Planetary geoscience had its inception with the birth of the Space Age in the early 1960s. In the ensuing decades, it has evolved into a discipline that is recognized by sections of professional organizations such as the Geological Society of America and the American Geophysical Union, as well as being taught at the university level. Much of our understanding of the geology of extra-terrestrial objects is derived from remote sensing data —primarily images that portray planetary surfaces. In fact, discoveries such as the dry river beds on Mars, the tectonic deformation of Venus, and the actively erupting volcanoes on Jupiter's moon lo all came from pictures taken from spacecraft. Thus, the focus of this book is on the geo-morphology of solid-surface objects in our Solar System and the interpretations of the processes that led to the diverse landforms observed. Geomorphology, however, must be analyzed in the context of broader geoscience; consequently, in the chapters on the individual planetary systems, the geophysics and interior characteristics are reviewed along with our current understanding of surface compositions and the general geologic histories. Of course, our knowledge of the Solar System is far from uniform from one planet to another, dependent upon the numbers and types of spacecraft that have returned data. Thus, the chapters on the Moon and Mars are more detailed than those on the outermost planet systems, Uranus and Neptune, because dozens of successful space-craft have visited our nearest planetary neighbors, in con-trast to the limited data returned from "flybys" of the Voyager spacecraft to the planets beyond Saturn.
Our journey to explore the geomorphology of the Solar System begins with introductory chapters that introduce the planets and other objects of planetary geoscience interest, discuss the methods used in studying extraterres-trial objects, and review the fundamental geomorphic processes on Earth that can be compared with what we see on other planets and satellites.
Key references are given in the text and listed at the back of the book. The end of this book includes additional reading for those who wish to delve into the chapter topic in more detail. Because images form the basis of much of planetary geomorphology, figure cap-tions generally include the basic NASA or other space agency data for the frames shown, to enable the use of various electronic search engines for obtaining additional information.
I hope that you find the exploration of the Solar System a rewarding experience. While many planets and satellites show landforms that are quite familiar to geologists, others hold surprises that have not yet been explained or understood. Have fun, and maybe you can solve some of these mysteries!

