Solar and Space Physics Research: the Coming Decade
Louis J. Lanzerotti
Distinguished Research Professor
New Jersey Institute of Technology
Bell Laboratories, Lucent Technologies,
Chairman of the Solar and Space Physics Survey Committee
Space Studies Board
National Research Council
The National Academies
Subcommittee on Science, Technology and Space
Committee on Commerce, Science, and Transportation
July 30, 2003
Good afternoon, Mr. Chairman and members of the committee. My name is Louis Lanzerotti, and I served as chairperson of the Solar and Space Physics Decadal Survey for the Space Studies Board of the National Research Council. The NRC is the operating arm of the National Academies, initially chartered by Congress in 1863 to advise the government on matters of science and technology. I am also Distinguished Research Professor at the New Jersey Institute of Technology and a consulting physicist at Bell Laboratories, Lucent Technologies.
I am here today to provide an overview of the future of solar and space physics during the coming decade. I would like to begin by giving you some context for this area of science.
The Sun is a variable, magnetic star. Solar and space physics research focuses on understanding the activity of our Sun and its effects on the Earth and the other planets. It also seeks to understand the physical processes that take place in the area in space around planets, including Earth. These planetary space environments are regions of ionized gas (or plasma) whose motions are subject to the influence of magnetic and electric fields. Solar and space physics seeks finally to explore and understand the interaction of the Sun with our galactic environment; that is, with the gas and dust between our solar system and near-by stars. Within this interstellar cloud, the solar wind, a continuous supersonic outflow of magnetized plasma from the Sun, not only interacts with the Earth and planets, but also inflates an enormous bubble, the heliosphere, whose boundaries lie far beyond the orbit of Pluto and have yet to be explored. It is the entire heliosphere that is the domain of solar and space physics.
The knowledge that space physicists gain through their study of the Sun and solar system plasmas are very often applicable to the study of distant stars and galaxies and are related to laboratory plasma research. And, very importantly, in the particular case of the interactions of solar emissions with the Earth, this research has considerable practical importance for technological systems and for humans in space.
The explosive release of energy from the Sun—solar storms—produces a variety of disturbances in the Earth’s space environment. These disturbances, known as “space weather,” can adversely affect critical space-based and ground-based technologies and pose potential health hazards to astronauts and to the crews and passengers of aircraft flying polar routes. Understanding solar activity and its effect on the Earth’s space environment is key to developing the means of understanding and ultimately mitigating the adverse effects of space weather. Recognition of the importance of achieving this understanding led to the establishment during the past decade of NASA’s Living with a Star Program and the NSF-led interagency National Space Weather Program.
Another area in which solar and space physics makes important contributions of practical value is the study of global climate change. Knowledge of both long- and short-term variations in the Sun’s activity and output is critical to distinguish between natural variability in the Earth’s climate and changes that result from human activity.
That, in brief, is the scope and content of the field of solar and space physics. Since the space age began over 40 years ago, we have learned much about the workings of the Sun and the space environments of Earth and the other planets. But there are many questions still to be answered. In late 2000 the National Aeronautics and Space Administration (NASA), the National Science Foundation (NSF), the National Oceanic and Atmospheric Administration (NOAA), the Office of Naval Research, and the Air Force Office of Scientific Research asked the NRC to conduct a comprehensive study of the current status and future directions of U.S. ground- and space-based solar and space physics research programs. To carry out this task, a Survey Committee and five specialized study panels were established. The findings of the study panels were presented to the Survey Committee, which prepared a summary report based on the recommendations of the panels as well as on its own deliberations. Throughout the study process, the study panels and Survey Committee actively sought a broad community consensus with input from the wider solar and space physics community.
The Survey Committee’s report, The Sun to the Earth—and Beyond: A Decadal Research Strategy in Solar and Space Physics, identifies five broad scientific challenges that define the focus and thrust of solar and space physics research in the decade 2003 through 2013. Further, the report develops specific program priorities that will be needed for the four sponsoring federal agencies, NASA, NSF, NOAA, and DoD, to meet these challenges. The Sun to the Earth—and Beyond also identifies key technologies that must be developed to meet the immediate and projected requirements of solar and space physics research and presents policy recommendations designed to strengthen the solar and space physics research enterprise. Throughout its deliberations, the Survey Committee paid particular attention to the applied aspects of solar and space physics—to the important role that these fields play in a society whose increasing dependence on space-based technologies renders it ever more vulnerable to space weather.
