FIGURE 1.1 The solar system and its nearby galactic neighborhood are illustrated here on a logarithmic scale extending from <1 to 1 million AU. The Sun and its planets are shielded by a bubble of solar wind—the heliosphere—and the boundary between the solar wind and interstellar plasma is called the heliopause. Beyond this bubble is a largely unknown region—interstellar space. NOTE: The G cloud is a cloud of interstellar gas near the Local Interstellar Cloud in which the solar system is embedded. SOURCE: Image and text adapted from NASA and available at Also see, “Living in the Atmosphere of the Sun,” at


have their own magnetospheres2 and atmospheres. These magnetosphere-atmosphere systems are often strongly coupled, and they mediate the solar wind interaction with the planet (or moon) in ways unique to each body. Moreover, as human exploration extends farther into space—by means of both robotic probes and human spaceflight—and as society’s technological infrastructure is linked increasingly to space-based assets and impacted by the dynamics of the space environment, the need to characterize, understand, and predict the dynamics of our environment in space becomes ever more pressing.

As a discipline, modern solar and space physics—now also referred to as heliophysics—can trace its origins back to the evening of January 31, 1958, when a Juno (Jupiter-C) rocket blasted into space, lofting the first U.S. artificial Earth satellite into orbit. This spacecraft, dubbed Explorer I, joined Sputnik II, a satellite that had been launched 2 months earlier by the Soviet Union. The Explorer I mission was truly groundbreaking because it carried a small scientific payload, prepared by a team of university researchers led by James A. Van Allen, that would make the first revolutionary discovery of the space age, namely, that


2 Earth’s magnetosphere is formed by the interaction of the solar wind and our planet’s intrinsic magnetic field.

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