Solar System Magnetospheres

This article proposes a short review of our present knowledge of solar system magnetospheres, with the purpose of placing the study of Saturn’s magnetosphere in the context of a comparative approach. We describe the diversity of solar system magnetospheres and the underlying causes of this diversity: nature and magnetization state of the planetary obstacle, presence or not of a dense atmosphere, rotation state of the planet, existence of a system of satellites, rings and neutral gas populations in orbit around the planet. We follow the “russian doll” hierarchy of solar system magnetospheres to briefly describe the different objects of this family: the heliosphere, which is the Sun’s magnetosphere; the “elementary” magnetospheres of the inner planets, Earth and Mercury; the “complex” magnetospheres of the giant planets, dominated by planetary rotation and the presence of interacting objects within their magnetospheric cavities, some of which, like Ganymede, Io or Titan, produce small intrinsic or induced magnetospheres inside the large one.We finally describe the main original features of Saturn’s magnetosphere as we see them after the Voyager fly-bys and before the arrival of Cassini at Saturn, and list some of the key questions which Cassini will have to address during its four-year orbital tour.