Boston University researchers have published the first clear evidence of how gases from Jupiter’s tiny moon’s volcanoes can lead to the largest visible gas cloud in the solar system.
In 1990, Boston University scientists discovered a large gas cloud of sodium atoms spanning great distances to either side of Jupiter.
http://www.bu.edu/news/2007/07/18/bu-researchers-produce-images-of-gases-escaping-from-jupiters-moon-io/