As the population of earth continues to soar and as resources get increasingly depleted—and if climate change makes less and less of the planet habitable—chances are we're going to need a new planet to live on. But so far our search for somewhere hasn't been fruitful.
So what are some of the other options? In the video "How Could We Create A Second Earth?" from YouTube channel Life Noggin they look at how terraforming—transforming a planet to become earth-like—might help turn Mars or Venus or even a planet's moon into somewhere habitable for humans.
Mars is the most popular choice because we know exactly where it is and it's relatively near. But at the moment it has a toxic, thin atmosphere, it's A LOT colder, and it doesn't have any protection against radiation, plus it has low gravity.
To turn it into somewhere we could live we would need to sort all this out. In the video they tackle Mar's atmosphere first, which would need to be made thicker and its composition changed. To do this we could trigger a greenhouse effect, trapping the sun's heat. It could be done numerous ways, one way would be to release ammonia by smashing ice-rich comets into Mars. If we were eventually able to create a sustainable atmosphere for humans though, the video then acknowledges it won't last, as it will eventually get stripped away by radiation.
OK, so let's move on to Venus. How could we terraform that planet with its 460 celsius temperature? Well, the video says we could bombard it with hydrogen from gas giants, which would create graphite and water that could turn into global oceans. These would dissolve nitrogen and make the planet more earth like.
Mercury is also an option, or parts of it. There's water and organic molecules in the northern polar region. We could heat the bottom of huge craters with mirrors to melt ice found there, then add a dome to create a "little life bubble" as the video calls it. Not quite the same as a whole planet to live on, but still.
It also posits we could possibly terraform Europa and Titan, moons orbiting Jupiter and Saturn respectively. Although Life Noggin admit this would be extra difficult.
It ends by acknowledging that, yeah, probably best that we should just look after earth. Because terraforming other planets isn't going to happen any time soon.