SP-1231 SP-1231 October 1999 Exobiology in the Solar System & The Search for Life on Mars for The Search Exobiology in the Solar System & Exobiology in the Solar System & The Search for Life on Mars Report from the ESA Exobiology Team Study 1997-1998 Contact: ESA Publications Division c/o ESTEC, PO Box 299, 2200 AG Noordwijk, The Netherlands Tel. (31) 71 565 3400 - Fax (31) 71 565 5433 SP-1231 October 1999 EXOBIOLOGY IN THE SOLAR SYSTEM AND THE SEARCH FOR LIFE ON MARS Report from the ESA Exobiology Team Study 1997-1998 Cover Fossil coccoid bacteria, 1 µm in diameter, found in sediment 3.3-3.5 Gyr old from the Early Archean of South Africa. See pages 160-161. Background: a portion of the meandering canyons of the Nanedi Valles system viewed by Mars Global Surveyor. The valley is about 2.5 km wide; the scene covers 9.8 km by 27.9 km centred on 5.1°N/48.26°W. The valley floor at top right exhibits a 200 m-wide channel covered by dunes and debris. This channel suggests that the valley might have been carved by water flowing through the system over a long period, in a manner similar to rivers on Earth. (Malin Space Science Systems/NASA) SP-1231 ‘Exobiology in the Solar System and The Search for Life on Mars’, ISBN 92-9092-520-5 Scientific Coordinators: André Brack, Brian Fitton and François Raulin Edited by: Andrew Wilson ESA Publications Division Published by: ESA Publications Division ESTEC, Noordwijk, The Netherlands Price: 70 Dutch Guilders/ EUR32 Copyright: © 1999 European Space Agency Contents Foreword 7 I An Exobiological View of the Solar System 15 I.1 Introduction 17 I.2 Chemical Evolution in the Solar System 19 2.1 Terrestrial Prebiotic Chemistry 19 2.1.1 Terrestrial Production of Reduced Organic Molecules 19 2.1.2 Extraterrestrial Delivery of Organic Molecules to the Earth 20 2.2 Chemical Evolution on Other Bodies of the Solar System 21 2.2.1 The Icy Bodies: Comets, Europa, Ganymede 21 2.2.2 The Non-Icy Bodies: Titan, Giant Planets, Venus, 22 Moon, Mars I.3 Limits of Life under Extreme Conditions 27 3.1 Introduction 27 3.2 Extreme Temperature Regimes 27 3.2.1 High Temperatures 27 3.2.2 Low Temperatures 29 3.3 High-Salt Environments 30 3.4 Acidic and Alkaline Environments 31 3.5 High-Pressure Environments 31 3.6 Subterranean Life 32 3.7 Survival of Lifeforms in Space 34 3.8 Implications for Exobiology in Future Searches 36 I.4 Morphological and Biochemical Signatures of Extraterrestrial Life: 41 Utility of Terrestrial Analogues 4.1 Introduction 41 4.2 Evidence of Extant Life 41 4.2.1 The Microbial World 41 4.2.2 Structural Indications of Life 42 4.2.3 Evidence of Microbial Activity as a Functional 44 Characteristic of Life 4.2.4 Chemical Signatures and Biomarkers 47 4.2.5 Indirect Fingerprints of Life 48 4.2.6 Conclusions 48 4.3 Evidence of Extinct (Fossil) Extraterrestrial Life 49 4.3.1 Paleontological Evidence 49 4.3.1.1 Microbialites 51 4.3.1.2 Cellular Microfossils 51 4.3.2 Biogeochemical Evidence 53 4.3.2.1 Sedimentary Organic Carbon as a Recorder 54 of Former Life Processes 4.3.2.2 13C/12C in Sedimentary Organic Matter: 54 Index of Autotrophic Carbon Fixation 4.3.2.3 Molecular Biomarkers (‘Chemical Fossils’) 57 in Sediments 3 I.5 Potential Non-Martian Sites for Extraterrestrial Life 65 5.1 The Icy Satellites 65 5.1.1 Europa 65 5.1.2 Ganymede 66 5.1.3 Other Icy Satellites 67 5.2 Titan 67 5.2.1 The Titan Atmosphere 67 5.2.2 The Titan Surface 69 5.2.3 The Cassini/Huygens Mission 71 I.6 Science and Experiment Strategy 73 6.1 Where to Search? 73 6.2 What to Search For? 75 6.3 What to Search With? 76 I.7 Summary of the Science Team Recommendations 77 7.1 The Search for Extant and Extinct Life 77 7.2 The Study of the Precursors of Life 77 7.3 Organic Chemistry Processes and Microorganisms in Space 78 7.4 Laboratory-based Studies 78 II The Search for Life on Mars 79 II.1 Introduction 81 II.2 The Planet Mars 83 2.1 The Geology of Mars 83 2.2 Volcanism and Tectonism 84 2.3 The Bulk Chemical Composition of Mars 85 2.4 The Geochemistry of the Martian Surface Layers 87 2.5 Water and Ground Ice 88 2.6 The Climate of Mars 89 2.7 NASA-Proposed Sites for Mars Exploration 90 2.7.1 Water and a Favourable Environment 91 2.7.2 Explorations for Extinct Life 92 2.7.3 Exploration for Extant Life 92 2.7.4 NASA Priority Landing Sites for Exobiology 93 II.3 The Martian