Colonizing Frozen Worlds

An alien civilization which has mastered the art and science of traveling between solar systems might have done something else which will surprise us. They might have decided that worlds like their origin world are fine for the origination of life and evolution and technology development, but there are better choices for an established, advanced, expanding civilization. They might like frozen worlds.

Back here on Earth, we are all excited about the developments in the detection of planets around other stars than ours, and are contemplating how we might search for life on them. The great hope is that oxygen in the atmosphere will be the clue. Oxygen is a reactive element, and would combine with exposed rock, removing it from the atmosphere. It is plant life which renews it, by taking in carbon dioxide and releasing oxygen. Before we had plant life on Earth, we had a different atmosphere. Nitrogen is not very reactive, and carbon dioxide even less; they were there. There may have been other constituents, but no matter. Oxygen was not one of them. If life all died out on Earth, the oxygen in the atmosphere would disappear. So atmospheric oxygen has been chosen as the signature of life.

This means that our search for oxygen in the atmosphere of all those exo-planets is directly solely at finding origin planets. To understand what this means, let’s consider an example. Civilization Z originated on planet A101, after a billion years or two of evolution. They used up all the resources, but being a very intelligent civilization, they developed star travel before that happened, so they could travel to other solar systems and use up the resources there, before traveling on. Maybe they had communication between the different colony worlds, and maybe not. Perhaps they always did more than one new world from each colony, after about a million years on each one. Then, to do the very simple math, after one million years there would be two colonies, plus the origin planet which can no longer support a civilization, lacking resources. After two million years there would be four colonies, plus two old colonies which had died out and old A101. After three million years, eight colonies, plus six old colony worlds, now without any civilization, and A101. Just remember, in the calendar of the galaxy, three million years is very, very short. Maybe they would run into some expansion problems at some time, as exponential growth gets large very quickly. For the sake of the example, suppose that at the time we start looking for life in the galaxy there are five thousand colony planets with life, meaning civilization Z, two or three thousand ex-colony planets, and that old origin planet.

So, if some brilliant astronomer wants to find life in the galaxy at this point, there might be five thousand planets with life and a civilization to boot, and one origin planet. Where should he look for life? Origin planets?

To try and figure out what planets might be serving as colonies for civilization Z, ask: "What are they going to need?" Resources, and principal among them, energy. If the planet being considered is not a rogue planet, floating free in interstellar space, there will be a star to orbit around, which is giving off energy in the form of photons. These might be collected. Otherwise, there is uranium and thorium to fission and deuterium and other light nuclei to fuse.

Perhaps there are two stages of resource needs. One relates to the initial time on the planet, after the alien colony ship arrives and lands. Since fission reactors are relatively simple to build, compared with fission ones, at least as far as we know, they might seek planets with lots of uranium, and uranium that is not too old so there is still lots of U-235. Old uranium has only the U-238 left, which is much harder to fission. As uranium ages, the fraction of U-235 goes down. The planet from which civilization Z is expanding might start a hundred thousand years before they need to migrate, and send out some exploration ships. A ten thousand year voyage, and they can start reporting back on what the target planet is made of. So, in this particular scenario of colonization, there is plenty of time to carefully plan their next planetary colonization.

To have uranium, which is thought to be produced in supernova explosions, there would have to have been a few in the previous billion years prior to the formation of the star they are considering. Then there would be uranium, young enough to be useful. Figuring that out might not be too difficult, by looking at the contents of the gas clouds around the solar system in question.

Do they want a larger planet, with an atmosphere, or a smaller planet, maybe Mars-sized, with almost none. This might depend on the details of how planets form crusts and how mineral deposits accumulate in the crust. We’re not too sure of these details now, but if Mars has good mineral deposits, then Mars-like planets might be just what they want. Low gravity means not so much propulsion needed to get out of the gravitational hole. Little atmosphere means no winds to worry about.

Our knowledge of exo-planets is fairly sparse at the current time, but it might be such smaller planets are typically cold. If the star is smaller, but there was a lot of residual angular momentum in the cloud it formed from, there might be many smaller planets, completely frozen, but with excellent mineral resources. Could an advanced alien civilization cope with extreme cold? Can they master insulation? Very likely. Thus, perhaps frozen smaller rocky planets are their preference. If so, even a rogue planet might be just fine. There may be huge numbers of them roaming the galaxy, largely invisible to us.

There is another follow-on conclusion from this possibility. Earth would be of no interest to an alien civilization which was colonizing all the mineral-rich, frozen, small planets in the Milky Way. Earth is too big, with too much atmosphere, too large with too much gravity, and also has the minor inconvenience of already having life on it. Perhaps we should think through the alienology of colonization a bit more to see if this option is a dominant one.