Io: A New View of Jupiter’s Moon (Astrophysics and Space Science Library, 468)

Written by expert researchers, this book covers all the major aspects of research in Jupiter's moon Io, from the interior to its space environment. Io is one of the Solar System’s most exotic satellites. The book discusses Io's interior, geology, atmosphere, and, in particular, its active volcanism, which was discovered from observations by the Voyager 1 spacecraft in 1979, confirming a possibility suggested from theoretical studies based on Io’s orbit. Our knowledge of Io’s volcanism, composition, and space environment was significantly increased as a result of observations by other spacecrafts, including Galileo. More than a decade after the 1 st edition, “Io After Galileo”, this 2 nd edition of the book now includes results obtained by the New Horizons mission and, more recently, Juno. It also presents observational results from ground-based telescopes using adaptive optics having provided resolutions that rival those of spacecraft. The book provides a review of the current status of Io research and gives an outlook to planned future observations. It thus serves as reference for researchers in the field and an introduction for PhD students and newcomers planning to study this exotic Solar System moon. Contents Contributors 1 Introduction 2 Understanding Io: Four Centuries of Study and Surprise 2.1 Introduction 2.2 Discovery and Bulk Properties 2.3 Celestial Mechanics Drives Tidal Heating 2.4 Tidal Heating Controls the Interior and Heat Flow 2.5 Heat Flow Generates Diverse Volcanic Styles 2.6 Volcanism Creates a Unique Landscape 2.7 Volcanism Sustains an Atmosphere Out of Balance 2.8 Rampant Atmospheric Escape Fuels the Magnetosphere 2.9 Summary and Outlook References 3 Setting the Stage: Formation and Earliest Evolution of Io 3.1 Formation of Jupiter and the Galilean Satellites 3.1.1 Classes of Satellite-Forming Disks 3.1.2 Pebbles vs. Planetesimals 3.1.3 When Did Io Form? 3.2 The Protojovian Circumplanetary Disk 3.2.1 Advantages of Gas-Starved/Limited Disk Scenarios 3.2.2 Major Issue: Supply of Solids 3.2.3 Major Issue: Central Magnetized Cavity? 3.2.4 Emerging Paradigms 3.2.5 A Perspective 3.3 Accretion of Io 3.3.1 Composition 3.3.2 Did Io Accrete Wet or Dry? 3.3.3 Disk Cooling 3.3.4 Initial Thermal State of Io 3.3.5 Core Formation and Io's Oxidation State 3.3.6 Spin State 3.4 Early Dynamical Evolution 3.5 Summary and Prospects 3.5.1 Future Spacecraft Measurements References 4 Tidal Heating and the Interior Structure of Io 4.1 Introduction 4.2 Theory, Part 1: Satellite Figures 4.2.1 Shape 4.2.2 Gravity 4.2.3 Inertia 4.2.4 Rotational Deformation 4.2.5 Tidal Deformation 4.2.5.1 Static Tides 4.2.5.2 Time-Dependent Tides 4.2.6 Libration 4.3 Theory, Part 2: Tidal Heating 4.3.1 Tidal Heating in the Solid Interior 4.3.2 The Impact of Rheology on Tidal Heating 4.3.3 The Influence of Internal Structure 4.3.4 Tidal Heating in a Magma Ocean 4.3.5 Heat Transport 4.3.6 Dissipation-Orbit Coupling 4.4 Observations 4.4.1 Long-Wavelength Shape 4.4.2 Short-Wavelength Shape 4.4.3 Gravity Field 4.4.4 Magnetic Induction 4.4.5 The Laplace Resonance and Astrometry 4.4.6 Hotspots, Volcanoes, and Mountains 4.4.7 Total Heat Flow 4.5 Synthesis and Open Questions References 5 Geology of Io 5.1 Introduction 5.2 Background 5.3 Plains 5.4 Paterae and Paterae Floors 5.5 Lava Flows 5.6 Mountains and Tholi 5.7 Diffuse Deposits 5.8 Structural and Tectonic Features 5.9 Large-Scale Topography 5.10 Summary and Future Work 5.10.1 Summary 5.10.2 Future Work References 6 Io's Thermal Emission and Heat Flow 6.1 Introduction 6.1.1 The State of Knowledge at the End of the Galileo