With the launching of Sputnik, Explorer 1, and the other early satellites, the new discipline of space physics was born, about 50 years ago. Although earlier ground-based observations had provided strong hints about the nature of our space environment above the upper atmosphere, those early satellites initiated a series of surprises and discoveries, including Van Allen's discovery of the Earth's radiation belts.
Young scientists were attracted to this new field, and it grew quickly. When the Journal of Geophysical Research was divided into two sections, in 1964, one section was devoted to space physics. The field explored not only new regions of space but also a new state of matter: the rarefied, fully ionized plasma that fills space and interacts intimately with magnetic fields.