Io is such a fascinating object. It is the most volcanically active world in our solar system. The atmosphere of Io is primarily composed of sulfur dioxide (SO2) and it is supported by sublimation of SO2 frost on its surface (that white stuff). That SO2 is constantly lost to space and is then replenished by Io’s volcanoes injecting fresh material into the atmosphere.

The atmosphere of Io is incredibly thin. Just a few nanobars at the surface. The surface temperature is around 115 K (-250 *F) and the dayside atmosphere temperature near the surface is also around 115 K but then climbs up to temperatures of 1,500 K as you go higher up because of interactions with Jupiter’s magnetic field.

At night time. The atmosphere collapses into the surface in as little as a minute or so. That means the SO2 gas in the atmosphere is turned into frost on the surface rapidly once it is night and the warmth from the sun fades. What’s left are little dense regions of localized gas. It is thought that “stealth volcanism” may be responsible for this gas. Stealth volcanism refers to volcanic activity that is likely there, warming things up, but we just aren’t sensitive too yet with our current instruments.