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SUMMARY 49 2.1 SOLAR WIND-MAGNETOSPHERE INTERACTIONS: THE REALM OF MAGNETIZED PLASMAS 53 Introduction 53 The Fourth State of Matter 53 Reconnection 54 Flowing Magnetized Plasmas 55 The Storage and Release of Energy Coupling in a Collisionless Plasma Impact and Relevance 58 Summary 58 57 57 2.2 MAG N ETOSPH ERES AN D TH El R PARTS 58 Overview 58 Bow Shock 59 Magnetosheath 62 Magnetopause, Cusp, Boundary Layers 63 Magnetotai 1 66 I n ner Magnetosphere 70 Plasmasphere 72 Sol ar Wi nd I Interactions with Weakly Magnetized Bod ies 73 Outer Planets 83 2.3 PROCESSES 87 Introduction 87 The Creation and Annihilation of Magnetic Fields 87 Magnetospheres as Shields and Accelerators 88 Magnetospheres as Complex Coupled Systems 89 2.4 CURRENT PROGRAM 90 Introduction 90 Programs 91 Critical Needs 98 47
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48 2.5 FUTURE PROJECTS 99 Introduction 99 Addressing the Major Themes 99 Project Summaries 100 Science Traceability 105 Prioritization: NASA and NSF 1 06 Prioritization of Other Agency and Interagency Initiatives 106 THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS TECHNOLOGY 1 08 Introduction 1 08 Propulsion Technology 1 09 S pacec raft Tech n o l ogy 1 1 1 Science Instrumentation Technology 1 1 3 Information Architecture Technology 1 1 4 Technology for Ground Systems and Operations 1 14 Recommendations and Priorities 1 1 4 2.7 SOLAR Wl N D-MAGN ETOSPHERE I INTERACTIONS: POLICY ISSU ES 1 1 5 I Introduction 1 1 5 Interagency Coordination 1 15 Coordination Between Programs and Divisions Within Agencies: NSF and NASA 117 Opportunities for Space Measurements in Entities Other Than NASA's Office of Space Science 118 Science in the Structure of Project Management 1 19 I International Cooperation 1 1 9 Model ing, Theory, and Data Assimi ration 1 20 Technology Development 1 21 Data Analysis, Dissemination, and Archiving 121 Extended Missions 1 22 ADDITIONAL READI NG 1 22
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS SUMMARY The study of solar wind-magnetosphere interactions at the turn of the 21 st century fi nds itself engaged in exciting exploration of exotic extraterrestrial environ- ments and consolidating a comprehensive, fundamental understanding of the terrestrial magnetosphere. To capi- talize on these discoveries, we need both classic mis- sions of exploration to the planets and modern multi- spacecraft probes in the near-Earth environment. This report summarizes what we now know about planetary magnetospheres and the processes within them, what we need to know, and how we should proceed in ob- tai n i ng th is knowledge. MAGNETIC FIELDS Magnetic fields play a crucial role in governing Earth's space environment. They organize the helio- spheric and magnetospheric plasmas, shield planetary bodies, such as Earth, from bombardment with charged particles, couple energy from one plasma regime to an- other, store that energy and later release it rapidly. More- over, they guide the motion of charged particles to re- gions where they can cause visible displays such as solar flares on the photosphere or the polar lights in the atmosphere. Partners in these processes are the plasmas, energetic particles, waves, and electromagnetic emis- sions from radio to x-ray wavelengths in the solar wind and the planetary magnetospheres. Solar and planetary magnetic fields organize space into normally well-separated regions. The principal plasma regimes are the corona, where the solar wind originates; the solar wind, the outward streaming plasma that carries the Sun's magnetic field to the outer helio- sphere; and the magnetospheres of planetary bodies, intrinsic or induced. The magnetospheres may act as flexible shields that deflect the solar wind and thereby protect the planet and its atmosphere from most of the direct impact of the solar wind particles. However, these shields are not impenetrable. One of the principal processes by which the shield is penetrated is called magnetic reconnection. This pro- cess is strongly controlled by the relative orientation of the magnetic fields in adjacent regions, leading to con- nection between the magnetosphere and the solar wind. Magnetic reconnection not only breaches the bound- aries between different plasma and magnetic field re- gions, it is also the main process involved in the rapid 49 release of magnetic energy in eruptions in the solar atmosphere and Earth's magnetosphere, in laboratory plasmas, and, presumably, in astrophysical settings. Other processes can breach the magnetic shield. In the case of weakly magnetized bodies such as comets, Venus and Mars, and the moons lo and Titan, neutral particle transport across plasma boundaries occurs, with subsequent ionization. In magnetically noisy environ- ments, particles can be scattered across the boundaries, and for small bodies finite gyroradius effects allow pen- etration. An important aspect of the plasmas in most of space is that the magnetic fields that guide the motion of the charged particles are, in turn, created by the motion of those very same particles. Thus the magnetized plasma can be quite nonlinear, enhancing, deflecting, or anni- hilating the original magnetic field. MAGNETOSPHERES Planetary magnetospheres are particularly acces- sible settings for studying the processes occurring in magnetized plasmas, providing unique insights into ba- sic physical processes not amenable to direct probing, processes such as particle acceleration, shock forma- tion, and magnetic reconnection. The solar wind inter- action with a magnetosphere produces thin boundaries, separating large regions of relatively uniform plasma. Within these thin boundaries microscale processes couple to the mesa- and macroscale processes, affecting the stability and dynamics not only of the thin boundary layer but also of the entire coupled magnetosphere system. The magnetospheric shields of planets and moons vary considerably. Some weakly magnetized planetary bodies like Earth's moon routinely lose their atmosphere to the solar wind, while others such asVenus and Mars have had thei r atmospheres sign if icantly altered, as indicated by the isotopic ratios of their atmo- spheric constituents, but not completely removed. Magnetospheres also exhibit rapid reconfigurations, such as the ejection of magnetic islands, or plasmoids, while the inner region collapses, as seen routinely in the tail regions of Earth and Jupiter. Overall planetary magnetospheres are complex, coupled systems, con- nected on one end to a supersonic flowing magnetized plasma, the solar wind, on the other end to a cold dense planetary atmosphere and ionosphere, and sometimes to embedded plasma sources such as satellites and rings. While each planetary magnetosphere presents great inter lectual chal lenges and its behavior provides insight into diverse astrophysical solar and laboratory systems,
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50 the terrestrial magnetosphere is of particular practical interest. It provides a home to many technological sys- tems that are increasingly sensitive to magnetospheric disturbances. Such disturbances affect the quality of communications, our ability to navigate, the capacity of power transmission lines, the orbits of low-altitude sat- ellites, and the operation of geosynchronous spacecraft carrying TV broadcasts, relaying phone calls, and moni- toring our weather. Both astronauts and flight crews on polar air routes can receive undesirable levels of radia- tion from energetic particles controlled by the magneto- sphere. Thus, understanding and predicting the response of the magnetosphere to varying interplanetary condi- tions, i.e., space weather, has become a particular con- cern. THE TERRESTRIAL MAGNETOSPHERE The study of Earth's magnetosphere began with ground-based measurements of the time variations of the magnetospheric magnetic field. These observations revealed not only the existence of the magnetosphere but also its variable state of energization. The Interna- tional Geophysical Year initiated an era of discovery in which single-spacecraft missions throughout the mag- netosphere provided an overview of the characteristic regions, boundaries, and plasma conditions, with some evidence of the processes therein, but they did not elu- cidate how the processes in the magnetosphere work. Therefore, current and future exploration of the terres- trial magnetosphere concentrates on the use of multi- spacecraft missions complemented by ground-based arrays of magnetic, radar, and optical sensors to charac- terize plasma behavior in a dynamic environment and to probe cause and effect in a complex system at various scales. At the other planets, with few exceptions, we remain in the discovery phase since thus far we have generally been restricted to single-spacecraft missions, often si ngle flybys, not orbiters. There are many success stories in magnetospheric exploration as well as continuing puzzles. The standing bow shock is well understood, but it is only the fastest of three waves that should stand in the solar wind flow. The other two waves the intermediate mode, which rotates field and flow, and the slow mode, which "stretches" field lines could also lead to standing struc- ture. Reconnection is now known to provide a time- varyi ng i ntercon nection of the terrestrial magnetosphere with the magnetized solar wind, driving the circulation in the magnetosphere, but in a manner that is as yet not well understood. Reconnection is recognized to be the THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS principal mechanism for the violent release of stored magnetic energy and for magnetic flux return from the tails of the magnetospheres of both Jupiter and Earth. Nevertheless there is not agreement on what triggers the rapid onset of magnetotai I reconnection. Radial diffusion and pitch angle scattering of ener- getic particles apparently produce many of the observed features in the radiation belts of planetary magneto- spheres, but the driver of the radial diffusion remains elusive, and the sources and acceleration mechanisms for the involved energetic particles are not always clear. At unmagnetized planets the mechanism for the forma- tion of induced magnetospheres is relatively well under- stood but the atmospheric loss is poorly understood. INTRINSIC AND INDUCED Magnetospheres can be divided into two types: in- duced, if any intrinsic magnetic field of the body is so weak that the ionosphere is directly exposed to the flow- ing solar wind plasma, and intrinsic, if the body has an internal magnetic field sufficiently strong to deflect the plasma that flows against it. Induced magnetospheres form around highly electrically conducting obstacles if the conductor, generally an ionosphere, can stave off the solar wind flow. Induced magnetospheres also form in strong mass-loading environments such as at a rap- id Iy outgassi ng cometary nucleus. Comets, Venus, Mars, and some of the moons of the gas giants have magneto- spheres induced by the rotating magnetospheric plasma. Mercury, Earth, Ganymede, and the gas giants have in- trinsic magnetospheres. Circulation inside the intrinsic magnetospheres can be driven by the externally flowing plasma or by an internal source such as plasma derived from the volcanic gases of lo, accelerated by the rapidly rotating Jovian magnetosphere. The centrifugal force of this plasma drives a massive circulation pattern in the Jovian magnetosphere, powering a massive magneto- spheric "engine." Thus Jupiter acts as a bridge in our understanding of the terrestrial and astrophysical mag- netospheres. For both intrinsic and induced magnetospheres the supersonically flowing solar wind is deflected by the magnetosphere, forming a bow shock. Behind the bow shock, the decelerated shocked plasma flows around the obstacle in a region known as the magnetosheath. In intrinsic magnetospheres, the boundary between the flowing plasma of the solar wind and the plasma, con- nected by the magnetic field to the planet, is called the magnetopause. In an induced magnetosphere, the analo- gous boundary is called an ionopause. Often the mag-
