygenic photosynthesis. Bibliography D. Condon, M.Y. Zhu, S. Bowring, et al., “U-Pb Ages from the Neoproterozoic Doushantuo Formation, China,” Science 308: 95-98, 2005. G.P. Halverson, P.F. Hoffman, D.P. Schrag, et al., “Toward a Neoproterozoic Composite Carbon-Isotope Record,” Bulletin of the Geological Society of America 117: 1181-1207, 2005. P.F. Hoffman and D.P. Schrag, “The Snowball Earth Hypothesis: Testing the Limits of Global Change,” Terra Nova 14: 129-155, 2002. M.-C. Liang, H. Hartman, R.E. Kopp, J. Kirschvink, and Y.L. Yung, “Production of Hydrogen Peroxide in the Atmosphere of a Snowball Earth and the Origin of Oxygenic Photosynthesis,” Proceedings of the National Academy of Sciences 10: 18896-18899, 2006. complex and phylogenetically diverse. Microbes in anoxic, deep sub-seafloor sediments respire at rates that are orders of magnitude slower than previously believed necessary to sustain life. Their metabolic pathways include new processes, such as the biological generation of ethane and propane.21-25 For additional details see Box 2.6. Metal isotope tracers of environment and biology. Studies of the biological and abiological fractionation of metal isotopes, particularly the redox-sensitive elements molybdenum and iron, were motivated by astrobiology objectives to study Earth’s redox evolution and to find new signatures for life. This work has been supported by the NAI from its earliest days (e.g., Kenneth Nealson’s team at the Jet Propulsion Laboratory) and is the focus of the new team headed by Clark Johnson (University of Wisconsin). Iron-isotope geochemistry is now being pursued in about 30 laboratories across the globe.26-31 For additional details see Box 2.7. Life without the Sun. NAI scientists from Princeton University and Indiana University have discovered deeply buried life in a South Africa gold mine that appears to thrive independent of the familiar surface biosphere, which is powered by sunlight. These microbes draw energy from hydrogen and sulfates produced when the decay of radioactive elements in the rocks disassociates water molecules.32 For additional details see Box 2.8. Early wet Mars. NAI astrobiologists such as Jack Farmer (Arizona State University team), David Des Marais (Ames Research Center team), Andrew Knoll (Harvard University team), Mark Allen (JPL team), John Grotzinger (MIT team), and Bruce Jakosky (University of Colorado team) have played major roles in recommending landing sites, defining objectives and spacecraft operations, and interpreting data from current Mars orbiters
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Assessment of the NASA Astrobiology Institute BOX 2.4 MICROBIAL MAT ECOLOGY NAI scientists from the team at the Ames Research Center led an interdisciplinary study of hypersaline cyanobacterial mats that has yielded important insights into the evolution of microbial systems, the role of biology in the chemical evolution of our planet, and the interpretation of biosignatures in Earth’s early rock record. As sunlight-dependent systems, microbial mats exhibit dramatic shifts in metabolic, ecological, and biogeochemical function from day to night. The Ames team demonstrated the critical importance of the less-studied dark, anoxic component of this cycle in several areas. Mats were found to deliver fluxes of H2, CH4, and CO gases to the atmosphere at rates up to several percent of their gross photosynthetic productivity. Such emissions might have augmented H2 escape to space and contributed substantially and irreversibly to the oxygenation of the ancient atmosphere. Anaerobic mat processes also produce sulfur-bearing volatile organics that are plausible atmospheric biosignatures. Such processes have been documented in their role as the final filter and ultimate arbiter of organic and carbon- and sulfur-isotopic biomarkers entering the rock record. Through collaborative efforts with the Ames, University of Colorado, Marine Biological Laboratory, and Arizona State University teams, the dynamic geochemistry of these systems has been linked to an enormous underlying microbial diversity. Bibliography D.C. Catling, K.J. Zahnle, and C.P. McKay, “Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth,” Science 293: 839-843, 2001. D.J. Des Marais, “The Biogeochemistry of Hypersaline Microbial Mats Illustrates the Dynamics of Modern Microbial Ecosystems and the Early Evolution of the Biosphere,” The Biological Bulletin 204: 160-167, 2003. T.M. Hoehler, B.M. Bebout, and D.J. Des Marais, “The Role of Microbial Mats in the Production of Reduced Gases on the Early Earth,” Nature 412: 324-327, 2001. R.E. Ley, J.K. Harris, J. Wilcox, J.R. Spear, S.M. Miller, B.M. Bebout, J.A. Maresca, D.A. Bryant, M.L. Sogin, and N.R. Pace, “Unexpected Diversity and Complexity of the Guerrero Negro Hypersaline Microbial Mat,” Applied and Environmental Microbiology 72: 3685-3695, 2006. and rovers—yielding key chemical and geological evidence for widespread liquid water on Mars in its first billion years. For additional details see Box 2.9. Methane on Mars. Michael Mumma (principal investigator of the NAI node at NASA’s Goddard Space Flight Center) heads one of three teams that have reported detection of methane in the martian atmosphere. Methane, often suggested as a biosignature gas, has a lifetime of only a few centuries under martian conditions, indicating a currently active source. This work thus suggests a line of research that could lead to the first positive evidence for extant life on another planet.33-36 For additional details see Box 2.10. Comets in space and in the laboratory. Comets were a major source of biogenic materials on planets. NAI members from the University of Hawaii, Goddard Space Flight Center, Carnegie Institution of Washington, and Ames Research Center teams carry out ground- and space-based research on organics in comets, including development of several state-of-the-art organic astrochemistry laboratories to help interpret the observational data. The Carnegie team and others have probed the molecular structure of organic matter in meteorites, as a complementary approach to understanding the chemical context for the formation of life.37-42 For additional details see Box 2.11. Exoplanet discovery and analysis. NAI members, primarily from the team at the Carnegie Institution of Washington, are playing important roles in the search for exoplanets,43 with particular attention to issues of habitability. They are part of a group that is building several new spectrometers that will accelerate this search, while others are using the Spitzer Space Telescope to study the infrared signatures of atmospheric composition in
