Ultimately, the Sun will become a red giant, hence swallowing up Mercury and Venus and scorching the Earth. The best solution is to migrate to Mars or the underground and underwater of the Earth, which has plenty of life as well. However, it’s better not to gamble. Ideally, we want to migrate to the moons of Jupiter and Saturn, because the heat of a red giant will destroy the Earth’s atmosphere, making it difficult to survive without wearing masks temporarily. In any case, that’s a bit too far from now. The imminent threat is a nuclear or meteor strike, which can happen at any time.
Consequently, we need to advance molecular computing through heavy financial investment to create the foundation for military nanodrones and commercial nanobots, whose base knowledge is naturally a very good understanding of quantum physics that governs the structures of atoms and molecules. Both physical chemistry and biochemistry are still too weak today. If the bridges of these different disciplines of physical science are not clear, it is very difficult to work in the world of micro-universe.
It seems impossible to convert an entire planet or a moon into an inhabitable environment for humanity. Planets and moons are simply too large. However, they become very small and easy to convert if we have nanobots that self-replicate and convert at an exponential rate. All of sudden, all planets and moons within the Solar System can harbor human civilizations. We don’t need military-grade re-programmable nanodrones yet. The conversion nanobots will be specialized for the specific environments of a target planet to begin with, because the financial yield of these robots is simply infinite. Are you willing to buy the Earth or Mars with a trillion dollars? That sounds cheap. How about heating? Isn’t that important for everything beyond Mars? Well, mirrors in space will direct enough sunlight to your home for the purpose of central air conditioning. It’s more important to have a crust and an atmosphere as a base condition.
Why is a Moon base safe from a nuclear strike from the Earth? Well, it takes at least 1 day to get to the Moon from the Earth. You may cut it to 2 hours, but your interplanetary nuclear missiles will be so large that everyone will simply laugh you off. Distance matters. If you have a day to intercept a missile, you will never fail. Will you build a nuclear missile base in space? Probably not. It will be highly visible and closely monitored that nothing interesting can be done from there.
Space is the answer to the survival of an advanced civilization. How many nations can make it today to be considered advanced? Not many.
With all these being said, I still must insist that security is always the top priority. We must first secure the space within 50,000 km above the surface of the Earth, and then the Moon, and then Mars, and finally the moons of Jupiter and Saturn. After that, we will go to Alpha Centauri and begin our galactic conquest. That’s more than enough time to develop propellant-less engines for interstellar travels.