I’m saying there are plenty of places on Earth that will still be more hospitable than Mars after a GRB or even a massive asteroid/comet impact. You could opera

I’m saying there are plenty of places on Earth that will still be more hospitable than Mars after a GRB or even a massive asteroid/comet impact. You could operate multiple colonies underground or underwater for a fraction of the cost of a Mars colony. Mars is so inhospitable that the only conceivable reason for using it as a backup plan is (1) you’re planning for events that completely destroy the Earth’s surface and oceans to a depth of hundreds of meters on all sides (this is not GRBs) or (2) you’re correctly worried about eight billion starving and well-armed humans trying to get in.