Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 1
Introduction
To understand the relationship between natural events on
Earth and changes in the Sun has been one of marks enduring
intellectual quests. The scientific discipline we now know as so-
lar system space physics is the modern culmination of efforts to
comprehend the relationships among a broad range of naturally
occurring physical ejects including solar phenomena, terrestrial
magnetism, and the aurora. Understanding the solutions to these
basic physics problems requires the study of ionized gases (plas-
mas), magnetohydrodynamics, and particle physics.
Space physics ~ an identifiable discipline began with the
launch of the first earth satellites ~ the late l950s and the dis-
covery in 1958 of the Van Allen radiation belts. The phenomena
associated with this field of study are among the earliest recorded
observations in many parts of the world. The ancient Greeks were
puzzled by the refires in the upper atmosphere that we now call
the aurora; there are several possible references to the aurora in
ancient Chinese writings before 2000 B.C.; there are also passages
in the first chapter of Ezekiel with vivid descriptions of what we
now recognize as auroral formations.
The observation of sunspots by Galileo in 1610 led to the
eighteenth-century discovery of the 11-year solar sunspot cycle
and the recognition that there was a connection between sunspot
1
OCR for page 2
2
variability and auroral activity. The large reduction of sunspots
during the second half of the seventeenth century during a period of
unusually coo} weather in Europe suggests a tantalizing connection
between some aspects of solar activity and climate.
This possible link between solar activity and terrestrial phe-
nomena could not be studied in detail until this century. We now
know that, in addition to the atmosphere that surrounds us, there
exists a region, at higher altitudes, consisting of an electrically
conducting plasma permeated by the Earth's magnetic field. It
is called the "magnetospheres because its structure and many of
its processes are controlled by the magnetic field. Since the early
years of the space program, we have learned that the Sun has
its own magnetosphere consisting of a hot (million degree KeIvin)
magnetized plasma wind (the solar wind) that extends beyond the
orbits of the planets and fills interplanetary space, forming a dis-
tinct cavity in the nearby interstellar medium the "heliosphere."
Using knowledge gained over the past 25 years, we can now
begin to identify some of the physical mechanisms linking the
Sun to our near-Earth environment. For example, motions in the
convective layers of the Sun are believed to generate the solar
magnetic field and solar wind variations; these in turn affect the
Earth's magnetosphere and regulate the amount of plasma energy
incident on the Earth's polar caps. Associated magnetospheric
activity drives strong winds in the upper atmosphere and may in-
fluence the dynamical and chemical composition of the mesosphere
and stratosphere as well. The upper atmosphere, in turn, is the
major source of heavy ions in the magnetosphere. Further, current
research suggests that small percentage changes (about 0.5 per-
cent) in the total energy output of the Sun (the solar "constant")
may influence short-term terrestrial climate. These and other
speculative suggestions should be addressed as part of a compre-
hensive research program in solar-terrestrial physics because of
their potential importance for the Earth. Indeed, the Earth and
its space environment contain coupled phenomena and need to be
studied as a system from the Sun and its plasma environment to
the Earth's magnetosphere, atmosphere, oceans, and biota.
Discoveries in solar and space physics over the past 25 years
have inspirer} a number of developments in theoretical plasma
physics. Concepts in charged particle transport theory, developed
to describe the behavior of energetic particles in the solar wind
and magnetosphere, are routinely used in studying extragalactic
OCR for page 3
3
radio sources and laboratory plasmas. Magnetic field reconnection
Convolving the explosive conversion of electromagnetic energy into
particle energy), collisioniess shock waves, electrostatic shocks,
and hydromagnetic turbulence are also among the fundamental
plasma phenomena first studied and elucidated in analyses of solar
and space plasmas.
Subsequently, these and other concepts have found application
to related branches of plasma physics, such as nuclear fusion. The
development of space plasma physics since the 1960s has influenced
nuclear fusion research. Pitch-angle scattering and magnetic re-
connection are now took of laboratory plasma theory, while ideas
developed in fusion work have influenced space plasma science
in unportant ways. Thus, the language of plasma physics links
two very important scientific endeavors: the search for a limit-
less supply of clean energy through thermonuclear fusion and the
exploration and understanding of our solar system environment,
most of which is in the plasma state.
New concepts developed in studies of solar and space plasmas
find important applications to astrophysical problems as well as
to laboratory plasmas. For example, the structure of collision-
less shock waves can be resolved only by spacecraft instruments.
Such shocks are invoked In some current models of star formation.
Furthermore, the study of propagating interplanetary shocks has
contributed to understanding and modeling of acceleration of cos-
rnic rays by shocks. Particle acceleration via direct electric fields,
observed in the Earth's magnetosphere, has been invoked in accel-
eration models of pulsar magnetospheres. The subject of cosmic-
ray transport owes much to detailed in situ studies of the solar
wind. Some stellar winds are thought to be associated with stars
that, like the Sun, have convective outer layers, while winds of
more massive stars are driven by racliation pressure. Explanations
of physical phenomena in astrophysical objects that will remain
forever inaccessible to direct observation rest heavily on insights
obtained through studies of solar system plasmas accessible to in
situ observations.
Even though space plasma physics AS a mature subject, new oh
servations continue to reveal facets of the physics not recognized
previously. For example, observations of "spokes in Saturn's
rings seemed to highlight the importance of electromagnetic forces
On charged dust particles. Similarly, the interaction of dust and
OCR for page 4
4
plasma in comets is thought to be a central element in understand-
ing the formation of comet ion tails. Such observations have given
rise to the study of "gravito-electrodynamics~ in dusty plasmas,
which in turn has important applications to the understanding of
the formation and evolution of the solar system, as pointed out by
Alfven some years ago.
The unclerstand~ng of the near-Earth space environment is
not only a basic research enterprise; it also has extremely impor-
tant practical aspects. Space is being used increasingly for many
different scientific, commercial, and national security purposes.
Well-known examples include communications and surveillance
satellites and such scientific platforms as the Space Telescope and
the Space Station. These space vehicles must function contin-
uously in the near-Earth environment, subject to the dynamic
variations of the heliosphere, the magnetosphere, and the upper
atmosphere. It is well established that many spacecraft systems
and subsystems exhibit anomalies, or even failures, under the influ-
ence of magnetospheric substorms, geomagnetic storms, and solar
flares. Processes such as spacecraft charging and "single-event
upsets" (owing to highly ionizing energetic particles) in processor
memories make the day-to-day operation of space systems diffi-
cult. Finally, these aspects of the near-Earth environment become
particularly important in view of the planned long-term presence
of man in space. The complement of programs outlined in this
report will allow us to mode! the global geospace environment and
will thus allow us to develop a global predictive capability. This,
in turn, should permit substar~tial improvements in our abilities
to operate all space-based systems in the near-Earth region.
We have advanced well beyond the exploratory stages in solar
and space physics, with some notable exceptions the solar inte-
rior, the environment near the Sun where the solar wind is accel-
erated, the atmospheres of some of the planets, and the boundary
of the heliosphere. The phenomenological approach appropriate
to a young science still in its discovery phase ho progressed to a
more mature approach where focused and quantitative investiga-
tions are made, interactive regimes are studied, and theory and
modeling play a central role in advancing understanding.
The future solar and space physics program will require tools
and techniques substantially different from those of the past. Con-
tinued progress will require development of complex, multifaceted,
OCR for page 5
5
experimental and observational projects that will be technologi-
cally challenging. The task group believes that the anticipated
scientific contributions fully justify the proposed undertakings.
The purpose of this report is to develop an overall program of
space research that will address the most significant topics in this
discipline, that will clearly define the priority of investigations,
and that will be affordable by NASA.
Several other National Research Council reports that are re-
lated to this document have appeared in recent years. The Colgate
report (Space Plasma Physics: The Study of Solar-System Plas-
mas, 1978) reviewed the status of the field and concluded that
"space plasma physics is intrinsically an important branch of sci-
ence." The Kennel report (Solar-System Space Physics in the
1980~: A Research Strategy, 1980) laid out the scientific goad and
objectives for the field. Other reports (Solar-Terrestrial Research
in the 1980s, 1981; National Solar-Terrestrial Research Program,
1984) integrated the ground-based segment of the field and stated
priorities for its unplementation. The Physics of the Sun (1985)
reviewed the scientific content of solar physics and described future
research directions. A Strategy for the Explorer Program for Solar
and Space Physics (1984) emphasized the need for a revitalized
Explorer program for solar and space physics and outlined several
specific examples of scientific investigations. An Implementation
Plan for Priorities in Solar-System Space Physics (1985) updated
the scientific goals and objectives of solar and space physics re-
search from the Kennel report and developed the prioritized im-
plementation plan for NASA that would accomplish these aims.
Chapter 2 of the task group's report reviews those scientific
objectives, and Chapter 3 describes the status of solar and space
physics expected in 1995, assuming a number of space programs
proceed according to present plans.
In Chapter 4, a variety of new programs intended for imple-
mentation after 1995 are identified that will employ new techniques
for the investigation of outstanding scientific questions, will ad-
dress new questions that arise as natural extensions of previous
studies, and will allow the pursuit of new topics that we cannot
address at present. This chapter also describes the developments
in technology that will be required for the era after 1995; Chapter
5 summarizes the technology needs.
This report also contains a number of appendixes—reports (or
excerpts of reports) of workshops that were conducted by NASA in
OCR for page 6
6
support of this study. The workshops brought together scientists
from diverse backgrounds to explore new ideas and technologies
for space science research. Those efforts were an important part
of the study they were largely responsible for some of the new
initiatives proposed in Chapter 4.
Representative terms from entire chapter:
plasma physics
