Would they always need earth to be habitable?
Because if they somehow managed to terraform and colonise another planet like mars, wouldnt they just make earth so uninhabitable that the rest of us would be forced to go where they are? (Prolly as slaves)
I think we would need to consider more than terraforming. Somehow, we would need to add mass to the planet to get out to hold water. That probably means deorbiting the Martian moons as well as heavy planetoids from the asteroid belt.
This would need to be done in a way that does not alter the Martian orbit, but doing this may also permanently destroy the current planetary balance.
My theory is that the planet would need to be reliquified. If glassing it by deorbiting mass onto it doesn’t cut it, we would probably need to use solar reflectors to increase the planet’s temperature. This also has the possibility of destabilizing the orbit.
Finally, as the planet finally begins cooling, we could lob ice chunks at it until there is sufficient water. At that point, if humans still exist, we could consider forming the planet into a proper habitat.
My thought is that we would have already figured out artificial gravity and left the planet due to falling rocks.