Too many planets

[dmm]

BB,
I agree that humans could not live undomed on the _surface_ of gas or ice planets. But why can't they live elsewhere, floating in the atmosphere of a gas planet, or in caverns or oceans under the surface of an ice planet? Then they might only need minor, reversible genetic engineering to allow them to live there, given the right atmosphere. (Yeah, yeah, I know I'm still ignoring a lot of biology. But this is space opera, not serious sci-fi.)