filling your bathtub with the drain open. The planet doesn't have an adequate magnetic field. It is a romantic notion, I loved Kim Stanley Robinson's series, he took the science seriously, but overlooked this fact.

If we are going to terraform a planet, we better get to work on this one. We've been doing for a couple of hundred years now and we are fucking it up. I'd rather see that money spent on fixing our mistakes than fucking up another planet. Imagine if we spent your hypothetical monies on fast tracking fusion power? Or building a L-point rotating space station? I think it be less expensive to build a high population, self sustaining station than trying to terraform another planet. The later would take thousands of years; the former maybe several decades.

I hope we sometime in my lifetime we visit mars. But even colonizing it is a bridge too far. Colonize the moon. If you can't do it there, you'll not be able to do it on mars.

Sorry to harsh on your thought experiment, V., but when I spend time drilling down on the details, I can't get over the magnetic field problem. Mars' core froze up. Unless a way can found to shield mars from the solar wind any effort to create an atmosphere is pissing in the wind and a waste of time and resources.

But it makes for fun Science Fiction.