Dynamic Planet (eBook)

Pamela Clark grew up in New England and, inspired by President John Kennedy, decided she wanted to explore outer space by the time she was thirteen years old. She was encouraged by several teachers, including her sixth grade teacher, Ed Vandall, and high school biology teacher, Robert Blake, as well as by Werner von Braun. She thought, "If they can put a man on the moon, they can put a woman (me) on Mars!" So, she left home to seek her fortune in the space program. She obtained her BA from St. Joseph College, a tiny Catholic women’s college run by the Sisters of Mercy in West Hartford, Connecticut. There, she had many opportunities to participate in laboratory research with Sr. Chlorophyll (Dr. Claire Markham) and Sr. Moon Rock (Dr. Mary Ellen Murphy) and to coordinate an NSF inter-disciplinary undergraduate field research project. While obtaining her PhD in planetary geochemistry from the University of Maryland, she worked at GSFC/NASA outside of Washington DC and the Astrogeology Branch of the USGS in Flagstaff, Arizona, simulating, analyzing, correlating, and interpreting lunar X-ray spectra. She was a member of the group, led by Isidore Adler and Jack Trombka, that pioneered the use of orbital x-ray and gamma-ray spectrometers to determine the composition of planetary surfaces. She participated in the Flagstaff Lunar Data Consortium, the first attempt to create a common format for all remote sensing data for a planetary body. After completing her PhD, she joined the technical staff at NASA/JPL outside of Los Angeles for awhile, working with the Ray Jurgens of the Goldstone Solar System Radar group, and expanding her remote sensing background to include radar and thermal and near infrared studies of planetary surfaces with particular emphasis on the study of the physical nature of Mercury’s surface. Dr. Clark helped to organize a consortium of scientists interested in Mercury and edits the Mercury Messenger newsletter. She eventually returned Goddard as a member of the XGRS team on the NEAR mission to asteroid Eros. Currently, as a member of the sciences and exploration division at GSFC, Dr. Clark is the science lead in a group initiated by Steve Curtis to develop new paradigms for the design of space missions and vehicles. She provides science support for the Magnetosphere Multi-Scale Mission, and continues to study the Moon, asteroids, and Mercury. Dr. Clark has done several stints in academic institutions, including Murray State University in Kentucky, Albright College in Reading, Pennsylvania, and Catholic University in Washington DC. She has developed courses in analytical and environmental chemistry, geochemistry, physical geology, mineralogy, optics, planetary