Meteorites 95 3.1 Introduction 95 3.2 The Origin of SNC Meteorites 96 3.3 The Martian Meteorites 97 3.4 Exobiology and the Martian Meteorites 98 3.5 Carbon Compounds in Other Meteorites (Carbonaceous Chondrites) 101 3.6 Carbon Compounds in Micrometeorites 103 II.4 Team I: Exobiology and the Mars Surface Environment 109 4.1 Environments and Rocks with Exobiology Potential 109 4.1.1 Lacustrine Environments 109 4.1.2 Sebkha Environments 110 4.1.3 Thermal-Spring Deposits 113 4.1.4 Duricrusts 113 4.1.5 Glacial Deposits 113 4 4.1.6 Polar Deposits 114 4.1.7 Ground Ice-Permafrost 114 4.2 General Remarks on Subsurface Microbial Fossils 115 4.3 Climatic and Environmental Models 115 4.4 The Radiation Environment 117 4.4.1 The Current Atmospheric Radiation Budget 118 4.4.2 The Current Particle and Radiation Environment 119 4.4.3 The Radiation Environment in the Past 119 4.5 The Rationale for Landing Site Selection 120 4.6 Rovers and Drilling Operations 122 4.7 Landing Sites 122 II.5 Team II: The Search for Chemical Indicators of Life 129 Scientific Objectives: 5.1 Sample Acquisition and Distribution Subsystem 129 5.2 Mineralogy, Petrology and Geochemistry 130 5.2.1 Mineralogy and Petrology 130 5.2.2 Geochemistry (Elemental Composition Analysis) 132 5.3 Isotopic Analysis 132 5.3.1 Carbon and Hydrogen 132 5.3.2 Sulphur 133 5.4 Molecular Analysis 133 5.4.1 Inorganics 133 5.4.2 Organics 133 5.5 The Search for Homochirality 135 Instrumentation to Satisfy the Scientific Objectives: 5.6 Sample Acquisition and Distribution Subsystem 135 5.7 Mineralogy, Petrology and Geochemistry 135 5.7.1 General Considerations 135 5.7.2 Optical Microscopy 138 5.7.3 Alpha-Proton-X-ray Spectrometer (APX) 138 5.7.4 Mössbauer Spectrometer 140 5.7.5 Ion/Electron Probes, X-ray Spectroscopy 142 5.7.6 IR Spectroscopy 142 5.7.7 Raman Spectroscopy 144 5.8 Isotopic Analysis 145 5.9 Molecular Analysis 147 5.9.1 Gas Chromatography (GC) 147 5.9.2 Mass Spectroscopy (MS) 148 5.9.3 Pyrolysis (PYR) 148 5.9.4 Available PYR-GC-MS Techniques 148 5.9.5 Laser Ablation-Inductive Coupled Plasma-MS (LA-ICP-MS) 149 5.9.6 Other Techniques 150 5.9.7 The Analysis of H2O2 150 5.10 Chirality Measurements 151 5.10.1 Bulk Chirality Measurements 151 5.10.2 Enantiomeric Separations 152 Recommended Payload and Technology Research Programme: 153 II.6 Team III: The Inspection of Subsurface Aliquots and Surface Rocks 157 Scientific Justification: 6.1 The Investigation of Unweathered Rock Material 157 5 6.2 Imaging of Fossilised Material in Sediments 157 6.2.1 Macroscopic Scale 158 6.2.2 Microscopic Scale 160 6.3 Investigation of Biominerals 161 6.4 Investigation of the Rock Structure 163 6.4.1 Extinct Microbes in Rock 163 6.4.2 Rock Formation and Composition 164 6.5 Investigation of Sedimentary Layering 165 6.6 Investigation of the Soil 165 6.7 Investigation of Dust Particles 166 Scientific Method and Requirements: 6.8 Initial Survey and Target Selection 167 6.9 High-Resolution Studies 168 6.10 Subsurface Investigations 170 6.11 Raman Spectrometry 170 6.12 Optical Spectroscopy 170 6.13 Mössbauer Spectroscopy 171 6.14 IR Spectroscopy 171 6.15 Thermal-IR Spectroscopy 171 6.16 Chemical Inspection of Subsurface Material 172 6.17 Summary of Possible Instrumentation 173 Sampling Aspects: 6.18 Mobility Requirements 173 6.19 Grinding/Polishing/Immersion 174 6.20 Drilling and Digging 174 6.21 Sieving and Magnetic Separation 174 6.22 Cutting and Sawing 174 6.23 Data Analysis 175 6.24 Summary of Major Conclusions 175 II.7 Conclusions 179 7.1 Landing Sites for Exobiology 179 7.2 The Sample Acquisition, Distribution and Preparation System 180 7.2.1 Subsurface Sample: Acquisition and Preparation 180 7.2.2 Surface Rock Sample: Acquisition and Preparation 180 7.2.3 Soil Samples 181 7.3 The Exobiology Observation System 181 7.4 The Exobiology Analysis System 181 7.5 A Possible Exobiology Experiment Package 184 and Operating Arrangement Annex 1: Team IV. A Manned Mars Station and Exobiology Research 185 6 FOREWORD The Exobiology Science Team was established in September 1996 by Dr. P. Clancy of ESA’s Directorate of Manned Spaceflight and Microgravity. The task of the Team was to survey current research in exobiology and related fields and then to make recommendations to ESA on the nature of a future search for life elsewhere in the Solar System.