The Sun and Heliosphere In Three Dimensions Report of the NASA Science Definition Team for the STEREO Mission Table of Contents Executive Summary ........................................................................................................... 1 1. Introduction ..................................................................................................................3 2. Scientific Objectives ..................................................................................................... 4 Coronal Mass Ejections ....................................................................................................................... 4 CME Onset ..................................................................................................................................... 4 CME Geometry and Onset Signatures............................................................................................ 5 Reconnection .................................................................................................................................. 6 Surface Evolution ........................................................................................................................... 6 The Heliosphere Between the Sun and Earth ...................................................................................... 7 CMEs in the Heliosphere ..................................................................................................................... 9 Tracking Disturbances from the Sun to Earth ................................................................................... 10 Particle Acceleration by CMEs .......................................................................................................... 11 Magnetic Clouds ................................................................................................................................ 12 Escape of Magnetic Flux and the Solar Dynamo .............................................................................. 15 Coronal Magnetic Fields ................................................................................................................... 15 Coronal Loop Heating ....................................................................................................................... 15 Loop Cross Sections ..................................................................................................................... 17 Scaling Laws................................................................................................................................. 18 Axial Gradients ............................................................................................................................. 18 Loop–Loop Interactions ............................................................................................................... 18 Solar Wind Origins ............................................................................................................................ 18 Solar-B Collaboration ........................................................................................................................ 19 Collateral Research ............................................................................................................................ 19 Helioseismology ........................................................................................................................... 19 Solar Irradiance............................................................................................................................. 20 X-ray and Gamma-ray Bursts ....................................................................................................... 20 Faint Objects ................................................................................................................................. 20 3. Making the Best Use of STEREO Images .................................................................. 21 Determining the 3-D Structure and Dynamics of the Corona ........................................................... 21 Resolving Line-of-Sight Ambiguities with Stereo Observations ................................................. 21 Use of Triangulation to Determine the 3-D Coordinates of Coronal Features ............................. 21 Automatic Feature Tracking ......................................................................................................... 22 Use of Magnetic Field Models in Conjunction with X-ray and EUV Observations .................... 22 Magnetic-Field-Constrained Tomographic Reconstruction of the Corona .................................. 23 Visual Evaluation of Stereo Images ................................................................................................... 24 4. Space Weather ............................................................................................................. 25 Solar Energetic Particles (SEPs) ........................................................................................................ 25 The STEREO Beacon ........................................................................................................................ 27 Space Weather Forecast Data ....................................................................................................... 27 Maximizing the Science Return ...................................................................................................28 5. Mission Overview ....................................................................................................... 28 6. Phases of the STEREO Mission ................................................................................. 31 Phase 1: The 3-D Structure of the Corona (first 400 days, α ≤ 50°) ................................................. 31 Phase 2: The Physics of CMEs (days 400 to 800, 50° ≤ α ≤ 110°) ................................................... 31 iii Phase 3: Earth-Directed CMEs (days 800 to 1100, 110° ≤ α ≤ 180°) ............................................... 31 Phase 4: Global Solar Evolution and Space Weather (after day 1100, α > 180°) ............................. 31 7. Observational Approach ............................................................................................. 31 Chromosphere and Low Corona Imager ............................................................................................ 32 Coronagraph ...................................................................................................................................... 32 Radio Burst Tracker ........................................................................................................................... 33 Heliosphere Imager ............................................................................................................................ 33 Solar Wind Plasma Analyzer ............................................................................................................. 33 Magnetometer .................................................................................................................................... 34 Solar Energetic Particle Detector ....................................................................................................... 34 8. Conclusions ................................................................................................................ 34 9. Bibliography ............................................................................................................... 35 Appendix I. Mission Requirements and Proof of Feasibility ..........................................I-1 Appendix II. Data Compression .................................................................................... II-1 Appendix III. The Case for Magnetographs ................................................................. III-1 iv Acknowledgements We are grateful for the encouragement and support of so many of our colleagues in the solar and space physics community. In particular, we thank Bernie Jackson, Allen Gary, Don Reames, Barbara Thompson, John Davis, Jeff Hall, and Eric De Jong for illustrations, and Ralph McNutt and Tom Potemra for review- ing a draft of this report. Jim Watzin led the Goddard study team. Murrie Burgan, Eric Benfer, and Patrice Zurvalec helped in editing the manuscript and preparing it for publication. Science Definition Team Members Chairman David Rust James Klimchuk The Johns Hopkins University Naval Research Laboratory Applied Physics Laboratory Washington, D. C. Laurel, Maryland Paulett Liewer NASA Study Scientist Jet Propulsion Laboratory Joseph Davila Pasadena, California NASA/Goddard Space Flight Center Richard Mewaldt Greenbelt, Maryland California Institute of Technology Members Pasadena, California Volker Bothmer University of Kiel Marcia Neugebauer Institut für Reine und Angewandte Kernphysik Jet Propulsion Laboratory Kiel, Germany Pasadena, California Lennard Culhane Victor Pizzo Mullard Laboratory NOAA/Space Environment Laboratory University College Boulder, Colorado London, United Kingdom Dennis Socker Richard Fisher Naval Research Laboratory NASA/Goddard Space Flight Center Washington, D. C. Greenbelt, Maryland Keith Strong John Gosling Lockheed Martin Advanced Technology Center Los Alamos National Laboratory Palo Alto, California Los Alamos, New Mexico NASA Study Scientist Lika Guhathakurta George Withbroe NASA/Goddard Space Flight Center NASA Headquarters Greenbelt, Maryland Washington, D. C.