 Strong volcanic eruptions on Io emit huge amounts of sulfur dioxide, a major part of which is dissociated into atoms and ionized by electron impacts and, to a lesser extent, solar ultraviolet radiation, producing ions of sulfur and oxygen.Further electron impacts produce higher charge state, resulting in a plasma of S+, O+, S2+, O2+ and S3+.These ions either escape from the satellite's atmosphere or are produced from neutral atoms and molecules which have escaped from the satellite.