Golan2072 said:What makes the present-day Mars Habitable rather than Inhospitable? After all, its atmosphere its so thin that you need a vacc suit to live on its surface due to the low pressure, temperature, solar radiation and lack of oxygen; habitats on Mars would have to be pressurized like ones on any other non-Earth planet in our solar system.
I agree that Mars is a better candidate for colonization than Luna due to massive amounts of frozen (and possibly liquid in subterranean areas) water and higher gravity. But without terraformation it isn't much more habitable than Luna or Titan.
I certainly cannot say this with any authority, but it would not surprise me if you could live underground on Mars with an air compressor and a power source. While I agree the surface in uninhabitable for the reasons you mentioned (plus other ones like random meteorites and 250mph winds), you go just a few feet underground and radiation (and winds and meteorites) stops being a factor, and temperature and pressure are easily handled with 1980s technology.
The atmosphere on Mars is 95% carbon dioxide and 5% argon, with other traces. So for your neutral gas you freeze the atmosphere, throw out the dry ice, keep the argon. For the oxygen, well, grow some plants.
I think that we'll find Mars to be pretty easy to inhabit without teraforming, as long as we stay off the surface. In fact, it seems so conducive to life that I would be shocked if we didn't find life just a few feet below the surface.