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS netopause and the ionopause are thin layers of current. Behind the magnetosphere proper the magnetic field and plasma are stretched by the solar wind flow, form- ing a long magnetotail. Inside the magnetosphere, differ- ing regions of plasma can be found, such as the plasma- sphere in Earth's magnetosphere and the lo torus in Jupiter's. In an induced magnetosphere, the plasma is generally relatively cold and affected by the external flow in ways much different than in an intrinsic mag- netosphere. For these i educed magnetospheres, the so- lar wind interaction acts to scavenge the atmosphere and may be responsible for the loss of water from the atmospheres of Venus and Mars and for alteration of isotopic ratios over the eons since the formation of the solar system. THE PRESENT PROGRAM The present program of studies of magnetized space plasmas is robust. There is a vigorous program of ground-based measurements, theory, modeling, and data analysis, supported jointly by NASA, NSF, and, to a lesser extent, by other agencies. Data are being returned from the solar wind, magnetotail, magnetosphere, and low Earth orbit. Galileo has recently completed its ex- ploration of the Jovian magnetosphere and Cassini is on its way to Saturn. The data are being analyzed promptly, and significant scientific discoveries are being made. Several important projects are under development and moving toward their launch opportunities. Nevertheless, there is still much to do. UNIFYING THEMES The outstanding questions that need to be addressed in planetary magnetospheres can be divided into three themes: the creation and annihilation of magnetic fields; magnetospheres as shields and accelerators; and mag- netospheres as complex, coupled systems. The first theme includes the formation of the major magneto- spheric current systems: the magnetopause, the tail cur- rent, the ring current, and the field-aligned currents. This theme also includes the disruption of some of these cur- rents and reconnection of the magnetic field across cur- rent layers, at the magnetopause, in the magnetotail, and in planetary magnetodisks. Under the second theme is the role that induced and intrinsic magnetic fields play in deflecting the solar wind and the energetic particle populations coming from the Sun. These magnetospheres also store energy for 51 later release, leading to sudden energization of the plasma in the magnetosphere and acceleration of mag- netospheric energetic particles. In the inner magneto- sphere, trapped charged particles are also accelerated slowly to high energies by stochastic processes. None of these processes is well understood. Even less well un- derstood are the interactions of flowing magnetized plasma with the remanent fields of bodies like Mars. The third theme encompasses some of the most dif- ficult areas of magnetospheric research: the interactions among the d isparate pi asma regi mes with i n a magneto- sphere. The bow shock interacts with the incoming solar wind upstream and the magnetosheath and magneto- pause downstream. Reconnection changes the topology of magnetic field lines, connecting interplanetary and terrestrial magnetic field lines so that the plasmas from the two regimes mix, and allowing momentum and energy to flow into the magnetosphere from the solar wind. The ionosphere interacts with the polar magneto- sphere and the magnetospheric regions at lower latitudes. Planetary magnetospheres have their own unique twists on these processes. In the Jovian magneto- sphere the ionosphere enforces co-rotation of the plasma over enormous scales and a giant circulation pattern is set up within the magnetosphere. At the unmagnetized planets there is direct coupling of the solar wind with the neutral atmosphere. RECOMMENDATIONS The discipline of space physics and the subdisci- pline of solar wind-magnetosphere interactions have experienced an explosion of knowledge and understand- ing in recent years. Still there are some very basic pro- cesses that we do not understand, especially at a predic- tive level. If we cannot predict the rate of reconnection at our own magnetopause or in the magnetotail (and today we cannot), we have little hope of extending our knowledge to planetary and astrophysical systems. Thus we recommend that the future exploration of the ter- restrial and extraterrestrial magnetospheres should be directed toward the deeper understanding of the funda- mental physical processes and the global coupled sys- tems, supported and guided by theoretical investigations and simulation efforts. This requires multisatellite mis- sions and the optimal use of simultaneous, coordinated, and overlapping spacecraft missions. The global coupled system extends all the way down to the upper atmo- sphere and ionosphere. Thus in the terrestrial magneto- sphere ground-based facilities play an important part in the exploration of the coupled system.
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52 In planning for the next decade of studies of solar wind-magnetosphere interactions we have been guided by four essentials. We must understand the physical pro- cesses involved and therefore need measurements with high resolution, capable of studying three-dimensional structure with support from theory and modeling. Our models must be predictive from knowledge of external cond itions. Th is req u i res gl obal, mu Iti poi nt observations and is best achieved with deep, theoretical insight rather than empirical models. We must investigate how re- gions couple, not simply how they work in isolation, and we must continue to explore new settings to de- velop greater understanding. Critical scientific objectives in the future exploration of solar system magnetospheres include the following: · A deeper physical understanding of fundamental plasma processes, such as particle acceleration, mag- netic reconnection, and the role of turbulence. Achieve- ment of this objective should be at the core of present and future space exploration, and the panel endorses the planned Magnetospheric Multiscale mission. · Understanding the scale sizes of the solar wind structures that power Earth's magnetosphere. Achieving this objective, which is needed for predictive purposes, wi I I requ i re mu Itispacecraft missions near 1 astronomi- cal unit (AU) with spacecraft separations measured in tenths of astronomical units. · Understanding the dynamics of the coupled mag- netospheric system and of space weather. Achievement of this objective requires arrays of instruments in space as well as on the ground (just as readings from ground weather stations are complemented by readings from space). A magnetospheric constellation of up to 100 spacecraft to monitor a significant volume of the magnetosphere is strongly recommended, along with complementary ground-based measurements. · Understanding the complex interaction between the solar wind and the polar ionosphere. Achievement of this objective requires the establishment at high lati- tudes of the long-awaited Advanced Modular Incoher- ent Scatter Radar (formerly known as the Relocatable Atmospheric Observatory). Th is faci I ity cou Id be en- hanced by many possible space missions, such as a stereo imager or a polesitter auroral imager. · Measurement of the density of the invisible popu- lations within the magnetosphere. To achieve this objec- tive, the panel recommends the establishment of mag- netometer arrays that can perform magnetoseismology, in analogy to terrestrial and solar seismology, recording transient waves and the ringing of the magnetosphere. THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS · Understanding the energization of the radiation belts. This long-sought objective requires knowledge of the radial swaths of the particle and field environment simultaneously at different local times and under differ- ent geomagnetic conditions to learn how and why par- ticle populations intensify and decay. · Understanding the complex interactions of the solar wind and planetary magnetospheres and atmo- spheres. To achieve this objective, particles and fields instruments will need to be flown on both Discovery- class and major space missions. · Understanding planetary magnetospheres. The exploration of planetary magnetospheres is in its infancy, yet comparisons between these magnetospheres and the terrestrial magnetosphere and with each other are criti- cal to fully understanding the processes taking place. Missions to study atmospheric loss fromVenus and Mars, the occurrence of lightning at Venus and Jupiter, the dynamics of Mercury's magnetosphere, and the joint control of the jovian aurora by lo and the solar wind are some of the many missions that could contribute to our understanding of planetary magnetospheres. TECHNOLOGY DEVELOPMENT While some of these objectives are already techni- cally within our grasp, additional technology develop- ment is needed for others. For example, several missions could be undertaken most effectively with a solar sail. Improved ion propulsion, nuclear-powered propulsion, and mid-size expendable launchers would also increase access to space. Smaller spacecraft systems and instru- ments would enable the constellation missions that are planned and would allow greater return from resource- limited planetary missions. Finally, attention needs to be given to the entire data chain, from operations to data transmission to their assimilation in models to reduce manpower and the total expense of the data chain. CHANGES IN POLICY Many of our programs would be enabled and en- hanced with some simple changes in policy. In some cases, this simply requires better coordination between or even within agencies. Sometimes data are obtained but funds are required for data access or archiving. We need to have processes to determine when a technique has moved from the research arena into the space- forecasting arena. We need to coordinate opportunities for access to space so that all such opportunities are
