FURTHER AND MORE ABUNDANT KNOWLEDGE

Albert Einstein once paraphrased an old Chinese proverb and wrote, “What does a fish know about the water in which he swims all his life?” For most of human history, the sea of space, through which our home planet and other solar system bodies travel as they orbit about the Sun, was a mystery, the subject of myth and of philosophical as well scientific speculation. It was just 40 years ago that the true nature of this realm finally became known, when measurements by the Mariner II spacecraft confirmed Eugene Parker’s 1958 theory that the Sun’s outer atmosphere expands supersonically to form the solar wind. Since then, numerous satellites have measured the properties of the solar wind and the near-Earth space environment; probes have visited all the planets except Pluto; and solar observatories in space and on the ground have provided detailed images of the Sun’s corona and probed the solar interior.

Solar and space physicists have learned much during the past four decades about the Sun and the heliosphere, Earth’s magnetosphere and space weather, and the space environments of other planets. But many important questions remain unanswered. As the famous 19th-century physicist Michael Faraday wrote, “It is the great beauty of our science that advancement in it, whether in a degree great or small, instead of exhausting the subject of research, opens the doors to further and more abundant knowledge, overflowing with beauty and utility.” Answers to the outstanding questions in solar and space physics have so far eluded our grasp owing to the lack of observations in critical regions of the solar system, limitations on the capability of our observational techniques and strategies to resolve critical processes, and constraints on computational resources and techniques. The research initiatives recommended by the Solar and Space Physics Survey Committee and described in this booklet are designed to overcome these obstacles and to allow us to answer some of the outstanding questions about the activity of the Sun and the objects immersed in and interacting with its atmosphere. These questions focus increasingly on how and why rather than what. They are the “doors to further and more abundant knowledge,” and to answer them will be to achieve a fundamental understanding of the physical processes that underlie the exotic and puzzling phenomena that occur in the fourth state of matter—an understanding that is not just of intrinsic intellectual importance but that also has practical benefits for humankind as it continues its evolution into a space-faring species.

It is the great beauty of our science that advancement in it, whether in a degree great or small, instead of exhausting the subject of research, opens the doors to further and more abundant knowledge, overflowing with beauty and utility.

—Michael Faraday



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Understanding the Sun and Solar System Plasmas: Future Directions in Solar and Space Physics FURTHER AND MORE ABUNDANT KNOWLEDGE Albert Einstein once paraphrased an old Chinese proverb and wrote, “What does a fish know about the water in which he swims all his life?” For most of human history, the sea of space, through which our home planet and other solar system bodies travel as they orbit about the Sun, was a mystery, the subject of myth and of philosophical as well scientific speculation. It was just 40 years ago that the true nature of this realm finally became known, when measurements by the Mariner II spacecraft confirmed Eugene Parker’s 1958 theory that the Sun’s outer atmosphere expands supersonically to form the solar wind. Since then, numerous satellites have measured the properties of the solar wind and the near-Earth space environment; probes have visited all the planets except Pluto; and solar observatories in space and on the ground have provided detailed images of the Sun’s corona and probed the solar interior. Solar and space physicists have learned much during the past four decades about the Sun and the heliosphere, Earth’s magnetosphere and space weather, and the space environments of other planets. But many important questions remain unanswered. As the famous 19th-century physicist Michael Faraday wrote, “It is the great beauty of our science that advancement in it, whether in a degree great or small, instead of exhausting the subject of research, opens the doors to further and more abundant knowledge, overflowing with beauty and utility.” Answers to the outstanding questions in solar and space physics have so far eluded our grasp owing to the lack of observations in critical regions of the solar system, limitations on the capability of our observational techniques and strategies to resolve critical processes, and constraints on computational resources and techniques. The research initiatives recommended by the Solar and Space Physics Survey Committee and described in this booklet are designed to overcome these obstacles and to allow us to answer some of the outstanding questions about the activity of the Sun and the objects immersed in and interacting with its atmosphere. These questions focus increasingly on how and why rather than what. They are the “doors to further and more abundant knowledge,” and to answer them will be to achieve a fundamental understanding of the physical processes that underlie the exotic and puzzling phenomena that occur in the fourth state of matter—an understanding that is not just of intrinsic intellectual importance but that also has practical benefits for humankind as it continues its evolution into a space-faring species. It is the great beauty of our science that advancement in it, whether in a degree great or small, instead of exhausting the subject of research, opens the doors to further and more abundant knowledge, overflowing with beauty and utility. —Michael Faraday

