If you ask the androids, they'll happily explain that they've managed to maintain the atmosphere of Struxta through artificial means. The planet would be ripped to pieces if it didn't maintain a certain gravity core.

In addition, the Library would also have information on that they maintain oxygen levels (or something close enough to oxygen) through artificial means. As the planet began to die, the androids worked to create an insulated atmosphere in a last-ditch effort to save the planet. It did not work, but they maintain the same atmsopheric field. They've never really seen a need to get rid of it.