Giant Space Mirrors Have Been Proposed

With time, the notion of small-scale terraforming—where we terraform only the area we now require—has gained popularity. Maintaining it poses fresh difficulties but also perhaps simpler answers. Massive orbital or sub-orbital mirrors are one suggested method for terraforming a region of Mars. These mirrors could be mounted on balloons to focus solar beams on the surface. That would raise the temperature and give colonists below solar power.

On a 1 km2 area of Martian terrain, 300 reflective balloons may be concentrated, raising the temperature by about 20 C. Any ice would convert into water, making it possible for scientists to work there without difficulty.