Io's dayside SO2 atmosphere

An extensive set of HI Lyman-α images obtained with the Hubble Space Telescope (HST) Space Telescope Imaging Spectrograph (STIS) from 1997–2001 has been analyzed to provide information about the spatial and temporal character of Io's SO2 atmosphere. An atmospheric distribution map derived from the observations reveals that the sunlit SO2 atmosphere is temporally stable on a global scale, with only small local changes. An anti-/sub-jovian asymmetry in the SO2 distribution is present in all 5 years of the observations. The average daytime atmosphere is densest on the anti-jovian hemisphere in the equatorial regions, with a maximum equatorial column density of 5.0×1016 cm−25.0×1016 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 appears to be best correlated with the location of hot spots and known volcanic plumes, although small number statistics for the plumes limits the correlation.