Discovering the Solar System Second Edition Discovering the Solar System Second Edition Barrie W. Jones The Open University, Milton Keynes, UK Copyright © 2007 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester, West Sussex PO19 8SQ, England Telephone +44 1243 779777 Email (for orders and customer service enquiries): [email protected] Visit our Home Page on www.wiley.com All Rights Reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording, scanning or otherwise, except under the terms of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London W1T 4LP, UK, without the permission in writing of the Publisher. 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To my wife Anne, the rest of my family, and to my friend and colleague Nick Sleep Contents List of Tables xiii Preface and Study Guide to the First Edition xiv Preface to the Second Edition xvi 1 The Sun and its Family 1 1.1 The Sun 1 1.1.1 The Solar Photosphere 1 1.1.2 The Solar Atmosphere 3 1.1.3 The Solar Interior 5 1.1.4 The Solar Neutrino Problem 8 1.2 The Sun’s Family – A Brief Introduction 9 1.2.1 The Terrestrial Planets and the Asteroids 11 1.2.2 The Giant Planets 11 1.2.3 Pluto and Beyond 13 1.3 Chemical Elements in the Solar System 14 1.4 Orbits of Solar System Bodies 15 1.4.1 Kepler’s Laws of Planetary Motion 15 1.4.2 Orbital Elements 18 1.4.3 Asteroids and the Titius–Bode Rule 20 1.4.4 A Theory of Orbits 20 1.4.5 Orbital Complications 24 1.4.6 Orbital Resonances 27 1.4.7 The Orbit of Mercury 29 1.5 Planetary Rotation 30 1.5.1 Precession of the Rotation Axis 33 1.6 The View from the Earth 35 1.6.1 The Other Planets 35 1.6.2 Solar and Lunar Eclipses 36 1.7 Summary of Chapter 1 40 2 The Origin of the Solar System 48 2.1 The Observational Basis 48 2.1.1 The Solar System 48 2.1.2 Exoplanetary Systems 49 2.1.3 Star Formation 53 2.1.4 Circumstellar Discs 55 2.2 Solar Nebular Theories 56 2.2.1 Angular Momentum in the Solar System 57 2.2.2 The Evaporation and Condensation of Dust in the Solar Nebula 60 2.2.3 From Dust to Planetesimals 64 viii CONTENTS 2.2.4 From Planetesimals to Planets in the Inner Solar System 65 2.2.5 From Planetesimals to Planets in the Outer Solar System 69 2.2.6 The Origin of the Oort Cloud, the E–K Belt, and Pluto 73 2.3 Formation of the Satellites and Rings of the Giant Planets 75 2.3.1 Formation of the Satellites of the Giant Planets 75 2.3.2 Formation and Evolution of the Rings of the Giant Planets 76 2.4 Successes and Shortcomings of Solar Nebular Theories 80 2.5 Summary of Chapter 2 81 3 Small Bodies in the Solar System 83 3.1 Asteroids 83 3.1.1 Asteroid Orbits in the Asteroid Belt 84 3.1.2 Asteroid Orbits Outside the Asteroid Belt 86 3.1.3 Asteroid Sizes 89 3.1.4 Asteroid Shapes and Surface Features 91 3.1.5 Asteroid Masses, Densities, and Overall Composition 93 3.1.6 Asteroid Classes and Surface Composition 94 3.2 Comets and Their Sources 98 3.2.1 The Orbits of Comets 99 3.2.2 The Coma, Hydrogen Cloud, and Tails of a Comet 101 3.2.3 The Cometary Nucleus 103 3.2.4 The Death of Comets 106 3.2.5 The Sources of Comets 107 3.2.6 The Oort Cloud 108 3.2.7 The E–K Belt 109 3.3 Meteorites 111 3.3.1 Meteors, Meteorites, and Micrometeorites 112 3.3.2 The Structure and Composition of Meteorites 113 3.3.3 Dating Meteorites 116 3.3.4 The Sources of Meteorites 118 3.3.5 The Sources of Micrometeorites 121 3.4 Summary of Chapter 3 123 4 Interiors of Planets and Satellites: The Observational and Theoretical Basis 126 4.1 Gravitational Field Data 126 4.1.1 Mean Density 126 4.1.2 Radial Variations of Density: