As the title says
Would there be a significant in between stage, where the planet is not fully habitable, but you won’t die the second you step outside. I’m imagining an environment analogous to the most extreme on earth, like the death zone at the tops of mountains or Antarctica, where outside activities are possible and don’t require a space suit per se, but still need heavy clothing and maybe breathing apparatus.
What would be the bottleneck? Would it be the atmosphere, the gravity and magnetosphere too low to keep one of the required thickness without constant input of more gas? Would it be water, rendering the planet a desert as the logistics of collecting and transporting a planets worth of water are simply immense
For a planet like Mars, what would this stage look like?I think it’d be something like a low-pressure, incredibly dry desert. I had the idea for a sci-fi setting where a Mars-government begins terraforming the planet and almost finishes, but then suffers some calamity or economic collapse that leaves the planet a half-inhabitable dust ball