Abstract :
Reconnection plays an important role in the energetics of the magnetospheres of both the magnetized and unmagnetized planets, but it seems to play the most dominant role in the dynamics of the magnetized planets. Most of our observations of magnetized planets have been obtained at Jupiter and the Earth. The magnetospheres of Earth and Jupiter both undergo substorm-like cycles as part of an unsteady magnetosphere-wide circulation despite the fact that they are driven by quite different processes: the solar wind interaction in the case of the Earth and mass loading by the moon, Io, in the case of Jupiter. Each magnetosphere provides lessons for the other and together they give a clearer insight as to how reconnection works at a magnetized planet. Most importantly the Alfven velocity controls the flow velocity of the accelerated plasma so the reconnection rate is very sensitive to the density. In regions in which the plasma density decreases away from a field reversing neutral sheet, the reconnection rate can increase with time as the neutral point moves from the high density to the low-density region. When regions of very low density are reached, reconnection appears to occur explosively. While most treatments of planetary magnetotails cover the behavior of a single neutral point, two or more neutral points may exist. In the Earthʹs magnetosphere these two neutral points can interact to control a variety of otherwise puzzling phenomena such as double onset substorms, pseudo breakups, and triggering of substorms by northward-turning IMF.