To address the five scientific challenges set forth in The Sun to the Earth—and Beyond, the Survey Committee devised an integrated and prioritized set of research initiatives to be implemented in the 2003-2013 time frame. Nearly all of these initiatives are either planned or have been recommended in previous NASA and NSF planning efforts. The recommended initiatives fall within four categories: small programs (<$250 million); moderate programs ($250-$400 million); one large program costing (>$400 million); and “vitality” programs that focus on the infrastructure for solar and space physics research. To arrive at the final recommended set of initiatives, the Committee relied on two criteria—scientific importance and societal benefit. Based on these criteria, the Committee assigned priorities to the recommended initiatives. A complete listing of the Survey Committee’s prioritized recommendations, along with a thumbnail description of each program, is given in Table ES.1 of the Executive Summary of the report, which is attached to this testimony. Instead of going through the entire list with you, it would be more instructive, I think, for me to outline the five science challenges identified by the Committee and to indicate the role that the four or five highest-priority initiatives will play in addressing those challenges during the coming decade.
Challenge 1: Understanding the Structure and Dynamics of the Sun. During the past decade, thanks to several space missions and new ground-based observations, we have achieved notable advances in our knowledge and understanding of the structure and workings of the Sun’s interior and the structure and dynamics of the million-degree solar atmosphere, the corona. However, answers to certain fundamental questions continue to elude us. Why, for example, is the Sun’s corona several hundred times hotter than the Sun’s surface? How is the solar wind, which expands from the corona, accelerated to the supersonic velocity that is measured in the solar system? How is the very intense magnetic energy that is stored in the Sun released both gradually and explosively? What is origin of the variability (“turbulence”) observed in the solar wind and that affects Earth? To answer these questions, the Committee strongly recommends implementation of a NASA Solar Probe mission to undertake the first exploration of the regions very near the Sun, which is the birthplace of the heliosphere itself. Measurements made close to the Sun by a Solar Probe will revolutionize our basic understanding of the solar wind. In addition, the Committee gave strong endorsement to the development of an advanced ground-based radio telescope (funded by NSF), the Frequency-Agile Solar Radiotelescope, that will provide a revolutionary new tool to study explosive energy release, three-dimensional structure, and magnetic fields in the corona.
Challenge 2: Understanding Heliospheric Structure and the Interaction of the Solar Wind with the Local Interstellar Medium. We have acquired a great deal of new knowledge during the last ten years about the inner heliosphere (within the distance of Jupiter’s orbit) and its changes over the course of a solar cycle—most of our data has come from the joint NASA/European Space Agency Ulysses mission, which has provided single-point measurements over the poles of the Sun, i.e. out of the plane of the planets. The Survey Committee now recommends the implementation of a Multispacecraft Heliospheric Mission that would place four or more spacecraft in orbit about the Sun at different distances and solar longitudes to monitor changes across its entire globe. This mission will provide insight into the connections between solar activity, heliospheric disturbances, and the effects of the solar wind on Earth. This mission will thus represent an important addition to our national space weather effort.
As I noted earlier in my statement, the solar wind inflates a giant bubble known as the heliosphere within the local interstellar medium. The outer reaches of the heliosphere and its boundary with the interstellar medium are among the last unexplored regions of the solar system. An Interstellar Probe that could directly sample these regions and move beyond the heliosphere to measure the material in the Sun’s galactic environment has long been a dream of the space science community and would be one of the grand scientific enterprises of the early 21st century. Implementing such a mission exceeds our present technological capacity, however, particularly with respect to propulsion and power. The development of nuclear power capabilities in the next decade, as is presently planned by NASA, or the development of solar sails, would greatly facilitate an interstellar probe mission in the future.
