Being so volcanic, and so close to Jupiter, Io is a major player in the Jovian magnetosphere. The active volcanoes spew sulfur dioxide and other materials out into space, where they then enter the Jovian magnetosphere as plasma. The result of this plasma is to create a "Torus" (doughnut-shape) of dense plasma that roughly follows Io's orbit around Jupiter. This dense plasma is a radiation hazard to any spaceships that might enter it. Although the Galileo spacecraft mademany passes through the Io Torus in 1999, and somehow managed to survive.