Earth is still more hospitable in the case of your giant asteroid. Those in nuclear submarines and bunkers will survive unless they're very close to the epicenter. When they emerge, they'll find temperatures and atmosphere which are much more hospitable than on Mars. The survivors will also be able to scavenge abundant refined metals from the dead for rebuilding.
We can also start improving these facilities today, if we care about the survival of homo sapiens. Even out the gender ratio at Cheyenne mountain, give it a small nuclear reactor, a hydroponic farm, and a seed bank and we can be reasonably confident in it weathering anything but a very near miss.
We can also start improving these facilities today, if we care about the survival of homo sapiens. Even out the gender ratio at Cheyenne mountain, give it a small nuclear reactor, a hydroponic farm, and a seed bank and we can be reasonably confident in it weathering anything but a very near miss.