Searching for an Alien Haven in the Heavens

Introduction

Searching for an alien haven in the heavens

he first few articles in this issue of PNAS paleontologist George Gaylord Simpson (2) quell or support Goldin’s enthusiasm and Tconstitute the beginning of a two-part summarized the search for extraterrestrial aspirations for astrobiology. However, re- Special Feature dedicated to the study of life—and more particularly intelligent life— cent advances like the discovery of sub- astrobiology. Astrobiology is not an auton- more bluntly, ‘‘a gamble of the most adverse surface water reservoirs on Europa and omous or self-sustaining discipline. Rather, odds in history.’’ Recent skeptics include aquifers on Mars, the increasing roster of it is a hybrid subject emerging at the cross- Peter Douglas Ward and Donald Brownlee ‘‘habitable’’ planets, and enhanced life roads of astronomy, geology, paleontology, (3), who reject the possibility of finding detection techniques all have fostered an physics, and biology. What at first pass may complex bioorganic material on other plan- air of confidence among astrobiologists. seem like an amalgamation of disparate etary bodies by emphasizing the staggering In this Special Feature issue the perspec- fields, upon further review, is a clear and statistical improbability. tive by Christopher Chyba and Cynthia Phil- increasingly defined discipline. The roots of However, there have also been Nobel lips (5) gives an overview of our current astrobiology are found in the 10 distinct Laureates, world-renowned scientists, and knowledge about the environmental condi- goals set by the National Aeronautics and trusted scholars who advocate astrobiology tions on Europa. Jeffrey Bada’s perspective Space Administration (NASA) Astrobiol- and the likelihood of finding bioorganic (6) discusses the instrumentation challenges ogy Institute. These objectives can be sum- molecules and extraterrestrial life. Carl Sa- faced when undertaking extraterrestrial ex- marized into three branches: How does life gan is perhaps the best-known father of ploration. The paper by Norman Pace (7) begin and develop? Does life exist else- astrobiology, but credit is also due to Chris- addresses the nontrivial question of what are where in the universe? What is life’s future tian de Duve, who heralded the existence of we looking for when we seek extraterrestrial on Earth and beyond? extraterrestrial biology as a ‘‘cosmic imper- biochemistry. Some preliminary answers to these ative’’ (4). During his term, Daniel Goldin, The next Special Feature issue will con- questions were addressed at the first large the first director of the NASA Astrobiology tain perspectives by John Rummel, NASA’s scientific conference dedicated entirely to Institute, secured funding, space and mis- planetary protection officer; and Baruch astrobiology, held April 25–26, 2000 at the sion time for the fledgling field. At the Blumberg, director of NASA’s astrobiology Ames Research Center at Moffett Field, summer of 1999 meeting of the American institute coauthored with Michael Meyer, a CA. A few months later an international Astronomical Society, Goldin optimistically NASA astrobiology discipline scientist. ‘‘Frontiers of Life’’ conference was held in declared that in the next century ‘‘scientists Their papers will cover topics including France’s Loire Valley. Sessions at those will debate the structure of continents and planetary protection, NASA’s astrobiology meetings ranged from ‘‘Water—the Sine oceans, weather patterns, climates, storms, directives, and life in extreme environments. Qua Non of Life,’’ which covered the and the nature of seasons on dozens of new The research articles in these Special Fea- water reservoirs on Jupiter’s moon Eu- worlds.’’ And with oceans, weather patterns, ture issues touch on, among other areas, the ropa; ‘‘Environment,’’ which covered and storms, some assume come environ- topics of biosignatures, extrasolar planets snowball earth, life in extreme environmental conditions ripe for biological chem- and their habitability, modeling of environments, the evolution of biochemisty, and istry to emerge. In 1953 Harold Urey and mental conditions and atmospheres, and life interstellar quinones; ‘‘Life Detection Stanley Miller from the University of Chi- in extreme environments. As with all past Methods and Biosignatures’’; and ‘‘Detec- cago created such an environment when Special Features, the perspectives and re- tion Methods for Extrasolar Planets.’’ they mimicked the proposed ‘‘early earth’’ search articles will be accessible without the need for a subscription at www.pnas.org. We Many of these topics are expounded in this atmospheric conditions. After passing elec- offer them to you as part of the Academy’s issue of PNAS, and it is clear that the two tricity through gaseous methane, ammonia, long-standing tradition to foster pioneering premier conferences marked the official water, and hydrogen they were left with a research and innovative academic discus- beginning of a wave of discourse that ‘‘soup’’ mixture of amino acids. Astrobiolo- sions. Fueled by science’s increasing inter- undoubtedly has as many opinions as gists hope to find a planet, other than Earth, stellar technology, funded by a $20 million voices. where similar conditions could occur. Such annual NASA budget, fostered by private Early astrobiology had some high-profile a Urey–Miller-like planet would indeed be a research funds of astronomical proportions, skeptics like French biologist Jacques rare, but not statistically impossible, Gold- and followed by the public’s unending curi- Monod who in 1971 categorically dismissed ilocks planet as it would have to be not too osity to know whether we are alone in the the field. He reasoned that the ‘‘unfeeling hot, not too cold, not too small, not too universe, astrobiology may well emerge as immensity of the Universe’’ left one to large, and, at least until our current detec- the scientific discipline of this millennium. conclude that biological organization tion technology improves, not too faraway. emerged alone and by chance in a phenom- With only a small fraction of the new Bridget C. Coughlin, Associate Recruiting enal chemical fluke (1). In 1964 American century underway it is premature to either Editor

1. Monod, J. (1971) Chance and Necessity: An Essay 3. Ward, P. D. & Brownlee, D. (2000) Rare Earth: Why Sci. USA 98, 801–804. on the Natural Philosophy of Modern Biology (Vin- Complex Life Is Uncommon in the Universe (Springer, 6. Bada, J. (2001) Proc. Natl. Acad. Sci. USA 98, tage, New York). New York). 797–800. 2. Simpson, G. G. (1964) This View of Life: The World 4. de Duve, C. (1995) Vital Dust: Life as a Cosmic 7. Pace, N. (2001) Proc. Natl. Acad. Sci. USA 98, of an Evolutionist (Harcourt, Brace, and World, Imperative (Basic Books, New York). 805–808. New York). 5. Chyba, C. & Phillips, C. (2001) Proc. Natl. Acad.

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