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NAS-NRC MAY ;] - i%6 LIBRARY

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BIOLOGY AND THE EXPLORATION OF MARS

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BIOLOGY AND THE EXPLORATION OF MARS Report of a Study Held under the Auspices a\ the SPACE SCIENCE BOARD NATIONAL ACADEMY OF SCIENCES NATIONAL RESEARCH COUNCIL 1964-1965 Edited by COLIN S. PITTENDRIGH, WOLF VISHN1AC, AND J. P. T. PEARMAN II Publication 1296 NATIONAL ACADEMY OF SCIENCES NATIONAL RESEARCH COUNCIL WASHINGTON, D. C. 1966

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Copies of this publication are available from Printing and Publishing Office National Academy of Sciences 2101 Constitution Avenue, N. W. Washington, D. C. 20418 Library of Congress Catalog Card Number 65-60913

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FOREWORD This volume presents the proceedings of the Exobiology Study conducted under the chairmanship of Dean Colin S. Pittendrigh of Princeton Uni- versity and the co-chairmanship of Professor Joshua Lederberg of Stanford University. The Study was initiated by the Space Science Board of the National Academy of Sciences, at the request of the National Aeronautics and Space Administration. Meetings were held on the campus of Stanford University and at the Rockefeller Institute in New York. These meetings began in the Summer of 1964 and concluded with a session in October 1965. The present volume consists of a general chapter summarizing the find- ings of the study, and a series of 29 technical chapters and 2 appendixes by the various participants. A companion volume, in press, provides an anthology and a selected bibliography of some 2,000 references: the study group believed that such a compilation would be useful to their colleagues. We are grateful to the 66 specialists from many disciplines who have contributed to this study and whose conscientious efforts as participants or correspondents have made this report and its companion volume possible. We are also very much indebted to Dean Colin S. Pittendrigh, whose lead- ership is most gratefully acknowledged. HARRY H. HESS, Chairman Space Science Board

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PREFACE Until recent years the origin of life and its possible occurrence elsewhere in the universe have been matters for speculation only. The rapid growth of molecular biology since 1940 has, to be sure, made it possible to discuss life's origins in far more precise and explicit terms than was possible earlier; and the subject entered a new experimental phase in the 1950's with suc- cessful abiogenic synthesis of important biochemical substances in condi- tions simulating the presumptive environment of the primitive Earth. But the real transformation that the subject has undergone stems from the spectacular growth of space technology in the last decade. The possibility of life's origin and occurrence on planets other than ours is no longer lim- ited to idle speculation: it has entered the realm of the testable, of science in the strict sense. Given the rockets now available, and especially those available by 1969, it has become fully realistic to consider plans for the biological exploration of Mars. The study that this report seeks to interpret was initiated in June, 1964, by the Space Science Board of the National Academy of Sciences to exam- ine this possibility. The working group comprised 36 people representing a broad spectrum of scientific interests: evolutionary biology, genetics, mi- crobiology, biochemistry and molecular biology, animal physiology, soil chemistry, organic chemistry, planetary astronomy, geochemistry, and theo- retical physics. The participants included some with considerable prior vii

