Spectrophotometry of IO: Preliminary Voyager 1 results

Multispectral images of Io acquired with the Voyager 1 narrow‐angle camera agree with Earth‐based spectrophotometry to better than 10%. Although the surface materials have general spectral properties similar to various allotropes of sulfur, their ultraviolet (UV) reflectances are much higher. It is likely that varying amounts of SO 2 frost mixed with or absorbed on sulfur‐rich materials raises the UV reflectance. The possible association with large amounts of SO 2 with low temperature forms of sulfur in the white patches on Io is consistent with Io surface models in which SO 2 and S exist in thermally stable stratified zones.