It is hoped that scientists and historians familiar with those areas will add their histories to the record.
- (1) Instrumentation:
- e.g. magnetometers [Heppner, 1963; Ness, 1970], electric field probes [Fahleson, 1967; Cauffman and Gurnett, 1972]; charged particle detectors and mass spectrometers. A sampling of articles or collection of articles (only first paper cited) on specific spacecraft and their instruments includes Injun 3 [O'Brien et al., 1964], the OGO series [Ludwig, 1963; Bostrom and Ludwig, 1966], Atmosphere Explorer 1 [Dalgarno et al., 1973], S3 or Explorer 45 [Longanecker and Hoffman, 1973], International Sun-Earth Explorer (ISEE) 1 and 2 [Ogilvie et al., 1978], Active Magnetospheric Particle Tracer Experiment (AMPTE) [Acuna et al., 1985] and Dynamics Explorer (DE) 1 and 2 [Hoffman et al., 1981]
- (2) Wave phenomena in the magnetosphere:
- [Shawhan, 1979], including whistlers [Helliwell, 1965; Al'pert, 1980; see also BH-1], auroral kilometric radiation [Gurnett, 1974], micropulsations [Hughes, 1983; Lanzerotti and Southwood 1979], 3/2 cyclotron frequency emissions, auroral hiss and other modes.
- (3) The bow shock of the Earth:
- [Dobrowolny and Formisano, 1973; Greenstadt and Fredricks, 1979; Kennel et al., 1985; Kennel, 1987].
The preceding brief history only covers scientific aspects of magnetospheric physics. In addition, magnetospheric physics also has institutional, personal and social aspects.
An institutional history traces the evolution of the field and its accomplishments in the framework of the organizations which led it, of institutions, committees, executive decisions and of the individuals involved in them [e.g. Ezell, 1988]. An instructive example is "Beyond the Atmosphere" [Newell, 1980], an account of NASA's effort in space science 1958-1975 by a former NASA Associate Administrator who led those efforts for many years. It covers all fields, not just magnetospheric physics, but where its subject overlaps this narrative, it often paints a strikingly different picture.
Personal histories are first-hand accounts by participants. At best they give an unequalled intimate view of the discovery process. At worst they are carefully filtered, and their writers also do not always have the necessary discrimination and writing skill. Such deficiencies would matter less if such accounts were plentiful enough to allow comparison and cross-checking: sadly, only very few exist, which makes them particularly valuable, and their coverage of the field is rather patchy [Van Allen, 1983a, 1990 ; Eather, 1980, chapt. 19; Frank, 1990; Gombosi et al., 1994].
The community of magnetospheric physics has never been properly studied. It is relatively small: the membership of AGU's Section on Space Physics and Aeronomy stands around 3000 (1980--1604; 1985--1922; 1990--about 2600). This also includes scientists whose main interests are the upper atmosphere, interplanetary space and the Sun, but on the other hand may miss many workers outside the USA. As noted, this discipline arose from three main sources--plasma physics, work with rockets, balloons and ground instruments, and the study of cosmic rays. It began assuming its separate identity in 1959, when (led by James Van Allen) it chose the American Geophysical Union (AGU) as its home organization and the Journal of Geophysics Research (JGR) as its main means of communication.
Today that community is in a serious crisis, made evident, for instance, by a frustrating slow-down in the rate of discovery during the last decade 1984-1994. It may be instructive to speculate about the causes of this slow-down and its implications to the community's future.
One can roughly divide the record of magnetospheric physics in the space age into three periods: (1) the era of discovery, 1958-1965; (2) the expansion stage, 1965-1977; and (3) the era of stagnation, setting in gradually after 1977.
In the first period, the large-scale morphology was surveyed--particle populations, the main regions and the boundaries. In addition, this was the beginning of our ideas on convection and reconnection.