Foreword by Robert T. Pappalardo xi

Preface xiii

Acknowledgments xiv

1 Introduction 1

1.1 Solar System overview 1

      1.1.1 The terrestrial planets 1

      1.1.2 The giant planets 3

      1.1.3 Small bodies, Pluto, and "dwarf planets" 4

1.2 Objectives of Solar System exploration 6

      1.2.1 Planetary geology objectives 6

      1.2.2 Astrobiology 7

1.3 Strategy for Solar System exploration 7

1.4 Flight projects 9

1.5 Planetary data 12

1.6 Planetary research results 13

Assignments 14

2 Planetary geomorphology methods 15

2.1 Introduction 15

2.2 Approach 15

2.3 Planetary geologic maps 17

2.4 Geologic time 20

2.5 Remote sensing data 22

      2.5.1 Visible imaging data 23

      2.5.2 Multispectral data 24

      2.5.3 Thermal data 24

      2.5.4 Radar imaging data 24

      2.5.5 Ultraviolet, X-ray, and gamma-ray data 25

2.6 Geophysical data 25

2.7 Image processing 26

2.8 Resolution 28

2.9 Electronic data records (EDRs) 30

2.10 Cartography 30

Assignments 33

3 Planetary morphologic processes 34

3.1 Introduction 34

3.2 Tectonism 34

3.3 Volcanic processes 37

      3.3.1 Volcanic eruptions 38

      3.3.2 Volcanic morphology 38

      3.3.3 Volcanic craters 40

      3.3.4 Intrusive structures 42

3.4 Impact cratering 43

      3.4.1 Impact cratering mechanics 43

      3.4.2 Impact craters on Earth 44

      3.4.3 Impact craters and planetary environments 50

3.5 Gradation 51

      3.5.1 Weathering 51

      3.5.2 Mass wasting 53

      3.5.3 Processes associated with the hydrologic cycle 53

      3.5.4 Aeolian processes 54

      3.5.5 Periglacial processes 56

3.6 Summary 58

Assignments 58

4 Earth's Moon 59

4.1 Introduction 59

4.2 Lunar exploration 59

      4.2.1 Pre-Apollo studies 59

      4.2.2 The Apollo era 62

      4.2.3 Post-Apollo exploration 65

4.3 Interior characteristics 71

4.4 Surface composition 72

4.5 Geomorphology 75

      4.5.1 Impact craters and basins 75

      4.5.2 Highland plains 77

      4.5.3 Mare terrains 77

      4.5.4 Sinuous rules 78

      4.5.5 Volcanic constructs 82

      4.5.6 Tectonic features 82

      4.5.7 Gradational features 84

4.6 Geologic history of the Moon 85

Assignments 90

5 Mercury 91

5.1 Introduction 91

5.2 Mercury exploration 91

5.3 Interior characteristics 91

5.4 Surface composition 92

5.5 Geomorphology 93

      5.5.1 General physiography 94

      5.5.2 Impact craters 94

      5.5.3 Multi-ring basins 95

      5.5.4 Volcanic features 99

      5.5.5 Tectonic features 102

      5.5.6 Gradation features 103

5.6 Geologic history 104

Assignments 104

6 Venus 105

6.1 Introduction 106

6.2 Venus exploration 106

6.3 Interior characteristics 106

6.4 Surface composition 112

6.5 Geomorphology 113

      6.5.1 General physiography 113

      6.5.2 Impact craters 114

      6.5.3 Volcanic features 116

      6.5.4 Tectonic features 118

      6.5.5 Gradation features 120

6.6 Geologic history 124

Assignments 125

7 Mars 126

7.1 Introduction 126

7.2 Exploration 126

7.3 Interior 129

7.4 Surface composition 130

7.5 Geomorphology 131

      7.5.1 Physiography 131

      7.5.2 Impact craters 132

      7.5.3 Volcanic features 134

      7.5.4 Tectonic features 137

      7.5.5 Gradation features 139

7.6 Geologic history 145

Assignments 146

8 The Jupiter system 147

8.1 Introduction 147

8.2 Exploration 147

8.3 Jupiter 148

8.4 Io 149

      8.4.1 Impact features (none!) 152

      8.4.2 Volcanic features 152

      8.4.3 Tectonic features 155

      8.4.4 Gradation features 155

      8.4.5 lo summary 156

8.5 Europa 156

      8.5.1 Impact features 157

      8.5.2 Tectonic features 158

      8.5.3 Volcanic features 160

      8.5.4 Gradation features 162

      8.5.5 Europa summary 162

8.6 Ganymede 162

      8.6.1 Physiography 162

      8.6.2 Impact features 163

      8.6.3 Tectonic features 165

      8.6.4 Volcanic features 168

      8.6.5 Gradation features 168

      8.6.6 Ganymede surrunary 169

8.7 Callisto 170

      8.7.1 Physiography 170

      8.7.2 Impact features 171

      8.7.3 Gradation features 173

      8.7.4 Callisto summary 174

8.8 Small moons and rings 174

8.9 Summary 175

Assignments 176

9 The Saturn system 177

9.1 Introduction 177

9.2 Exploration 177

9.3 Saturn 178

9.4 Satellites 178

9.5 Titan 179

9.6 Enceladus 185

9.7 Intermediate-size satellites 188

      9.7.1 Mimas 188

      9.7.2 Tethys 190

      9.7.3 Dione 192

      9.7.4 Rhea 193

      9.7.5 Iapetus 194

      9.7.6 Small satellites 197

9.8 The ring system 198

9.9 Summary 199

Assignments 200

10 The Uranus and Neptune systems 201

10.1 Introduction 201

10.2 Uranus and Neptune 201

10.3 Uranian moons 202

10.4 Neptunian moons 206

10.5 Summary 208

Assignments 209

11 Planetary geoscience future 210

11.1 Introduction 210

11.2 Planetary protection 210

11.3 Missions in flight and anticipated for launch 211

11.4 Extended missions 214

11.5 Summary 214

Assignments 215

Appendices 216

References 221

Further reading 225

Index 227

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