Did anyone but me catch the whole "It's a cannon that can fire anything anywhere" deal? Goombella says, when you tattle on the first area of the X-Naut base (with the conveyer belts) "It's all encased in a glass bubble to keep the air in. Come to think of it, we were OK out there with no air... Maybe we shouldn't think about that..." or maybe... was the whole "Maybe they faked the whole lunar landing in '69" issue around in '04? Goombella mentions putting a Goomba on the moon in '69 if she's with you in the cannon, so maybe not. It's kind of a "Just... don't think about it" thing. Just don't think about it. Besides, Mario could breathe underwater way back when, but has clearly lost that ability... maybe he traded that ability for the ability to breathe in space (He could stay underwater forever in SML2, correct? And he couldn't breathe in space. There you go.)