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1 The Roadmaps BACKGROUND OF NASA'S 1998-1999 ASTROBIOLOGY ROADMAP The word astrobiology was used in a published text as far back as 1953i but was superseded by the term exobiology, which came to represent the NASA effort to understand the origin of life and to search for life elsewhere. In 1995, then-Associate Administrator for Space Science Wesley Huntress, in trying to infuse the biological sciences into NASA's Space Science activities, used the term Astrobiology to connote a proposed new multidisciplinary program in the space and biological sciences. The program would be in large measure (but not exclusively) an intellectual outgrowth of the NASA Exobiology and Astronomical Search for Origins research and analysis programs, within which important progress had been made already on specific questions regarding the origin and ubiquity of life in the cosmos. In 1996, then-NASA Administrator Daniel Goldin recognized and sought to capitalize on the immense public interest generated by the 1996 report of putative fossil organisms in the martian meteorite ALH84001,2 and by the discovery of planets orbiting nearby stars like the Sun.3 With the help of NASA's Ames Research Center and the late Gerald Soffen, who was project scientist for the Viking missions to Mars in the 1970s, NASA began the definition of the new program in Astrobiology, broadly construed as the investigation of the origin, distribution, and future of life in the universe.4 In 1997, the agency announced its intention to create a geographically distributed institute for the study of astrobiology, to provide general research funding under this rubric, and to use the institute as an experiment in the use of new communications technology to enable scientists to work intimately on collaborative research regardless of geographical limitations. Eleven initial nodes were selected, each headed by a lead university, research institute, or NASA center. The Ames Research Center serves as the central administration for what became known as the NASA Astrobiology Institute, or the NAI. In 2001, four additional nodes were selected, bringing the total to 15. Because the NAI is such a central part of the NASA Astrobiology program, the Committee on the Origins and Evolution of Life (COEL) devotes a separate chapter to its evaluation (see Chapter 2~. Subsequent to the formation of the NAI in 1998, NASA began the process of developing an Astrobiology Roadmap. The stated purpose of this document was to guide research not only in the NAI but in general research and analysis (R&A) programs related to astrobiology, and to develop a complementary technology program for space-based experiments. 8

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THE ROADMAPS 9 CONTENT OF THE ASTROBIOLOGY ROADMAP While the detailed events that transpired during the development of the Astrobiology Roadmap are an interest- ing exercise in scientific sociology, they are not immediately germane to the task given to COEL and so their retelling is left to others. The output of the roadmapping effort was a series of subject areas motivated by the following questions, which were developed by NASA and the external scientists who comprised the Roadmap Team.5 The roadmap begins with three overarching questions, whose ultimate answers lie far in the future but which motivate the research: 1. How does life begin and evolve? 2. Does life exist elsewhere in the universe? 3. What is life's future on Earth and beyond? These questions, in turn, motivate a set of 10 more detailed "goals" for the scientific research to be conducted within the context of the Astrobiology program. Possible research projects to address these goals have a more detailed set of objectives, but the Astrobiology Roadmap itself offers a set of 17 generic objectives on which, arguably, significant progress can be made in the near-term future. Those objectives, which sample well a more detailed set of objectives formulated by scientific researchers, are listed verbatim in Table 1.1. The 10 goals developed in the roadmap process are summarized below, as a narrative set of questions: 1. Understand how life arose on Earth. The origin of life on Earth represents the starting point for assessing the degree of commonality of life in the cosmos. Where did the raw materials for life on Earth come from? How were the elements manufactured in previous generations of stars, and in what sorts of molecular arrangements were these materials found in the nascent disk of gas and dust from which our planetary system formed? How and from where was this material delivered to Earth? What were the environments in which life evolved from nonliving chemical systems? What were the phenotypic features of the first organism? When did life begin on Earth? Is the origin of life a common part of the processes of planetary formation and evolution? 