Exploration of the Outer Heliosphere and the Local Interstellar Medium
A WORKSHOP REPORT
THE NATIONAL ACADEMIES PRESS
Washington, D.C.
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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the panels responsible for the report were chosen for their special competences and with regard for appropriate balance.
Support for this project was provided by Contract NASW 01001 between the National Academy of Sciences and the National Aeronautics and Space Administration. Any opinions, findings, conclusions, or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the sponsors.
Cover: Results from a self-consistent numerical simulation of the interaction of the solar wind with the partially ionized local interstellar medium (LISM). Shown in color is the temperature distribution (plotted on a logarithmic scale) of the solar wind and interstellar plasma for the two-dimensional, steady-state, two-shock heliosphere. The plasma boundaries—termination shock, heliopause, and bow shock—are labeled. The heliosheath comprises solar wind material, both supersonic and subsonic, and extends into the heliotail (labeled). The solid lines show the stream lines of the plasma. A key feature of the interaction of the solar wind with the LISM is the ability of neutral hydrogen to enter the heliosphere, where it can then couple to the solar wind by the process of charge exchange, depicted schematically by the arrow. The distances along the x and y axes are measured in astronomical units (AU). Image courtesy of H.R. Mueller and G.P. Zank, University of California, Riverside.
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OTHER REPORTS OF THE SPACE STUDIES BOARD
Issues and Opportunities Regarding the U.S. Space Program: A Summary Report of a Workshop on National Space Policy (2004)
Plasma Physics of the Local Cosmos (2004)
Steps to Facilitate Principal-Investigator-Led Earth Science Missions (2004)
“Assessment of NASA’s Draft 2003 Earth Science Enterprise Strategy” (2003)
“Assessment of NASA’s Draft 2003 Space Science Enterprise Strategy” (2003)
Satellite Observations of the Earth’s Environment: Accelerating the Transition of Research to Operations (2003)
The Sun to the Earth—and Beyond: Panel Reports (2003)
Assessment of Directions in Microgravity and Physical Sciences Research at NASA (2002)
Assessment of the Usefulness and Availability of NASA’s Earth and Space Science Mission Data (2002)
Factors Affecting the Utilization of the International Space Station for Research in the Biological and Physical Sciences (2002)
Life in the Universe: An Examination of U.S. and International Programs in Astrobiology (2002)
New Frontiers in the Solar System: An Integrated Exploration Strategy (2002)
Review of NASA’s Earth Science Enterprise Applications Program Plan (2002)
“Review of the Redesigned Space Interferometry Mission (SIM)” (2002)
Safe on Mars: Precursor Measurements Necessary to Support Human Operations on the Martian Surface (2002)
The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics (2002)
Toward New Partnerships in Remote Sensing: Government, the Private Sector, and Earth Science Research (2002)
Using Remote Sensing in State and Local Government: Information for Management and Decision Making (2002)
Assessment of Mars Science and Mission Priorities (2001)
The Mission of Microgravity and Physical Sciences Research at NASA (2001)
The Quarantine and Certification of Martian Samples (2001)
Readiness Issues Related to Research in the Biological and Physical Sciences on the International Space Station (2001)
“Scientific Assessment of the Descoped Mission Concept for the Next Generation Space Telescope (NGST)” (2001)
Signs of Life: A Report Based on the April 2000 Workshop on Life Detection Techniques (2001)
Transforming Remote Sensing Data into Information and Applications (2001)
U.S. Astronomy and Astrophysics: Managing an Integrated Program (2001)
Limited copies of these reports are available free of charge from:
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www.nationalacademies.org/ssb/ssb.html
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COMMITTEE ON SOLAR AND SPACE PHYSICS
JAMES L. BURCH,
Southwest Research Institute,
Chair
CLAUDIA J. ALEXANDER,
Jet Propulsion Laboratory
VASSILIS ANGELOPOULOS,
University of California, Berkeley
ANTHONY CHAN,
Rice University
ANDREW F. CHENG,
Johns Hopkins University
JAMES F. DRAKE,
University of Maryland
JOHN C. FOSTER,
Massachusetts Institute of Technology
STEPHEN A. FUSELIER,
Lockheed Martin Advanced Technology Center
SARAH GIBSON,
National Center for Atmospheric Research
CRAIG KLETZING,
University of Iowa
GANG LU,
National Center for Atmospheric Research
BARRY H. MAUK,
Johns Hopkins University
FRANK B. McDONALD,
University of Maryland
EUGENE N. PARKER,
University of Chicago,
Professor Emeritus
ROBERT W. SCHUNK,
Utah State University
GARY P. ZANK,
University of California, Riverside
ARTHUR CHARO, Study Director
THERESA M. FISHER, Senior Program Assistant
SPACE STUDIES BOARD
LENNARD A. FISK,
University of Michigan,
Chair
GEORGE A. PAULIKAS,
The Aerospace Corporation (retired),
Vice Chair
J. ROGER P. ANGEL,
University of Arizona
ANA P. BARROS,
Harvard University
RETA F. BEEBE,
New Mexico State University
ROGER D. BLANDFORD,
Stanford University
JAMES L. BURCH,
Southwest Research Institute
RADFORD BYERLY, JR.,
University of Colorado
HOWARD M. EINSPAHR,
Bristol-Myers Squibb Pharmaceutical Research Institute (retired)
STEVEN H. FLAJSER,
Loral Space and Communications, Ltd.