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Vttt PREFACE involvement in problems of space exploration and others with none. Advice was also sought outside the group of immediate participants on the poten- tialities of selected analytical methods for the experimental study of extra- terrestrial life and its environment. More than 30 individuals contributed in this fashion written assessments of techniques in which they were partic- ularly well versed. Our task was to examine the scientific foundations and merits of the pro- posal to undertake a biological exploration of Mars. What are the potential scientific yields? How valuable, if attained, would they be? What, in fact, is the possibility of life occurring on Mars? And of our detecting it with available and foreseeable technology? What could be achieved by further astronomical work from Earth? by Martian fly-by missions? by Martian orbiters? and Martian Landers? What payloads would we recommend for planetary missions? What timing and over-all strategy would we recom- mend for Martian exploration were we to consider it worthwhile at all? In brief, the over-all purpose was to recommend to the government, through the Academy's Space Science Board, whether or not a biological exploration of Mars should be included in the nation's space program over the next few decades; and, further, to outline what that program, if any, should be. We emphasize that our conclusions were reached on strictly scientific grounds, and that we recognize that a much wider array of considerations bears upon any ultimate decision to undertake Martian exploration. We were not charged with, nor did we attempt, the broad overview that entails these other considerations. We predicated our discussion on the continued vigor of a national space program. We did not, for instance, address our- selves to the question of whether the very large cost of developing the Saturn boosters could be justified on scientific grounds. Nor should we have; the development of the Saturn boosters is already firmly committed for other reasons. The question we faced was whether the application of such boosters to the biological exploration of the solar system—of Mars in particular—can answer well-defined and important scientific questions; and what priority such a question merits within the space program. The essence of our conclusions (pages 15-18) is that the exploration of Mars—motivated by biological questions—does indeed merit the highest scientific priority in the nation's space program over the next decades. We concluded, further, that the favorable opportunities for exploration between 1969 and 1973 can and should be exploited as vigorously as possible. Con- sidering the diversity of discipline and persuasion represented by so large a group as ours, the unanimity achieved on these basic conclusions itself merits emphasis. We achieved, understandably, less unanimity on precisely what course

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PREFACE IX the exploration should take. There was a small minority among us that insisted that the first opportunity be taken to land a mission on Mars equipped with even a minimum of analytical devices. The majority view leaned toward a more gradualistic approach. Its foundation was twofold: (1) the tenet that specifically biological questions should be asked in an ordered sequence of exploration whose purpose is to understand the over-all evolution of the planet's crust and atmosphere; and (2) the large amount of work that remains to be done in designing and equipping a lander with the diversity of sensors necessary for study of a life of uncertain character- istics. The program emerging from this approach begins with emphasis on orbiter missions designed to enlarge our knowledge of the astronomical, geophysical, and geochemical features of Mars and its seasonal changes. Such new knowledge of the Martian environment will greatly enhance chances for the success of subsequent landing missions. And, further, it will also permit, prior to landing, a substantial re-evaluation of all those features on which our present judgment of the plausibility of Martian life depends. This study was prompted by a specific request from the National Aero- nautics and Space Administration to the National Academy of Sciences, and was carried out with its support. But it has also been a natural culmi- nation of a discussion of many years in which many of the working group members have participated. Thus, to the extent that it has succeeded in accomplishing its assigned mission, it has depended on the work of several earlier committees and smaller symposia; and the conclusions and recom- mendations it presents are the product of prolonged deliberation and scru- tiny. None of the working group failed to sense the burden of responsibility that such a costly program as Martian exploration entails; and none failed to sense the magnificent challenge and opportunity that is now before scientific man. The present volume contains the findings of the study, a postscript dis- cussing the significance of the observations obtained during the flight of Mariner IV past Mars, and a collection of the working papers that formed the basis of our discussions. As a guide to the reader, a synopsis of the principal sections is given below. The conclusions and recommendations arising from the discussions are set forth in PART I. These statements express the agreements of the working group of the study and the rationale on which they were based. PART II. Life: its Nature and Origin. An understanding of the nature of life is a prerequisite to any attempt to find evidence of it, but a concise definition is elusive. The salient properties and characteristics of living organisms are discussed. Contemporary views on the chemical and physical processes that led

