Io's atmosphere collapses every time it passes into Jupiter's shadow

A new study shows another unique connection between Io and Jupiter: Io's atmosphere collapses every time it passes into Jupiter's shadow, and scientists just watched it happen for the first time ever.
Scientists already knew that Io's grip on its atmosphere was tenuous at best, and they suspected that it might frequently be lost to space and recreated by volcanic activity. The mostly sulfur-dioxide atmosphere has a surface pressure just one billionth of the one on Earth at sea level.
Every time Jupiter passes between Io and the sun, casting the moon into cold darkness (from a balmy -235 degrees Fahrenheit in sunlight to -270 degrees in shadow, to be precise), that sulfur-dioxide gas cools and drops down to the surface, freezing into a solid. The atmosphere is collapsed and trapped as surface ice for about two hours every day on Io (which equates to 1.7 Earth days).
And after that two hours, the atmosphere is reborn: The (sort of) warmth of the sun casts itself upon Io's surface once again, causing the newly formed frost to sublimate, or heat from a solid back into a gas.
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. Though Io's hyperactive volcanoes are the ultimate source of the SO2, sunlight controls the atmospheric pressure on a daily basis by controlling the temperature of the ice on the surface. Scientists have long suspected this, but they could finally watch it happen.

https://www.washingtonpost.com/news...ns-to-jupiters-moon-io-for-2-hours-every-day/

Study: http://onlinelibrary.wiley.com/doi/10.1002/2016JE005025/full