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CASSINI FINAL MISSION REPORT 2019 1 S MAPS Prior to Cassini’s arrival, scientists had little information about Saturn’s magnetosphere, the giant, invisible magnetic bubble surrounding the planet. Cassini studied Saturn’s magnetosphere as never before by mapping the magnetic field, studying the flow of excited plasma within, and observing the influence of the solar wind and how it affects Saturn’s auroras. Fields and particles data have provided powerful insights about how Saturn’s magnetic field provide linkages between charged particle sources and the rings, moons, and atmospheres, in addition to the inner workings of Saturn’s interior. The Magnetospheres and Plasma Science (MAPS) Discipline Working Group (DWG) facilitated and coordinated the data sharing and collective science among the six MAPS instrument teams to ensure that all Cassini’s MAPS mission objectives were successfully met. The MAPS DWG has achieved and exceeded in every way the Cassini mission goals and objectives, and has provided a legacy for the outer planets community that will reach far into the future. 2 VOLUME 1: MISSION OVERVIEW & SCIENCE OBJECTIVES AND RESULTS CONTENTS MAPS ................................................................................................................................................................................ 1 Executive Summary................................................................................................................................................ 6 Key Science Results ............................................................................................................................................... 6 Top Science Findings for MAPS .................................................................................................................. 6 Discovery of the Enceladus plumes and their interaction with Saturn’s magnetosphere .................. 6 Identifying the highly axisymmetric internal magnetic field of Saturn ................................................ 7 Discovery of periodicities while the intrinsic rotation rate remains elusive ........................................ 7 Discovery of new radiation belts ........................................................................................................ 8 Identifying the main plasma sources in Saturn’s magnetosphere ..................................................... 8 Global configuration and dynamics of the magnetosphere ............................................................... 9 First in situ measurements of Saturn’s topside ionosphere ............................................................... 9 Detection of lightning in Saturn’s atmosphere and the evolution of a once-per-Saturn-year Great White Spot storm ............................................................................................................................. 10 Detailed studies of Saturn’s auroras................................................................................................ 10 Discovery of ring-ionosphere-magnetosphere interaction ............................................................... 11 Discovery of heavy positive and negative ions in Titan’s ionosphere.............................................. 12 Dust–plasma interactions ................................................................................................................ 12 Discovery of nanodust between the planet and the D-ring .............................................................. 12 Discovery of the shape of the heliosphere ...................................................................................... 13 Assessment of Overall DWG Science ....................................................................................................... 13 Key Open Questions .................................................................................................................................. 14 Key Objectives for MAPS DWG ........................................................................................................................... 14 MAPS DWG Science Assessment ....................................................................................................................... 17 MAPS DWG Magnetosphere Science Results ..................................................................................................... 18 Titan Science ............................................................................................................................................. 18 Titan’s upper atmosphere and its interaction with the surrounding plasma .................................... 18 Icy Satellite Science ................................................................................................................................... 30 Interaction of the Enceladus plume with the magnetosphere .......................................................... 30 Ring Science .............................................................................................................................................. 40 Ring-magnetosphere-ionosphere interaction .................................................................................. 40 Magnetosphere Science ............................................................................................................................ 49 Seasonal and solar cycle variations ................................................................................................ 49 Magnetotail configuration and dynamics ......................................................................................... 53 Magnetospheric structure and convection ....................................................................................... 59 Plasma loss into the magnetotail ..................................................................................................... 74 Plasma composition, distribution, sources, and sinks ..................................................................... 78 Plasma kinetics and wave-particle interactions ............................................................................... 87 Radiation belts ................................................................................................................................. 89 Saturn Science ........................................................................................................................................... 91 High-order magnetic moments of Saturn ........................................................................................ 91 Time varying modulation of SKR and associated PPO signals ....................................................... 94 Aurora and satellite footprints ........................................................................................................ 101 Composition of ionosphere and thermosphere ............................................................................. 107 Open Questions for Saturn System Science ........................................................................................... 112 Internal rotation rate and internal magnetic field of Saturn ............................................................ 112 Rotational modulation in axisymmetric configuration .................................................................... 113 CASSINI FINAL MISSION REPORT 2019 3 How are mass and magnetic flux transported in the middle and outer magnetosphere? ............. 114 Solar wind control of the Saturnian magnetosphere...................................................................... 114 Neutral particle dominated Saturnian magnetosphere related to difference if compared to Jupiter? .......................................................................................................................................... 114 Very limited plasma measurements in auroral acceleration and source region of related SKR .... 115 Understanding the Enceladus plume-magnetosphere interaction ................................................. 115 Composition of the negative ions at Titan and > 100 amu positive ions ....................................... 115 MAPS DWG Non-Saturn Science Results ......................................................................................................... 115 Cruise-specific Science ............................................................................................................................ 115 Solar wind from Earth to Saturn .................................................................................................... 115 Other Non-Saturn System Science .......................................................................................................... 118 Interstellar neutrals and the Heliotail ............................................................................................. 118 Jupiter ...................................................................................................................................................... 122 Jupiter’s magnetotail ..................................................................................................................... 122 Jupiter’s radio emissions ............................................................................................................... 126 Venus ....................................................................................................................................................... 129 Earth .......................................................................................................................................................
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