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS utilized, and we need to ensure that funding for space experiments is available when possible flight opportuni- ties arise. Presently, missions of opportunity are solicited far too seldom and on time scales incongruent with the duration of the opportunity. We also have to guard against using the space science budget to cover short- falls in other programs such as the space station. Budget raids can devastate smaller programs. Moreover, we need to find ways to reduce regulatory burdens, such as International Traffic in Arms Regulations (ITAR) and information technology security regulations, which have led to more and more obstacles to international collabo- ration and to university participation. These policies often have results much different than originally intended. High-level communication and coordination between regulatory agencies and NASA are needed to achieve reasonable implementation standards and procedures. SYNOPSIS In short, the research enterprise in solar wind-mag- netosphere interactions is strong, and much has been accomplished. Nevertheless, some very fundamental understanding is still needed to reach the quantitative level of a fully predictive science. Fortunately, the means to attain this understanding now exist. In some cases an investment in technology will bring us to the threshold of the needed breakthroughs. The next decade of this discipline, launched with the momentum of the last decade's discoveries, fueled by an exciting series of new observations, and supported by a strong program of theory and modeling, promises to usher in a new, quan- titative level of understanding of the Sun-Earth connec- tion. In the next section, the panel provides an overview of the workings of planetary magnetospheres. This over- view is followed in Section 2.2 by a detailed discussion of current understanding of the processes in the terres- trial magnetosphere and the environments of the plan- etary magnetospheres. This description is needed to understand why the panel has chosen the paths it rec- ommends, but it may be skipped by those seeking only to learn the recommendations. Section 2.3 is an attempt to provide three unifying themes that order the remain- ing tasks. Section 2.4 summarizes the existing program and presents recommendations. Sections 2.5, 2.6, and 2.7 describe, respectively, the recommended future pro- gram, the recommended technology developments, and the recommended policy changes that will enable the progress needed i n th is field. 53 2.1 SOLAR WIND- MAGNETOSPHERE INTERACTIONS: THE REALM OF MAGNETIZED PLASMAS INTRODUCTION Our i ncreasi ngly technological society rel ies more and more on assets launched into space. In addition, our investigations extend well past the local space plas- mas into those of the solar and astrophysical systems. Understanding the behavior of magnetized plasmas has become increasingly important. We must understand the environment in which our satellites operate. We need to predict how the solar wind affects the terrestrial mag- netosphere. We require insight into how the Sun gener- ates explosive events, and we desire to comprehend the workings of distant astrophysical systems that are clearly also affected by magnetic processes. The solar wind's interaction with the terrestrial and planetary magnetospheres allows us to treat a problem of much practical importance and learn how these plas- mas work in a most general manner. We can then ex- tend this knowledge to other plasma systems in regions we cannot probe directly. For users of this report who are not familiar with the physics of space plasmas, this section offers some brief insight into the basic plasma processes that occur in space. This section also provides a preview of the themes introduced in Section 2.3 and the rationale for the rec- ommendations made in subsequent sections. THE FOURTH STATE OF MATTER Plasmas are often referred to as the fourth state of matter. The behavior of this state, especially of magne- tized plasmas, can be nonintuitive. We are most familiar with the other three states solid, liquid, and gas- whose dynamical properties are governed by the differ- ing intermolecular forces of each state. Our intuition usually serves us well here. In an ideal gas, the forces between the molecu les are transmitted through col I i- sions. The random motions of the gas are characterized by a temperature and, in collisional equilibrium, all con- stituents come to the same temperature. The pressure in the gas is proportional to the product of the density and the temperature. A pressure gradient exerts a force. For example, in Earth's atmosphere we know that the pres- sure decreases with altitude. The force associated with
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~ do. JO this pressure gradient acts on a parcel of air to support it agai nst the force of gravity. In space plasmas there often are no collisions in the usual sense. Thus, different components of the plasma can have d ifferent temperate res. Fu rther, temperate res along the magnetic field and across it can differ. Still, and counterintuitively, a plasma can exert pressure forces not only through the thermal motion of its par- ticles but also through its magnetic (and electric) fields. These fields do have pressure (proportional to the square of the field strength) and, as in the case of a gas, the gradient of that pressure exerts a force. In a magnetized plasma, the magnetic field orders the charged particle motion, the energy of the gyrating particles provides the plasma pressure perpendicular to the field, and the par- al lel thermal motions provide pressure along the field. An example of the interplay between these pres- sures is provided by the boundary between the solar wind flow and the magnetosphere. This region, the mag- netopause, is often treated as a boundary between a plasma with at most a weak magnetic field (the shocked solar wind) and a strong magnetic field (Earth's mag- netosphere) containing very little plasma. The pressure on the solar wind side is contained in the thermal mo- tions of the plasma. At the boundary of the plasma the thermal-pressure gradient exerts a force toward the mag- netosphere. The pressure in the magnetic field similarly exerts a force into the solar wind plasma, where the magnetic pressure decreases. Thus there is force bal- ance, and the magnetosphere and the solar wind estab- lish a pressure equilibrium in the absence of collisions. The ratio of the proton mass to the electron mass is 1,836. Thus an electron at the same temperature as a proton moves at 43 times the speed of the proton, and for this reason electrons can communicate rapidly in a plasma. Protons, though, have all the inertia and mo- mentum, and electrons tend to follow the dynamics of the protons, setting up small ambipolar electric fields to maintain quasi-neutrality in the plasma. As a result, ex- cept on the microscale, the electric field seldom builds up to such a degree that its pressure is important. How- ever, when electric fields do arise parallel to the mag- netic field they can be very important to the processes in the plasma, so much so that it is critical to be able to observe such generally small electric fields. The panel notes that these electric fields are frame independent, while the electric field in the direction perpendicular to the magnetic field is frame dependent, so that the per- pendicular electric field detected depends on the veloc- ity of the observer relative to the magnetic plasma. Thus the flowing solar wind has an electric field as seen in THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS Earth's reference frame. In short, while a plasma has many similarities to fluids and gases, it is different enough that our physical intuition is often ill-prepared to understand processes that occur therein. RECONNECTION The very large mass ratio between the proton and electron affects their gyromotion as well as their typical speeds. Because of the nature of the Lorentz force, which keeps a charged particle in orbit about a magnetic field, the radii of gyration of different charged particles are proportional to their mass times their velocity and in- versely proportional to their charge. If protons and elec- trons have the same energy perpendicular to the mag- netic field, the radius of the gyrating electron is 2.3 percent of that of the proton. In a collisionless plasma, the gyrating particles define the magnetic field lines. Particles in orbit about a magnetic field line stay with that magnetic field line. The ability of a charged particle to orbit a magnetic field line depends on the scale size for changes in the field. A small change can cause drift motion, and too large a change in the field on the scale of a gyroradius can cause a charged particle to become unmagnetized and move to orbit another field line. Owing to their smaller gyroradii, electrons can follow small-scale field variations to sizes roughly 43 times smaller than protons. One might think that this is moot for a system as large as Earth's magnetosphere, because its scale sizes are vast compared with those of the gyro- radii. In fact, it is standard practice to average over the gyromotion and treat the magnetized plasma as a mag- netic fluid. This formulation is known as magnetobydro- dynamics (MHD). However, the vast scale of the mag- netosphere does not allow us to completely ignore the kinetic motion of its particles. It just reduces the region in which that kinetic motion is crucial to small areas called neutral points. Close to these points the protons first become unmagnetized, and then closer yet the elec- trons become unmagnetized. This process in which charged particles lose their ability to define a magnetic field line is called reconnec- tion. If they are antiparallel, two neighboring magnetic field lines, say one that starts and ends on Earth and another that starts and ends on the Sun, can become connected so that two new field lines are created, both of which have one end on Earth and one end on the Sun. This topological change enables the plasmas in the two regions (terrestrial and solar in this case) to mix. It also allows momentum and energy to be supplied from one plasma to the other. Figure 2.1 illustrates the
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS geometry of this situation. The magnetic field at the re- connection point forms an x-type configuration with plasma flowing into it from the left (Earth's magneto- spheric plasma) and from the right (Sun's solar wind plasma). Field lines switch partners at the x-point, and plasma and cojoined field lines flow rapidly outward (top and bottom). Since an electric field is frame depen- dent, these moving magnetized plasmas have electric fields in the frame of the reconnection point, as sketched in Figure 2.1. Collisions, either particle-particle or wave-particle, can also demagnetize orbiting charged particles, and in numerical simulations numerical dissipation can mimic the reconnection process. Thus it is not always clear how the magnetosphere undergoes this most critical pro- cess. Much continued in situ study with high temporal Exhaust ZNIF .\ . Magnetosphere <~ \ \ YN ~ For i/ XNIF Exhaust Magnetosheath ME MINX N I F inflow FIGURE 2.1 The geometry of reconnecting antiparallel mag- netic fields at a neutral point. Courtesy of J.D. Scudder. 55 and spatial resolution is required, as well as investiga- tion with state-of-the-art numerical codes. From the above it is obvious that magnetic recon- nection is the crucial process enabling plasma (and momentum, energy, and magnetic flux) to cross magnetospheric boundaries. In addition, the partner- swapping process in reconnection can dramatically alter the stress balance in a plasma, leading to catastrophic energy release processes, such as solar flares and mag- netospheric substorms, discussed below. FLOWING MAGNETIZED PLASMAS A solid can support both compressional and trans- verse oscillations but a normal liquid and a gas cannot. Thus the dynamics of the flow around an object in a flowing gas is dominated by compressions and rarefac- tions. However, in a magnetized plasma that otherwise resembles a gas, there are transverse oscillations as well as two compressional waves. These three waves are usu- ally called fast, intermediate, and slow. They are all necessary to transmit an arbitrarily shaped perturbation through a magnetized plasma. For example, in the inter- action of the flowing solar wind with Earth's magneto- sphere, the fast mode slows, heats, and deflects the flow and magnetic field, but in general the intermediate mode is needed for additional field and flow deflection, and the slow mode is needed to prevent a density pileup at the subsolar point. Just as in a solid or gas, perturbations travel at a finite velocity, and in the magnetized plasma as in many other situations the velocity of each wave Separator mode is different. When it arrives at each of the planets the solar wind flow is supersonic, moving faster than the speed of the -YNIF compressional (fast mode) wave that could deflect it around the planetary obstacle. The momentum flux of the solar wind represents a dynamic pressure that con- fines the planetary magnetic field, but in order for it to be applied to the magnetosphere, the flow must pass through a bow shock that slows, deflects, and heats the flow, making it subsonic. Then the three wave modes (fast, intermediate, and slow) can act on the plasma to cause the deflection of the flow and alter the plasma conditions at the boundary of the magnetosphere. It is very important to magnetospheric processes that there are finite propagation times and finite transport times in the magnetosphere. When the solar wind mag- netic field reconnects with the subsolar magnetospheric magnetic field, it begins to transport magnetic flux to the geomagnetic tail, as illustrated in Figure 2.2. The tail may increase in size for about an hour. Then, when
