Io and Jupiter constitute a moon-planet system that is unique in our solar system. Io is the most volcanically active planetary body, while Jupiter is the first among the planets in terms of size, mass, magnetic field strength, spin rate, and volume of the magnetosphere. That Io is electrodynamically linked to Jupiter is known for nearly four decades from the radio emissions. Io influences Jupiter by supplying heavy ions to its magnetosphere, which dominates its energetic and dynamics. Jupiter influences Io by tidally heating its interior, which in turn drives the volcanic activity on Io. The role of Io and Jupiter in their mutual interaction and the nature of their coupling were first elaborated in greater detail by the two Voyagers flybys in 1979. Subsequent exploration of this system by ground-based and Earth-satellite-borne observatories and by the Galileo orbiter mission has improved our understanding of the highly complex electrodynamical interaction between Io and Jupiter many fold. A distinct feature of this interaction has been discovered in Jupiter's atmosphere as a auroral-like bright emission spot along with a comet-like tail in infrared (IR), ultraviolet (UV), and visible wavelengths at the foot of Io flux tube (IFT). The HST and Galileo and Cassini imagining experiments have observed emissions from the Io's atmosphere at UV and visible wavelengths, which could be produced by energetic electrons in IFT. In this paper an overview on these aspects of the Io-Jupiter system is presented, which by virtue of its electrodynamical coupling, has implications for the extra-solar planetary system and binary stars.

7 pages, 4 figures, Proc.36th ESLAB Symposium "Earth-Like Planets and Moons", June 3-7, 2002, ESTEC, The Netherlands, ESA SP-514, Ed. Bruce Battrick