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Understanding the Sun and Solar System Plasmas: Future Directions in Solar and Space Physics CREDITS FOR ILLUSTRATIONS Cover The background photo is of the aurora borealis as viewed from the vicinity of Fairbanks, Alaska. The three figures in the inset show the magnetically structured plasma of the Sun’s million-degree corona (left); the plasmasphere, a cloud of low-energy plasma that surrounds Earth and co-rotates with it (top right); and an artist’s conception of Jupiter’s inner magnetosphere, with the Io plasma torus and the magnetic flux tubes that couple the planet’s upper atmosphere with the magnetosphere. Ground-based aurora photo courtesy of Jan Curtis; coronal image courtesy of the Stanford-Lockheed Institute for Space Research and NASA; plasmasphere image courtesy of the IMAGE EUV team and NASA; rendering of the jovian magnetosphere courtesy of J.R. Spencer (Lowell Observatory). Page 6 Image of a prominence extending from the Sun’s northwest limb viewed at 304 Å with the Extreme-ultraviolet Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory (SOHO). Courtesy of SOHO (ESA and NASA). Page 9 Courtesy of R. Mewaldt (California Institute of Technology) and the NASA/Jet Propulsion Laboratory. Page 12 Image of the solar corona viewed in the extreme ultraviolet (171 Å) with the telescope on board the Transition Region and Corona Explorer (TRACE) spacecraft. Courtesy of NASA and the Stanford-Lockheed Institute for Space Research. Page 13 (top) Courtesy of SOHO (ESA and NASA). Page 13 (bottom) Courtesy of J.W. Harvey and the GONG Project (National Solar Observatory/AURA/NSF). Page 14 Courtesy of the Johns Hopkins University Applied Physics Laboratory. Page 15 (top) Courtesy of D.E. Gary (New Jersey Institute of Technology). Page 15 (bottom) Courtesy of D.J. McComas (Southwest Research Institute) and Ulysses (ESA and NASA). Page 17 Courtesy of R. Treumann (Max-Planck-Institut für extraterrestrische Physik). Page 18 (top) Courtesy of J. Curtis. Page 18 (bottom) Courtesy of NASA/Goddard Space Flight Center. Page 19 Original illustration by R.O. Menchaca (Southwest Research Institute). Page 21 (left) Courtesy of NASA/Goddard Space Flight Center. Page 21 (right) Courtesy of J. Kelly and C.J. Heinselman (SRI International). Page 23 Courtesy of R.V. Hilmer (Air Force Research Laboratory/Hanscom AFB). Page 25 Courtesy of NASA/Living With a Star Program. Page 26 The image of Earth’s aurora courtesy of the IMAGE FUV imaging team and NASA. The images of Jupiter and Saturn were obtained with the Hubble Space Telescope and are used courtesy of NASA/STSci/AURA.

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Understanding the Sun and Solar System Plasmas: Future Directions in Solar and Space Physics Page 27 Hubble Space Telescope image courtesy of J.T. Clarke (Boston University) and NASA/STScI. Artist’s rendering of the jovian inner magnetosphere courtesy of J.R. Spencer (Lowell Observatory). Reprinted by permission from Nature 415, 997-999 and cover, copyright 2002, Macmillan Publishers Ltd.; http://www.nature.com. Page 29 Courtesy of R.A. Mewaldt (California Institute of Technology) and P. Liewer (NASA/Jet Propulsion Laboratory). Page 30 Very Large Array image adapted from C. Palma et al., Multiwavelength observations of the second-largest known Fanroff-Riley type II radio galaxy, NVSS 2146+82, Astronomical Journal 119(5), 2068-2084, copyright 2000, American Astronomical Society. Courtesy of A. Bridle and W. Cotton (NRAO/NSF/AUI) and C. Palma (Pennsylvania State University). Page 31 Courtesy of M.A. Shay (University of Maryland). Page 33 Courtesy of J.C. Foster (MIT Haystack Observatory). Page 35 (top) Courtesy of NASA/Goddard Space Flight Center. Page 35 (bottom) Courtesy of NASA/Marshall Space Flight Center. Page 36 Courtesy of P.J. Eberspeaker (NASA/Wallops Flight Facility). Page 40 The northern and southern lights—the aurora borealis and aurora australis—are produced when energetic electrons and protons from the magnetosphere spiral downward along geomagnetic field lines into Earth’s upper atmosphere and excite the atoms and molecules there, causing them to emit light at various wavelengths. Photo of the aurora borealis courtesy of Jan Curtis. By quickly flipping the pages of this booklet from front to back, you can watch the development of an auroral storm as viewed from an Earth-orbiting satellite. By flipping from back to front, you can track the changes in the Sun’s activity during the declining phase of one solar cycle and the rising phase of another. Images from the Wideband Imaging Camera (WIC) on NASA’s IMAGE spacecraft show the development of a typical auroral storm on October 22, 2001. The spacecraft is looking down onto the north pole from an initial altitude of 34,000 kilometers. Earth’s daylit face is to the right. The auroral sequence, which spans an interval of roughly one hour, begins with a localized brightening over northern Russia. Within minutes the nightside oval has become active and expanded poleward, with bright, highly structured emissions embedded in a broad region of more diffuse emissions. WIC is a part of the IMAGE far-ultraviolet (FUV) imaging system and detects ultraviolet emissions produced by nitrogen molecules as they are bombarded by electrons from Earth’s magnetosphere. Courtesy of the IMAGE FUV imaging team and NASA. Images of x-ray emissions from the Sun’s million-degree corona capture the change in solar activity during the declining phase of sunspot cycle 22 (September 1986 to May 1996) and the rising phase of sunspot cycle 23 (May 1996 to 2007). The images cover the interval from March 1992 to September 1999 and were acquired with the soft x-ray telescope (SXT) on board the Earth-orbiting Yohkoh solar observatory. Yohkoh (1991-2001) was a Japanese mission with collaboration from researchers in the United States and United Kingdom. Courtesy of the Lockheed Martin Solar and Astrophysics Laboratory.

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Understanding the Sun and Solar System Plasmas: Future Directions in Solar and Space Physics