Magnetospheric imaging: Promise to reality

Measurements of the plasmas, energetic particles, and electric and magnetic fields within the Earth's magnetosphere have been made with ever greater coverage and precision throughout the past 46 years; but until recently, no images of this important environment were available. However, for 2 decades or more, theoretical estimates, data from sounding rockets, and background signals from orbiting instruments designed for in situ ion measurements accumulated to show that most of the plasmas contained in the inner magnetosphere could be imaged if new instruments designed for the purpose could be placed in a suitable high-altitude orbit. With the launch of the NASA IMAGE satellite in March 2000 the promise of magnetospheric imaging began to be realized. IMAGE provides nearly continuous imaging of the inner magnetosphere on a nominal timescale of 2 min. The discoveries made by IMAGE during its first 5 years of operation are reviewed in this paper.