USGS has just released a geological map of Io:
http://pubs.usgs.gov/sim/3168/sim3168_sheet.pdf
http://pubs.usgs.gov/sim/3168/sim3168_pamphlet.pdf
Sulphur dioxide snow, metastable sulphur polymers, red plains, 14 km mountains, mysterious green deposits, radioactivity, violent volcanism and and a plasma torus... it makes me want to set an adventure on this grand moon.
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