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56 Inter~lanetarv Polar Cusp -Magnetopause Current FIGURE 2.2 A cutaway diagram of Earth's magnetosphere.Cour- tesy of C.T. Russell, University of California, Los Angeles. reconnection begins in the tail, it may require another hour to transport the magnetic flux out of the tail, but the signals denoting the onset of each reconnection event can travel through the magnetosphere within minutes. Other manifestations of the finite travel time of perturba- tions in the plasma include the resonant behavior of individual dipole flux tubes, with waves bouncing back and forth in the magnetic tube and the propagation of shock-initiated disturbances through the magnetosphere. These signals can be used to probe the magnetosphere much as seismology uses waves triggered by earth- quakes to probe the structure of Earth. The waves discussed above have very long wave- lengths, generally a large fraction of the dimension of the system. Waves at shorter wavelengths are also pres- ent in magnetized plasmas. Often these waves are responsible for releasing free energy from the plasma, ultimately into heating of the system. Examples of such waves include those caused by the upstream ions reflected at the bow shock and ion cyclotron waves produced both in the solar wind interaction with comets and in the flow of the lo torus past the mass-loading region at lo. THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS When a flowing magnetized plasma interacts with an unmagnetized planet there are important simi rarities and differences from the magnetized case. First, if the unmagnetized planet has an atmosphere, then it will be ionized by the solar UV and EUV radiation. The solar wind magnetic field will be draped across this electri- cally conducting ionosphere and will pile up in front of it, as illustrated in Figure 2.3. This pileup region deflects the solar wind particles around the ionospheric obstacle while the magnetic field begins to diffuse into the iono- sphere. However, the solar wind magnetic field is quite variable in direction, and the long-term (days) vector average field is close to zero. The diffusion time into the interior of the ionosphere, high in the collisionless exo- sphere, is long. Thus, the deep ionosphere does not generally become strongly magnetized by this external magnetic field. Second, the neutral atmosphere often has a great enough extent that the neutral density is significant on solar wind stream tubes that are flowing rapidly. When the neutral atoms and molecules of the atmosphere become ions they are accelerated by the solar wind and lost to the planet. This loss can lead to significant changes in a planetary atmosphere over the age of the solar system. Hence the magnetic field is both an accelerator and a shield at unmagnetized planets. tow Shank Shock s (Outside Tail) FIGURE 2.3 The solar wind interaction with an unmagnetized planet, illustrating the effect of the shock on the field and the stretching of the field to form an induced magnetotail. Courtesy of C.T. Russell, University of California, Los Angeles.
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS THE STORAGE AND RELEASE OF ENERGY The interaction of the solar wind with a planet cre- ates a magnetic cavity with a long magnetic tail. Since a magnetic field has an energy density, the formation of a planetary magnetotail or its expansion involves the stor- age of energy. The additional energy in a magnetotail can be provided externally when the magnetosphere reconnects with the interplanetary magnetic field at the dayside if the fields are in opposite directions. The stored energy is extracted from the mechanical energy of the solar wind flow as the magnetic field lines joining the magnetosphere to the solar wind slow its flow. The two nearly antiparallel magnetic lobes of the tail can also reconnect in a manner similar to the fields at the magnetopause, and energy can be released rap- idly from the tail lobes, in a process called a substorm. Some of this energy accelerates the bulk of the plasma, some heats the plasma, and some energizes a few par- ticles to very high energies. On Earth these high-energy particles help populate the radiation belt. Over the au- roral zones beams of particles are created that cause the auroral emissions during the reconfiguration of the night magnetosphere associated with these acceleration pro- cesses. On the Sun, solar flares are seen when highly energetic particles strike the solar surface after a re- connection event in the magnetic field above the photo- sphere. The creation of a small number of energetic par- ticles (a "high-energy tail," as these energetic particles are often called) is another nonintuitive phenomenon in a collisionless plasma. In a collisional environment the number of particles as a function of energy follows a Maxwellian distribution in which there are very few par- ticles that deviate much from the bulk of the distribu- tion. However, in a collisionless plasma, the high-en- ergy particles can receive a disproportionate amount of the energy being put into the plasma. Understanding the conditions under which this occurs is important, be- cause these high-energy particles can be deleterious to a spacecraft system in orbit in the magnetosphere. In the broader astrophysical setting, we are interested in un- derstanding how cosmic rays reach energies much, much higher than those of particles accelerated by pro- cesses in the solar system. COUPLING IN A COLLISIONLESS PLASMA The large proton-to-electron mass ratio not only affects the relative speeds of the two particles under normal circumstances and also their relative gyroradii, 17 .~ . but also the charge separation. In general, electrons will stay close to the ions to maintain charge neutrality. Al- though in the absence of collisions charged particles will stay on a single magnetic field line, any charge imbalances that arise can generally be removed by mo- tion along the magnetic field. Thus most plasmas are quasi-charge-neutral. The magnetic field in most space plasmas is strong enough to divide space into different plasma regimes with little communication across the boundaries be- tween them. When the magnetic fields in two adjacent regions are in nearly opposite directions, reconnection, discussed above, can occur, linking the two regions. If one of these regions is flowing past the other, this link- age can transfer momentum from the flowing plasma to the initially stationary plasma. This is the way in which Earth's magnetosphere is stirred by the solar wind that flows past it. Surface waves can also transfer momentum across such a boundary if the system is dissipative. The waves may be generated at the bow shock and blown back against the magnetopause, or they may arise in the interaction due to a velocity-shear instability, such as the Kelvin-Helmholtz instability, that is akin to the pro- cess by which the wind creates ocean waves. An important coupling occurs between the plasma and the neutral gas in Earth's magnetosphere at the foot of the field line. The stress that is applied at the interface between the solar wind and the magnetosphere must eventually be taken up by Earth, and this occurs ulti- mately through collisional transfer between the ions and the neutrals. To get the ions moving at the feet of mag- netic field lines and overcome the drag of the neutral atmosphere, the magnetosphere sets up a large current system that connects the outer magnetosphere with the ionosphere along magnetic field lines. The closure of the current across field lines in the collisional, electri- cal Iy conducting ionosphere accelerates the low-altitude ions via the J x B force or ponderomotive force. This force is the macroscale manifestation of the Lorentz force, which maintains charged particles in their orbits around magnetic field lines. It can also transfer stress from the ionosphere to the magnetosphere such as to enforce co-rotation of the cold magnetospheric ions. This mechanism is especially important in the jovian magnetosphere. In the terrestrial auroral ionosphere, the chain of momentum transfer is completed when the moving ionospheric ions transfer their momentum to the neutral gas, generating high-altitude winds. The overall coupling from the solar wind down to the ionosphere is a very complex process, and it is fair to say that while we now understand this process much better than even