In the expansion stage, details were filled in--correlations with the IMF, substorm morphology, Birkeland currents, E//, auroral kilometric radiation, O+ ions in the ring current, ion beams and conics, injections at synchronous orbits, etc. Additional theoretical ideas were also introduced--the NENL theory of substorms, the Brice-Nishida theory, the Coroniti-Kennel theory, theories on the consequences of convection by Schield et al. and by Vasyliunas, and others not touched on here.
Since 1977 some observational details were added., e.g., about the magnetosphere with IMF Bz > 0, about the distant tail (by ISEE-3 and Geotail), the ring current (by AMPTE-CCE) and the plasma sheet (by ISEE 1-2 and AMPTE-IRM). Theories, too, have improved, but the main problems continue to elude us--the nature of substorms, structure of the open magnetopause, specifics of reconnection, convection in the tail, global structure during northward IMF and similar questions.
Why this apparent pause? Three possible reasons will be noted here: the nature of discovery, the choice of mission strategy and a missed transition in the evolution of magnetospheric physics.
(1) There exist two kinds of discovery in this field--discovery of new problems and discovery of solutions. The heady early period seemed packed with discoveries, but most of them belonged to the first kind. It was inevitable that satelites passing for the first time through the radiation belt, the magnetopause, cusp, bow shock or plasma sheet would make an important discovery; but while new phenomena accumulated, explanations of their features lagged, and they still do. In laboratory physics, when a new phenomenon is discovered, one can design experiments to focus on it; but magnetospheric physics, in common with the rest of geophysics, offers few controlled experiments and depends primarily on observations. Thus progress towards explanations is slow and uncertain.
(2) The cost of spacecraft is high, both in funds and efforts. All early space missions therefore involved isolated spacecraft, but it seems that the amount of information available from this mode is just about exhausted. Magnetospheric physics is synergistic: to understand global behavior, a coordinated network of satellites is needed.
After 1977 the field was ripe for such a network, but unfortunately the use of isolated spacecraft is still the norm. The Russian Interball (two spacecraft launched in 1995) and the European Cluster (due in 1996) each contain four coordinated spacecraft and promise to give valuable results, in particular in conjunction with the "Wind" and "Polar" spacecraft of the US. But a meaningful coverage demands a much larger number of platforms, as was made clear by CDAWs, Coordinated Data Analysis Workshops [e.g. Manka et al., 1982], which tried to analyze specific events and generally found that even with all available data, important questions could not be resolved.
(3) As noted, the magnetospheric community first assumed a separate identity around 1960. Independent space physics departments were established at selected universities--Iowa, UCLA, Rice, Alaska, then more--and space research groups were set up at NASA, Johns Hopkins Applied Physics Lab., Los Alamos etc. As the community expanded in 1965-77, it also began raising its first generation of internally-trained scientists.
But something seemed missing. A community needs not only its institutional identity but also a core of its accumulated knowledge, set up in an orderly way that can be passed on. Research and symposia lead to review talks and papers, which in turn lead to textbooks and courses, telling "such-and-such we are pretty sure of and can teach, this-or-that is unclear or controversial, and here are the boundaries of our knowledge."
Even now, rather little of this process of distillation has taken place, especially in observations: in substorm morphology, for instance, there is surprisingly little that can be regarded well-established. Possible reasons are too long and too controversial to list here, but the result has been a narrowness of scope and a lack of broad vision which even now hamper further progress and further planning.
This review is altogether too short to properly describe what such "core knowledge" may contain. Still, one hopes it will give its readers, especially younger members of the community, a uniform historical framework of the overall structure of their field.
A draft of this article was given for review to a large number of scientists involved in the discoveries described here, most of whom provided useful comments. The author thanks A. Dessler, J. Heppner, P. Hart, W. Hess, R. Hoffman, E. Hones Jr., G. Ludwig, M. Peredo, H. Petschek, J. Slavin, E. Smith, J. Van Allen, M. Walt and R. Wolf for their help in compiling this review, as well as two editors and three referees of the journal.