The Limits of Organic Life in Planetary Systems

117 Pages·2007·1.78 MB·English

by  National Research Council, Committee on the Limits of Organic Life in Planetary Systems, Committee on the Origins and Evolution of Life

The Limits of Organic Life
in Planetary Systems
Committee on the Limits of Organic Life in Planetary Systems
Committee on the Origins and Evolution of Life
Space Studies Board
Division on Engineering and Physical Sciences
Board on Life Sciences
Division on Earth and Life Studies
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International Standard Book Number-13: 978-0-309-10484-5
International Standard Book Number-10: 0-309-10484-X
Cover: Cover design by Penny E. Margolskee. The lower half of the cover is an image of a microbial mat community found at
a depth of about 15 meters in Lake Vanda, Wright Valley, Antarctica; photo courtesy of Dale Andersen, SETI Institution. The
upper half of the cover is a composite image of the Orion Nebula made by combining data from the Hubble Space Telescope
and the Spitzer Space Telescope; image courtesy of NASA/Jet Propulsion Laboratory-California Institute of Technology,
T. Megeath (University of Toledo), and M. Robberto (Space Telescope Science Institute). The crescent on the center right is an
ultraviolet image of the planet Venus as seen by the Hubble Space Telescope; image courtesy of NASA/JPL/Space Telescope
Science Institute.
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OTHER REPORTS OF THE SPACE STUDIES BOARD
Building a Better NASA Workforce: Meeting the Workforce Needs for the National Vision for Space Explora-
tion (2007)
Earth Science and Applications from Space: National Imperatives for the Next Decade and Beyond (2007)
Exploring Organic Environments in the Solar System (SSB with the Board on Chemical Sciences and
Technology, 2007)
A Performance Assessment of NASA’s Astrophysics Program (SSB with the Board on Physics and
Astronomy, 2007)
An Assessment of Balance in NASA’s Science Programs (2006)
Assessment of NASA’s Mars Architecture 2007-2016 (2006)
Assessment of Planetary Protection Requirements for Venus Missions: Letter Report (2006)
Distributed Arrays of Small Instruments for Solar-Terrestrial Research: Report of a Workshop (2006)
Issues Affecting the Future of the U.S. Space Science and Engineering Workforce: Interim Report (SSB with the
Aeronautics and Space Engineering Board [ASEB], 2006)
Review of NASA’s 2006 Draft Science Plan: Letter Report (2006)
The Scientific Context for Exploration of the Moon:⎯Interim Report (2006)
Space Radiation Hazards and the Vision for Space Exploration (2006)
The Astrophysical Context of Life (SSB with the Board on Life Sciences, 2005)
Earth Science and Applications from Space: Urgent Needs and Opportunities to Serve the Nation (2005)
Extending the Effective Lifetimes of Earth Observing Research Missions (2005)
Preventing the Forward Contamination of Mars (2005)
Principal-Investigator-Led Missions in the Space Sciences (2005)
Priorities in Space Science Enabled by Nuclear Power and Propulsion (SSB with ASEB, 2005)
Review of Goals and Plans for NASA’s Space and Earth Sciences (2005)
Review of NASA Plans for the International Space Station (2005)
Science in NASA’s Vision for Space Exploration (2005)
Assessment of Options for Extending the Life of the Hubble Space Telescope: Final Report (SSB with ASEB, 2004)
Exploration of the Outer Heliosphere and the Local Interstellar Medium: A Workshop Report (2004)
Issues and Opportunities Regarding the U.S. Space Program: A Summary Report of a Workshop on National Space
Policy (SSB with ASEB, 2004)
Plasma Physics of the Local Cosmos (2004)
Review of Science Requirements for the Terrestrial Planet Finder: Letter Report (2004)
Understanding the Sun and Solar System Plasmas: Future Directions in Solar and Space Physics (2004)
Utilization of Operational Environmental Satellite Data: Ensuring Readiness for 2010 and Beyond (SSB with
ASEB and the Board on Atmospheric Sciences and Climate [BASC], 2004)
Limited copies of these reports are available free of charge from:
Space Studies Board
National Research Council
The Keck Center of the National Academies
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COMMITTEE ON THE LIMITS OF
ORGANIC LIFE IN PLANETARY SYSTEMS
JOHN A. BAROSS, University of Washington, Chair
STEVEN A. BENNER, Foundation for Applied Molecular Evolution
GEORGE D. CODY, Carnegie Institution of Washington
SHELLEY D. COPLEY, University of Colorado at Boulder
NORMAN R. PACE, University of Colorado at Boulder
JAMES H. SCOTT, Dartmouth College
ROBERT SHAPIRO, New York University
MITCHELL L. SOGIN, Marine Biological Laboratory
JEFFREY L. STEIN, Sofinnova Ventures
ROGER SUMMONS, Massachusetts Institute of Technology
JACK W. SZOSTAK, Howard Hughes Medical Institute, Harvard University
Staff
DAVID H. SMITH, Study Director
JOSEPH K. ALEXANDER, Senior Staff Officer
ROBERT L. RIEMER, Senior Staff Officer (shared with the Board on Physics and Astronomy)
CATHERINE A. GRUBER, Assistant Editor