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Assessment of the NASA Astrobiology Institute BOX 2.5 DISCOVERY OF THE “RARE BIOSPHERE” A previously unknown “rare biosphere” that co-exists with more familiar life in the deep ocean was discovered by a multi-institution consortium under the leadership of Mitchell Sogin, principal investigator of the NAI team at the Marine Biological Laboratory. These scientists used new genetic analysis tools to sample the much rarer microbes that have previously gone undetected, using samples collected from both normal cold seawater and hydrothermal vents. This new analysis reveals enormous diversity within this rare biosphere. The techniques used do not permit individual organisms to be isolated for study, but they allow statistical estimates of the population. Although the numbers of such microbes are small, there is at least 100 times greater species diversity than had been expected. This rare biosphere is very ancient and may represent a nearly inexhaustible source of genomic innovation. Members of the rare biosphere are highly divergent from each other and, at different times in Earth’s history, may have had a profound impact on shaping planetary processes. Perhaps they represent a kind of natural “back-up system” that could repopulate a habitat if environmental conditions were to change in ways that threaten the dominant ecosystem. Related research from the NAI team at the University of California, Berkeley, has found novel low-abundance archaeal species in biofilms from acidic water at the Richmond Mine in California. These enigmatic microorganisms are ubiquitous at the smallest size level. The Marine Biological Laboratory team, in collaboration with astrobiologists at the Centro de Astrobiología in Madrid, have also discovered high levels of protist diversity in iron-rich acidic environments in the Rio Tinto system in Spain. Bibliography B.J. Baker, G.W. Tyson, R.I. Webb, J. Flanagan, P. Huguenots, E.E. Allen, and J.F. Banfield, “Lineages of Acidophilic Archaea Revealed by Community Genomic Analysis,” Science 314: 1933-1935, 2006. V.P. Edgecombe, D.T. Cypsela, A. Tasked, A. de Vera Gomez, and M.L. Sogin, “Benthic Eukaryotic Diversity in a Hydrothermal Vent,” Proceedings of the National Academy of Sciences 99: 7658-7662, 2002. M.L. Sogin, H.G. Morrison, J.A. Huber, D. Mark Welch, S.M. Huse, P.R. Neal, J.M. Arietta, and G.J. Herd, “Microbial Diversity in the Deep Sea and the Under-explored ‘Rare Biosphere’,” Proceedings of the National Academy of Sciences 103: 12115-12120, 2006. L.A. Zettler, F. Gomez, E. Settler, B.G. Keenan, R. Amils, and M.L. Sogin, “Heavy-metal, Acid-loving Eukaryotes from Spain’s ‘River of Fire’,” Nature 417: 137, 2002. transiting planets. Giovanna Tinetti of the NAI’s Virtual Planetary Laboratory team used this approach to discover evidence suggesting the presence of water vapor in the atmosphere of an extrasolar planet.44 For additional details see Box 2.12. Modeling exoplanet biospheres. The NAI’s Virtual Planetary Laboratory, led by Victoria Meadows, has organized a highly multidisciplinary team to undertake research focusing on habitability, extrasolar terrestrial planets, and biosignatures. This is a fundamentally new effort to develop models for the co-evolution of planets and life, addressed to NASA’s requirements for future missions to search for life beyond the solar system.45-48 For additional details see Box 2.13. This list, like all such lists, raises multiple questions: Are these contributions really important? Will they stand the test of time? What fraction of these contributions was influenced by or due directly to the NAI? Do they represent unique contributions that would not have been made absent the NAI? Are they the result of a dispassionate assessment or do they represent the most favorable interpretations of NAI research results? However, the committee was not charged to answer such specific questions. Rather, it was asked to evaluate the NAI’s success in conducting, supporting, and catalyzing collaborative interdisciplinary research. While it will be very interesting to look back in another decade and see which of these contributions have flowered into major discoveries, and
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Assessment of the NASA Astrobiology Institute BOX 2.6 SUB-SEAFLOOR LIFE NAI-supported investigators from the University of Rhode Island, Woods Hole Oceanographic Institution, and the University of North Carolina have investigated life deep beneath Earth’s seafloor. Their results from Ocean Drilling Program Leg 201 demonstrated that deep sub-seafloor communities are metabolically complex. Mutualistic interactions sustain these communities for millions of years with extremely little ongoing input of organic matter. In many aspects, these communities serve as a model for possible life on other worlds. These aspects include their extraordinarily low rates of maintenance activity, their complexity of energetic interactions, and their generation of compounds not previously known to be biomarkers (i.e., ethane and propane). Collaborations involving the NAI teams at the Marine Biological Laboratory, University of Rhode Island, and Pennsylvania State University have helped to advance understanding of microbial diversity in this remote environment. In pursuit of this research, NAI investigators have developed many tools that can also be applied to the study of life in other extreme environments and on other worlds: these include an assay for quantifying extremely low levels of fundamental enzymatic activity (hydrogenase), refined techniques for quantification of microbial contamination, and a simple technique for quantifying concentrations of dissolved volatile metabolites (such as methane). Bibliography J.F. Biddle, J.S. Lipp, M.A. Lever, K.G. Lloyd, K.B. Sørensen, R. Anderson, H.F. Fredricks, M. Elvert, T.J. Kelly, D.P. Schrag, M.L. Sogin, J.E. Brenchley, A. Teske, C.H. House, and K.-U. Hinrichs, “Heterotrophic Archaea Dominate Sedimentary Subsurface Ecosystems Off Peru,” Proceedings of the National Academy of Sciences 103: 3846-3851, 2006. S. D’Hondt, S. Rutherford, and A.J. Spivack, “Metabolic Activity of Subsurface Life in Deep-sea Sediments,” Science 295: 2067-2070, 2002. S. D’Hondt, B.B. Jørgensen, D.J. Miller, A. Batzke, et al., “Distributions of Microbial Activities in Deep Subseafloor Sediments,” Science 306: 2216-2221, 2004. K.