MICHAEL H. FREILICH,
Oregon State University
DON P. GIDDENS,
Georgia Institute of Technology/Emory University
DONALD INGBER,
Harvard Medical Center
RALPH H. JACOBSON,
The Charles Stark Draper Laboratory (retired)
TAMARA E. JERNIGAN,
Lawrence Livermore National Laboratory
MARGARET G. KIVELSON,
University of California, Los Angeles
CALVIN W. LOWE,
Bowie State University
BRUCE D. MARCUS,
TRW, Inc. (retired)
HARRY Y. McSWEEN, JR.,
University of Tennessee
DENNIS W. READEY,
Colorado School of Mines
ANNA-LOUISE REYSENBACH,
Portland State University
ROALD S. SAGDEEV,
University of Maryland
CAROLUS J. SCHRIJVER,
Lockheed Martin Solar and Astrophysics Laboratory
ROBERT J. SERAFIN,
National Center for Atmospheric Research
MITCHELL SOGIN,
Marine Biological Laboratory
C. MEGAN URRY,
Yale University
J. CRAIG WHEELER,
University of Texas, Austin
JOSEPH K. ALEXANDER, Director
Foreword
The outward expansion of the solar wind carves out a region from the local interstellar medium (LISM) known as the heliosphere. We live in the inner part of this region, which is dominated by the Sun. Far beyond the orbit of the known planets, in the outer heliosphere, a complex interaction occurs between the solar wind and the LISM. The observation and study of this interaction region, and of the pristine interstellar medium that lies beyond, will be exploration in the truest sense, an epic journey that helps define our place in the universe.
As this report went to press in mid-2004, the Voyager spacecraft appeared to be approaching, or perhaps even encountering, the termination shock of the solar wind—the region where the supersonic flow goes subsonic. Already, the Voyagers’ observations have demonstrated that the interaction region will be complex, surprising, and fascinating. Theories and models of the interaction region will have to be modified to account for the observed complexity.
Interstellar neutral gas penetrates far into the heliosphere and can be observed in its recently ionized form as pickup ions in the solar wind, in particular by Ulysses. These two missions, Voyager and Ulysses, represent our best immediate hope to increase our understanding of the properties of the LISM and its interactions with the heliosphere.
Real progress in this field, however, demands new observations and improved theories. It is possible to make far better and more insightful observations of neutral interstellar gas in the inner heliosphere, and to exploit other remote sensing techniques that may be demonstrated to provide important information on the termination shock and the interaction region beyond. Theories and models always can be improved, incorporating and explaining current and future observations.
The real journey will occur when we embark on an interstellar probe, with sufficient instrumentation and the capability to rapidly access the distant heliosphere. This journey will be one of the great explorations of humankind, when we leave the safety of our solar system and venture forth into interstellar space.
This report provides a strategy to prepare for this exploration.
Lennard A. Fisk, Chair
Space Studies Board
Preface
In 2003, the National Research Council (NRC) produced The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics.1 In addition, an internal advisory committee at the National Aeronautics and Space Administration (NASA) completed a roadmap for the Office of Space Sciences’ Sun-Earth Connection Theme.2 Recognizing that exploration of the outer heliosphere was the least thoroughly developed aspect of either document and that planning and technology development for such an effort would require a long lead time, NASA requested that the NRC conduct a workshop that would further investigate the challenges and opportunities for space missions to explore this region (see Appendix A, Statement of Task).
The workshop, which was organized by the Space Studies Board’s Committee on Solar and Space Physics (CSSP), took place May 6-7, 2003, at the National Academies’ Beckman Center, located at the University of California at Irvine (see Appendix B for the agenda). Gary Zank, a member of the CSSP, led the committee’s effort in developing the following report, which summarizes the discussions and conclusions of workshop participants.
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1 |
National Research Council, 2003, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, National Academies Press, Washington, D.C. |
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2 |
See NASA, 2003, The Sun-Earth Connection Roadmap 2003-2028: Understand the Sun, Heliosphere and Planetary Environments as a Single Connected System, NASA, Washington, D.C. Available at http://sec.gsfc.nasa.gov./sec_roadmap.htm. |
Acknowledgment of Reviewers
This report has been reviewed in draft form by individuals chosen for their diverse perspectives and technical expertise, in accordance with procedures approved by the National Research Council’s Report Review Committee. The purpose of this independent review is to provide candid and critical comments that will assist the institution in making its published report as sound as possible and to ensure that the report meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The review comments and draft manuscript remain confidential to protect the integrity of the deliberative process. We wish to thank the following individuals for their review of this report:
Leonard F. Burlaga, NASA Goddard Space Flight Center,
George Gloeckler, University of Maryland,
Michael Gruntman, University of Southern California,
Les Johnson, NASA Marshall Space Flight Center,
J.R. (Randy) Jokipii, University of Arizona,
Martin Lee, University of New Hampshire,
Paulett C. Liewer, Jet Propulsion Laboratory,
David J. McComas, Southwest Research Institute, and
Ralph McNutt, Jr., Johns Hopkins University.
Although the reviewers listed above have provided many constructive comments and suggestions, they were not asked to endorse the conclusions or recommendations, nor did they see the final draft of the report before its release. The review of this report was overseen by Donald J. Williams, Johns Hopkins University. Appointed by the National Research Council, he was responsible for making certain that an independent examination of this report was carried out in accordance with institutional procedures and that all review comments were carefully considered. Responsibility for the final content of this report rests entirely with the authoring committee and the institution.
