Preventing the Forward Contamination of Europa

Task Group on the Forward Contamination of Europa

Space Studies Board

Commission on Physical Sciences, Mathematics, and Applications

National Research Council

Washington, D.C.

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Preventing the Forward Contamination of Europa Preventing the Forward Contamination of Europa Task Group on the Forward Contamination of Europa Space Studies Board Commission on Physical Sciences, Mathematics, and Applications National Research Council NATIONAL ACADEMY PRESS Washington, D.C.

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Preventing the Forward Contamination of Europa NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the task group responsible for the report were chosen for their special competences and with regard for appropriate balance. Support for this project was provided by Contract NASW 96013 between the National Academy of Sciences and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the organizations or agencies that provided support for this project. Copyright 2000 by the National Academy of Sciences. All rights reserved. COVER: Cover design by Anne Simmons. Europa image courtesy of the Jet Propulsion Laboratory. Copies of this report are available free of charge from: Space Studies Board National Research Council 2101 Constitution Avenue, NW Washington, DC 20418 Printed in the United States of America

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Preventing the Forward Contamination of Europa THE NATIONAL ACADEMIES National Academy of Sciences National Academy of Engineering Institute of Medicine National Research Council The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Kenneth I. Shine is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy’s purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chairman and vice chairman, respectively, of the National Research Council.

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Preventing the Forward Contamination of Europa TASK GROUP ON THE FORWARD CONTAMINATION OF EUROPA LARRY W. ESPOSITO, University of Colorado, Chair ANDREW F. CHENG, Applied Physics Laboratory BENTON C. CLARK, Lockheed Martin Astronautics MICHAEL J. DALY, Uniformed Services University of the Health Sciences E. IMRE FRIEDMANN, Florida State University BRUCE M. JAKOSKY, University of Colorado RICHARD Y. MORITA, Oregon State University ANNA-LOUISE REYSENBACH, Portland State University DAVID A. STAHL, Northwestern University Staff DAVID H. SMITH, Study Director SHARON S. SEAWARD, Senior Program Assistant CRAIG W. HERBOLD, Research Assistant ACHAL BHATT, Research Assistant

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Preventing the Forward Contamination of Europa SPACE STUDIES BOARD CLAUDE R. CANIZARES, Massachusetts Institute of Technology, Chair MARK R. ABBOTT, Oregon State University FRAN BAGENAL, University of Colorado DANIEL N. BAKER, University of Colorado ROBERT E. CLELAND, University of Washington MARILYN L. FOGEL, Carnegie Institution of Washington BILL GREEN, former member, U.S. House of Representatives JOHN H. HOPPS, JR., Morehouse College CHRISTIAN J. JOHANNSEN, Purdue University RICHARD G. KRON, University of Chicago JONATHAN I. LUNINE, University of Arizona ROBERTA BALSTAD MILLER, Columbia University GARY J. OLSEN, University of Illinois, Urbana-Champaign MARY JANE OSBORN, University of Connecticut Health Center GEORGE A. PAULIKAS, The Aerospace Corporation JOYCE E. PENNER, University of Michigan THOMAS A. PRINCE, California Institute of Technology PEDRO L. RUSTAN, JR., Ellipso Inc. GEORGE L. SISCOE, Boston University EUGENE B. SKOLNIKOFF, Massachusetts Institute of Technology MITCHELL SOGIN, Marine Biological Laboratory NORMAN E. THAGARD, Florida State University ALAN M. TITLE, Lockheed Martin Advanced Technology Center RAYMOND VISKANTA, Purdue University PETER W. VOORHEES, Northwestern University JOHN A. WOOD, Harvard-Smithsonian Center for Astrophysics JOSEPH K. ALEXANDER, Director

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Preventing the Forward Contamination of Europa COMMISSION ON PHYSICAL SCIENCES, MATHEMATICS, AND APPLICATIONS PETER M. BANKS, Veridian ERIM International Inc., Co-chair W. CARL LINEBERGER, University of Colorado, Co-chair WILLIAM BALLHAUS, Jr., Lockheed Martin Corporation SHIRLEY CHIANG, University of California, Davis MARSHALL H. COHEN, California Institute of Technology RONALD G. DOUGLAS, Texas A&M University SAMUEL H. FULLER, Analog Devices Inc. JERRY P. GOLLUB, Haverford College MICHAEL F. GOODCHILD, University of California, Santa Barbara MARTHA P. HAYNES, Cornell University WESLEY T. HUNTRESS, Jr., Carnegie Institution of Washington CAROL M. JANTZEN, Westinghouse Savannah River Company PAUL KAMINSKI, Technovation Inc. KENNETH H. KELLER, University of Minnesota JOHN R. KREICK, Sanders, a Lockheed Martin Company (retired) MARSHA I. LESTER, University of Pennsylvania DUSA M. McDUFF, State University of New York at Stony Brook JANET L. NORWOOD, Former Commissioner, Bureau of Labor Statistics M. ELISABETH PATÉ-CORNELL, Stanford University NICHOLAS P. SAMIOS, Brookhaven National Laboratory ROBERT J. SPINRAD, Xerox PARC (retired) MYRON F. UMAN, Acting Executive Director