-U. Hinrichs, J.M. Hayes, W. Bach, A.J. Spivack, C.G. Johnson, and S.P. Sylva, “Biological Formation of Ethane and Propane in the Deep Marine Subsurface,” Proceedings of the National Academy of Sciences 103: 14684-14689, 2006. F. Inagaki, T. Nunoura, S. Nakagawa, A. Teske, M. Lever, A. Lauer, M. Suzuki, K. Takai, M. Delwiche, F.S. Colwell, K.H. Nealson, K. Horikoshi, S. D’Hondt, and B.B. Jørgensen, “Biogeographical Distribution and Diversity of Microbes in Methane Hydrate-bearing Deep Marine Sediments on the Pacific Ocean Margin,” Proceedings of the National Academy of Sciences 103: 2815-2820, 2006. which are ascribed to the NAI, the committee does not have that luxury. Without commenting on the specifics of any of NAI’s self-selected scientific contributions, the committee believes that taken together they do represent a substantial body of scientific results. An important question then is, since some of the NAI’s scientific contributions listed above are more interdisciplinary than others, should the NAI only take credit for research that is truly interdisciplinary? The answer must be no. Research that is predominantly the domain of a single discipline (e.g., the search for and characterization of exoplanets) is a necessary precursor to more interdisciplinary activities (e.g., modeling exoplanet biospheres). Thus, interdisciplinarity must be viewed as the orientation and emergent quality of an overall enterprise and not as a requirement or expectation levied on every piece of work produced by that enterprise. Too great an emphasis on what is and is not interdisciplinary science could potentially lead to an overly bureaucratic emphasis on proxy measures of intellectual achievements such as counts of the relative number of papers with multiple authors from different disciplines. Progress in addressing interdisciplinary science goals can be made by independent experts working singly or in concert with colleagues from other disciplines. Since it is the result that counts, and not the
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Assessment of the NASA Astrobiology Institute BOX 2.7 METAL ISOTOPE TRACERS OF ENVIRONMENT AND BIOLOGY Isotopic variations among the transition metals and other heavy elements permit tracing the redox cycling of metals and hence environmental redox change. Some of the largest isotopic fractionations are produced by microbially mediated redox changes, such as the fractionation in 34S/32S ratios that occurs upon bacterial reduction of SO42− to S2−. Significant isotopic fractionations may also be found among the transition metals that have multiple redox states. The greatest focus has been on Fe because it is a major element in the crust and serves as an electron donor for anaerobic photosynthesis and an electron acceptor for metabolic Fe reduction. Studies of the coupled C-S-Fe system provide insights into the co-evolution of photosynthetic and heterotrophic respiration pathways. Molybdenum (Mo) provides another useful probe of global ocean conditions. NAI-sponsored research has shown that the Mo isotope composition of the oceans reflects the extent of seafloor oxygenation. Under oxidized conditions, Mo exists as MoO42− in the oceans, and significant fractionations in 97Mo/95Mo ratios occur upon sorption to Fe-Mn oxides. Under reduced conditions, Mo (present as MoS42−) is relatively insoluble and would be expected to have isotopic compositions reflecting bulk continental crust. This area of research is just beginning to be fully explored. Bibliography A.D. Anbar and O. Rouxel, “Metal Stable Isotopes in Paleoceanography,” Annual Reviews of Earth and Planetary Science 35: 717-746, 2007. G.L. Arnold, A.D. Anbar, J. Barling, and T.W. Lyons, “Molybdenum Isotope Evidence for Widespread Anoxia in Mid-Proterozoic Oceans,” Science 304: 87-90, 2004. B.L. Beard, C.M. Johnson, L. Cox, H. Sun, and K.H. Nealson “Iron Isotope Biosignatures,” Science 285: 1889-1892, 1999. C.M. Johnson and B.L. Beard, “Biogeochemical Cycling of Iron Isotopes,” Science 309: 1025-1027, 2005. C.M. Johnson, B.L. Beard, and E.E. Roden, “The Iron Isotope Fingerprints of Redox and Biogeochemical Cycling in the Modern and Ancient Earth,” Annual Reviews of Earth and Planetary Science, 2008 (in press). O.J. Rouxel, A. Bekker, and K.J. Edwards, “Iron Isotope Constraints on the Archean and Paleoproterozoic Ocean Redox State,” Science 307: 1088-1091, 2005. methodology chosen to achieve it, the committee determined that the NAI has been successful in conducting, supporting, and catalyzing collaborative interdisciplinary research. RELATIONSHIP TO OTHER ASTROBIOLOGY PROGRAMS NAI programs appear to complement the other elements of NASA’s Science Mission Directorate Astrobiology program: i.e., the Exobiology and Evolutionary Biology grants to individual scientists, the technology development activities of the Astrobiology Science and Technology Instrument Development (ASTID) program, and field-testing activities supported by the Astrobiology Science and Technology for Exploring Planets (ASTEP) program. BALANCE OF NAI ACTIVITIES Interdisciplinary, collaborative research is a requirement for NAI funding. As a result, proposals that address questions best answered using interdisciplinary and collaborative approaches are favored. The effectiveness of the NAI’s strategy can, therefore, be judged, in part, by its success in advancing interdisciplinary science. This work ranges from purely theoretical studies to observational science based on field expeditions. The NAI researchers
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Assessment of the NASA Astrobiology Institute BOX 2.8 LIFE WITHOUT THE SUN Potentially among the most important recent discoveries in astrobiology is the finding of specific examples of deeply buried life forms that appear to thrive independent of the familiar surface biosphere, which is powered by sunlight. These particular microbes, discovered by scientists from the NAI’s Indiana-Princeton-Tennessee team, live in hot groundwater 2.8 km below the surface in a South African gold mine.1 They ultimately draw their energy from the slow decay of radioactive elements in the rocks. The radiation dissociates water, and the resulting oxygen reacts with pyrite to form iron sulfate. This iron sulfate, in turn, is utilized along with hydrogen from the dissociated water to support microbial metabolism. The existence of such a deep subsurface microbial community on Earth suggests that similar isolated biospheres could persist on other planets, such as Mars, in spite of hostile conditions on their surfaces. Using modern genetic analysis tools, the NAI team was able to compare the microbes with other anaerobic microbial communities that derive their energy from sulfate reduction. A detailed study of the water chemistry from this environment indicates that there is sufficient naturally produced sulfate and hydrogen to sustain life indefinitely. The base of the food chain is a sulfate reducer belonging to the phylum called Firmicutes, and other microbes in the community may subsist on products from this primary producer. The water itself was dated at approximately 10 million years, during which time it has had no physical or chemical contact with the familiar world far above. 