Earth's magnetism has captured human attention since the first innovator noticed that a freely moving piece of magnetized iron would always align itself with Earth's poles. Throughout most of history, the origins and physics of this magnetism remained mysterious, though by the 20th century certain things had been learned by measuring the magnetic field at Earth's surface. These measurements suggested that Earth's magnetic field was consistent with that of a giant bar magnet embedded deep inside Earth. However, the magnetic field observed at the surface of our planet is constantly fluctuating. During the 1930s scientists pioneered explanations that such fluctuations were due to streams of particles from the sun striking and becoming entrapped within Earth’s magnetic field.
Truly understanding Earth's magnetic environment, however, required traveling to space. In 1958, the first US rocket -- known as Explorer 1 and led by James Van Allen at the University of Iowa -- was launched. By providing observations of a giant swath of magnetized radiation trapped around Earth, now known as the Van Allen Belts, Explorer 1 confirmed that Earth's magnetic environment, the magnetosphere, was not a simple place. We now know that it has a complex shape – compressed on the side facing the sun, but stretched out into a long tail trailing off away from the sun -- affected as much by incoming material from the sun as Earth's own intrinsic magnetism. This magnetic field constantly fluctuates in response to both internal instabilities and events on the sun. It also provides a home for a host of electrified particles spiraling through this complex system.
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