astronomy, remote sensing, and physics. A space scientist by day, Dr. Clark is otherwise engaged in prison ministry, or in writing about or giving workshops in her wide-ranging fields of interest, including oral and local history, genealogy, Irish history, Celtic spirituality, herb gardening, and cooking. One of her major goals in life is to increase the awareness and the sense of wonder about the planet Mercury.Information about her work can be found at http://www.lpi.usra.edu/publications/newsletters/mercmessenger/ or http://ants.gsfc.nasa.gov

CONTENTS 8
LIST OF FIGURES 12
LIST OF TABLES 15
Chapter 1 MERCURY FROM A SYSTEMS PERSPECTIVE 16
1.1 MERCURY IN CONTEXT 16
1.2 PHYSICAL AND ORBITAL MEASUREMENTS 16
1.3 DIFFICULTIES AND ANOMALIES UNCOVERED IN OBSERVING MERCURY 17
1.4 A PLANET AS A SYSTEM OF SUBSYSTEMS 21
1.5 TYPES OF SYSTEMS 21
1.6 IN THE BEGINNING: SOLAR NEBULA SYSTEM FOR PLANET FORMATION 23
1.7 INTERIOR AND SURFACE FORMATION: SOURCES, SINKS, PROCESSES 27
1.8 ATMOSPHERE FORMATION: SOURCES, SINKS, AND PROCESSES 29
1.9 MAGNETOSPHERE FORMATION: SOURCES, SINKS, AND PROCESSES 30
1.10 SUMMARY 32
1.11 REFERENCES 32
1.12 SOME QUESTIONS FOR DISCUSSION 34
Chapter 2 PAST AND PLANNED MISSIONS TO MERCURY 35
2.1 NASA’S SUCCESSFUL MARINER 10 MISSION TO MERCURY 35
2.2 THE MARINER 10 SPACECRAFT 37
2.3 THE MARINER 10 SCIENTIFIC PAYLOAD 39
2.4 OVERVIEW OF MARINER 10 OBSERVATIONS 39
2.5 MARINER 10 MISSION OBJECTIVES 41
2.6 NASA’S ONGOING MESSENGER MISSION 41
2.7 THE MESSENGER SPACECRAFT AND PAYLOAD 43
2.8 THE MESSENGER MISSION OBJECTIVES 45
2.9 THE ESA/ISAS PLANNED BEPI COLOMBO MISSION 45
2.10 THE BEPI COLOMBO SPACECRAFT AND PAYLOAD 47
2.11 THE BEPI COLOMBO MISSION OBJECTIVES 48
2.12 SUMMARY 50
2.13 REFERENCES 50
2.14 SOME QUESTION FOR DISCUSSION 51
Chapter 3 MERCURY’S INTERIOR 52
3.1 PRESENT UNDERSTANDING OF MERCURY’S INTERIOR 52
3.2 BULK PROPERTIES 52
3.3 MAGNETIC FIELD AND CORE FORMATION 53
3.4 STRUCTURE OF MERCURY’S CORE 55
3.5 SHAPE, GRAVITY FIELD, AND INTERNAL STRUCTURE OF MERCURY 59
3.6 SEARCH FOR A LIQUID CORE/SHELL 60
3.7 SOLAR SYSTEM FORMATION 61
3.8 EQUILIBRIUM CONDENSATION MODEL 61
3.9 MERCURY’S HIGH BULK ABUNDANCE OF IRON 64
3.10 DIRECT ACCRETION OF REDUCED COMPONENTS 64
3.11 THE SELECTIVE ACCRETION MODEL 65
3.12 POST-ACCRETION VAPORIZATION AND GIANT IMPACT MODELS 66
3.13 INFALL OF COMETARY/ASTEROID MATERIALS 68
3.14 DISCRIMINATION BETWEEN THE MODELS 68
3.15 SUMMARY 70
3.16 REFERENCES 71
3.17 SOME QUESTIONS FOR DISCUSSION 75
Chapter 4 MERCURY’S SURFACE 76
4.1 PRESENT UNDERSTANDING OF MERCURY’S SURFACE 76
4.2 PHYSICAL PROPERTIES OF THE SURFACE AND REGOLITH 80
4.3 COMPOSITION OF MERCURY’S SURFACE AND REGOLITH 83
4.4 SPACE WEATHERING AS A REGOLITH MODIFICATION PROCESS 91
4.5 THE NATURE AND COMPOSITION OF MAJOR TERRANES 92
