  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.