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X PREFACE to the appearance of life on Earth contribute to an assessment of the prob- ability of finding evidence of biological activity elsewhere. Laboratory syntheses of biologically significant compounds are reviewed in the light of geochemical pertinence. PART III. The Cosmic Setting. Some astronomical evidence bears on the distribution of environments that may be suitable for life. The planets of the solar system that are, or may become, accessible for closer study are examined as possible sites of biological activity. The reported presence of organic compounds in certain meteorites is discussed in terms of possible origins. PART IV. Recognition of Life and some Terrestrial Precedents. Systematic problems in the experimental detection of biological activity are reviewed. Optical asymmetry, so characteristic of terrestrial life, is dis- cussed in terms of its diagnostic significance. The special properties of terrestrial soils are reviewed in relation to the problem of detecting bio- logical activity, and the possibility of recognizing terrestrial life by observa- tion of the Earth from a distance is examined. PART V. Some Extrapolations and Speculations. Synthetic materials and structures produced in the laboratory from amino acids imitate some of the properties of living material. These effects are discussed in con- nection with the enumeration of tests for living systems. An hypothetical anaerobic ecological system, capable of operating under presumed Martian conditions, is outlined in theoretical fashion. Some speculative possibilities for the existence of biochemical systems radically different from the ter- restrial are discussed in relation to adaptation to the environment and impli- cations for experimental procedures for detection of life. The improba- bility of the existence of higher organisms on Mars is briefly discussed. PART VI. Approaches to the Exploration of Mars. Practical means for confirming and enlarging our knowledge of Mars by laboratory work, astronomical observation and the use of spacecraft for remote observations, are discussed. The characteristics of space vehicles for planetary explora- tion are reviewed, together with the limitations and special conditions that govern their use for Martian investigations. Although unlikely to provide direct detection of life, observations from the Earth and its vicinity, from Martian fly-bys and particularly from orbiters are essential preliminaries to more detailed investigations at the planet's surface. Potentialities of these kinds of observations for aiding the definition of phenomena of biological relevance are discussed. PART VII. Martian Landings: Unmanned. Precise determination of the Martian environment and the identification and characterization of any living organisms requires that suitable instruments be landed on the surface, after preliminary investigations have identified sites of interest. Special

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PREFACE XI problems attending the design of landers for biological studies are dis- cussed and analytical techniques of potential application are reviewed. PART VIII. Martian Landings: Manned. If the study of Mars by means of automatic devices obtains evidence of an indigenous biota, the scope of further investigations would be markedly increased by the ability to dispatch manned expeditions and to return samples to Earth. Some,current estimates of the prospects of undertaking such flights are outlined and problems of quarantine that might arise are discussed. PART IX. Avoiding the Contamination of Mars. Preventing the intro- duction of viable terrestrial microorganisms has been recognized as an essential condition to the experimental study of the Martian environment. The importance of this condition and some possible consequences of violating it are discussed, together with procedures that might be followed if contamination were known to have occurred. Present aims and methods of sterilization are outlined, quantitative standards proposed and the prob- lem of embedded microorganisms reviewed. A companion volume, Extraterrestrial Life: Anthology and Bibliography (National Academy of Sciences—National Research Council Publication 1296A), was prepared on the recommendation of the working group and with its guidance. It contains a selected anthology and bibliography on the origin of life, its possible existence beyond the Earth, and related subjects. A supplementary group of papers on Mariner IV and rocket observations of Mars that were made during 1965 is also included. The working group of the study acknowledges with gratitude the help it received from the many outside contributors and from the staff of the National Aeronautics and Space Administration and the Jet Propulsion Laboratory. We are grateful also, to the authorities of Stanford University and the Rockefeller Institute for providing facilities for our meetings. It is a pleasure to express on behalf of the entire working group a special note of thanks to the study's secretariat. The devoted effort and the imagination of Mr. J. P. T. Pearman (Executive Director) carried us over many difficult problems in the course of a long summer's work; and the whole task was made easier by the tireless support of his staff—Dr. E. A. Shneour, Miss A. K. Grittner, Mr. E. Ottesen, Mr. R. A. Fisher, Miss J. A. Durbin, and Mrs. A. E. Carlson. The assistance of Miss Ann Wagoner, of the Space Science Board staff, was invaluable in the final stages of preparation of our report for press. COLIN S. PtTTENDRIGH Chairman of the Study