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THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS INFORMATION ARCHITECTURE TECHNOLOGY As the density and complexity of information in- crease, science missions are driven by the need to handle and ingest the resultant data. New technologies and concepts are required to make massive amounts of data accessible to science and scientists. The science and engineering community, with support from NASA, needs to continuously evolve this process. There is no clear-cut separation between data processing, data com- pression, data retrieval, data storage, and data distribu- tion and assimilation onboard the spacecraft and like processing on the ground. Different missions will require that different parts of the process be done in different places. For example, a deep space or outer planet mis- sion may send back mostly highly processed data to reduce bandwidth requirements. In future missions there may be a need to assimilate the observational data into models onboard the spacecraft and telemeter the results to the ground. The different technologies used must be migrated to the appropriate platforms. The constel ration-type missions, i n particu far, have a recognized need to assimilate the data into global models. This requires development of software and sys- tems that can take the data inputs in real time indepen- dent of their quality and completeness. The concept is to use adaptive physical models (like adaptive MHD codes) to provide connectivity between the indepen- dent in situ observations and to generate a complete moving picture of the dynamic system being studied. This is not a current capability except for single-point interplanetary data inputs to MHD codes. What the con- stellation science teams envision is to dynamically modify the MHD codes to best represent the totality of the observations. Data from constel ration missions im- pose constraints on the modeling codes. An intensive effort is required to construct codes with appropriate data assimilation technologies. Model development itself is driven by a need for new tech nology, i n some cases a new computational tech nology. I n other cases it is the development of new software technology and numerical techniques. Model development is a cross-enterprise issue, and theoretical and modeling missions should be considered to be as important as experimental missions. TECHNOLOGY FOR GROUND SYSTEMS AND OPERATIONS As noted above, the cost of ground systems and operations can be very large, especially for long-dura- tion missions. Technologies that reduce and simpl ify the systems free resources that can be redi rected i nto the science component of the missions. Just as autonomous satellites can reduce the burden on ground and opera- tions systems, autonomous ground systems can reduce the manpower required for mission support. With sev- eral upcoming missions being multisatellite or constel- lation missions, it is imperative that new operation con- cepts and technology be developed and implemented. Examples of possible technologies can be found in com- mercial communications satellite organizations. Many of these companies run large numbers of satellites with relatively small crews. In fact, these organizations are ahead of NASA in the area of autonomous operations of systems of spacecraft. Their technologies should be stud- ied and emulated where appropriate; otherwise they should be used as a starting point for the development of the operations and ground systems that will be required by MagCon and other mu Itisatel I ite science missions. A separate issue is the retrieval and handling of the science data from modern missions. Again, in the past this has been a manpower-intensive and costly effort throughout the mission. Intensive support is required to find and implement architectures and technologies able to handle the massive increase in data that new missions will generate. New technologies are required to make such massive amounts of data easily accessible by all scientists. The science and engineering community as a whole needs to continuously evolve this process. The different technologies must be migrated to the appropri- ate platforms. RECOMMENDATIONS AND PRIORITIES As noted above, there needs to be a significant fo- cus on developing new instrument, satellite, propulsion, operations, data assimilation, and processing technolo- gies. The top priority in each of these areas is addressed below: · Science measurements. A space-science enter- prise-wide instrument development program is needed that is separate from SR&T budgets. This issue clearly needs to be addressed if quality measurements are to be made on the smaller micro/nanosatellites being envi- sioned for future multisatellite and constellation mis- sions. In addition, new management and team struc- tures must be generated for developing highly integrated, micro/nano, science-craft-type spacecraft. This must be done on a time scale that meets the development needs and implementation of multisatellite missions.
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS · Propulsion. The top priority is to push the devel- opment of solar sail technology to support missions that require non-Keplerian orbits in the interplanetary me- d i u m to make the necessary science measu remeets at appropriate locations. NASA has a good start in this area but needs to move forward with hardware development and spaceflight demonstrations so the technology is flight qualified in this decade. · Satellite technology. The push shou Id be to de- velop fabrication, integration, and testing technology for micro/nanosatel I ites that wi 11 enable constel ration mis- sion science. This requires bringing together new mate- rial and electronics technologies, new management techniques and structures, and new integration and test- ing processes. A way of integrating the development of spacecraft and science instruments is needed. Test-bed- type development programs that take multiple micro/ nanosatellite systems from concept to flight should be considered as one way of developing and testing the new processes. This work needs to be done soon if it is to support missions that are identified in NASA's Strate- gic Plan. · Operations and data handling. The focus should be on implementing evolving technologies that reduce manpower and costs for all missions. In particular, at- tention should be given to the complete data chain, from the operations required to get the science data to the manner in which the data are brought to Earth, as- similated into models, and ultimately presented to sci- entists. This must be started now if the needed capabili- ties are to mature on a time scale that meets planned schedules for complex new interplanetary observatories and mu Itisatel I ite constel ration missions. 2.7 SOLAR WIND- MAGNETOSPHERE INTERACTIONS: POLICY ISSUES INTRODUCTION The need to observe coupled dynamics of the large magnetospheric system in response to solar wind condi- tions has several implications. First, the difficulty of ad- equately specifying the state of the dynamic system means that the number of observing platforms should be as large as possible. This goal would be best achieved by interagency coordination to maximize the opportuni- 1 1 5 ties for instrumentation on non-NASA platforms. Sec- ond, because ground-based observations provide dis- tributed knowledge of convection and boundaries that cannot be achieved in space, ground-based capabilities must not only be sustained but enhanced, and coordina- tion between space- and ground-based observations needs to be exploited worldwide to the fullest extent possible. Third, it is now firmly established that knowl- edge of solar wind conditions is critical to developing further understanding of the magnetosphere-ionosphere system, so that sustained, continuous monitoring of solar wind input is essential. Fourth, global physics-based computer si mu ration codes are an essential component of the research program because they will play a central role in maximizing the information that can be extracted from the observations and unifying disparate data sets within a comprehensive framework. These implications in turn have specific ramifications for the policies that should be pursued to achieve the key science objectives identified above. INTERAGENCY COORDINATION Because the resources required to make the neces- sary observations exceed those available from any one agency and because the societal impact of the science return is relevant to a variety of agencies and interests, efficient coordination between agencies is a preeminent policy concern. In fact, one could argue that the coordi- nated system is much more valuable than the sum of its components. NOAA:Transitioning New Operational Observing Platforms and Models The National Oceanic and Atmospheric Adminis- tration has two roles to play. First, the transitioning of space instrument platforms from basic science research to operational systems needs to be anticipated and implemented in a timely fashion. Since space-based sci- ence platforms are almost exclusively the substance of NASA programs, these transitions will require coordina- tion with NASA. Typically, this is done by taking the key instrumentation and data reduction techniques devel- aped under NASA research programs and implementing them under NOAA. Observations that are or should be planned for transition i ncl ude the fol lowi ng: · Interplanetary magnetic field and solar wind ob- servations analogous to those provided in rea/ time from
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1 1 6 the ACE spacecraft at the L1 point. The necessity for continuous IMF/solar wind observations from L1 has been abundantly demonstrated scientifically and opera- tionally. Nearly all predictive models of magnetospheric response depend pri nci pal Iy on IMF/sol ar wi nd i nputs. Since the ACE spacecraft is operating beyond its design life, it would be prudent to implement a new L1 plat- form for this purpose in the very near future (<2 years). Steps should be taken to continue such L1 in situ moni- toring as an operational system. · Solar coronal observations. The dramatic ad- vance in our appreciation and understanding of the causative link between coronal dynamics, coronal mass ejections, and high-speed streams, in particular, and major geomagnetic disturbances made possible by re- sults from the instrumentation on YOHKOH and SOHO has motivated both the Solar Dynamics Observatory of the LWS program and the STEREO mission. There is now little doubt that observations of this class will play a central role in operational space forecasting, and steps should be taken to coordinate operations with NASA in the short term (next 5 years) and to deploy a line of operational monitors in the medium term (5-8 years). The GOES SXI instrument is an important first step. · Auroral imaging. The advances i n u nderstand i ng magnetospheric dynamics, particularly nightside/mag- netotail processes made possible with global auroral imaging, demonstrate the value of these observations for monitoring intrinsic magnetospheric dynamics as well as energy transport to the ionosphere. New results from the IMAGE mission promise to increase our understand- ing of the physical correlates of these observations, thereby improving their operational value. It is already clear that real-time auroral imaging will prove opera- tionally valuable, and plans should be laid for NOAA to provide global auroral imaging on an operational plat- form in the long term (8-10 years). The second role for NOAA concerns the transition- ing of models from science research tools to operational resources. NOAA, NSF, DOD, and NASA al I have theory and modeling efforts in magnetospheric physics. The Space Environment Center of NOAA supports a small effort to transition science models to operational use. Discussions with both agency and scientific community personnel indicate that this transition effort is undersupported. They note that there appear to be many more models available in the community that could be useful to space weather than are being actively con- verted to operational status. THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS A parallel concern exists in the research commu- nity, which has a separate need for standard models. In the next decade, the research community also will re- quire access to realistic global models, including MHD simulations. The Coordinated Community Modeling Center at GSFC5 is providing the first community access to such global models, in part in coordination with the NSF's GEM program. The challenge of providing sophis- ticated models to the community is a significant one and will require an advisory structure to prioritize and ensure maximum efficiency in coordination