The solar wind does more than supply some of the particles for a magnetosphere. The pressure of the solar wind also pushes on and compresses the magnetosphere. The size and shape of a planet’s magnetosphere can change a great deal, depending on how the solar wind is blowing at any particular time. Planetary magnetic fields also divert the solar wind, which flows around magnetospheres the way a stream flows around boulders. Just as a rock in a river creates a wake that extends downstream (Figure 10.19a), the magnetosphere of a planet produces a wake that can extend for great distances. The wake of Jupiter’s magnetosphere (Figure 10.19b) extends more than 6 astronomical units (AU) outward from the planet—well past the orbit of Saturn. Jupiter’s magnetosphere is the largest permanent “object” in the Solar System, surpassed in size only by the tail of an occasional comet. The magnetic wakes of Uranus and Neptune have a curious structure. Because of the tilt and the large displacements of their magnetic fields from the centers of these planets, their magnetospheres wobble as the planets rotate. This wobble causes the wakes of the magnetospheres to twist like corkscrews as they stretch away from the planets.