Well, the voidwalker states that "those who have stared into the void are not bound by the laws of space and time", meaning they can defy reality. The traveler came from the void, meaning it can change anything. So, it would be able to make saturn and jupiter playable. A reasonable and logical way of putting "space magic".
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You could have floating cities (see The Empire Strikes Back or the Saga of Seven Suns) or just have the moons as playable. Or have deep sea like cities low inside the gas layer, something Rapture like. That would be cool. It's not hard to come up with something way more interesting than "Lets just say it is solid cause space magic!"