There’s no planet B
Let&#x27;s set aside the part that making a planet where we could live is hard. Just presume we did that, to start.<p>Let&#x27;s talk <i>Logistics</i>.<p>Presume there are only 1 billion people left on Earth when we decide it&#x27;s time to go. How do you get them <i>there</i>? The gravity well holding us here (and holding the air down so we can breath it) is pretty darn strong. Today we&#x27;re hoping to get cost-to-orbit down to around $100&#x2F;kg. I weigh a bit less than 100kg, so that&#x27;s $10,000 just for my mass- not including the life support system I need.<p>And then I&#x27;m just in orbit.<p>If I&#x27;m moving to some kind of spin-gravity station in orbit, that&#x27;s not too far away. But Mars? Mars is a months long trip in a best case.<p>And don&#x27;t get me started on planets on other stars. Even the most optimistic generation ships would be taking 10s of thousands of years to get there- longer than all of human history so far. If each ship held 100,000 people, you&#x27;d need 10,000 of them. And what power source would you use to move that massive ship, and keep the light and heat on between stars? (Antimatter, I guess?)<p>If we can make Mars habitable, we can make Earth habitable for far less cost.<p>I&#x27;m entirely in favour of building spin-gravity stations, Mars habitats, even terraformation of Mars and Venus. I just feel like it&#x27;s never going to be the case that anything more than a tiny fraction of humans will leave Earth to go see those things.