I know you said "But mars is out" But it really isn't.
Mars is out, too, because we already established colonies of domes there and no one wants these destroyed / or unusable for a time either.
You probably didn't establish colonies of domes. If you had the materials to withstand micrometeorites and the radiation issues from being on the surface of mars, then you've basically either already solved the terraforming issue on mars, or you've got the technology to terraform most arbitrary bodies in our solar system.
Just building domes in an un-terraformed mars is far more likely to result in habitats becoming "destroyed or unusable for a time" because of collisions with micrometeorites not burnt up in a thick-ish atmosphere and radiation frying hardware, people, and the structures themselves.
You know what stops these two issues? Lots and lots of rocks. What you would have probably built were underground structures, full stop. No radiation issues, no meteorite issues, and you don't even have to terraform. This also presents even less issue to worry about terraforming making the colony structures unusable.
As for the terraforming issues of mars, people often cite solar wind as a huge hurdle for terraforming mars due to its thin atmosphere. Solar wind has the effect of exciting air molecules enough to escape the gravity of a planet, and presents a radiation risk, but it appears that there are reasonable solutions to this problem ie not outside of current tech.
During the Planetary Science Vision 2050 Workshop[23] in late February 2017, NASA scientist <PERSON> proposed a concept of placing a magnetic dipole field between the planet and the Sun to protect it from high-energy solar particles. It would be located at the L1 orbit at about 320 R♂. The field would need to be "Earth comparable" and sustain 50000 nT as measured at 1 Earth-radius. The paper abstract cites that this could be achieved by a magnet with a strength of 1–2 teslas (10,000–20,000 gauss).[65] If constructed, the shield may allow the planet to restore its atmosphere. Simulations indicate that within years, the planet would be able to achieve half the atmospheric pressure of Earth.
The "half of earths pressure" idea may or may not be realistic, but there are other ways to deal with this that I'll get to.
Then with that comes the issue of the fact that mars's gravity is simply much weaker than earths, and particles can escape the atmosphere on their own. 778
Combine that with the fact that mars is much colder on average compared to earth, it appears that this will be accelerated when trying to heat up the planet with the terraforming process.
Source
I asked a question about this a while back on space exploration, and the conclusion I got was interesting:
it appears that water loss reasoning is in contention, and that the primary method of loss may have been through the weaker gravity, and not solar wind at all.
The loss of these particles regardless happened over hundreds of millions to billions of years.
At the same time that same magnetic energy release powered a much stronger Solar Wind. The protons and other ions of the Solar Wind cause all the non-Jeans Escape processes listed in the Table above. Collectively several metres of water and perhaps 80 millibars of Carbon Dioxide would be lost over 4.2 billion years – at current rates of loss. As the bare minimum for terraforming is about ~300 millibars of carbon dioxide (equivalent to about 250 millibars of Oxygen) this doesn’t seem like a show stopper for terraforming. If we can supply modern day Mars with ~300 millibars in a few hundred years, then replacing 80 millibars in 4 billion doesn’t seem excessive.
If we were to provide mars with atmosphere, it might go away in 500 million years, but is that really that big of a deal on a human timescale?
So solar wind is not a problem on mars. Neither is losing atmosphere we get on mars. So what are the issues left?
* Atmospheric pressure
* Inert gas composition
* Sunlight
* Temperature
* Plantlife
Atmospheric pressure
With out proper atmospheric pressure, water, and you, will boil when exposed to the martian atmosphere directly. Liquid water will just boil off which is a non starter. If the lagrange point solar wind protector doesn't actually build up the atmosphere to half of earths, then here are your other options:
* you'll need to manually use mars's own materials to do so ie through some industrial extraction. This is probably possible in human timescales but there still may not be enough atmosphere.
* you'll need to crash meteorites into mars to release enough gasses. 778