In a paper published today in the Journal of Geophysical Research: Planets, researchers announced that they had discovered an odd pattern on Io, the most volcanically active place in our Solar System. The thin atmosphere, made up mostly of sulfur dioxide (SO 2 ) gasses produced by erupting volcanoes, collapses every time Jupiter passes between the moon and the Sun. The collapse lasts for about 2 hours every 1.7 Earth days, then the light from the sun warms the moon, sublimating the sulfur dioxide back into a gas from its solid state.