1L-H. Lin, P-L. Wang, D. Rumble, J. Lippmann-Pipke, E. Boice, L.M. Pratt, B. Sherwood Lollar, E.L. Brodie, T.C. Hazen, G.L. Andersen, T.Z. DeSantis, D.P. Moser, D. Kershaw, and T.C. Onstott, “Long-Term Sustainability of a High-Energy, Low-Diversity Crustal Biome,” Science 314: 479-482, 2006. who spoke to the committee—including those from the Marine Biological Laboratory, the California Institute of Technology, the University of Washington, Pennsylvania State University, and the Ames Research Center—believe that many of these efforts would not have been conceived and brought to fruition without the unique interdisciplinary focus supported by the NAI. Examples of specific efforts catalyzed by involvement in the NAI are described in Boxes 2.2 (Pennsylvania State University), 2.4 (Ames Research Center), 2.5 (Marine Biological Laboratory), and 2.13 (California Institute of Technology and University of Washington). Also significant are the international relationships that the NAI has nurtured through the systematic definition and promotion of astrobiology goals, the free exchange of information, and a general willingness to cooperate with both individual scientists and research organizations outside the United States. The creation of astrobiology research centers and scientific organizations in Europe (e.g., Spain’s Centro de Astrobiología,49 France’s Groupement de Recherche en Exobiologie,50 the Astrobiology Society of Britain,51 the Russian Astrobiology Center,52 and the European Exo/Astrobiology Network Association53), Australia (e.g., the Australian Center for Astrobiology54), the Middle East (e.g., the Israel Society for Astrobiology and the Study of the Origin of Life55), and Latin America (e.g., the Red Mexicana de Astrobiología56) would not have been realized without the catalytic role of the NAI in prompting a tightly knitted international community of astrobiologists with similar scientific goals. The level of distributed, collaborative, interdisciplinary research performed by active NAI science teams varies, ranging from some truly interdisciplinary work that demands expertise, collaboration, and contributions from the many fields within astrobiology, to cases that are best described as multidisciplinary, performed by groups of researchers with limited collaborative interactions among members of the same node or with other NAI nodes. The committee notes that competition for NAI funding can discourage collaboration among teams by inhibiting the free exchange of ideas and data between the competing teams. To offset this tendency, the NAI established the Director’s Discretionary Fund (DDF). The establishment of the DDF was agreed to at the NAI’s January 2007 Strategic Impact Workshop. The principal investigators of the NAI teams agreed to take a somewhat larger
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Assessment of the NASA Astrobiology Institute BOX 2.9 EARLY WET MARS From its inception, the NAI provided a multidisciplinary forum (e.g., in the NAI Mars Focus Group, as well as topical workshops, the NAI General Meeting, and so on) for ideas concerning the habitability of Mars. These discussions and interactions have played a significant role in recent and ongoing Mars missions that are transforming current understanding of the planet and reviving interest in the possibility of extant life there. Two of the most important recent discoveries on Mars were “gullies” that indicate relatively recent surface flows, less than a million years old, and the evidence from the Mars Exploration Rovers on the surface that shallow ponds or seas of salty water once covered much of the surface, although they may have been transient. The rover Opportunity, which was targeted toward a region where hematite had been discovered, has repeatedly surprised and delighted astrobiologists with its measurements of sedimentary rocks exposed in crater walls that provide convincing chemical and physical evidence of past water. These discoveries are the result of an astrobiology-inspired strategy for Mars exploration called “follow the water.” This focus on issues of past and present habitability is the logical prelude to resuming the search for life itself. One metric of NAI influence on Mars-mission science is the participation of NAI members in the competitively selected mission teams: Mars Exploration Rover—David Des Marais, Andrew Knoll, Ronald Greeley, John Grotzinger, Phillip Christensen, and Jack Farmer; Mars Reconnaissance Orbiter—David Des Marais and John Grotzinger; Mars Science Laboratory—Paul Mahaffy, Wesley Huntress, James Scott, Andrew Steele, Edward Vicenzi, John Grotzinger, and David Blake; and Mars Atmosphere and Volatile Evolution (Mars Scout Proposal)—Bruce Jakosky. percentage cut to their individual budgets than was called for in the Administration’s budget for the 2007 fiscal year. The resulting savings were pooled to create a $1.8 million fund for strategic investments addressing the following goals: Advancing the science of astrobiology, Demonstrating impact on NASA’s spaceflight programs or its broader science activities, and/or Contributing to NASA’s role as a federal research and development agency through the development of strategic partnerships. Proposals to the DDF were solicited and were required to be cross-nodal and to address strategic astrobiology goals, and they could involve researchers not affiliated with the NAI. In April 2007, 18 DDF proposals were selected for funding. Approximately half were for research projects; the other half were for workshops or conferences. The research projects ranged from development of Mars-related instrument concepts, to an inter-laboratory cross-calibration of sample-analysis instruments, to a geomicrobiology study of an Arctic ice-sulfur spring ecosystem as a testbed for Europa exploration technology. The DDF awards are an important mechanism for addressing strategic issues and for promoting interdisciplinary research. Perhaps the most important metric of the success of the NAI is the publication record of its members, past and present. Unfortunately, the extent to which the publications of the NAI are interdisciplinary is very much subject to interpretation. Some of the papers are truly interdisciplinary. But there also appears to be a large body of work arising from NAI-funded research that contributes only to specialized fields, i.e., activities than could be
