Artist’s concept of Jupiter’s volcanic moon Io, whose volcanoes create an ephemeral atmosphere during sunlit hours. Image: Southwest Research Institute

Reason number 9,000 not to colonize Jupiter’s moon Io: not only is it a frigid hellscape covered in eruptive ice volcanoes and lashed by the gas giant’s powerful radiation belts, but the atmosphere just collapsed.

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In fact, it collapses all the time, according to observations by astronomers at the Southwest Research Institute that are published today in the Journal of Geophysical Research. It turns out that every time Io is eclipsed by mighty Jupiter (which happens for about 2 hours a day), the surface temperature plummets and the moon’s sulfur dioxide (SO2)-rich atmosphere begins to deflate.

By the time Io is in full shadow, the atmosphere is like a punctured balloon, blanketing the moon’s surface in a thin coating of SO2 frost. As Io migrates back into the sun, this frost layer re-sublimates, and a new atmosphere develops.

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“This confirms that Io’s atmosphere is in a constant state of collapse and repair, and shows that a large fraction of the atmosphere is supported by sublimation of SO2 ice,” study co-author John Spencer said in a statement. “We’ve long suspected this, but can finally watch it happen.”

So there you have it—full atmospheric collapse happening in our cosmic backyard just about every day. Who knows what other nightmares await us in orbit around Jupiter?

[Journal of Geophysical Research]