Io's surface composition - Observational constraints and theoretical considerations

Observations of line emission from neutral and ionic species in the Io-surrounding cloud, reflectance studies and theoretical considerations suggest Io's surface is unlike that of any other body in the solar system. The cloud has a peculiar composition which we show is probably not due to cloud/surface fractionation. Io's surface may be largely covered with an endogenically produced mixture of S and dehydrated salts, or by accretion-fractionated compounds modified by charge particle bombardment.