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Assessment of the NASA Astrobiology Institute BOX 2.10 METHANE ON MARS Three research teams reported detecting the gas methane in the martian atmosphere, at the low concentration of 10-50 parts per billion. Most methane on Earth is produced in biological processes, both contemporary production by microbes and as underground natural gas formed by earlier generations of microbial life. Since methane is relatively short-lived once it is released into the atmospheres of either Earth or Mars, its presence has long been considered a biomarker. Identification of a biomarker on Mars would qualify as one of the most important discoveries of astrobiology and space exploration. The three reported detections of methane were all made spectroscopically, by one team led by Michael Mumma (principal investigator of the NAI team at NASA’s Goddard Space Flight Center), by other astronomers led by V. Krasnopolsky of Catholic University of America, and from the Planetary Fourier Spectrometer instrument on the European Space Agency’s Mars Express spacecraft (Vittorio Formisano, principal investigator). Both biological and non-biological possibilities are being pursued, for example in recent work by members of the NAI team at the University of California, Berkeley, on hydrate dissociation. The amount of methane detected on Mars is about a factor of 100 less than the amount that would result if martian methane production were equal to Earth’s non-biological production. A timely NAI contribution to this important debate was the workshop “Methane on Mars” conducted on May 18, 2005, shortly after the first detections were presented. The NAI used its video and Internet-based communications network to link participants at a number of sites. A workshop report was published in EOS in 2006. Bibliography M. Allen, B. Sherwood Lollar, B. Runnegar, D.Z. Oehlar, J.R. Lyons, C.E. Manning, and M.E. Summers, “Is Mars Alive?” EOS 87: 433-448, 2006. M.E. Elwood Madden, S.M. Ulrich, T.C. Onstott, and T.J. Phelps, “Salinity-induced Hydrate Dissociation: A Mechanism for Recent CH4 Release on Mars,” Geophysical Research Letters 34: L11202, 2007. M.J. Mumma, R.E. Novak, M.A. DiSanto, B.P. Boner, and N. Dello Russo, “Detection and Mapping of Methane and Water on Mars,” Bulletin of the American Astronomical Society 36: 1127, 2004. T.C. Onstott, D. McGown, J. Kessler, B. Sherwood Lollar, K.K. Lehmann, and S. Clifford, “Martian CH4: Sources, Flux and Detection,” Astrobiology 6: 377-395, 2006. described as “business as usual.” Of course, not all contributions addressing interdisciplinary science goals need to be made in an interdisciplinary manner. Nevertheless, it is the committee’s assessment that a growing number of publications being produced by some of the NAI nodes report truly interdisciplinary work. For example, many of the research contributions outlined above (and in Boxes 2.1-2.13) involved collaborations between individuals who categorize themselves primarily as Earth scientists and life scientists (e.g., the work on microbial mats, metal isotopes, and subsurface biospheres) or as Earth scientists and physicists (e.g., the work on Snowball Earth). Other contributions involved more complex collaborations between researchers who call themselves Earth scientists, planetary scientists, astronomers, and chemists (e.g., studies of cometary materials) or Earth scientists, life scientists, planetary scientists, astronomers, and physicists (e.g., modeling of exoplanet biospheres).57 Moreover, the publications that result from these multidisciplinary collaborations are generally of a high quality. This is attested to by the fact that 60 percent of the papers referenced above in the list of the NAI’s most significant scientific contributions (see also Boxes 2.1-2.13) were published in high-impact, general science journals such as Nature (13 percent), Proceedings of the National Academy of Sciences (15 percent), and Science (32
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Assessment of the NASA Astrobiology Institute BOX 2.11 COMETS IN SPACE AND IN THE LABORATORY Construction at NASA’s Goddard Space Flight Center (GSFC) and Ames Research Center (ARC) of premier organic analytical laboratories for astrobiology permits analysis of returned samples from the Stardust mission (Donald Brownlee, a member of the NAI team at the University of Washington team and the principal investigator of the Stardust mission) and simulations of organic synthesis that takes place in the interstellar material and on the surfaces of icy bodies. The GSFC team’s study of Stardust samples has provided identification of specific cometary organic compounds (i.e., methylamine and ethylamine). Laboratory work has led to the discovery that the reaction mechanism for the formation of amino acids from ultraviolet photolyzed ices varies by amino acid. The laboratory study at ARC of the properties of polycyclic aromatic hydrocarbons has led to the identification of this ubiquitous compound in many solar system bodies and as an important reservoir of carbon throughout this (and other) galaxies. Astronomical observations of comets—undertaken by the NAI teams at GSFC and the University of Hawaii—have shown that Kuiper Belt and Oort cloud reservoirs both contain compositionally-distinct comets formed in diverse nebular regions, with both organics-normal and organics-depleted comets found in both reservoirs. These results support the emerging new paradigm in which icy planetesimals from diverse regions of the protoplanetary disk are injected into each reservoir, albeit in different fractions. Bibliography D. Brownlee, P. Tsou, J. Aléon, C.M. O’D. Alexander, et al., “Comet 81P/Wild 2 Under a Microscope,” Science 314: 1711, 2006. J. E. Elsila, J.P. Dworkin, M.P. Bernstein, M.P. Martin, and S.A. Sandford, “Mechanisms of Amino Acid Formation in Interstellar Ice Analog,” Astrophysical Journal 660: 911-918, 2007. D.M. Hudgins and L.J. Allamandola, “Interstellar PAH Emission in the 11-14 Micron Region: New Insights from Laboratory Data and a Tracer of Ionized PAHs,” Astrophysical Journal 516: L41-L44, 1999. M.J. Mumma, M.A. DiSanti, K. Magee-Sauer, B.P. Bonev, et al., “Parent Volatiles in Comet 9P/Tempel-1: Before and After Impact,” Science 310: 270-274, 2005. S.A. Sandford, J. Aléon, C.M. O’D. Alexander, T. Araki, et al., “Organics Captured from Comet 81P/Wild 2 by the Stardust Spacecraft,” Science 314: 1720, 2006. M.G. Trainer, A.A. Pavlov, H.L. DeWitt, J.L. Jimenez, C.P. McKay, and M.A. Tolbert, “Organic Haze on Titan and the Early Earth,” Proceedings of the National Academy of Sciences 103: 18035-18042, 2006. percent). Of the remaining papers referenced, a significant number were published in high-impact, specialized journals such as the Astrophysical Journal (9 percent). Entrepreneurial researchers within nodes use NAI resources effectively to leverage funding from their home institutions, other federal agencies (e.g., the National Science