Also on a slightly separate point, colonisation of planets, really bad idea.
Planets suck to live on. Space faring civilisations are unlikely to terraform planets.
You are basically stuck with wherever they happen to be because they are really hard to alter their orbits.
They almost never have the right level of gravity.
They are deep down gravity wells which means they are really hard to get off of.
Also they are really rare, trying to find one that is suitable is going to involve many many light year long journeys
and severely restrict the number of star systems that you can colonise.
Even looking at this solar system for our own expansion we only have 2 potential even vaguely viable options for
terraforming in the shape of Mars and Venus, and that gives us about 1.5 times more surface area extra to the earth.
For the entire world population to live like those in Europe Would require something like 3 extra Earth's.
To live like the average in the USA would take over 5 extra Earth's.
The solution is man made space habitats built out of asteroids.
They don't have any significant gravity well, so you can travel and trade from one to another with ease.
They are small areas that can be terraformed quickly (as opposed to be centuries it would take to terraform a planet)
They can be placed in any orbit you like.
They have whatever gravity you like, and there is enough materiel out there to build habitat space for over a trillion people.
Habitats beat planets hands down.
