Galileo imaging of atmospheric emissions from Io

The Galileo spacecraft has detected diffuse optical emissions from to in hi gh-resolution images acquired while the satellite was eclipsed by Jupiter. Three distinct components make up lo's visible emissions. Bright blue glows of more than 300 kilorayleighs emanate from volcanic plumes, probably due to electron impact on molecular sulfur dioxide. Weaker red emissions, possi bly due to atomic oxygen, are seen along the Limbs, brighter on the pole cl osest to the plasma torus. A faint green glow appears concentrated on the n ight side of to, possibly produced by atomic sodium. to's disk-averaged emi ssion diminishes with time after entering eclipse, whereas the localized bl ue glows brighten instead.