Foundation, the National Oceanic and Atmospheric Administration, the National Institutes of Health, and the Department of Energy), and private sources. This appears to be critical to the success of NAI nodes, and it is not clear that any of the nodes could accomplish their research goals without these additional funds. Two NAI teams, those based at Harvard University and the Scripps Research Institute, decided to forgo re-competing for additional NAI funds when their 5-year funding term expired and obtained more substantial funding from other sources. Former members of the Harvard team and others are now developing a major origins-of-life initiative independent of NAI funding.58 Other nodes reported the attrition of researchers when available resources dwindled to levels that could not sustain effective collaborations. An example of the effective leveraging of NASA funds is given by the NAI’s Astrobiology Drilling Program (ADP), which has given researchers unprecedented access to pristine rock cores obtained from stratigraphic intervals that encompass critical periods in Earth’s biogeological history. The ADP consisted of two separate but
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Assessment of the NASA Astrobiology Institute BOX 2.12 EXOPLANET DISCOVERY AND ANALYSIS The NAI has contributed to perhaps the most astronomical aspect of astrobiology, the discovery of extrasolar planetary systems. The majority of the 250 known exoplanets have been discovered by Paul Butler (Carnegie Institution of Washington team), Geoffrey Marcy (University of California, Berkeley, team), and their colleagues in the California-Carnegie Planet Search. Marcy, Butler, and their colleagues are conducting long-term precision Doppler surveys with the Keck 10-m, Magellan 6.5-m, Lick 3-m, and Anglo-Australian 3.9-m telescopes. These surveys have found about 140 planets over the past 12 years. This group (partially sponsored by the NAI) is nearing completion of a Planet Hunting Spectrometer for the Carnegie team’s Magellan 6.5-m telescope, a 2.4-m robotic planet-finding telescope at the Lick Observatory, and two 80-cm robotic photometry telescopes at the Carnegie team’s Las Campanas Observatory in Chile. The Lick Robotic Telescope should allow the team to detect the small-amplitude signals of Earth-mass planets by searching every night. Carnegie astronomers Alan Boss and Alycia Weinberger are searching for gas giant planets around nearby low-mass stars using their new astrometric camera on the du Pont 2.5-m telescope at Las Campanas. While a habitable Earth has not yet been found, the astronomers of the NAI’s Carnegie team are working toward this ultimate goal. Astronomers from the NAI’s Virtual Planetary Laboratory team are using the Spitzer Space Telescope to study the atmospheric composition of giant planets from their transit signals, including the tantalizing possibility of the discovery of water vapor in the atmosphere of a hot giant planet. Bibliography R.P. Butler, J.T. Wright, G.W. Marcy, D.A. Fischer, et al., “Catalog of Nearby Exoplanets,” Astrophysical Journal 646: 505-522, 2006. G. Tinetti, A. Vidal-Madjar, M.-C. Liang, J.-P. Beaulieu, et al., “Water Vapour in the Atmosphere of a Transiting Extrasolar Planet,” Nature 448: 169-171, 2007. related drilling campaigns in Western Australia. The first, the Archean Biosphere Drilling Project, involved an international collaboration linking Japan’s Kagoshima University, the Geological Survey of Western Australia, the University of Western Australia, and the NAI team at Pennsylvania State University. The second, the Deep Time Drilling Project, was an NAI-wide activity involving members of the NAI teams at the University of Washington, University of Colorado, and Harvard University. The cores extracted in both campaigns have been archived and a sample-distribution process defined that involves the submission of a proposal to a scientific review committee. Anyone in the scientific community can apply to receive samples for analysis, and the analytical results are archived and made available to the entire community. This has been an effective means for stimulating research in critical areas. Other examples of leveraging involve international cooperative activities that have provided U.S. astrobiologists with access to field sites that might not otherwise be readily accessible. Notable examples of such activities include the 2006 NAI-Russian Expedition to Klyuchevsky Volcano in Kamchatka and the cooperative development with Spanish astrobiologists of Rio Tinto of southwestern Spain as an analogue site for studies relating to habitable zones on early Mars. RECOMMENDATIONS FOR FUTURE NAI ACTIVITIES With respect to the goal of conducting, supporting, and catalyzing collaborative interdisciplinary research, the committee finds that the NAI has:
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Assessment of the NASA Astrobiology Institute BOX 2.13 MODELING EXOPLANET BIOSPHERES The NAI’s Virtual Planetary Laboratory, led by Victoria Meadows, has organized a highly multidisciplinary team to undertake research on habitability, extrasolar terrestrial planets, and biosignatures. This is a fundamentally new effort to develop models for the co-evolution of planets and life, addressed to NASA’s requirements for future missions to search for life beyond the solar system. The NAI’s Virtual Planetary Laboratory (VPL) has undertaken a broadly based theoretical effort to understand the co-evolution of terrestrial-type planets and their biospheres. At a time when direct observations of extrasolar terrestrial planets are not yet possible, theoretical research has been used to constrain the likely prevalence of habitable planets and the nature and detectability of biosignatures. Working with NAI colleagues on the Pennsylvania State University, University of Colorado, University of Arizona, Ames, Arizona State University, and University of Washington teams, the VPL’s highly interdisciplinary team used planet formation models to understand the likelihood of habitability and water content for terrestrial planets around M stars, or those formed in the wake of a migrating Jupiter. Climate-chemistry and radiative transfer models were used to constrain the surface habitability of model planets. Other studies by the VPL team included the formation and detectability of gaseous photosynthetic byproducts, and the discovery of the enhanced detectability of known and new biosignatures and photosynthetic pigments for planets around stars that are hotter and cooler than our Sun. The VPL has received its primary support from the NAI, and it exemplifies a new kind of multidisciplinary research organization focused on a single class of problems. Disciplines represented by the VPL team include atmospheric chemistry, planetary science, biochemistry, computational geoscience, infrared astronomy, atmospheric physics, ecosystems, astrophysics, astrochemistry, biometeorology, planetary dynamics, biogeochemistry, high-energy radiation, oceanography, bioinformatics, geophysics, heliophysics, chemical physics, and astrobiology. Bibliography N.Y. Kiang, A. Segura, G. Tinetti, Govindjee, R.E. Blankenship, M. Cohen, J. Siefert, D. Crisp, and V.S. Meadows, “Spectral Signatures of Photosynthesis. II. Coevolution with Other Stars and the Atmosphere on Extrasolar Worlds,” Astrobiology 7: 252-274, 2007. A.M. Mandell, S.N. Raymond, and S. Sigurdsson, “Formation of Earth-like Planets During and After Giant Planet Migration,” Astrophysical Journal 660: 823-844, 2007. S.N. Raymond, T. Quinn, and J.I. Lunine, “High-resolution Simulations of the Final Assembly of Earth-Like Planets. 