between agencies and to minimize duplication of effort. The panel recom- mends that these transitioning efforts be supported aggressively to meet the science and applications objec- tives of the space environment community. DOD-DOE: Coordinated Planning for Launch and Flight Opportunities and Access to Relevant Data Sets The Department of Defense and the Department of Energy conduct operational flight and observation pro- grams that are directly relevant to the science objectives of magnetospheric-solar wind interactions. Ensuring ap- propriate use of these resources is an extraordinarily cost-effective means of achieving several of the observa- tional goals described above. Launch opportunities will be avai lable, particularly for sending smal ler payloads, ~300 kg, into geosynchronous transfer and low Earth orbits on DOD vehicles. These are key regions for magnetospheric dynamics, particularly radiation belt dynamics. H istorical Iy, launches of opportunity have proven problematic in practice because of cost con- cerns associated with launch schedules. (The cost growth and resulting cancellation of IMEX were due in part to probl ems of th is sort.) Mechan isms for accom- modating NASA payloads on DOD launch schedules without raising NASA mission costs via prolonged launch delays need to be studied. In addition, agree- ments between NASA and DOD regarding launch op- portunities need to be formalized so that the availability of these opportunities and the mutual commitment to support the programs that use them do not hinge on agency personnel remaining in key positions. Discus- sions with DOD representatives indicate that launch opportunities will continue to be available, but at present arrangements to use these opportunities are made only on an ad hoc or informal basis. 5See .
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS Current, future, and planned DOD and DOE plat- forms obtain or will obtain measurements for opera- tional purposes that are directly relevant to magneto- sphere-solar wind interaction science objectives. These measu remeets i ncl ude data from DMSP and N POESS particle and fields detectors and from auroral imagers, particle data from DOD and GPS satellites, and total electron content from ground-based GPS receivers. These data sets provide valuable augmentation of space- based observations and need to be exploited to the full- est extent possible. Support for preliminary processing and archiving of these data for retrospective scientific analyses is essential if the scientific community is to make meaningful use of these assets. NASA and NSF are urged to coordinate with DOD and DOE to facilitate preliminary processing and archiving activities so that these resources are leveraged to the fullest extent possible. NSF: Central Role for Ground-Space Coordinated Observations Global magnetospheric dynamics are reflected in ground processes. Our understanding of the specific correlation between ground observables and magneto- spheric configuration and dynamics has dramatically increased in recent years, in part through the efforts of NSF's GEM campaign. We now understand the relation- ship between convection distribution and the underly- ing magnetopause reconnection geometry. We also ap- preciate how to identify time variations in reconnection in ground observations. We now know how to relate auroral spectra to the precipitating source population and critical bou ndaries i n the magnetosphere, both i n the magnetotail and on the dayside. Ground-based observations provide distributed measurements of quantities that are difficult or impos- sible to measure with comparable distribution in space. These measurements include radar and ground magne- tometer observations of convection; multispectral and high time and spatial resolution auroral imagery, merid- ian scanning photometers, and ULF pulsations. The ground observations therefore provide a means of moni- toring the enormous system with remarkable efficiency. Historical Iy, NSF assumed the central role in both estab- lishing the ground-based observatories and coordinat- ing these observations with measurements from space. Mai ntai n i ng and expand i ng these grou nd observa- tion assets is critical for two reasons. First, ground obser- vation assets will prove even more valuable as new space measurements are made and as models become able to assimilate these data. Recent advances in identi- 1 1 7 tying ground signatures with specific magnetosphere- solar wind interaction phenomena make the obser- vations even more valuable because they provide quan- titative contextual and distributed information that is key to specifying the system and unavailable any other way. Second, some impediments remain to establishing an unambiguous link between phenomena that can be ob- served from the ground and magnetospheric-solar wind dynamics. These impediments include our incomplete understanding of ionospheric conductivities and the dif- ficulty of specifying the net result of auroral processes that couple the high-altitude magnetosphere to the iono- sphere. Only by comparing extensive ground observa- tions with space-based observations will it be possible to further improve the power of ground-based observa- tions. COORDINATION BETWEEN PROGRAMS AND DIVISIONS WITHIN AGENCIES: NSF AND NASA Because magnetospheric physics is one of a number of priorities in NSF and NASA space science programs, and because responsibility for it is split between NASA and NSF, it is important to recognize and eliminate un- necessary compartmentalization. The panel encourages cooperation and coordination between agencies and between programs within each agency. Several areas in which coordination is desirable are discussed next. Comparative Magnetospheres and Planetary Exploration Comparative magnetospheres remains a vital prov- ing ground for theories of magnetospheric dynamics, because different systems present configurations and conditions not found at Earth. Our understanding of magnetosphere-solar wind physics will be seriously de- ficient unless these extraterrestrial systems are explored in ways that allow us to test our theories of their dynami- cal behavior. Solar system exploration therefore needs to provide avenues for observations of other magneto- spheres. In the past, major solar system missions could ac- commodate planetary geology and atmospheric and magnetospheric science payloads. This has not proven to be true under the Discovery program, whose missions are more highly focused. Instruments whose purpose is to further the understanding of comparative magneto- spheres have less appeal in the Discovery mission envi- ronment than instruments that provide new information on a particular solar system body. The Solar Terrestrial
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1 1 8 Probe missions and, to a greater degree, the Living With a Star missions tend to focus on the Sun-Earth Connec- tion rather than on comparative magnetospheres. The panel encourages the Solar System Exploration and Sun- Earth Con nection programs to coord i n ate thei r programs in the upper atmospheres and magnetospheres of the planets and to develop missions that address the out- standing problems in these areas. Ties Across Organizational Boundaries As the science of the solar wind, magnetospheres, and ionospheres matures and a new emphasis on serv- ing the needs of space weather emerges, it is natural that new programmatic structures are being adopted within and between funding agencies. As these new structures are adopted, however, it must be recognized that the physical systems whose study is being overseen are closely linked and do not respect administrative bound- aries. These structures may be reasonable and based on general distinctions between disciplines, but are none- theless artificial constructions. Science disciplines must be allowed the freedom to explore the linkages between these physical systems. As new organizational structures are adopted, the ties between subdisciplines must not be lost, and research that spans administratively differ- ent areas must not be allowed to fall through the cracks. Often, cross-discipl inary research is not given priority by either discipline and therefore languishes. Planetary magnetospheres and solar wind interactions are an ex- ample of disciplines where such a lacuna occurs. A for- mal mechanism to fairly evaluate and support cross- discipl inary research should be adopted. Broadening the categories within NASA's SR&T program to allow mag- netospheric and ionospheric research to be considered together is commendable in this regard.6 Similar coordi- nation between NSF's magnetospheric program i n its Division of Atmospheric Sciences and its planetary mag- netospheres and atmospheres research in its Division of Astronomical Sciences would also be most welcome. Steps appropriate to each case and agency need to be taken to ensure healthy cross-disciplinary research in other areas, including comparative magnetospheres, solar wind-magnetospheric physics, and the transition- ing of research to application tools. 6See NRC, 2000, "Interim Assessment of Research and DataAnalysis in NASA's Office of Space Science," letter report, Sept. 22. THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS OPPORTUNITIES FOR SPACE MEASUREMENTS IN ENTITIES OTHER THAN NASA'S OFFICE OF SPACE SCIENCE NASA's Office of Space Science provides the most regu Iar opportunities to gain access to space through its major missions and principal-investigator-led missions, but there are other opportunities to have instrumenta- tion carried into space. One of these is payloads at- tached to the International Space Station (ISS); another is launches by DOD or its foreign partners. In this section the panel discusses issues related to these two opportu- . . n Itles. Space Station Attached Payloads The knowledge gained in studies of the interaction of the solar wind with the magnetosphere and the en- suing understanding of the entry of solar energetic par- ticles into the magnetosphere is particularly beneficial to the ISS and its occupants.7 On the other hand, the ISS is not a natural or optimum platform for observing mag- netosphere-solar wind interactions. It provides at best a limited opportunity for space physics research, owing to its orbit and facility configuration constraints. Fur- thermore, the additional qualification and safety issues pertaining to flight aboard a crowed vehicle add sig- nificantly to the cost of development, further diluting research resources. For these reasons, ISS is not a pre- ferred platform for conducting magnetospheric physics research. The panel emphasizes that continued progress in magnetosphere-solar wind interactions is of importance to ISS. The space environment plays a significant role in constraining ISS operations, as it does in constraining all space-based technology assets. Thus, continued basic research on the science of Earth's space environment is a high priority for ISS even when space physics instru- ments cannot be attached to the ISS per se. Missions of Opportunity Theabilitytooptimize the return on launch oppor- tunities by funding individual researchers to build in- struments for opportunities on non-NASA missions is an excellent concept. Nevertheless, as presently executed, it is not achieving its full potential. 7See NRC, 2000, Radiation and the international Space Station: Recommendations to Reduce Risk, National Academy Press, Wash- ington, D.C.
