If you made me the effectively immortal and locally omnipotent King of Mars, I would deny access to the Robert Zubrins and Elon Musks of the world, at least for thousands of years. My first goal would be to establish a magnetic field to stop the hydrodynamic stripping of the atmosphere. I’d hate to see all my efforts degraded. A solar powered electromagnet at, say, L1, would be fine, but if one could actually spin up a liquid core, that would be cool too. Then I would poison the planet.
That is, I would bombard it with iceteroids of cyanide (HCN), ammonia (NH3), and water (H2O). Well, the water isn’t toxic but the other two are. Hit Mars incessantly with volatiles. Other atoms as needed to achieve the desired balance. Get the atmo inside that triple point so that widespread liquid surface water would be available. This bombardment would pulse some frictional heat in – one could even disassemble Phobos and Diemos to create a hard hot rain, maybe even doing the same with some asteroids. Sill, sustainable heat retention would be necessary, perhaps a large Fresnel lens associated with the L1 electromagnet.
Create seas and lakes and streams and see if any Mars life finds that water and starts proliferating. Pump it down deep injection wells. I’m really only interested in using highly sterilized robots, which would build mines, refineries, and factories for indigenous, production of the necessary infrastructure. After a thousand years of terraforming and another thousand to search or wait for native life, I would start inoculating.
Algae cells and spores of ferns and mosses. Paulinella. By the way, when I speak of algae, I include cyanobacteria without specifying “blue-green” (Nucleus, schmucleus; photosynthesis and nutrient removal are my sibboleths). And look at Paulinella: a cyanobacterial symbiosis far more recent than that of the other eukarytoic photosynthesizers. Yet another alga to me. Heck even some non-oxygenic photosynthesizers like Chlorobium (not quite algae to me, at this time).
During this microbial and macrophyte proliferation, I would continue my embargo on surface humans. I want to see what evolution does under ambient conditions, sort of let things metaphorically anneal, before subjecting my world to the more directed attention of deliberate interventions. Create sort of an abbreviated, truncated, curtailed carboniferous era. I note that if a plethora of indigenous life erupts during the first thousand years of waiting, I might well delay my indulgence in terraspermia, and proceed most carefully when I do start, again with the goal of annealing, in this latter case with an “alloy” rather than a pure “metal”. Eventually, human settlement would be allowed. Again, much more carefully if there is indigenous Martian life. So, with a thousand years for bombardment and infrastructure development, potentially ten thousand for indigenous life development followed by another ten thousand of terrestrial plant life introduction, I might start adding animals, eventually allowing humans in.
What a spell. Lovely fantasy. Anyway, the more I think about it, the less interested I am in developing Mars for habitation. For exploration I’m not yet worried about surface contamination, but drilling disturbs me. I think I would ban it until we get really convincing evidence that we can do effective planetary protection.