2. Water Delivery and Planetary Habitability,” Astrobiology 7: 66-84, 2007. A. Segura, J.F. Kasting, V. Meadows, M. Cohen, J. Scalo, D. Crisp, R.A.H. Butler, and G. Tinetti, “Biosignatures from Earth-like Planets Around M Dwarfs,” Astrobiology 5: 706-725, 2005. Successfully promoted interdisciplinary science. This is evidenced by the publication record and feedback from the NAI’s principal investigators and the establishment of two new scientific journals, Astrobiology and ZThe International Journal of Astrobiology, specializing in the publication of interdisciplinary results. Although the publications are somewhat difficult to analyze in their entirety, they do indicate that a significant amount of interdisciplinary and collaborative research has been accomplished. Stimulated many scientific achievements. The field of astrobiology has grown tremendously in the past decade. A partial indication of the NAI’s contributions to this growth is given in the NAI’s list of its top research contributions (see Boxes 2.1-2.13). Particularly notable are important contributions to the developing field of metagenomics—the application of the techniques of genomic analysis to the study of entire communities of microorganisms59—undertaken by several NAI teams as highlighted, for example, by the activities relating to the ecology of microbial mats (see Box 2.4) and the unexpected diversity of marine microbial communities (see Box 2.5).
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Assessment of the NASA Astrobiology Institute Successfully integrated life sciences into NASA programs. There is much evidence of successful collaboration between biologists and non-biologists in the context of NASA activities, as evidenced by many of the NAI contributions highlighted in Boxes 2.1-2.13. Often effectively leveraged ongoing and new research. To be productive, some of the successful astrobiology programs, especially those at various universities, have required funding and other support from non-NASA sources. The NAI’s programs have facilitated these relationships. A prime example of leveraging of funds is recounted in the discussion above concerning sub-seafloor life (see Box 2.6): a relatively small NAI contribution was more than matched by significant contributions in the form of infrastructure and operating costs borne by the Ocean Drilling Program. Similarly, the NAI support for the laboratory analysis of cometary materials (see Box 2.11) was an insignificant addition to the cost borne by NASA’s Planetary Science Division for the design, construction, launch, and operation of the Stardust spacecraft that actually collected the cometary samples and returned them to Earth. Finally, the Astrobiology Drilling Program could not have been undertaken without significant foreign contributions. Contributed to the establishment of new astrobiology programs worldwide. There are now astrobiology institutes, centers, and programs in many countries. Most, if not all, trace their origins to the encouragement and inspiration provided by the NASA program. Supported programs that are widely distributed throughout the United States. The universities and research institutions currently engaged in research in astrobiology are located throughout the United States, which will facilitate the continued growth of the field. Recommendation: The NAI should institute better measures of performance and progress to improve the accountability of its nodes in promoting astrobiology as a field of interdisciplinary and collaborative study. The committee suggests the following actions to implement this recommendation: The NAI could consider conducting thorough, unbiased reviews of its nodes to ensure that they continue to nurture the NAI’s original intent to promote astrobiology as a field of interdisciplinary and collaborative study. These reviews could assess the extent to which the NAI strategy has promoted new approaches resulting in science or discoveries that would not have been pursued by traditional programs. An iterative schedule of review, evaluation, and response during the active period of each award might serve to increase attention to facilitating interdisciplinary collaborations within nodes. The nodes could be required to demonstrate their collaborative, interdisciplinary activities through annual reporting that explicitly documents what is truly interdisciplinary. Site visits (virtual or actual) approximately midway through a node’s 5-year funding period could be instituted, and these visits could focus on evaluation of interdisciplinary, collaborative accomplishments. Nodes submitting re-competition proposals could be required to show evidence of sustained and productive interdisciplinary interactions, specifically peer-reviewed papers by authors in different fields. Interdisciplinary, collaborative research could be encouraged throughout all aspects of NAI activities. Proposals that clearly target questions that can only be addressed using interdisciplinary approaches could be favored, even if this means fewer nodes for a given announcement of opportunity. This is especially important if there is not sufficient funding to adequately support the desired number of nodes. The NAI could seek ways to increase communication between nodes and reduce competitiveness between teams by offering incentives to promote interteam collaborative interactions. One simple incentive-based approach might be to institute a yearly award to recognize a team or teams that have been particularly successful in collaborative research. NAI Central could continue to balance the number of nodes with projects funded by the DDF, so that all astrobiology activities in the NAI roadmap are represented. The DDF could be retained and could serve as a predictable and effective funding instrument. The majority of the DDF could be reserved for projects that explicitly support the NAI’s goal of conducting, supporting, and catalyzing collaborative interdisciplinary research. Recommendation: The NAI should improve the tracking and critical assessment of its publications. The committee suggests the following actions to implement this recommendation:
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Assessment of the NASA Astrobiology Institute NAI Central could consider carrying out a detailed review of publications by NAI-funded teams on an annual basis. To enable this review, NAI Central could develop and maintain a single unified database of the NAI publications. Furthermore, NAI Central could develop and maintain the procedures and tools needed to analyze the impact, relevance to astrobiology, originality, and interdisciplinary character of publications, with feedback to individual NAI members, individual NAI nodes, and the NAI as a whole. Although computerized techniques and the expertise of information-technology specialists will play an essential role in this effort, scientists with broad experience must be involved in the evaluation of individual publications. The NAI director could have a role in the evaluation of papers, and self-evaluation by the principal investigators of the individual NAI nodes could be useful. The details of how the database is organized and how the evaluation is carried out are the responsibility of the NAI. However, the committee offers the following suggestions: (1) The individual nodes could include a detailed bibliography of the papers actually published during the reporting period as part of their annual reports; (2) papers in preparation would not be included; (3) the bibliographies could include complete citations, including titles and abstracts or links to abstracts; (4) the analysis would only consider papers in refereed journals or books; (5) duplicate entries in the master database would be avoided; (6) the disciplines and NAI node affiliations of each author could be part of the database and could be available for analysis; (7) measures of impact, relevance to astrobiology, and originality could be part of the database and available for analysis; and (8) only papers that acknowledge the NAI explicitly, either for support or for inspiration, would be included in the analysis. The committee recognizes that the details of the database will require additional thought and consideration beyond that which was feasible within the context of this study. To successfully accomplish item 7, for example, requires a determination of how to measure such things as impact, relevance, and so on. Similarly, determining the criteria for item 8 may require the adoption of a policy concerning the leveraging of NAI funds with those from other sources. Recommendation: The NAI should encourage and cultivate interactions with non-NAI astrobiology teams and organizations throughout the world. The committee suggests the following actions to implement this recommendation: Care should be taken to ensure that the NAI promotes an open program that engages the entire astrobiology community and scientists in related fields of endeavor to avoid the perception that it and its activities are exclusive privileges of NAI membership. The NAI could continue its efforts to develop astrobiology at the international level through co-sponsored educational activities (e.g., the Pilbara field conference with the Australian Center of Astrobiology) and public outreach (e.g., sessions at international conferences such as those of the International Society for the Study of the Origin of Life and the IAU-sponsored Bioastronomy meetings). The NAI could make its existing Web site a more effective portal for astrobiology by promoting access to it by all interested parties (not just NAI members) and by more inclusive coverage of pertinent astrobiology science, sources, and non-NASA sites. NOTES 1. The NAI Web site can be found at http://www.nai.nasa.gov. 2. C.E. Manning, S.J. Mojzsis, and T.M. Harrison, “Geology, Age and Origin of Supracrustal Rocks at Akilia, West Greenland,” American Journal of Science 306: 303-366, 2003. 3. S.J. Mojzsis, T.M. Harrison, and R.T. Pidgeon, “Oxygen-isotope Evidence from Ancient Zircons for Liquid Water at the Earth’s Surface 4,300 Myr Ago,” Nature 409: 178-181, 2001. 4. A.D. Anbar and A.H. Knoll, “Proterozoic Ocean Chemistry and Evolution: A Bioinorganic Bridge?” Science 297: 1137-1142, 2002. 5. Y. Shen, A.H. Knol, and M.R. Walter, “Evidence for Low Sulphate and Anoxia in a Mid-Proterozoic Marine Basin,” Nature 423: 632-635, 2003. 6. S. Ono, B. Wing, D. Johnston, D. Rumble, and J. Farquhar, “Mass-dependent Fractionation of Quadruple Stable Sulfur Isotope System as a New Tracer of Sulfur Biogeochemical Cycles,” Geochimica et Cosmochimica Acta, 70: 2238-2252, 2006. 7. H. Ohmoto, Y. Watanabe, H. Ikemi, S.R. Poulson, and B.E. Taylor, “Sulphur Isotope Evidence for an Oxic Archaean Atmosphere,”
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Assessment of the NASA Astrobiology Institute Nature 442: 908-911, 2006. 8. A.D. Anbar, Y. Duan, T.W. Lyons, G.L. Arnold, B. Kendall, R.A. Creaser, A.J. Kaufman, G. Gordon, C. Scott, J. Garvin, and R. Buick, “A Whiff of Oxygen Before the Great Oxidation Event?” Science 317: 1903-1906, 2007. 9. G.P. Halverson, P.F. Hoffman, D.P. Schrag, A.C. Maloof, and A.H.N. Rice, “Toward a Neoproterozoic Composite Carbon-isotope Record,” Bulletin of the Geological Society of America 117: 1181-1207, 2005. 10. P.F. Hoffman and D.P. Schrag, “The Snowball Earth Hypothesis: Testing the Limits of Global Change,” Terra Nova 14: 129-155, 2002. 11. D. Condon, M.Y. Zhu, S. Bowring, W. Wang, A. Yang, and Y. Jin, “U-Pb Ages from the Neoproterozoic Doushantuo Formation, China,” Science 308: 95-98, 2005. 12. M.-C. Liang, H. Hartman, R.E. Kopp, J. Kirschvink, and Y.L. Yung, “Production of Hydrogen Peroxide in the Atmosphere of a Snowball Earth and the Origin of Oxygenic Photosynthesis,” Proceedings of the National Academy of Sciences 10: 18896-18899, 2006. 13. T.M. Hoehler, B.M. Bebout, and D.J. Des Marais, “The Role of Microbial Mats in the Production of Reduced Gases on the Early Earth,” Nature 412: 324-327, 2001. 14. D.C. Catling, K.J. Zahnle, and C.P. McKay, “Biogenic Methane, Hydrogen Escape, and the Irreversible Oxidation of Early Earth,” Science 293: 839-843, 2001. 15. D.J. Des Marais, “The Biogeochemistry of Hypersaline Microbial Mats Illustrates the Dynamics of Modern Microbial Ecosystems and the Early Evolution of the Biosphere,” The Biological Bulletin 204: 160-167, 2003. 16. R.E. Ley, J.K. Harris, J. Wilcox, J.R. Spear, S.M. Miller, B.M. Bebout, J.A. Maresca, D.A. Bryant, M.L. Sogin, and N.R. 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