4.6 CONCISE SUMMARY OF MERCURY’S GEOLOGICAL HISTORY 96
4.7 IMPACT ACTIVITY AND CHRONOLOGY 98
4.8 VOLCANISM 104
4.9 TECTONIC ACTIVITY 106
4.10 POLAR FEATURES 111
4.11 SUMMARY 114
4.12 REFERENCES 115
4.13 SOME QUESTIONS FOR DISCUSSION 121
Chapter 5 MERCURY’S EXOSPHERE 122
5.1 THE EXOSPHERE CONCEPT 122
5.2 FROM ATMOSPHERE TO EXOSPHERE 122
5.3 MARINER 10 OBSERVATIONS 123
5.4 POST-MARINER 10 UNDERSTANDING OF MERCURY’S ATMOSPHERE 124
5.5 GROUND BASED OBSERVATIONS OF SODIUM AND POTASSIUM 126
5.6 THE SODIUM TAIL OF MERCURY 130
5.7 DISCOVERY OF CALCIUM IN MERCURY’S ATMOSPHERE 130
5.8 MERCURY’S EXOSPHERE AFTER SODIUM AND POTASSIUM DETECTION 131
5.9 CURRENT UNDERSTANDING OF SOURCE AND LOSS PROCESSES 134
5.10 PROPOSED SOURCE AND LOSS PROCESSES 136
5.11 MODELS OF MERCURY’S ATMOSPHERE 139
5.12 SUMMARY OF CONSTITUENT SOURCE AND LOSS MECHANISMS 141
5.13 MERCURY’S EXO-IONOSPHERE 143
5.14 SPACE WEATHERING AS AN ATMOSPHERE MODIFICATION PROCESS 143
5.15 SUMMARY 147
5.14 REFERENCES 147
5.15 SOME QUESTIONS FOR DISCUSSION 153
Chapter 6 MERCURY’S MAGNETOSPHERE 154
6.1 PRE-MARINER 10 KNOWLEDGE OF MERCURY’S MAGNETOSPHERE 154
6.2 MARINER 10 MAGNETOSPHERE DETECTION 154
6.3 MARINER 10 MAGNETOMETER MEASUREMENTS 158
6.4 ORIGIN OF MERCURY’S MAGNETIC FIELD 163
6.5 MARINER 10 PLASMA OBSERVATIONS 163
6.6 MARINER 10 ULF OBSERVATIONS 165
6.7 MAGNETOSPHERE STRUCTURE 167
6.8 MAGNETOPAUSE STRUCTURE 169
6.9 MAGNETOSPHERE DYNAMICS 172
6.10 SUBSTORM ACTIVITY 178
6.11 FIELD ALIGNED CURRENTS 179
6.12 DETECTABLE MAGNETOSPHERE/EXOSPHERE INTERACTIONS 184
6.13 MAGNETOSPHERE/SURFACE INTERACTIONS 189
6.14 RECENT MODELING OF THE MAGNETOSPHERE 189
6.15 SUMMARY 194
6.16 REFERENCES 194
6.17 SOME QUESTIONS FOR DISCUSSION 199
Chapter 7 THE FUTURE OF MERCURY EXPLORATION 200
7.1 NEED FOR FURTHER INVESTIGATION OF MERCURY’S INTERIOR 200
7.2 GROUND-BASED OBSERVATIONS FOR INTERIOR EXPLORATION 201
7.3 PLANNED MISSIONS AND THE INTERIOR 201
7.4 THE FUTURE EXPLORATION OF MERCURY’S INTERIOR 202
7.5 NEED FOR FURTHER INVESTIGATION OF MERCURY’S SURFACE 204
7.6 GROUND-BASED OBSERVATIONS FOR SURFACE EXPLORATION 204
7.7 PLANNED MISSIONS AND THE SURFACE 205
7.8 THE FUTURE EXPLORATION OF MERCURY’S SURFACE 207
7.9 NEED FOR FURTHER INVESTIGATION OF MERCURY’S EXOSPHERE 209
7.10 GROUND-BASED OBSERVATIONS AND THE EXOSPHERE 209
7.11 PLANNED MISSIONS AND THE EXOSPHERE 210
7.12 THE FUTURE EXPLORATION OF MERCURY’S EXOSPHERE 211
7.13 NEED FOR FURTHER INVESTIGATION OF MERCURY’S MAGNETOSPHERE 212
7.14 GROUND-BASED OBSERVATIONS FOR MAGNETOSPHERE EXPLORATION 213
7.15 PLANNED MISSIONS AND THE MAGNETOSPHERE 213
7.16 THE FUTURE EXPLORATION OF MERCURY’S MAGNETOSPHERE 214
7.17 CONCLUSIONS: A NEW APPROACH 216
7.18 REFERENCES 223
7.19 SOME QUESTIONS FOR DISCUSSION 226
Index 227