Challenge 3: Understanding the behavior of the space environments of Earth and other solar system bodies. Earth’s space environment draws energy from its interaction with the supersonic solar wind. This interaction drives the flow of plasma within the magnetosphere—the volume of space controlled by Earth’s magnetic field—and leads to the storage and subsequent explosive release of magnetic energy in disturbances known as geomagnetic storms. (The northern and southern auroras are dramatic manifestations of this convulsive energy release.) The transfer of energy from the solar wind to the magnetosphere results from episodic merging of Earth’s geomagnetic field with the portion of the Sun’s magnetic field that is swept along with the solar wind. This process is known as magnetic reconnection. While the general role of this energy transfer in affecting the Earth’s space environment has long been recognized, there are numerous unanswered fundamental questions. Therefore the Survey Committee endorsed as its highest priority in the moderate program category the NASA Magnetospheric Multiscale (MMS) mission, a four-spacecraft Solar Terrestrial Probe mission that is designed to study magnetic reconnection inside the magnetosphere and at its boundaries.
Some of the energy extracted from the solar wind is deposited in Earth’s high-latitude upper atmosphere, thus creating the aurora. To study the effects of magnetosphere disturbances on the structure and dynamics of the upper atmosphere, the Committee has assigned high-priority in the small program category to the NSF’s Advanced Modular Incoherent Scatter Radar (AMISR). AMISR’s ground-based observations at high latitudes will provide essential contextual information for in situ, orbital “snapshot” measurements by spacecraft missions such as the NASA Geospace Electrodynamics Connections (GEC) mission, a Solar Terrestrial Probe mission also recommended by the Committee.
The Committee also emphasizes the scientific importance of investigating the complex space environments of other planets. Such investigations serve as rigorous tests of the ideas developed from the study of Earth’s own environment while extending our knowledge base to other solar-system bodies. Therefore the Committee strongly recommends a NASA Jupiter Polar Mission (JPM), which will study energy transfer in a magnetosphere that, unlike Earth’s, is powered principally by planetary rotation instead of by the solar wind. All previous missions to Jupiter have flown in or near the equatorial plane, leaving the energetically important polar regions unexplored.
Challenge 4: Understanding the basic physical principles of solar and space plasma physics. The heliosphere is a natural laboratory for the study of plasma physics, and a number of the initiatives proposed by the Committee will lead to advances in understanding fundamental plasma physical processes. For example, as noted above, MMS is specifically designed to study magnetic reconnection, a physical process of fundamental importance in all astrophysical systems, from the Earth to the solar system to our galaxy and beyond. To complement the observational study of such fundamental processes in naturally occurring solar system plasmas, the Survey Committee recommends vigorous support of existing NASA and NSF theory and modeling programs as well as support for new initiatives such as the Coupling Complexity Research Initiative, a joint NASA/NSF theory and modeling program.
Challenge 5: Developing a near-real-time predictive capability for the impact of space weather on human activities. Most technologies that fly in space and some that are on Earth’s surface are affected severely by the geomagnetic storms whose origins can be traced to the Sun. These events produce subsidiary space weather phenomena, such as the blackouts of high frequency communications and disturbances of satellite transmissions, including those from spacecraft such as the global positioning system. The high energy solar particles can severely disrupt spacecraft operations and present serious radiation hazards to astronauts and to the crews and passengers of aircraft flying on polar routes. In addition to interfering with communications and navigation systems, strong geomagnetic storms often disturb spacecraft orbits because of increased drag in the high altitude atmosphere, and they even have caused electric utility blackouts over wide areas.
Both our understanding of the basic physics of space weather and our appreciation of its importance for human activity has increased considerably during recent years. Much remains to be learned, however, about processes—such as changes in the Earth’s radiation—that affect the environment in which many satellites operate; about the variations in the properties of the highest regions of the atmosphere that can adversely affect GPS navigation systems and high frequency radio propagation; and, finally, about the changes that occur on the Sun that ultimately cause the detrimental effects of space weather. The Survey Committee has therefore ranked as its second highest priority in the moderate-program category the Geospace Missions of NASA’s Living with a Star program. These missions consist of two pairs of spacecraft that will be instrumented to study, respectively, changes in the upper atmosphere and the behavior of the Earth’s radiation belts during geomagnetic storms.
