Comparison of the sizes of magnetospheres of the outer planets, the Earth and Mercury. Boxes illustrate the relative size of the magnetospheres. The conical at the left of each planet represents the bow shock, whereas the swept-back lines represent the planetary magnetic field. (a) Mercury. (b) The Earth. (c) Saturn (left) and Jupiter (right). (d) Uranus or Neptune. Adapted from Kivelson & Russell (1995).