| Io's molecular and atomic atmosphere has been studied via far-ultraviolet spectroscopy obtained with the Hubble Space Telescope . Examination of an extensive data set reveals a sunlit SO2 atmosphere which is temporally stable on a global scale, with only small local changes. An anti-/sub-Jovian asymmetry in the SO2 distribution persists in all of the observations. The atmosphere is densest in the anti-Jovian equatorial regions, with a maximum column density of 5.0 x 10 16 cm-2 at 140° longitude. The SO2 atmosphere also has greater latitudinal extent on the anti-Jovian hemisphere as compared to the sub-Jovian. The atmospheric distribution is best correlated with the location of known volcanic plumes. Theoretical sublimation atmosphere models cannot reproduce the asymmetry alone. Atomic S, O and Cl are also detected. Their abundances are derived and compared to the SO2. Sulfur is measured at a relative abundance of 9 x 10-3 compared to SO2, oxygen at 0.05, and chlorine at 3-8.5 x 10 -4. |
