At last, a decades-old mystery has been solved about the atmosphere on Jupiter's volcano-riffic moon Io. This moon, whose super-lavalicious geological situation has earned it the titles "pizza face" and "most volcanically active body in the solar system," is special to the heart of io9 because we love fire. Turns out that constant fire-spewage will get you an atmosphere. According to, new photographs from the New Horizon satellite revealed what Io's atmosphere is made of.

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Io's volcanoes spew out sulfur dioxide, which is a gas that stinks of freshly lit matches and almost entirely makes up the moon's atmosphere. As Io rotates from daylight into darkness, chilling the yellowish rock down to -226 F (-143 C), the gas freezes into a solid, much like dry ice (frozen carbon dioxide gas). About 1 to 3 percent of Io's dayside atmosphere, it turns out, is created by the volcanoes. The rest is generated from frozen sulfur dioxide turning directly into gas which, over eons, has accumulated on Io's surface.

New Horizon also got a cool image of Io's "aurora," which is caused by all that volcanic gas getting hurled into the air. Looks awesome.