In the inner magnetosphere, the Galilean satellites have a powerful influence on the populations of fast-moving particles. During the Voyager 1 encounter, the primary effect was observed at Io, where the satellite apparently sweeps up energetic electrons. In the million-volt energy range, these particles are depleted near Io, with peaks observed both inside and outside the satellite’s orbit. Voyager 2 passed close to Ganymede, and here also major effects were seen, with the satellite apparently absorbing electrons. In the wake created by the motion of the co-rotating plasma past Ganymede, the particle populations showed large and complex variations. [Illustration: The magnetosphere of Jupiter can be “seen” from Earth by its emissions at radio wavelengths. The recent development of imaging radio telescopes in Great Britain, The Netherlands, and the United States allows frequent mapping of the large-scale features of the innermost magnetosphere, inside the orbit of Io. These six images showing one rotation of Jupiter were obtained near the time of the Voyager 1 flyby by Imke de Pater at the Westerbork Radio Observatory near Leiden. The brightest emission is shown by dark red or black. The size of the planet is indicated by a dotted white circle. The tilt of the magnetosphere relative to the rotation axis of the planet can be seen by the wobble of the magnetosphere as Jupiter rotates.] Just inside the Jovian magnetosphere is the “hot spot” of the solar system: a 300-400 million degree plasma detected by Voyager 1 while it was still about 5 million kilometers from Jupiter. T. P. Armstrong commented, “Even the interior of the Sun is estimated to be less than 20 million degrees.” S. M. Krimigis added that the temperature of this plasma is “the highest yet measured anywhere in the solar system.” Fortunately for Voyager, this region of incredibly hot plasma is also one of the solar system’s best vacuums. The spacecraft was in little danger because the bow shock protects this region from the solar wind, and most of the particles in Jupiter’s magnetosphere are held in much closer to the planet. [Illustration: Each Voyager passed through the boundaries of the magnetosphere—the bow shock (BS) and the magnetopause (MP)—on both the inbound and the outbound legs of its passage through the Jovian system. In this diagram, the heavy solid line represents the spacecraft trajectory, as seen looking down from the north. Also shown are the positions of the bow shock in March and of the magnetosphere in both March and July.]