2. Determine the general principles governing the organization of matter into living systems. Complemen- tary to the first goal is the "holy grail" of experimental biologists and chemists who work on life's origins: by just what processes does organic (here meaning "carbon-bearing") matter become organized into self-sustaining, living things, that is, life? Does the organization proceed within organic chemical systems themselves, or is templating within mineralogical or other inorganic systems required? What are the temporal and spatial scales and the levels of starting system complexity required for the origin of life? What sources of energy are required? What other kinds of chemical or physical systems can self-organize into patterns that we might call life? Is liquid water required for life? Is life a phenomenon requiring at least two basic kinds of polymers (molecules composed of repeated fundamental units), one devoted to information, the other to structure and catalysis? Indeed, what is the most general but useful definition of life? 3. Explore how life evolves on the molecular, organismal, and ecosystem levels. The history of life is recorded both in the rocks of Earth and in the genetic information stored in every organism. From these disparate types of records, it is possible to map out an extraordinarily complex history of evolutionary changes in life, punctuated by environmental catastrophes that in part (sometimes nearly in whole) emptied ecosystems. What are the detailed genetic relationships among Earth's organisms? How much has the evolution of life been driven by large-scale transfer of genetic molecules among types of microorganisms? How have the mutability and duplica- tive nature of the genetic material, coupled with environmental changes, driven the evolution of life? Why are there three major domains of life, when did they arise, and have other domains become extinct? What factors internal and external to life led to the origin of complex cells (eukaryotes), and to multicellular complex organ- isms? What is the evolutionary origin of human intelligence, how is it coupled to self-awareness, and has it arisen in other organisms? 4. Determine how the terrestrial biosphere has convolved with Earth. The evolution of life on Earth has proceeded over the course of 4 billion years, during which the planet itself has undergone profound changes to the

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10 TABLE 1.1 Objectives Offered for Astrobiology by the NASA Astrobiology Roadmap LIFE IN THE UNIVERSE Overarching Questions and Topical Areas Scientific Goals 1. How does life begin and evolve? Sources of organics on Earth Determine whether the atmosphere of the early Earth, hydrothermal systems or exogenous bodies were significant sources of organic matter. Origin of life's cellular Develop plausible pathways by which ancient counterparts of membrane systems, proteins and components nucleic acids were synthesized from simpler precursors and assembled into protocells. Models for life Create lab models of replicating, catalytic systems capable of evolution, and metabolism in primitive living systems. Genomic clues to evolution Expand and interpret the genomic database of a select group of microorganisms so as to reveal the history of evolution. Linking planetary and Describe the causes and effects associated with development of Earth's early biosphere and the biological evolution global environment. Microbial ecology Define how single-organism and group physiological processes structure microbial communities, influence their adaptation and evolution, and affect detection on other planets. 2. Does life exist elsewhere in the universe? The extremes of life Identify the environmental limits for life by examining biological adaptations to extremes in conditions. Past and present life on Mars Search for evidence of ancient climates, extinct life and potential habitats for extant life on Mars. Life's precursors and habitats Determine the presence of life's chemical precursors and potential habitats for life in the outer in the outer solar system solar system. Natural migration of life Understand the natural processes by which life can migrate from one planet to another, and quantify the probabilities. Origin of habitable planets Determine (theoretically and empirically) the ultimate outcome of the planet-forming process around other stars. Effects of climate and Define climatological and geological effects upon the limits of habitable zones around the Sun geology on habitability and other stars to help define the frequency of habitable planets in the universe. Extrasolar biomarkers Define an array of astronomically detectable spectroscopic features that indicate habitable conditions and/or the presence of life on an extrasolar planet. 3. What is life's future on Earth and beyond? Ecosystem response to rapid Determine the resilience of local and global ecosystems to natural and human-induced environmental change disturbances. Earth's future habitability Model the future habitability of Earth by examining the interactions between the biosphere and the chemistry and radiation balance of the atmosphere. Bringing life with us Understand the human-directed processes by which life can migrate from one world to beyond Earth another. Planetary protection Refine planetary protection guidelines and develop protection technology for human and robotic . . mlsslons. SOURCE: Office of Space Science, National Aeronautics and Space Administration, Astrobiology Roadmap, Ames Research Center, Moffett Field, Calif., 1999, available online at .