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS To achieve the greatest science return, adjustments need to be made in the mission of opportunity (MOO) program to increase the frequency of these opportuni- ties. The panel strongly endorses a change that would separate MOO from the SMEX and MIDEX announce- ments of opportunity, thereby allowing more frequent consideration and implementation of MOO proposals. To accomplish this change, the cost cap for MOO, in- cluding attached payloads on the ISS, should be ap- proximately halved, from $35 million to approximately $15 million. This is one mechanism whereby launches of opportunity with DOD could be more effectively le- veraged for science. (The panel recommends semian- nual considerations to provide a better match with the frequency of such opportunities and with the develop- ment times of the missions.) SCIENCE IN THE STRUCTURE OF PROJECT MANAGEMENT The principal investigator model for missions has proven highly successful in terms of science return on the investment. One important reason for this success is that science issues are given the same weight as space- craft and mission design issues. Strategic missions such as Solar Terrestrial Probes and Living with a Star mis- sions could benefit from emulating some of the manage- ment structure of these missions. A position of science manager, equal in importance to the project manager, should be established for future strategic missions. To ensure the highest quality leadership, this position should be selected competitively. The panel believes that a science consortium lead by a competitively selected PI would be another way to infuse science into the management process. INTERNATIONAL COOPERATION Historically, research in space science, especially in solar wind-magnetosphere interactions, has had a strong international element. This international element arises first from the need for globally situated, ground-based measurements and then from the immensity of the task, which requires a cooperative effort to obtain the critical mass for its successful outcome. Recently, barriers have arisen to mean i ngfu I i International cooperation. ITAR and Export Controls The International Traffic in Arms Regulations govern the export of both information and equipment that might 1 19 be used by foreign entities against the United States. All space-associated investigations are now included under these regulations, which as implemented by the State Department have placed substantial burdens on the nation's space science community. These burdens are manifested in two ways. Space physics missions have always been conducted in close collaboration with our international colleagues in Europe and Asia, primarily Japan, and in Canada. The ITAR restrictions have made it extremely difficult to continue working with these col- leagues on U.S. missions like STEREO, in which interna- tional contributions to the science payload are major elements of the design. Even rudimentary essential infor- mation concerning mission design concepts and space- craft design plans has been subject to control, making it extremely difficult, if not impossible, to involve our for- eign colleagues in making fully informed scientific judgements. It is simply impossible to properly design and build a scientific instrument without free access to relevant data on the spacecraft and mission design. The problem is even more acute in cases where instrument subsystems are provided by ou r foreign partners. One cannot team effectively if the instrument designs to which the team members contribute are sequestered. The latter point suggests the second debilitating effect that these new restrictions are having on the nation's scientific community. The tremendous return to the United States from participation in foreign missions is illustrated by the SOHO (ESA), GEOTAIL (ISAS), and CLUSTER (ESA) missions, which were implemented by foreign agencies in Europe and Japan with significant NASA instrumentation, operations, and science partici- pation. Now, however, the burdensome impact on foreign collaborating agencies has jeopardized opportunities to participate in foreign missions in the future. It is even harder to build an instrument jointly with our foreign col- laborators. Clearly, the U.S. science community would not be on an equal footing with its international colleagues had it not been able to join them in these missions. The ITAR situation is serious. Research scientists have been subjected to criminal charges and penalties. Consequently, some universities have refused to allow their researchers to accept grants and contracts with restrictive ITAR clauses. The inability to share informa- tion among partners in a mission could lead to mistakes and mission fai I u res. An amended ITAR rule was published on March 29, 2002, which applies only to university-based space re- search. The rule attempts to clarify the regulations and to remove obstacles to the conduct of university-based fundamental research in space. However, there remain
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1 20 a number of serious practical problems with the new rule, including continued restrictions on which students and staff at a university can have access to information and who in partner nations can gain access. The univer- s iti es sti I I may fi n d the regu I ati ons too restri ctive and ban thei r staff from enter) ng i nto such programs. More- over, the revised statutes do not address the equally serious problem namely, that U.S. universities cannot work with the U.S. space industry without being subject to ITAR regulations. Here the restrictions are even greater than the restrictions on foreign collaborations. Information Security Presentfederal policies require all personnel having access to NASA spacecraft and science payload com- mand systems to have background security cheeks. This is enforced by ensuring that contracts with universities are consistent with NPG 281 0. This regulation requires that any individual having access to a spacecraft or its subsystems (such as science payloads) above a certain value, including the computers used to command sci- ence payloads, must be so screened. The universities are not generally convinced that they can require this of employees, especially those already hired. NASA's rul- ing means that university computer systems managers, project managers, and certain technicians and program- mers must submit to background checks as part of their i nstitution's contractual agreement with NASA on fl ight projects. However, university mission participants typi- cally have no access to spacecraft system commands or controls. Firewalls are generally placed between the external workstations from which commands are sent to the science payload and the mission operations center that sends them. The investigation teams historically as- sume responsibility for the correctness of the commands sent to their instruments on board the spacecraft, and this has not presented a security problem in the past. For a few low-cost missions, some academic institutions have assumed ful I responsibility for operations and com- manding. These missions present an information tech- nology security conundrum, for they have been extremely successful. MODELING,THEORY, AND DATA ASSIMILATION Modeling and theory need to be integrated into on- going research. Because the terrestrial magnetosphere's reconfiguration time scale is tens of minutes, far shorter than satellite orbit periods of hours to tens of hours, data sampl i ng i n Earth's magnetosphere wi 11 always be sparse THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS and i Incomplete. For th is reason, theoretical models and global simulations play a crucial role by forming a framework of understanding and context for the obser- vations. The modeling and observations need to be wed- ded closely via data assimilation in global models. This willensure that the modelsareproperlyconstrainedby the observations and can provide a suitable basis for extrapolating the observations to characterize the state and dynamics of the whole system. Because of the central role that theory and global models play, support for them needs to be robust and sustained. Global simulation codes require teams of re- searchers, each with specialized expertise in the under- lying physics, in numerical techniques, in visualization, and in user interfaces. To attract and maintain qualified researchers for efforts of this scope, the efforts cannot be supported by small (<$100,000) 3-year research grants but must be supported by larger grants (>$300,000 per year) for longer durations (5 years). It is also critical that more than one code be developed and used, because different techniques can sometimes lead to different be- havior in the simulations, and comparisons between dif- ferent codes are essential to identify consistent behavior potentially reflecting the real behavior of the system. Theory, simulation, and modeling will also become increasingly instrumental in the planning and implemen- tation of future missions. Understanding the character of the measurements required and the degree of improved understanding afforded by them and assessing the num- bers and locations of observations to most efficiently achieve definitive results will require detailed analysis with models. Mission definition and design will there- fore need to draw on the modeling resources of the community. Reliance on models will continue through- out each phase of future missions, including data analy- sis and assimilation. The dependence of future mission success on modeling underscores the need for sustained and substantial support for this effort. The increasingly integral role played by models in data analysis implies that community access to models is another aspect of the theory, modeling, and simula- tion work that needs to be supported. As discussed in the section "NOAA: Transitioning New Operational Ob- serving Platforms and Models," modeling is an area that is very appropriate for coordination with NOAA, which needs operational models. Furthermore, even in the arena of pure scientific inquiry, such coordination and community availability are important. Under NSF the GEM program has made initial strides in this direction, but making state-of-the-art models available to the com- munity remains a challenging task that requires re-