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CONTENTS PART I—BIOLOGY AND THE EXPLORATION OF MARS Summary and Conclusions 3 Postscript: October 1965 19 PART II—LIFE: ITS NATURE AND ORIGIN 1. What Is Life? 25 Daniel Mazia 2. The Origin of Life 41 5. L. Miller and N. H. Horowitz PART III—THE COSMIC SETTING 3. The Solar System as an Abode of Life 73 Carl Sagan 4. Biological Materials in Carbonaceous Chondrites 114 H. C. Urey andJ.R. Arnold PART IV—RECOGNITION OF LIFE AND SOME TERRESTRIAL PRECEDENTS 5. Signs of Life 127 Joshua Lederberg xiii

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XIV CONTENTS 6. Optical Asymmetry 141 Lubert Stryer 7. The Biochemistry of Terrestrial Soils 147 A. D. McLaren 8. Properties of Desert Soils 164 R. E. Cameron 9. Remote Detection of Terrestrial Life 187 Carl Sagan, R. N. Colwell, S. Q. Duntley, V. R. Eshleman, D. M. Gates, Amron Katz, Joshua Lederberg, Harold Masursky, D. G. Rea, W. G. Stroud, Verner Suomi, and Ralph Zirkind PART V—SOME EXTRAPOLATIONS AND SPECULATIONS 10. Development of Rigorous Tests For Extraterrestrial Life . . 213 S. W. Fox 11. A Model of Martian Ecology 229 Wolf Vishniac, K. C. Atwood, R. M. Bock, Hans Gaffron, T. H. Jukes, A. D. McLaren, Carl Sagan, and Hyron Spinrad 12. Exotic Biochemistries in Exobiology 243 G. C. Pimentel, K. C. Atwood, Hans Gaffron, H. K. Hart- line, T. H. Jukes, E. C. Pollard, and Carl Sagan 13. Higher Organisms on Mars 252 Carl Sagan PART VI—APPROACHES TO THE EXPLORATION OF MARS AND REMOTE OBSERVATIONS 14. Some Terrestrial Programs 259 S. L. Miller, G. C. Pimentel, and Carl Sagan 15. Potential Yields of Biological Relevance from Remote Investi- gations of Mars 264 Carl Sagan 16. Launch Opportunities and Seasonal Activity on Mars .... 283 Carl Sagan and J. W. Haughey 17. Space Vehicles for Planetary Missions 292 E. C. Levinthal PART VII—MARTIAN LANDINGS: UNMANNED 18. Biological Objectives and Strategy for the Design of a Space Vehicle to be Landed on Mars 325 D. A. Gloser

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CONTENTS XV 19. The Automated Biological Laboratory 331 D. A. Gloser, John McCarthy, and Marvin Minsky 20. Analytical Methods for Landers 347 D. G. Rea, Editor 21. The Use of Martian Materials in the Search for Extraterrestrial Life 427 Alexander Rich PART VIII—MARTIAN LANDINGS: MANNED 22. Impact of Manned Spacecraft on the Exobiology Program . . 433 N. H. Horowitz 23. Prospects for Manned Mars Missions 436 E. C. Levinthal 24. "Back Contamination" and Quarantine—Problems and Per- spectives 443 A. H. Brown PART IX—AVOIDING THE CONTAMINATION OF MARS 25. The Nature of the Problem 449 K. C. Atwood 26. Objectives and Technology of Spacecraft Sterilization .... 463 L, B. Hall 27. Spacecraft Sterilization 467 N. H. Horowitz 28. Standards for Spacecraft Sterilization 470 Carl Sagan and Sidney Coleman 29. The Special Problem of Encapsulated Contaminants .... 4.82 A. H. Brown APPENDIXES I. Instrumentation for the Detection of Extraterrestrial Life . . 487 C. W. Bruch II. Potential Application of Electron-Optical Methods to Storage of Information for Direct Retrieval 503 Humberto Ferndndez-Mordn III. List of Participants and Contributors to the Study 507 IV. Note on the Space Science Board 510

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