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THE ROADMAPS 11 atmosphere, oceans, and geology. The atmosphere has evolved from being rich in carbon dioxide to being rich in oxygen; correspondingly, the oceans have evolved from being anoxic to being oxygen-rich. The cycling of Earth's outer layer, or crust, has slowed with time, and buoyant masses of granites called continents have come to cover about 40 percent of a surface that initially may have been almost entirely basaltic and largely submerged. The rate of impacts on the surface of Earth diminished rapidly in the first 10 percent of the history of the planet, then declined more slowly with time. When did conditions allow the first organisms and ecosystems to survive? To what extent has the evolution of life been determined by evolving global conditions and sudden environmental catastrophes versus the long-term changes in the genetic code itself? 5. Establish limits for life in environments that provide analogues for conditions on other worlds. Over the past couple of decades, scientists have found life flourishing in environments previously thought to be uninhabit- able from ocean floor vents at high temperatures and extreme pressures to ecosystems buried beneath a kilometer of basaltic rock. Such extreme environments are potentially the refuge of organisms with primitive qualities, which suggests that these organisms are the modern descendants of ancient life forms. What are the most extreme environments of temperature, pressure, salinity, acidity, desiccation, radiation (both acute and chronic), and other parameters under which organisms can survive? What are the limits under which spores can exist and be success- fully revived? Can organisms survive impacts from cometary or asteroidal bodies? Can they survive transport on the fragments of ejected crust to a neighboring world? 6. Determine what makes a planet habitable and how common those worlds are in the universe. The fundamental requirements for life on Earth are an adequate source of thermodynamic-free energy, appropriate sources of carbon and other critical elements, and liquid water. Therefore, the simplest definition of a habitable world would be one that supports the three fundamental requirements. Determining which planets have liquid water today, when and how much liquid water occurred in the past, and whether adequate stores of biogenic elements and energy exist is a daunting problem. In our own solar system, the debates rage on regarding when and where Mars had liquid water, and whether it exists today a quarter century after the valley networks on that planet were first revealed. Compelling but circumstantial evidence exists for a liquid-water ocean under the icy crust of Europa, maintained by tidal heating; if life exists there, it is a long way from the traditional "habitable zone" defined by orbital distances similar to that of Earth around Sun-like stars. Do Mars and Europa support life now, or has Mars supported life in the past? Does the profoundly cold but organic-rich Titan, the giant moon of Saturn, support at least the early steps toward life's origin? What is the range of possibilities for habitable zones around stars like and unlike the Sun? How do Earth-like planets gain their water and organics, and how many are in planetary systems environments that, over billions of years, resemble that of Earth? Could an Earth-sized body orbiting a star like the Sun at a Mars-like distance support life, and for how long? 7. Determine how to recognize the signature of life on other worlds beyond the solar system. The detection of planets orbiting stars that shine a billion or more times more brightly than the planets themselves is a daunting task; as yet it has been done indirectly, with one exception. Even when large ground- and spaced-based telescopic systems become capable of teasing the light of a planet out from under the glare of its parent star, the challenging task of determining whether such planets are habitable remains unsolved even if the biosphere that one is looking for is Earth-like. Indeed, distinguishing a planet whose atmosphere contains gases in chemical disequilibrium is not enough, because one must know whether the disequilibrium is caused by biological processes or by rapid evolution of the planet's atmosphere itself. The cases of planets where primitive life has only a toehold, or on which life forms different from Earth's exist, or which have only subsurface life beneath an inhospitable surface such as Europa's, may represent those that are impossible to detect remotely. How could one detect the effects of biospheres on parent planets many light years away? How can one separate rapid abiotic planetary evolution from the biochemical modification of surface and atmosphere? To what extent could one detect the signature of life on planets with atmospheres very different from Earth's, or on planets with no atmospheres at all? Finally, how can the search for signals from extraterrestrial civilizations be designed to provide a useful negative answer in the absence of a history-changing positive result? 8. Determine whether there is (or once was) life elsewhere in our solar system, particularly on Mars and Europa. The first directed search for life in our own solar system, the Viking expeditions to Mars, yielded negative results regarding the presence of life at the landing sites. Debate continues on the claim of evidence for biological

