Whenever the idea of establishing a colony off-world comes to mind the first place many think of is Mars. Primarily this is due to Mars being the most similar of all the other planets to ours, having an atmosphere and land features that look very similar to some of our own. However that’s where the likeness ends as its lack of magnetic field has meant that its atmosphere has been stripped bar to a thin layer of carbon dioxide, taking all of the surface water along with it. Thus whilst it would seem like the best candidate for humans to establish themselves elsewhere in this solar system there are other potential sites that have distinct advantages over what Mars can provide.
One surprisingly good candidate for a potential human colony is Mercury. Now initially this would seem like a pretty bad idea as its surface temperatures regularly exceed several hundred degrees celsius and the only atmosphere to speak of is a tenuous layer is mostly made up of solar wind and vaporized surface material. However it’s close proximity to the sun gives it access to abundant solar power, orders of magnitude more than what is available on the surface of Mars. Considering that power is probably one of the biggest limiting factors for a colony and the size it can grow this advantage could prove invaluable, so long as the initial challenges could be overcome.
Probably the biggest thing that Mercury has going against it is the time it would take to get a mission there. Whilst we’ve got craft today capable of covering the distance in under 40 days or so its tight orbit around our sun makes it incredibly difficult to get into orbit with it. It’s not so much that it’s hard to do, more that the time typically required to transit to there with an approach that will get you into orbit takes on the order of years, not days. This would mean the development of systems to support humans for a sustained period in space which would open up other alternative locations for a human colony.
Interestingly such systems could be used to establish a colony on Venus, although not the type you’d think of. Whilst Venus’ surface is a hellish place where it rains metal it would be quite possible to create cloud cities that float around an area that’s much more hospitable to humans. Indeed the pressure at 50KM above the surface is the same as Earths and thanks to the dense, mostly carbon dioxide atmosphere a lifting gas that’s simply breathing air has a lifting power of 50 times that of helium on earth. The protections required then are far less strenuous than those required to get to Mercury initially and the dangers posed by the atmosphere are far less severe than that of a harsh vacuum.
Past these planets though are options start to get limited as whilst many moons of the gas giants of the outer solar system have an abundance of things like water or other useful materials they’re typically quite harsh environments, either being flooded with ionizing radiation or lacking any kind of atmosphere without the benefit of having high amounts of light to take advantage of. They’re essentially equivalent to space itself in that regard and whilst I love the idea of large human colonies in space there’s really no substitute for colonizing another planet.
For what its worth we’re likely going to see a Mars colony within our lifetimes, one that will likely be limited to a few one way pioneers or entrepreneurs looking to take advantage of the first new frontier in a century. The other options, whilst being only slightly more fantastical than that of a Mars colony, aren’t likely to happen any time soon as there needs to be much more ground broken in engineering terms before they become viable. Regardless of where it happens a human colony off our planet is fast becoming a necessity if we want to ensure the human race doesn’t have a single point of failure in our own planet.