The problem is really the lack of a magnetic field. Even if you manage to increase the atmospheric pressure, ionizing particles strip it away. What you would ne

The problem is really the lack of a magnetic field. Even if you manage to increase the atmospheric pressure, ionizing particles strip it away. What you would need to build is a superconducting ring on the equator to generate a artificial magnetic field. Unfortunatly the amount of material required with current superconducting materials (for a magnetic field compared to earth's) is several times the world-production and we don't even know how abundant the materials are on mars. But we can always hope for a breakthrough in super-conductance research.