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2 LIFE IN THE UNIVERSE activity in the martian meteorite ALH84001 more than 6 years after the initial exciting announcement.6 What are the most robust sets of life-detection experiments to carry to Mars, or to Europa? What types of robotic exploration capabilities are required to find and access sites at which such tools would be useful? Is it best to search for life directly on the surface of a body (e.g., in situ) or to return a sample to Earth? What are the hazards of contaminating a planet with organisms carried from Earth, or of contaminating Earth with a returned sample? How would one recognize life that had an origin separate from earthly life? 9. Determine how ecosystems respond to environmental change on time scales relevant to human life on Earth. Life on Earth today, while still dominated in numbers by the prokaryotes (archaea and bacteria), may be profoundly challenged by the vigor and power of human industrial activities. The species extinction rate today has been amplified directly and indirectly by human activity, relative to that of the average background seen in the geologic record of the last half-billion years (10 percent) of Earth's history. What does the geologic record tell us of the range of climatic extremes and time scales for change over the last half-billion years? How does the coupled air-ocean-land system on Earth respond to rapid changes in basic properties? 10. Understand the response of terrestrial life to conditions in space and on other planets. Humanity first left Earth to set foot on another world in 1969. For the astronauts who went to the Moon, even the span of a few days on an alien world was a profoundly moving and lonely experience. While the pace of human expansion beyond Earth slowed after that initial burst of activity, robotic emissaries continue to push outward through the solar system to the realm of nearby interstellar space. Ultimately, humankind might try to colonize the nearby planets and the space around them. ANALYSIS OF THE 1998-1999 ASTROBIOLOGY ROADMAP Scope The scope of the Astrobiology Roadmap is exceedingly broad, encompassing research from the astronomical study of star formation to global change research. While there is a temporal, evolutionary sequence that connects these and many other fields of endeavor as a kind of "story" of the origin and evolution of life, astrobiology as a working endeavor is not as intellectually cohesive as it might be. This lack of cohesion manifests itself to different degrees in different research areas. In global climate change, for example, the connection with astrobiology needs to be more carefully and clearly defined. The specific means by which research on the causes and behaviors of global climate change on decadal time scales a key thrust of the U.S. Global Change Research Program informs research on overarching question 3 in Table 1.1 is not well articulated in the roadmap. It is easier to see the relevance of studies of longer-term climate changes (e.g., periods of glaciation) and abrupt large-scale climate events (such as those seen toward the end of the last glaciation)7 to the key questions associated with planetary habitability. Resolving this issue requires a more careful examination of the role of the U.S. Global Change ~ . ~ . . . . . . . . . ~ . ~ . . ~ . Research Program In astrobiology, a task that should form an Important part of the preparation of the next roadmap. COEL would also like to see a more careful study of the relevance of microgravity research in Earth orbit to NASA' s Astrobiology program, since NASA itself makes this connection in a cursory way in the current roadmap. While gravity has influenced biological processes on Earth, the study of extant organisms subject to varying values of the gravitational acceleration (from zero to terrestrial) may not inform us as to how fundamental biological processes might be reinvented elsewhere under vastly different gravitational conditions. Thus, scientific research planned for the International Space Station (ISS) may not be directly relevant to the central goals of NASA's Astrobiology program. While it is true that the ISS is advertised as the stepping-stone to colonizing other worlds and hence to moving life from Earth into space, this is a symbolic and philosophical linkage rather than a scien- tific one. COEL does not view as constructive NASA's effort to embrace virtually the totality of physical and life sciences in its roadmap definition of astrobiology. The intellectual center of astrobiology remains in the scien- tific activities that NASA refers to as evolutionary biology, exobiology, cosmochemistry, and (in part) the astronomical search for origins and planetary sciences. While there should be no impediment to scientists