Gravitational Coefficients 131 4.1.3 Radial Variations of Density: The Polar Moment of Inertia 134 4.1.4 Love Numbers 135 4.1.5 Local Mass Distribution, and Isostasy 135 4.2 Magnetic Field Data 136 4.3 Seismic Wave Data 139 4.3.1 Seismic Waves 139 4.3.2 Planetary Seismic Wave Data 142 4.4 Composition and Properties of Accessible Materials 143 4.4.1 Surface Materials 143 4.4.2 Elements, Compounds, Affinities 144 CONTENTS ix 4.4.3 Equations of State, and Phase Diagrams 145 4.5 Energy Sources, Energy Losses, and Interior Temperatures 149 4.5.1 Energy Sources 150 4.5.2 Energy Losses and Transfers 154 4.5.3 Observational Indicators of Interior Temperatures 159 4.5.4 Interior Temperatures 159 4.6 Summary of Chapter 4 161 5 Interiors of Planets and Satellites: Models of Individual Bodies 163 5.1 The Terrestrial Planets 163 5.1.1 The Earth 166 5.1.2 Venus 169 5.1.3 Mercury 170 5.1.4 Mars 171 5.2 Planetary Satellites, Pluto, EKOs 173 5.2.1 The Moon 173 5.2.2 Large Icy–Rocky Bodies: Titan, Triton, Pluto, and EKOs 176 5.2.3 The Galilean Satellites of Jupiter 179 5.2.4 Small Satellites 183 5.3 The Giant Planets 183 5.3.1 Jupiter and Saturn 185 5.3.2 Uranus and Neptune 189 5.4 Magnetospheres 190 5.4.1 An Idealised Magnetosphere 191 5.4.2 Real Magnetospheres 192 5.5 Summary of Chapter 5 194 6 Surfaces of Planets and Satellites: Methods and Processes 197 6.1 Some Methods of Investigating Surfaces 197 6.1.1 Surface Mapping in Two and Three Dimensions 197 6.1.2 Analysis of Electromagnetic Radiation Reflected or Emitted by a Surface 200 6.1.3 Sample Analysis 201 6.2 Processes that Produce the Surfaces of Planetary Bodies 201 6.2.1 Differentiation, Melting, Fractional Crystallisation, and Partial Melting 202 6.2.2 Volcanism and Magmatic Processes 204 6.2.3 Tectonic Processes 206 6.2.4 Impact Cratering 207 6.2.5 Craters as Chronometers 212 6.2.6 Gradation 216 6.2.7 Formation of Sedimentary Rocks 219 6.2.8 Formation of Metamorphic Rocks 220 6.3 Summary of Chapter 6 220 7 Surfaces of Planets and Satellites: Weakly Active Surfaces 223 7.1 The Moon 223 7.1.1 Impact Basins and Maria 224 7.1.2 The Nature of the Mare Infill 225 x CONTENTS 7.1.3 Two Contrasting Hemispheres 226 7.1.4 Tectonic Features; Gradation and Weathering 227 7.1.5 Localised Water Ice? 227 7.1.6 Crustal and Mantle Materials 227 7.1.7 Radiometric Dating of Lunar Events 230 7.1.8 Lunar Evolution 231 7.2 Mercury 232 7.2.1 Mercurian Craters 233 7.2.2 The Highlands and Plains of Mercury 233 7.2.3 Surface Composition 236 7.2.4 Other Surface Features on Mercury 236 7.2.5 The Evolution of Mercury 236 7.3 Mars 238 7.3.1 Albedo Features 238 7.3.2 The Global View 239 7.3.3 The Northerly Hemisphere 241 7.3.4 The Southerly Hemisphere 243 7.3.5 The Polar Regions 245 7.3.6 Water-related Features 247 7.3.7 Observations at the Martian Surface 253 7.3.8 Martian Meteorites 256 7.3.9 The Evolution of Mars 257 7.4 Icy Surfaces 258 7.4.1 Pluto and Charon 258 7.4.2 Ganymede and Callisto 260 7.5 Summary of Chapter 7 262 8 Surfaces of Planets and Satellites: Active Surfaces 264 8.1 The Earth 264 8.1.1 The Earth’s Lithosphere 264 8.1.2 Plate Tectonics 266 8.1.3 The Success of Plate Tectonics 270 8.1.4 The Causes of Plate Motion 271 8.1.5 The Evolution of the Earth 272 8.2 Venus 273 8.2.1 Topological Overview 273 8.2.2 Radar Reflectivity 275 8.2.3 Impact Craters and Possible Global Resurfacing 275 8.2.4 Volcanic Features 277 8.2.5 Surface Analyses and Surface Images 278 8.2.6 Tectonic Features 278 8.2.7 Tectonic and Volcanic Processes 279 8.2.8 Internal Energy Loss 282 8.2.9 The Evolution