THE CAMBRIDGE ENCYCLOPEDIA OF METEORITES O. RICHARD NORTON The Pitt Building, Trumpington Street, Cambridge, United Kingdom The Edinburgh Building, Cambridge CB2 2RU, UK 40 West 20th Street, New York, NY 10011-4211, USA 477 Williamstown Road, Port Melbourne, VIC 3207, Australia Ruiz de Alarcón 13, 28014 Madrid, Spain Dock House, The Waterfront, Cape Town 8001, South Africa http://www.cambridge.org © O.R. Norton 2002 This book is in copyright. Subject to statutory exception and to the provisions of relevant collective licensing agreements, no reproduction of any part may take place without the written permission of Cambridge University Press. First published 2002 Printed in the United Kingdom at the University Press, Cambridge Typeface Joanna 10.25/12.5pt. System QuarkXPress® [] A catalogue record for this book is available from the British Library Library of Congress Cataloguing-in-Publication Data Norton, O. Richard. The Cambridge encyclopedia of meteorites / O. Richard Norton. p. cm. Includes bibliographical references and index. ISBN 0 521 62143 7 1, Meteorites. I. Title. QB755.N65 2002 523.5Ј1Ј03–dc21 2001035621 ISBN 0 521 62143 7 hardback Contents Preface xv Foreword xix 11 Cosmic dust: interplanetary dust particles 1 The smallest meteoroids – interplanetary dust particles (IDPs) 1 The zodiacal light 2 A solar connection 3 Lifetime of interplanetary dust particles 3 Density of interplanetary dust particles 4 Comets as sources of interplanetary dust particles 4 Atmospheric collection of interplanetary dust particles 5 Collection of deep sea interplanetary dust particles 8 Impacts close to home – a practical matter 8 Meteors 11 Sporadic meteors 11 Origin of sporadic meteors 11 Shower meteors 12 The Leonid meteor storm 13 Harvesting interplanetary dust particles in the space environment 18 To touch a star 19 Celestial diamonds 19 Celestial silicon carbide 20 Interstellar graphite 21 PAHs in graphite 21 A final word 24 References 25 12 The fall of meteorites 27 Orbits of meteoroids 28 The fireball networks 28 Characteristics of a meteoroid’s atmospheric passage 32 The true trajectory 32 Height and angle of descent 32 Meteoroid velocity 33 Atmospheric drag 33 Light phenomena 34 Sound phenomena 36 Electrophonic sounds 37 Meteoroids to meteorites: a lesson in survival 39 Ablation 39 The distribution ellipse 40 “Fossil” strewn fields 42 vii viii Contents The temperature myth – hot or cold? 42 The final resting place 44 References 46 13 External morphology of meteorites 47 Some general characteristics 48 Falls and finds 48 Density 48 Size 49 Meteorite shapes 50 Oriented meteorites 52 Fusion crust 53 Weathering of meteorites 58 Mechanical weathering 58 Chemical weathering 58 The myth of lawrencite in iron meteorites 61 A weathering scale 63 Terrestrial lifetimes of meteorites 65 “Fossil” meteorites 67 The Brunflo “paleo” fossils 67 The oldest “paleo” iron? 67 A K–T boundary meteorite? 67 References 69 14 Classification of meteorites: a historical viewpoint 71 The early years 72 The Rose–Tschermak–Brezina classification 73 The Prior classification 75 References 77 15 Primitive meteorites: the chondrites 79 Petrologic–chemical classification of the chondrites 81 Cosmic abundances 82 Chemical classification of the chondrites 83 The Van Schmus–Wood criteria for the petrologic–chemical classification of chondrites 86 1. Chondrule texture 86 2. Matrix texture 86 3. Homogeneity of olivine and pyroxene compositions 89 4. Structural states of low-calcium pyroxene 90 5. Degree of development of secondary feldspar 90 6. Igneous glass in chondrules 90 7. Metallic minerals (maximum weight percent nickel in FeNi) 90 8. Sulfide minerals (average nickel in FeS) 90 9. Weight percent carbon 90 10. Water content 91 Contents ix Shock metamorphism and shock stage classification 93 The Stöffler–Keil–Scott shock classification system 93 S1 – unshocked 93 S2 – very weakly shocked 93 S3 – weakly shocked 93 S4 – moderately shocked 93 S5 – strongly shocked 95 S6 – very strongly shocked 95 Brecciated chondrites 96 Regolith breccias 96 Impact-melt breccia 98 References 100 16 Chondrites: a closer look 101 Chondrite density and porosity 103 Chondrules 106 Chondrule sizes and abundances 106 Chondrule textures and compositions 106 Porphyritic chondrules 108 Granular olivine–pyroxene chondrules (GOP) 110 Nonporphyritic or droplet chondrules 110 The other chondrites 115 Enstatite chondrites (E) 115 “Rumuruti” chondrites (R) 116 Summary 117 References 118 17 Primitive meteorites: the carbonaceous chondrites 119 Ordinary vs carbonaceous chondrites 120 Carbonaceous chondrite groups 121 CI chondrites (C1) 121 A new CI chondrite? 122 CM chondrites 123 Are CI and CM chondrites related to comets? 