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THE ROADMAPS 13 talking across disciplinary boundaries to gain new insights, astrobiology ought not to be oversold as being broader than it really is. Recommendations NASA should more carefully craft its definition of astrobiology as a discipline whose central focus is a selected set of issues directly linked to the origin, evolution, and ubiquity of life in the cosmos. An important operational goal of astrobiology is to inform NASA missions with respect to the tech- niques and targets for the search for life elsewhere, and the search for clues to the steps leading to the origin of life on Earth. The core scientific areas within astrobiology ought to be specifically and selectively defined as those that deal with the origin, evolution, and occurrence of life in the cosmos as embraced in NASA's research and analysis programs in the general areas of exobiology, evolutionary biology, planetary origin and evolution, cosmochemistry, and astronomical studies relating to the search for origins. Global change should be defined more carefully in the next roadmap with respect to the time scales that are relevant to the astrobiological goals of understanding environments conducive to the origin and evolution of life. A critical analysis should be undertaken of the relevance of microgravity research to the central scientific goals of astrobiology. Advances Significant scientific advances have occurred in the past 5 years in addressing some of the questions identified in the Astrobiology Roadmap. Examples of a few areas that have borne particular fruit, with examples of refer- ences, include the following: Analysis of complex organic chemistry in interstellar clouds of gas and dust that give rise to new stars and solar systems;8 Direct study of extrasolar giant planets through transits and spectra;9 Discovery that living organisms, normally found on Earth's surface, can survive at extreme pressure;~ Evidence from geologic features that liquid water once flowed on the surface of the planet Mars; Indications from magnetic field geometry that liquid water likely exists today below the icy crust of three of Jupiter's large moons, most notably, Europa; Ground-based studies of Titan, indicating both temporal and spatial variability and the presence of organic molecules;~3 Chemical-isotopic hints that microbial life on Earth existed 3.9 billion years ago, almost to the period of early heavy cometary bombardment;~4 Evidence that liquid water existed in the crust of Earth some 4.3 billion years ago;~5 Elucidation of the detailed history of evolution and the phylogenetic relationships among organisms; and In vitro evolution experiments that have come close to developing self-replicating systems in the laboratory. i7 Some of these advances will necessitate modifications to the roadmap to reflect insights that were not available 5 years ago. For example, the roadmap played down the study of extrasolar giant planets as a precursor to the study of extrasolar terrestrial planets, in part because there was no opportunity to determine the physical and atmospheric parameters of an extrasolar giant planet 5 years ago; the opportunity exists now, through study of transits and possibly other techniques. Likewise, the assumption in the roadmap that an aggressive and near-term program of exploration of Europa would make it an important astrobiological target on a decadal time scale (i.e., 1999 to 2009) turned out to be overly optimistic. It appears now that the next mission to Europa will launch well after 2010. Nonetheless, in general, the roadmap was well conceived in identifying the larger questions, without micromanaging at the more detailed level.

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14 LIFE IN THE UNIVERSE After almost 5 years of funded research within the Astrobiology program, enough additional evolution of the field of astrobiology has occurred that a new roadmap will be of value; COEL understands that NASA has begun a new roadmap planning process and applauds that efforts CONTENT OF THE NASA ORIGINS ROADMAP The roadmap for NASA's Astronomical Search for Origins program,~9 revised in late-2002, considers all programs that deal with the origin of physical and biological structures in the cosmos, and hence formally includes astrobiology within its themes. The current Origins Roadmap takes as its starting point four goals:20 1. To understand how galaxies formed in the early universe, 2. To understand how stars and planetary systems form and evolve, 3. To determine whether habitable or life-bearing planets exist around nearby stars, and 4. To understand how life forms and evolves.

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THE ROADMAPS 15 their characterization in terms of habitability, the observation of stars and planets in the act of formation, the investigation of interstellar and interplanetary chemistry, and the context of a galaxy replete with ultraviolet radiation, ionization, and fast particles all are scientific elements strongly identified with astrobiology. Yet, paradoxically, with the exception of astrochemistry, in which work on organic chemistry in molecular clouds and primitive solar system bodies informs the earliest stages of life's origins, astronomers engaged in astrobiologically relevant pursuits do not in the main interact with the Astrobiology program. Few participate in the NAI nodes or attempt to or successfully obtain funding through opportunities tagged by NASA as being part of the Astrobiology program. The bulk of the intellectual contributions that astronomy makes to astrobiology are enabled by other programs, such as the Jet Propulsion Laboratory (JPL) Navigator flight programs, National Science Foundation (NSF) Astronomy program, and NASA R&A grants for astronomical studies of origins. Despite two rounds of NAI selections, there is no NAI node whose principal focus is astronomical research in support