Mission 6.1.2 Advances Since the Galileo Mission 6.2 Hot Spot Observations and Techniques 6.2.1 Earth-Based Observations and Techniques 6.2.1.1 Occultations 6.2.1.2 Adaptive Optics 6.2.1.3 Other Telescopic Techniques 6.2.2 Space-Based Observations 6.2.2.1 Recent Analyses of Voyager and Galileo Data 6.2.2.2 Cassini, New Horizons, and Juno 6.3 Volcanic Styles 6.3.1 Persistent vs. Transient Hot Spots 6.3.2 Determining Volcanic Style from Thermal Emission 6.3.3 Outburst Eruptions 6.3.4 Notable Volcanoes 6.3.4.1 Pillan Patera: Source of Repeated Outbursts 6.3.4.2 Pele: A Persistent Volcano Turns Off 6.3.4.3 Marduk Fluctus: Strombolian-like Activity on Io? 6.3.4.4 Violent Outbursts at Tvashtar Catena 6.3.4.5 Loki Patera: The Trickster Powerhouse 6.4 Io's Volcanoes and Tidal Heating 6.4.1 Magma Temperature 6.4.2 The Spatial Distribution of Io's Volcanism and Heat Flow 6.4.2.1 Spatial Trends in Volcanic Style 6.4.3 Periodicities in Thermal Emission 6.5 Non-volcanic Thermal Emission 6.5.1 Global Heat Flow 6.5.2 Thermal Surface Properties 6.6 Outlook References 7 The Composition of Io 7.1 Introduction 7.2 Observations 7.2.1 Magnetosphere and Atmosphere 7.2.2 Surface Mantling Volatiles 7.2.3 Lava 7.2.4 Geophysics 7.3 Compositional Models 7.3.1 A Chondritic Model for Io 7.3.2 Exotic Compositional Models for Io 7.4 Future Observations 7.5 Summary References 8 The Plumes and Atmosphere of Io 8.1 Introduction 8.2 Global Atmospheric Properties 8.2.1 Observational Methods 8.2.2 Timescales Relevant to Observations and Modeling 8.2.3 Atmospheric Composition 8.2.4 Thermal Structure 8.3 Spatial Distribution and Temporal Variability of Io'sAtmosphere 8.3.1 Dayside Atmosphere 8.3.2 Eclipse Response 8.3.2.1 SO2 Observations 8.3.2.2 SO Observations 8.3.3 Auroral Emissions 8.3.4 Atmospheric Escape 8.4 Plumes: Characteristics, Deposits, and Models 8.4.1 Observations of Plumes and Their Deposits 8.4.2 Thermodynamic Properties of Plume Classes 8.4.3 Models of Plumes 8.5 What Drives Io's Atmosphere? 8.5.1 Sublimation-Supported Atmosphere 8.5.2 Volcanically-Supported Atmosphere 8.5.3 Sputtering 8.5.4 Dynamics/winds 8.6 Conclusions and Next Steps References 9 Space Environment of Io 9.1 Introduction 9.2 Plasma Interactions with Io 9.2.1 Electrodynamics 9.2.2 Physical Chemistry 9.2.3 Atmospheric Loss 9.2.4 Aurora at Io 9.2.5 Induction 9.3 Neutral Clouds 9.3.1 Observations 9.3.2 Models 9.3.3 The Mendillodisk 9.4 Plasma Torus 9.5 Conclusions 9.5.1 Outstanding Questions 9.5.2 Future Observations References 10 Io as an Analog for Tidally Heated Exoplanets 10.1 Introduction 10.2 Planetary Composition 10.3 Orbital Configuration and Tidal Heating 10.3.1 The Galilean Satellites 10.3.2 Resonant Exoplanets 10.4 Tidal Heating and Interior Modeling 10.4.1 Tidal Heating 10.4.2 Convection and Conduction 10.4.3 Results 10.4.3.1 Io 10.4.3.2 The TRAPPIST-1 Planets 10.4.3.3 Planetary Habitability 10.5 Geological Consequences 10.6 Prospects for Future Observations References 11 Outstanding Questions and Future Observations of Io 11.1 Introduction 11.2 Outstanding Questions 11.2.1 Formation and Evolution of Io 11.2.2 Tidal Heating and the Interior of Io 11.2.3 Geology and Composition of Io 11.2.4 “Hot Spots” and Thermal Emission from Io 11.2.5 The Plumes and Atmosphere of Io 11.2.6 The Magnetosphere and Plasma Environment Around Io 11.2.7 Io as an Analog for Exoplanets and Exomoons 11.3 Future Observations of Io 11.3.1 Telescopic Observations 11.3.2 Future Spacecraft Observations 11.4 New NASA Mission Concepts 11.5 Io Orbiter Mission Challenges 11.6 Summary: Top Ten Questions (Fig. 11.6) References Correction to: Understanding Io: Four Centuries of Study and Surprise Index