Coupling of the Ionosphere and Magnetosphere at Other Planets and Moons in the Solar System

An important aspect of solar system plasma physics is the linkage and coupling of denser, colder ionospheric plasma found at planets and satellites with more energetic external plasma environments such as the solar wind and magnetospheres. How energy and momentum are exchanged depends on the coupling processes, and field-aligned electrical currents play an important role in these processes. The nature of the linkage obviously depends on the characteristics of the planets and of the external plasma. Particularly important is the existence of, or lack of, a significant intrinsic magnetic field for the solar system body of interest. For example, the strong magnetic fields at Earth, Jupiter, and Saturn carve out large magnetospheres within which the dynamics is enforced by current systems, some of which close in the respective planetary ionospheres. Auroral emission from the planetary or satellite upper atmospheres often, but not always, accompanies the field-aligned currents. Objects like Venus, and Saturn’s satellite Titan, have ionospheres but lack significant intrinsic magnetic fields, but the external plasma, such as the solar wind, still links with the ionospheres and upper atmospheres. A broad review of magnetosphere-ionosphere (MI) coupling at other planets will be given in this talk, but special attention will be given to Jupiter and to the Saturn/Titan system. A brief discussion of how Enceladus, and its water plume, affect Saturn’s magnetosphere will also be given. At Jupiter, rotation plus the Io source of plasma are the key determinants of the magnetospheric dynamics and the associated MI coupling and auroral emissions. Precipitation of energetic electrons from the middle magnetosphere is responsible for the main auroral oval at Jupiter, but both energetic electron and ion precipitation take place in the polar caps. X-ray emission observed from Jupiter’s polar regions appears to be due to the precipitation of energetic heavy ions from the outer magnetosphere and magnetopause region. The upcoming NASA mission to Juno will shed much light on Jovian MI coupling. Plasma in the ionospheres of non-magnetic bodies flows in response to thermal pressure gradients, magnetic forces associated with induced magnetic fields, gravity, and ion-neutral collisions. Magnetic fields are induced by the external interaction either in the ionospheres or near the “ionopause” boundaries. These fields are not only important for the dynamics but they also control the entry of external energetic particles into the upper atmosphere, thus affecting ionization rates and ionospheric composition and structure. The copious data returned from instruments on the NASA-ESA Cassini Orbiter has improved our understanding of Titan’s linkage to Saturn’s magnetosphere. Titan usually resides in Saturn’s outer magnetosphere, with occasional forays into the magnetosheath, and this determines the external plasma populations (electrons, protons, and water group ions such a oxygen ions) that can possibly be channeled into the upper atmosphere