of astrobiology goals, although one or two of the nodes laudably include some astronomical research. Chapter 3 analyzes this divide further and proposes specific steps to encourage more intimate interaction between the astronomers on the one hand and the geologists, biologists, chemists, and planetary scientists fully engaged in astrobiology on the other. Recommendation In the current respective roadmap processes, careful attention should be paid to the relationship between the Astrobiology and the Astronomical Search for Origins programs in order to identify overlaps, common areas of research, and approaches to enhance the level of interaction in research. THE 2000 SPACE SCIENCE STRATEGIC PLAN The Strategic Plan issued by NASA's Office of Space Science in 2000 is an overarching document that implicitly includes both the Astrobiology and the Origins Roadmaps.24 Because the details of these programs and how they interact are really the purview of the roadmaps themselves, COEL does not make specific comments about the much more general material present in the strategic plan. It would be helpful, however, for the next strategic plan to include a discussion of the relationship between NASA's Astrobiology and Astronomical Search for Origins programs. ESTABLISHMENT OF A COMMUNITY IN ASTROBIOLOGY NSF's Ridge Program which began in 1990 and was intended to focus multidisciplinary investigations to understand the midoceanic ridges and their biology provided an opportunity for a self-selection process to occur among interested scientists. Those unwilling to extend their interests from their own particular areas of expertise to embrace the larger goals and techniques of the multidisciplinary program drifted away from the effort, leaving behind a core community of broad-based scientists. These in turn established their own journals and degree programs and held special sessions at meetings of established scientific societies. Astrobiology today has been through a similar experience. Only a subset of individuals from the fields underpinning this endeavor have embraced the larger goals of astrobiology beyond their particular discipline, but they form the core of a very active and exciting new science. Several institutions had established degree or certificate programs in astrobiology with non-NASA funding (e.g., from NSF) before the NAI was even founded. The number of courses, degree programs (which are usually concentrations or minors supplementing degrees in traditional areas), and textbooks in astrobiology is increasing. More than a dozen faculty lines have been estab- lished within the NAI nodes. Commercial publishers have established two peer-reviewed journals of astrobiol- ogy Astrobiology, published by Mary Ann Liebert, Inc.,25 and The International Journal of Astrobiology, pub- lished by Cambridge University Press.26 Special sessions on astrobiology have taken place at society conferences such as those of the American Chemical Society, the American Geophysical Union, and the American Astronomi- cal Society, and a biennial NAI science meeting and other plenary conferences are also held. All of these signs indicate that astrobiology is beginning to evolve into a distinctive area of research and perhaps will become a new

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16 LIFE IN THE UNIVERSE field in much the way that planetology did in the 1960s. As one of the long-term goals of the NASA Astrobiology Roadmap, this apparent emergence must be seen as encouraging. However, ultimately it makes sense to foster the emergence of a new discipline only if the result is to bring new insights to bear on scientific problems so that the fundamental goal of basic research, to create new knowledge, is achieved. Given the NAI's relative youth, its principal investigators (PIs) found it difficult to provide a list of new discoveries that would not have been made in the absence of the NAI structure or the Astrobiology program as a whole. COEL sent a letter to each of the PIs requesting their response to this issue, and with only a few exceptions, the response was that the question was premature. Throughout the program, several areas can be identified where focused research on traditional issues continues under the aegis of Astrobiology funding. In other cases new . .. . .. .. . . . . ~ . Hi. . . . 0~ 0 interdisciplinary collaborations have been forged. The NAI has given a broader focus to work whose genesis was in the disciplinary research and analysis programs and it has opened up paths of interdisciplinary connections. ~ ~ . . . .. ~ .. ~~ A. . . . . .. . . . .. . . . some of these connections are merely colleagues from different fields coming together to discuss their Individual research; in other cases, specific collaborative experimental or field investigations are being conducted. Further, one cannot come away from the national astrobiology meetings without remarking how well the big questions are being addressed, how easy it is to explain to the informed layperson what the research means, and how readily talented students are attracted to this research area. In summary, anecdotal evidence has been provided by scientists from a number of institutions centrally involved in astrobiology, through the NAI or NSF-funded programs, that their science is gaining an intellectual identity of its own. The evidence includes more diverse and better