Chaos,
You may not have read the article he's linking to.
Io's atmosphere completely freezes out at night, except for the hot gasses being ejected by the volcanoes.
The new information is that they used the night-side aurora to estimate just how much gas the volcanoes are ejecting at night -- which is about 1-3% of the day-side atmosphere.
In other words, it'd be nice if Celestia could simulate atmospheres which are only present on the day-side of a body.
