Perhaps the largest structure in the solar system is the magnetosphere
of Jupiter. This is the region of space which is filled with Jupiter’s
magnetic field and is bounded by the interaction of that magnetic field
with the solar wind, which is the Sun’s outward flow of charged
particles. The plasma of electrically charged particles that exists in
the magnetosphere is flattened into a large disk more than 4.8 million
kilometers (3 million miles) in diameter, is coupled to the magnetic
field, and rotates around Jupiter. The Galilean satellites are located
in the inner regions of the magnetosphere where they are subjected to
intense radiation bombardment. It appears that Io is a source of the
sulfur and oxygen ions which fill the magnetosphere. Another
magnetospheric interaction is the electrical connection between Io and
Jupiter along the magnetic field lines that leave Jupiter and intersect
Io. This magnetic flux tube was examined by Voyager 1 and a flow of
about five million amperes of current was measured, which was
considerably more than anticipated. Voyager also discovered a new
low-frequency radio emission coming from Jupiter, which is possibly
associated with the Io torus.