students, researchers from different disciplines attacking Problems that they never would have encroached creviouslv. and state-of-the-art tools to which they ~7 ~ ~ ~ ~ ~ of, ~ might not otherw. ise have access. The committee does recommend in Chanter 2~ that the NAI nodes themselves O , ~ , . . . . .. . . . . . , . . . . ~ . . ~ . . . . conduct detailed, soul-search~ng reviews (perhaps through the use of nonadvocate panels) of the extent to which their programs have generated genuinely new discoveries that could not have been achieved in the absence of the NAI structure. The enthusiasm and drive of scientists who have aligned their central research foci toward astrobiology, and in particular those involved in the NAI, made a deep impression on COEL. NASA Headquarters, the Ames Research Center, and key members of the scientific community have done a good job in designing and initiating the institute, in encouraging a broader community of astrobiology researchers, and in developing and implement- ing training and degree programs. Recommendation NASA should undertake a comprehensive review of the scientific and educational results of its Astrobi- ology program in general, and of the NASA Astrobiology Institute (NAI) in particular, at the end of a decade of activity, in order to assess the longer-term effects of the founding of the new program and the new institute on the research area. This review would include analysis of the significant scientific contributions that have arisen from the program. It should be undertaken no later than 2008, when the NAI is a decade old. NOTES AND REFERENCES 1. Hubertus Stughold, The Green and Red PlanetA Physiological Study of the Possibility of Life on Mars, University of New Mexico Press, Albuquerque, 1953. 2. Space Studies Board/Board on Life Sciences, National Research Council, Signs of Life: A Report Based on the April 2000 Workshop on Life Detection Techniques, National Academies Press, Washington, D.C., 2002. 3. G.W. Marcy, W.D. Cochran, and M. Mayor, "Extrasolar Planets Around Main Sequence Stars," pp. 1285-1311 in Protostars and Planets IV, V. Mannings, S. Russel, and A.P. Boss, eds., University of Arizona Press, Tucson, 2000. 4. In this report, Astrobiology (capitalized) refers to the NASA program, whose elements are given in Figure 2.1 in Chapter 2, while the lower-case term astrobiology refers to the broader intellectual endeavor itself. 5. The 1999 Astrobiology Roadmap is available online at . 6. Space Studies Board/Board on Life Sciences, National Research Council, Signs of Life: A Report Based on the April 2000 Workshop on Life Detection Techniques, National Academies Press, Washington, D.C., 2002. 7. P.U. Clark, S.J. Marshall, G.K.C. Clarke, S.W. Hostetler, J.M. Licciardi, and J.T. Teller, "Freshwater Forcing of Abrupt Climate Change During the Last Glaciation," Science 293: 283-286, 2001.

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THE ROADMAPS 17 8. P. Ehrenfreund, M.P. Bernstein, J.P. Dworkin, S.A. Sandford, and L.J. Allamandola, "The Photostability of Amino Acids in Space," Astrophysical Journal Letters 550: 95-99, 2001. 9. D. Charbonneau, T.M. Brown, R.W. Noyes, and R.L. Gilliland, "Detection of an Extrasolar Planet Atmosphere," Astrophysical Journal 568: 377-384, 2002. 10. A. Sharma, J.H. Scott, G.D. Cody, M.L. Fogel, R.M. Hazen, R.J. Hemley, and W.T. Huntress, "Microbial Activity at Gigapascal Pressures," Science 295: 1514-1516, 2002. 11. V.R. Baker, "Water and the Martian Landscape," Nature 412: 228-236, 2001. 12. M.G. Kivelson, K.K. Khurana, C.T. Russell, M. Volwerk, R.J. Walker, and C. Zimmer, "Galileo Magnetometer Measurements: A Stronger Case for a Subsurface Ocean at Europa," Science 289: 1340-1341, 2000. 13. R. Meier, B.A. Smith, T.C. Owen, and R. Terrile, "The Surface of Titan from NICMOS Observations with the Hubble Space Tele- scope," Icarus 145: 462-473, 2000. 14. S.J. Mojzsis, G. Arrhenius, K.D. McKeegan, T.M. Harrison, A.P. Nutman, and C.R.L. Friend, "Evidence for Life on Earth Before 3,800 Million Years Ago," Nature 384: 55-59, 1996. 15. 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, 2002. 16. N.R. Pace, "A Molecular View of Microbial Diversity and the Biosphere," Science 276: 734-740, 1997. 17. S.J. Butcher, J.M. Grimes, E.V. Makeyev, D.H. Bamford, and D.I. Stuart, "A Mechanism for Initiating RNA-Dependent RNA Polymer- ization," Nature 410: 235-240, 2001. 18. The new Astrobiology Roadmap was finalized in late 2002, following the completion of this study. It can be found online at . 19. Office of Space Science, National Aeronautics and Space Administration, OriginsRoadmap for the Office of Space Science Origins Theme, JPL 400-887 4/00, Jet Propulsion Laboratory, Pasadena, Calif., 2000. 20. See more details online at . 21. C. Chiappini, "The Formation and Evolution of the Milky Way," American Scientist 89(6): 506-515, 2001. 22. G. Gonzalez, D. Brownlee, and P. Ward, "The Galactic Habitable Zone I. Galactic Chemical Evolution," Icarus 152: 185-200, 2001. 23. More details are available online at . 24. Office of Space Science, National Aeronautics and Space Administration, The Space Science Enterprise Strategic Plan, NP-2000-08- 258-HQ, National Aeronautics and Space Administration, Washington, D.C., 2000. 25. Information on the journal Astrobiology is available online at . 26. More information on the International Journal of Astrobiology is available online at .