125 CV chondrites 128 Matrix 128 Chondrules 129 Olivine aggregates, dark inclusions 131 Calcium–aluminum inclusions (CAIs) 131 CO chondrites 135 CK chondrites 136 CR chondrites 138 CH chondrites 139 Organic carbon 140 Summary 142 References 143 x Contents 18Differentiated meteorites: the achondrites 145 Major characteristics of differentiated meteorites 146 Differentiation 147 Fractional crystallization and the igneous process 148 Asteroidal achondrites 151 The HED association 151 Eucrites 151 Diogenites 153 Howardites 156 The mesosiderite connection 157 Aubrites – the enstatite achondrites 159 Ureilites 161 Angrites 162 Brachinites 163 Primitive achondrites 165 Acapulcoites and lodranites 165 Winonaites 165 Martian meteorites – the SNC group 166 Shergottites 166 Nakhlites 167 Chassignites 168 Origin of the SNC meteorites 170 The saga of martian meteorite ALH 84001 172 Lunar meteorites – lunaites 175 History’s lesson 176 Baldwin’s Moon 177 A history of discovery 177 Anorthositic regolith breccias 178 Mare basalts 179 References 182 19Differentiated meteorites: irons and stony-irons 183 Mineralogy of meteoritic iron–nickel 184 Crystal structure of meteoritic iron–nickel minerals 185 Iron–nickel stability phase diagram 185 Formation of the Widmanstätten structure 187 Classification of iron meteorites 190 Structural classification of iron meteorites 190 Hexahedrites (H) 190 Octahedrites (O) 190 Ataxites (D) 191 Anomalous irons 191 Chemical classification of iron meteorites 191 Chemical vs structural classification 197 Silicate inclusions in iron meteorites 199 Cooling the core 201 Stony-irons: the pallasites 203 Contents xi Texture 203 Composition and classification 203 Formation of pallasites 205 Metallic inclusions in iron meteorites 207 Swathing kamacite 207 Troilite 207 Schreibersite 208 Cohenite 209 Graphite 209 References 212 10 Meteorites and the early Solar System 213 Radioisotopes – some basics 215 Decay constant and half-life 216 Rubidium/strontium method 217 Types of meteorite ages 218 In the beginning 220 The solar nebula 221 The first-condensed refractory minerals 224 Formation of the first chondrules 226 Multiple melting and recycling of chondrules? 227 The age of the Solar System 234 Aluminum-26 and the age of chondrules and CAIs 234 Absolute age of the Solar System 236 Impact metamorphism 236 Cosmic-ray exposure ages 237 Terrestrial age 238 References 239 11 Asteroid parent bodies 241 The asteroid belt 242 Titius–Bode Rule 242 Discovery of the first asteroids 242 Modern discoveries 243 Numbering and naming asteroids 243 Main belt asteroids 246 Trojan asteroids 247 Near-Earth and Earth-crossing asteroids 247 Asteroids as parent bodies of meteorites 249 Meteoroid orbits and the asteroid belt 249 Classifying asteroids through infrared reflectance spectrophotometry 249 Distribution of asteroid types 250 Matching meteorites with parent asteroids 252 C-type carbonaceous asteroids 252 S-type asteroids and ordinary chondrites 252 M-type metal asteroids 254 Physical characteristics of asteroids 255 Space weathering 256 xii Contents Onion shell vs rubble pile asteroid models 256 Asteroid 4 Vesta and HED meteorites 258 Where are the mantle rocks? 259 Close encounters: flyby of asteroids 951 Gaspra and 243 Ida 260 Finale: NEAR encounter with 433 Eros 262 Flyby of 253 Mathilde 263 NEAR-Shoemaker orbits 433 Eros 263 The final approach 266 References 269 12 Terrestrial impact craters 271 An impact crater misjudged 273 Impact cratering in the Solar System 276 Mechanism of impact cratering 279 Stage 1: contact/compression 279 Stage 2: excavation 279 Stage 3: modification 281 Effects of changing parameters on crater size 281 Morphology of impact craters 285 Simple craters 285 Complex craters 285 Criteria for the definitive recognition of terrestrial impact structures 291 Surface structures 291 Remnants of the meteorite 291 Shatter cones 292 Impactites 293 Coesite and stishovite 296 Shocked minerals 297 Catastrophic impacts on Earth 300 The Tunguska event 300 When catastrophism had its day 301 The Chicxulub crater 304 Asteroid or comet? 305 The Permian–Triassic extinction 305 References 306 Appendices Appendix A Classification of meteorites (A.E. Rubin, 2000) 307 Appendix B Formation ages of selected meteorites 309 Appendix C Minerals in meteorites 311 Appendix D Preparing and etching iron meteorites 315 Appendix E Testing a meteorite for nickel 319 Appendix F Meteorite museum collections and selected research facilities 321 Appendix G Known terrestrial impact craters 325 Contents xiii Appendix H Summary of meteorites by classification (compiled by Bernd Pauli, June 2001) 331 Glossary 341 General index 349 Meteorite index 353 Chapter Three External morphology of meteorites Ask anyone you know to describe the most general charac- for the secrets it holds. H.H. Nininger, the great meteorite teristics