RODNEY N. HOWARD, Senior Project Assistant
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SPACE STUDIES BOARD
LENNARD A. FISK, University of Michigan, Chair
A. THOMAS YOUNG, Lockheed Martin Corporation (retired), Vice Chair
SPIRO K. ANTIOCHOS, Naval Research Laboratory
DANIEL N. BAKER, University of Colorado
STEVEN J. BATTEL, Battel Engineering
CHARLES L. BENNETT, Johns Hopkins University
JUDITH A. CURRY, Georgia Institute of Technology
JACK D. FARMER, Arizona State University
JACK D. FELLOWS, University Corporation for Atmospheric Research
JACQUELINE N. HEWITT, Massachusetts Institute of Technology
TAMARA E. JERNIGAN, Lawrence Livermore National Laboratory
KLAUS KEIL, University of Hawaii
BERRIEN MOORE III, University of New Hampshire
KENNETH H. NEALSON, University of Southern California
NORMAN P. NEUREITER, American Association for the Advancement of Science
SUZANNE OPARIL, University of Alabama, Birmingham
JAMES PAWELCZYK, Pennsylvania State University
RONALD F. PROBSTEIN, Massachusetts Institute of Technology
HARVEY D. TANANBAUM, Harvard-Smithsonian Astrophysical Observatory
RICHARD H. TRULY, National Renewable Energy Laboratory (retired)
JOSEPH F. VEVERKA, Cornell University
WARREN M. WASHINGTON, National Center for Atmospheric Research
GARY P. ZANK, University of California, Riverside
MARCIA S. SMITH, Director
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BOARD ON LIFE SCIENCES
KEITH YAMAMOTO, University of California, San Francisco, Chair
ANN M. ARVIN, Stanford University School of Medicine
JEFFREY L. BENNETZEN, University of Georgia
RUTH BERKELMAN, Emory University
DEBORAH BLUM, University of Wisconsin
R. ALTA CHARO, University of Wisconsin
JEFFREY L. DANGL, University of North Carolina
PAUL R. EHRLICH, Stanford University
MARK D. FITZSIMMONS, John D. and Catherine T. MacArthur Foundation
JO HANDELSMAN, University of Wisconsin, Madison
ED HARLOW, Harvard Medical School
KENNETH H. KELLER, University of Minnesota
RANDALL MURCH, Virginia Polytechnic Institute and State University
GREGORY A. PETSKO, Brandeis University
MURIEL E. POSTON, Skidmore College
JAMES REICHMAN, University of California, Santa Barbara
MARC T. TESSIER-LAVIGNE, Genentech, Inc.
JAMES TIEDJE, Michigan State University
TERRY L. YATES, University of New Mexico
FRANCES SHARPLES, Director
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Dedicated to
Non-Human-Like Life Forms,
Wherever They Are
Preface
As the search for life in the solar system expands, it is important to know what exactly to search for. Previous
life-detection experiments have been criticized for being too geocentric. This study aims to inform research pro-
gram managers, policymakers, and mission designers about the possibilities for life on other solar system bodies.
Further, during planetary protection exercises at the National Aeronautics and Space Administration (NASA),
questions concerning the possibility of nonterrana life recur repeatedly. Remarkably little knowledge is organized
that might shed light on the plausibility of bizarre life as a concern for planetary protection.
The search for signs of life, present or past, is an important goal of NASA’s robotic solar system exploration
programs and, ultimately, for its astronomical programs designed to probe the gross characteristics of extrasolar
planetary systems. To date, that search has been governed by a model of life that is based on the life that we know
on Earth—terran life. Several features of terran life have attracted particular focus:
• Terran life uses water as a solvent;
• It is built from cells and exploits a metabolism that focuses on the carbonyl group (C " O);
• It is thermodynamically dissipative, exploiting chemical-energy gradients; and
• It exploits a two-biopolymer architecture that uses nucleic acids to perform most genetic functions and proteins
to perform most catalytic functions.
As a consequence, most of NASA’s mission planning is focused on locations where liquid water is possible,
and it emphasizes searches for structures that resemble cells of terran organisms, small molecules that might be
the products of carbonyl metabolism, particular kinds of chemical-energy gradients, and tests for amino acids and
nucleotides similar to those found in terrestrial proteins and DNA. This approach is defensible given the absence
of a general understanding of how life might appear if it had an origin independent of Earth. Experiments in the
laboratory, however, are suggesting that life might be based on molecular structures substantially different from
aThe Committee on the Limits of Organic Life in Planetary Systems uses the term “terran” to denote a particular set of biological and
chemical characteristics that are displayed by all life on Earth. Thus “Earth life” has the same meaning as “terran life” when the committee
is discussing life on Earth, but if life were discovered on Mars or any other nonterrestrial body, it might be found to be terran or nonterran,
depending on its characteristics.
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