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Preventing the Forward Contamination of Europa Foreword Jupiter’s moon Europa is widely regarded as the most promising extraterrestrial habitat for life in the solar system. This view is based on recent evidence suggesting the presence of a water ocean beneath Europa ’s fractured icy surface together with studies of microbial life in extreme environments on Earth, which suggest that living organisms emerge wherever liquid water and some form of usable energy are found. Naturally, there is now great interest in learning much more about Europa, primarily through a series of space probes to survey and eventually to land on the surface. But any spacecraft that transports scientific instruments can also carry terrestrial microbes. This report deals with the important issue of how to protect Europa from such inadvertent biological contamination. To reach their conclusions, the task group had to consider many dimensions of the question. These included techniques for cleaning a spacecraft, the resilience of terrestrial organisms, the space environment at Jupiter, and cost implications of alternative planetary protection approaches. The complexity of these issues, no doubt, contributed to the fact that the task group could not reach consensus on some, but not all, aspects of their charge. The task group’s deliberations illuminate several thorny questions dwelling on the boundary of science and ethics and point the way for further study of both technical and ethical considerations. Although one might have wished for an unequivocal answer, the complexity of the recommendations appropriately reflects the complexity of the underlying issues. In that sense, the report gives NASA’s Planetary Protection Officer a very clear message. Claude R. Canizares, Chair Space Studies Board

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Preventing the Forward Contamination of Europa Preface Europa, a planetary satellite of Jupiter, is a solar system body that may have a significant potential for past or present life. Europa has a radius of about 1,600 km, slightly less than the Moon’s, and it is probably mostly silicate and metal by mass. It has an upper layer, on the order of 80 to 170 km deep, rich in water ice. There is evidence for liquid water beneath the icy crust, first surmised from Voyager data and reinforced by Galileo data. The investigation of Europa’s biological potential forms much of the rationale for continued investigation of the satellite. In accordance with international treaty obligations, the National Aeronautics and Space Administration (NASA) maintains a policy of planetary protection to limit the contamination of extraterrestrial bodies by terrestrial microorganisms and organic compounds during spaceflight missions. Thus, preventing the contamination of Europa ’s environment by terrestrial organisms will be required during upcoming spaceflight missions such as the orbiter that is currently scheduled for launch later in this decade. The planetary protection procedures applied to a given spacecraft are currently determined by the nature of its mission (e.g., flyby, orbiter, or lander) and the biological interest posed by the celestial object that is its destination. A lander targeted at an object of great biological interest must undergo careful cleaning, and heat sterilization may be required if it is carrying life-detection experiments. These requirements are, however, specifically tied to the historical development of our understanding of Mars and its biological potential. Given Europa’s unique environment, applying the criteria developed for Mars may not be appropriate, and a separate assessment is warranted of the levels of cleanliness and sterilization required to prevent the contamination of Europa by spacecraft missions. Against this background, NASA’s Planetary Protection Officer requested that the Space Studies Board undertake a study to evaluate the planetary protection requirements and methods used to prevent contamination of Europa by terrestrial organisms in future orbiter and lander missions and that it recommend any necessary changes. In particular, the Space Studies Board was asked to do the following: Assess the levels of cleanliness and sterilization required to prevent the forward contamination of Europa by future spacecraft missions (orbiters and landers), given Europa’s unique environment and our current understanding of terrestrial microorganisms; Review methods used to achieve the appropriate level of cleanliness and sterilization for Europa spacecraft and recommend alternatives in light of recent advancements in science and technology; and Identify scientific investigations that should be accomplished to reduce the uncertainty in the above assessment. In response to this request, the Space Studies Board established the Task Group on the Forward Contamination of Europa. The work of the task group began in early April 1999 and proceeded with a series of meetings and associated presentations, discussions, and deliberations. Despite its best efforts, however, the task group was unable to reach complete agreement on a number of issues. This report describes the majority and minority viewpoints resulting from the task group’s deliberations. In particular, it describes their areas of agreement and disagreement and the implications for implementation of planetary protection requirements for future Europa missions. The work of the task group benefited from contributions, presentations, or comments made by Amy Baker (Technical Administrative Services), Mark Guman (Jet Propulsion Laboratory), Torrence Johnson (Jet Propulsion Laboratory), Harold Klein (SETI Institute), Robert Koukol (Jet Propulsion Laboratory), Jan Ludwinski (Jet Propulsion Laboratory), Christopher McKay (NASA Ames Research Center), William McKinnon (Washington University), Chris Paranicas (Applied Physics Laboratory, Johns Hopkins University), Pericles Stabekis (Lockheed Martin Life Sciences), David Relman (Stanford University), John Rummel (NASA headquarters), Partha Shakkotai (Jet Propulsion Laboratory), Norman Wainwright (Marine Biological Laboratory), and Wayne Zimmerman (Jet Propulsion Laboratory). This report has been reviewed by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s (NRC’s) Report Review Committee.

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Preventing the Forward Contamination of Europa The purpose of this independent review is to provide candid and critical comments that will assist the authors and the NRC in making the published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The contents of the review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. The task group thanks reviewers John Battista (Louisiana State University), Russell Doolittle (University of California, San Diego), John Kerridge (University of California, San Diego, retired), Krishan Khurana (University of California, Los Angeles), Leslie Orgel (Salk Institute for Biological Studies), Robert Pappalardo (Brown University), and M. Elisabeth Paté-Cornell (Stanford University) for their many constructive comments and suggestions. Responsibility for the final content of this report rests solely with the authoring task group and the NRC.