Dynamic Planet

CONTENTS Preface .................................................................................................. vii List of Figures .............................................................................................xiii List of Tables............................................................................................... xvi 1. Mercury From A Systems Perspective..................................................... 1 1.1 Mercury in Context ..................................................................... 1 1.2 Physical and Orbital Measurements............................................ 1 1.3 Difficulties and Anomalies Uncovered in Observing Mercury .. 2 1.4 A Planet as a System of Subsystems........................................... 6 1.5 Types of Systems ........................................................................ 6 1.6 In the Beginning: Solar Nebula System for Planet Formation.... 8 1.7 Interior and Surface Formation: Sources, Sinks, Processes...... 12 1.8 Atmosphere Formation: Sources, Sinks, and Processes ........... 14 1.9 Magnetosphere Formation: Sources, Sinks, and Processes ...... 15 1.10 Summary................................................................................... 17 1.11 References................................................................................. 17 1.12 Some Questions for Discussion ................................................ 19 2. Past and Planned Missions to Mercury .................................................. 20 2.1 NASA’s Successful Mariner 10 Mission to Mercury ............... 20 2.2 The Mariner 10 Spacecraft........................................................ 22 2.3 The Mariner 10 Scientific Payload ........................................... 24 2.4 Overview of Mariner 10 Observations ..................................... 24 2.5 Mariner 10 Mission Objectives................................................. 26 2.6 NASA’s Ongoing MESSENGER Mission ............................... 26 2.7 The MESSENGER Spacecraft and Payload ............................. 28 2.8 The MESSENGER Mission Objectives.................................... 30 2.9 The ESA/ISAS Planned Bepi Colombo Mission...................... 30 2.10 The Bepi Colombo Spacecraft and Payload ............................. 32 x Contents 2.11 The Bepi Colombo Mission Objectives ....................................33 2.12 Summary ...................................................................................35 2.13 References .................................................................................35 2.14 Some Questions for Discussion.................................................36 3. Mercury’s Interior ..................................................................................37 3.1 Present understanding of Mercury’s Interior.............................37 3.2 Bulk Properties ..........................................................................37 3.3 Magnetic Field and Core Formation..........................................38 3.4 Structure of Mercury’s Core......................................................40 3.5 Shape, Gravity Field, and Internal Structure of Mercury ..........44 3.6 Search for a Liquid Core/Shell ..................................................45 3.7 Solar system Formation.............................................................46 3.8 Equilibrium Condensation Model .............................................46 3.9 Mercury’s High Bulk Abundance of Iron .................................49 3.10 Direct Accretion of Reduced Components................................49 3.11 The Selective Accretion Model .................................................50 3.12 Post-Accretion Vaporization and Giant Impact Models............51 3.13 Infall of Cometary/Asteroid Materials ......................................53 3.14 Discrimination between the Models..........................................53 3.15 Summary ...................................................................................55 3.16 References .................................................................................56 3.17 Some Questions for Discussion.................................................60 4. Mercury’s Surface ..................................................................................61 4.1 Present Understanding of Mercury’s Surface............................61 4.2 Physical Properties of the Surface and Regolith .......................65 4.3 Composition of Mercury’s Surface and Regolith......................68 4.4 Space Weathering as Regolith Modification Process................76 4.5 Nature and Composition of Major Terranes..............................77 4.6 Concise Summary of Mercury’s Geological History ................81 4.7 Impact activity and Chronology ................................................83 4.8 Volcanism..................................................................................89 4.9 Tectonic Activity.......................................................................91 4.10 Polar Features ............................................................................96 4.11 Summary ...................................................................................99 4.12 References ...............................................................................100 4.13 Some Questions for Discussion...............................................106 5. Mercury’s Exosphere ...........................................................................107 5.1 The Exosphere Concept...........................................................107 Contents xi 5.2 From Atmosphere to Exosphere ............................................. 107 5.3 Mariner 10 Observations......................................................... 108 5.4 Post-Mariner 10 Understanding Mercury’s Atmosphere........ 109 5.5 Ground-based Observations of Sodium and Potassium.......... 111 5.6 The Sodium Tail of Mercury .................................................. 115 5.7 Discovery of Calcium in Mercury’s Atmosphere ................... 115 5.8 Mercury’s Exosphere after Sodium and Potassium Detection 116 5.9 Current Understanding of Source and Loss Processes............ 119 5.10 Proposed Source and Loss Processes...................................... 121 5.11 Models of Mercury’s Atmosphere .......................................... 124 5.12 Summary of Constituent Source and Loss Mechanisms......... 126 5.13 Mercury’s Exo-Ionosphere ..................................................... 128 5.14 Space Weathering as Atmosphere Modification Process ....... 128 5.15 Summary................................................................................. 132 5.16 References............................................................................... 132 5.17 Some Questions for Discussion .............................................. 138 6. Mercury’s Magnetosphere ................................................................... 139 6.1 Pre-Mariner 10 Knowledge of Mercury’s Magnetosphere ..... 139 6.2 Mariner 10 Magnetosphere Detection..................................... 139 6.3 Mariner 10 Magnetometer Measurements .............................. 143 6.4 Origin of Mercury’s Magnetic Field....................................... 148 6.5 Mariner 10 Plasma Observations ............................................ 148 6.6 Mariner 10 ULF Observations ................................................ 150 6.7 Magnetosphere Structure ........................................................ 152 6.8 Magnetopause Structure.......................................................... 154 6.9 Magnetosphere Dynamics....................................................... 157 6.10 Substorm Activity ................................................................... 163 6.11 Field Aligned Currents............................................................ 164 6.12 Detectable Magnetosphere/Exosphere Interactions ................ 169 6.13 Magnetosphere/Surface Interactions....................................... 174 6.14 Recent Modeling of Mercury’s Magnetosphere ..................... 174 6.15 Summary................................................................................. 179 6.16 References............................................................................... 179 6.17 Some Questions for Discussion .............................................. 184 7. The Future of Mercury Exploration ..................................................... 185 7.1 Need for Further Investigation of Mercury’s Interior ............. 185 7.2 Ground-based Observations for Interior Exploration ............. 186 7.3 Planned Missions and the Interior........................................... 186 7.4 The Future Exploration of Mercury’s Interior ........................ 187 7.5 Need for Further Investigation of Mercury’s Surface............. 189 7.6 Ground-based Observations for Surface Exploration ............. 189 xii Contents 7.7 Planned Missions and the Surface...........................................190 7.8 The Future Exploration of Mercury’s Surface ........................192 7.9 Need for Further Investigation of Mercury’s Exosphere.........194 7.10 Ground-based Observations and the Exosphere......................194 7.11 Planned Missions and the Exosphere ......................................195 7.12 The Future Exploration of Mercury’s Exosphere....................196 7.13 Need for Further Investigation of Mercury’s Magnetosphere.197 7.14 Ground-based Observations for Magnetosphere Exploration .198 7.15 Planned Missions and the Magnetosphere ..............................198 7.16 The Future Exploration of Mercury’s Magnetosphere ............199 7.17 Conclusions: A New Approach ...............................................201 7.18 References ...............................................................................208 7.19 Some Questions for Discussion...............................................211 Index ......................................................................................... 213