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS sources as well. Attempting to achieve this objective by requiring modeling teams to make their models avail- able is manifestly the wrong approach, since these teams are already hard-pressed to develop robust models. Rather, the effort to convert research models into community models is a separate task, which requires support for developing interfaces and computational architecture. In many ways the community model is an intermediate step in the conversion of models to opera- tional use. Support for this task should therefore derive not only from basic science, which is its primary pur- pose, but also from those agencies with an interest in developing more robust, physics-based models for pre- diction and forecasting. Support for theory and model ing is therefore a natu- ral area for interagency coordination. The benefits of modeling extend across all areas of interest, from basic science to prediction and forecasting, to mission devel- opment and planning. All of the relevant agencies- NSF, NASA, NOAA, and DOD have a vested interest in maintaining a strong theory and modeling effort, and they should find ways to coordinate their activities to ensure that support is provided in a coherent way that add resees the concerns descri bed above. TECHNOLOGY DEVELOPMENT The technological challenges for future solar-terrestrial missions are substantial and will require an effort dis- tinct from SR&T, including an SEC program similar to the Planetary Instrument Definition and Development Program of the planetary community. The primary chal- lenge for future magnetospheric missions will be meeting the need for constellation-class observations. For a new generation of spacecraft, the task is to design and develop a spacecraft architecture that can realize dramatic economies of scale even in limited production runs (tens of units). How low the ultimate cost per unit can go is not known, but the cost of the Iridium satellites, which were quite large, was ultimately reduced almost to $5 mil- lion. There are no fundamental technological reasons why a smaller platform could not be designed to cost less than this, but the task faces significant systems engi- neeri ng, management, i Integration, and testi ng problems. It is not insurmountable, however, and is the type of ambi- tious but achievable goal that should be a focus for NASA or DOD. The New Millennium Program has been suc- cessful in developing spacecraft technologies and it would seem most appropriate for it to focus some of its techno- logical investments on enabling constellation missions. 1 21 A comparable development effort is required to gain the ability to deliver tens of calibrated scientific instru- ments. Similar challenges of system engineering, man- power management, integration, and testing activities confront instrument builders contemplating the delivery of large quantities of instruments. Again, although the task is not an easy one, it does not appear to be impos- sible, and an instrument incubator program would pro- vide a mechanism to fund the long-lead-time develop- ment of instrument technologies for this purpose. For both the spacecraft and instrumentation devel- opment efforts, proper consideration must be given to an inherent feature of constellation-class missions- namely, that the large number of spacecraft and mea- surement points mitigates risk concerns and relieves the demands on instrument performance. The risk to the mission posed by the failure of a single spacecraft unit is extremely low, because the science return from, say, 45 satellites is nearly the same as that from 50. Because the redundancy is built into the constellation concept itself, one can accept single-string concepts in the spacecraft design. In a similar way, the science return is enhanced primarily by the large number of distributed measure- ments rather than by the high precision of the measure- ments, so that the requ i remeets for i nstru ment perfor- mance relative to that demanded for single-satellite missions should be critically examined. Experience with non-science-grade instrumentation strongly suggests that individual instruments performing at a much lower level can yield dramatic scientific advances when deployed in constellations. Finally, innovative and commercial solutions to spacecraft communications should be encouraged to reduce mission operations costs. Requiring the use of already overloaded systems such as the Deep Space Network for satellite tracking and communications for constel I ation missions is patently u nworkable because of the enormous operating costs that such an approach necessarily entails. Innovative, automated communica- tions approaches exist for Earth-orbiting satellites; such approaches were used very successfully for missions such as Freja and FAST and are being applied for other programs. These low-cost approaches to satellite com- munications and tracking need to be expanded aggres- sively to support constel ration missions. DATA ANALYSIS, DISSEMINATION, AND ARCHIVING The analysis, dissemination, and archiving of data acquired from NASA and non-NASA missions as well as
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1 22 from ground observatories and networks are of para- mou nt i mportance to successfu I Iy ach ievi ng the science advances descri bed above. G iven that the i nterrel ated data sets to be acquired will be complex and more diffi- cult to analyze than any acquired previously, the re- sources devoted to their analysis will need to be more substantial than those for earlier missions. The man- power that needs to be brought to bear will be corre- spondingly greater, and the best way of mobilizing this expertise will be to ensure that the data are available community-wide. Data dissemination is therefore a key element of future research that advances in information technology have made much easier than in the past. The experience with missions such as ACE, SOHO, and IMAGE demon- strate that electronic dissemination of data works ex- tremely well and facilitates community involvement in their analysis. There is no reason this success cannot carry over into the next decade with equal or greater success. Given that the missions envisioned in the coming decade will not be superseded or repeated in the fore- seeable future, the preservation of their data for subsequent analysis is critically important. The standard- ization system developed for the ISTP data exemplifies the level of commonality that will be needed for these new data sets. The standardization should be extended to ground data sets as well, so that their community use can be equally widespread. Standardization is also cru- cial for preservation of the data sets. While it is expected that the distributed data systems associated with differ- ent investigators and investigations will be maintained for some period of time after the prime mission or obser- vation campaign, a centralized repository for the data will also be required and needs to be supported. It is almost certain that the number of basic issues that these data can be used to resolve will not be exhausted in the normal mission or observation lifetime of the spacecraft or the facilities used to obtain the data.8 EXTENDED MISSIONS It is widely recognized that extended missions can provide a high science return for modest additional investment, and they are strongly encouraged. The panel See NRC, 2002, Assessment of the Usefulness and Avai/abi/ity of NASA's Earth and Space Science Mission Data, National Academy Press, Washington, D.C., pp. 41~4. THE SUN TO THE EARTH AND BEYOND: PANEL REPORTS endorses the practice of giving priority to those candi- dates for extension that most clearly support new research missions and strengthen or expand the science achieved. However, the costs of mission operations and data acquisition could be reduced considerably if track- ing and communications for extended missions could be transferred to commercial or academic institutions at the discretion of the mission PI or project management. The use of this option is consistent with the philosophy of extended missions since their prime mission objec- tives would already have been achieved, fulfilling their intended charter. If the cost of extending missions could be significantly reduced and the pressure on mission operations and data analysis resources relieved to allow more simultaneous operations, a broader array of pro- ductive observatories could be maintained for magneto- sphere-solar wind interaction science. ADDITIONAL READING A strategy for the conduct of space physics research has been set down in a number of reports by the NRC's Space Studies Board and its predecessor, the Space Sci- ence Board. These reports i nc I ude the fo I I owi ng: Space Science Board, National Research Counci 1. 1985. An Implementation Plan for Priorities in Solar-System Space Physics. National Academy Press, Washington, D.C. Space Science Board, National Research Counci 1. 1983. The Role of Theory in Space Science. National Academy Press, Washington, D.C. Space Science Board, National Research Counci 1. 1 980. Solar-System Space Physics in the 1980's: A Research Strategy. National Academy of Sciences, Washington, D.C. Space Studies Board, National Research Counci 1. 1995. A Science Strategy for Space Physics. National Academy Press, Washington, D.C. Space Stud ies Board and Board on Atmospheric Sciences and Climate, National Research Council. 1991. Assessment of Programs in Solar and Space Physics—1991. National Academy Press, Washington, D.C. The research in this field is summarized in both textbooks and conference proceedings, including the fol lowi ng:
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PANEL ON SOLAR WIND AND MAGNETOSPHERE INTERACTIONS M.G. Kivelson and C.T. Russell (eds.~. 1995. Introduction to Space Physics. Cambridge U n ive rs ity P ress, N ew Yo rk. A. Nishida, D.N. Baker, and S.W.H. Cowley (eds.~. 1998. New Perspectives on the Earth's Magnetotail. Monograph 105. American Geophysical Union, Washington, D.C. B. Hultqvist, M. Oieroset, G. Paschmann, and R. Treumann (eds.~. 1999. Magnetospheric Plasma 1 23 Sources and Losses. Kluwer Academic Publishers, Dordrecht. S.l. Ohtani, R. Fujii, M. Hesse, and R.L. Lysak. 2000. Magnetospheric Current Systems. Monograph 118. American Geophysical U n ion, Wash i ngton, D.C. P. Song, H.J. Singer, and G.L. Siscoe (eds.~. 2001. Space Weather. Monograph 1 25. American Geophysical U n ion, Wash i ngton, D.C. Note added in proof: New Horizons, the first Pluto probe, has been selected as the first mission in NASA's New Frontiers program and is now in development. The probe, which will arrive at Pluto in 2015, carries solar wind plasma and energetic particle detectors in addition to its suite of remote sensing instruments and a dust experiment. In addition to its reconnaissance of the Pluto-Charon system, the probe is expected to encounter one or more Kuiper Belt objects.
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Representative terms from entire chapter: