NEXT MOVE IN GEOSPACE
What is the origin of turbulent forces that sweep by Earth, becoming
visible as auroral displays, confounding radio broadcasts, civilian and military
electronics, power distribution, and satellite systems? Invisible magnetic
storms can induce currents in long, power-transmission lines, affect power
station transformers, and even cause power blackouts.
Disturbances in nearby space are consequences of the reactions in
Earth's neighborhood to the violent behavior of the Sun. The past 20 years of
space observations have led to a quiet but remarkable revolution in concepts
of the Sun—Earth system. No longer is Earth visualized as simply a body traveling through a vacuum around the Sun and being warmed to life by its visible emissions. Rather, the data from spacecraft show that Earth on its course is plowing through an energy-laden flood from the Sun — magnetic fields, energetic charged particles, radiations throughout the electromagnetic spectrum, and electrified gases (called plasmas) flowing at speeds up to 1000 kilometers per second (2.2 million mph). Collisions with Earth's magnetic envelope create a dynamic environment surrounding Earth that reaches far beyond previous environmental concepts. This region, called geospace, extends to millions of kilometers around Earth and contains the atmosphere, the ionosphere, the magnetosphere and the near-Earth interplanetary medium.
Geospace is an integrated, strongly interactive system throughout which
energy is continuously being generated, stored, transformed and released. Not only do geospace processes affect Earth's atmosphere and ground systems, but geospace is now known to be representative of plasma systems commonly found throughout the universe.
Data from single spacecraft have led scientists through evolutionary
stages — first discovery, then exploration sufficient to provide a schematic
representation of the solar—terrestrial environment like the one to the right. It is now time to proceed to a comprehensive understanding of geospace dynamics with a multi—spacecraft mission that can return coordinated, simultaneous observations.
Recent advances in geospace knowledge and satellite technology make
it possible for the National Aeronautics and Space Administration to propose, for the mid-1980's, a four-satellite mission called Origins of Plasma in the Earth's Neighborhood, or the OPEN Program. Hundreds of investigators in the United States and in more than a dozen other nations are poised to participate in the first systematic, quantitative study of the flow of plasma and energy through geospace.
DISCOVERY OF GEOSPACE
Before the 1950's, little was known about the region outside the thin
cocoon formed by Earth's atmosphere and ionosphere. The existence of a
magnetic field had been known for centuries. It was believed to extend into
the void of space with a shape much like the field of a simple bar magnet. There was evidence for some cause-and-effect association between such episodic events on the Sun as solar flares and events at Earth such as brilliant enhancement of auroral lights at high latitudes and transient disturbances in Earth's magnetic field. But neither the terrestrial phenomena nor their apparent connection with the active Sun was understood. The successful launching of artificial satellites, begun in 1957, dramatically changed this situation. The in situ observations ushered in a series of new and exciting discoveries about Earth's space environment.
Using simple radiation counters on Explorer—1, Professor James Van
Allen and his colleagues were startled to discover very energetic charged
particles trapped in belts around the Earth far above the upper atmosphere.
Later, spacecraft traveling to other planets discovered that essentially
all of interplanetary space is filled with a hot, tenuous plasma continuously
flowing away from the Sun behaving as though it were an electrified wind. When this solar wind strikes Earth's magnetic field, a shock wave forms upstream of the Earth. The shape of the magnetic field is compressed on the dayside and blown into an extended tear-drop on the nightside. Early satellite measurements also indicated that the magnetic field carved out a cavity in which large amounts of energy could be stored and whose flow was linked to the Earth by terrestrial magnetic field lines.