Of critical importance both for our efforts to understand and predict space weather and for basic solar and space physics research is information about solar wind conditions prior to their reaching Earth. Such information is currently being provided by the NASA Advanced Composition Explorer (ACE) spacecraft and the NASA Wind satellite. However, both spacecraft are now operating beyond their design lifetimes. The Survey Committee considers it of paramount importance to ensure uninterrupted monitoring of the solar wind and therefore assigned high priority to the implementation of an Upstream Solar Wind Monitor as a replacement for ACE and Wind. Given the operational importance of the measurements that such a monitor would provide, the Committee recommends that responsibility for its implementation be transferred from NASA to NOAA. The importance of space weather and of this challenge to national needs is also reflected in the high prioritization that the Committee assigned to the multi-agency National Space Weather Program.
In addition to specific research initiatives to address the five science challenges, the Survey Committee gave careful consideration to the “infrastructural” requirements for a robust solar and space physics research program during the coming decade. The Sun to the Earth—and Beyond thus offers a number of recommendations in the following areas: technology development, solar and space physics education, and space research policy and program management, including space weather policy. All of the recommendations in these areas are given in the Executive Summary attached to my statement, so I will summarize only a few of the key ones here.
High-priority areas of technology development identified by the Committee include advanced propulsion and power, highly miniaturized spacecraft, advanced spacecraft subsystems, and highly miniaturized sensors of charged and neutral particles and photons. A number of initiatives in these areas are already under way within NASA such as the New Millennium Program, the Sun-Earth Connection and Living With a Star instrument development programs, and the In-Space Propulsion program, and the Committee strongly endorses these initiatives.
The Survey Committee’s consideration of issues related to education was driven by two main concerns: how to provide a sufficient number of trained scientists to carry out the research program set forth in The Sun to the Earth—and Beyond and how solar and space physics can contribute to the development of a scientifically and technologically literate public. Here I will mention only one of the Survey Committee’s recommendations—namely, that NSF and NASA jointly establish a program to provide partial salary, start-up funding, and research support for four new faculty members a year for five years in the field of solar and space physics. I was pleased to learn recently that the NSF has already taken significant steps in this direction. Such a program will augment the number of university faculty in solar and space physics and is essential for a strong national solar and space physics research program during the coming decade.
As I noted earlier, in my comments on the space weather challenge, the Survey Committee strongly recommends that NOAA assume responsibility for the implementation of an upstream solar wind monitor. Other Survey Committee recommendations regarding space weather policy address measures to facilitate the transition from research to operations, the acquisition and availability of data on solar activity and the geospace environment, and the roles of the public and private sectors in space weather applications. NOAA and the DoD, as the two operational agencies, are primarily responsible for implementing most of the Survey Committee’s recommendations in this area.
Finally, the Survey Committee developed a number of policy recommendations for strengthening the national solar and space physics research program. For example, a vital space research program depends on cost-effective, reliable, and readily available access to space that meets the requirements of a broad spectrum of missions. The Survey Committee therefore recommends revitalization of NASA’s Suborbital Program, the development by NASA of a range of low-cost launch vehicles, and the establishment of procedures of “ride shares” on DoD (and possibly foreign) launch vehicles. The Committee also addressed the impact of export controls on solar and space physics research, which inevitably involves international collaboration, and recommended that the relevant federal agencies implement procedures to expedite international collaborations involving exchanges of scientific data or information on instrument characteristics.
Let me now conclude my comments with a quote from Marcel Proust: “The real voyage of discovery consists not in seeking new landscapes, but in having new eyes.” The solar and space physics research program envisioned by the Survey Committee for the coming decade offers both: visits to new solar system landscapes—the unexplored near-Sun region, Jupiter’s polar magnetosphere—and the “new eyes” of observational initiatives such as MMS, FASR, and AMISR and of advanced theoretical and computational initiatives such as the Coupling Complexity Research Initiative, which will enable us to “see” the fundamental connections underlying the complex phenomena captured in our observational data.