Too many planets

[dmm]

OK, I think I see the main reason why we're not understanding each other. You're assuming that "undomed" means the people are totally free to walk about the planet unaided by technology. I was assuming that, domed or undomed, they are using various colonization techs to allow them to live there.

Regarding the atmospheric pressure on a gas giant: the pressure only gets huge if you go deep into the atmosphere. It is strictly a function of how much the atmosphere on top of you weighs. My colonists are smart enough not to go too deep. And, as we've been discussing in another topic, the gravitational acceleration at the outer edge of a gas giant's atmosphere is also not that large. (For Jupiter, at its equator, gravity is only 2.3x Earth's. For Neptune and Uranus, it is comparable to Earth. Source: Handbook of Chemistry and Physics, 62nd Ed., 1982) On the negative side, I was surprised to find that our solar system's gas giants are COLD. However, there have been discoveries recently of gas giants orbiting Sun-like stars at Earth-like radii, so perhaps gas giants don't _have_ to be cold either.

Regarding ice planets being way too cold, even under their surface: I was assuming that they were not a solid hunk of frozen nitrogen, but instead that they were like some of the huge moons of Jupiter and Saturn are thought to be, with a frozen surface covering a liquid (or maybe rock) interior. The interior is kept warm by volcanism induced by gravitational tides or radioactivity or pressure.