Monday, April 18, 2016

Alpha-habitable Planets

Habitable is such a vague word, covering such an important concept in the study of alien civilizations. In astronomy circles it somehow was used to denote what we call here Liquid Water Zone planets, or LWZ planets, which is simply a comment on the temperature somewhere on the planet's surface, specifically that it be between the melting point and the boiling point of water, at the atmospheric pressure on the surface. While an interesting concept and a measurable or estimatable one, just barely, with today's astronomical knowledge and equipment, it doesn't figure very much into trying to figure out where aliens are, including both where they originated and where they moved to. Also included is where they might have seeded life.

Let's try and make a parameter out of this concept, following the recipe for thinking about aliens posted elsewhere. Let's call a planet which can harbor alien life on the surface within a hundred years of their first ship or fleet of ships touching down, an alpha-habitable planet. Obviously, these are the most desirable, at least at first glance. If an alien civilization is of the type that likes to disperse their civilization, then finding one of these planets close by is an gold-plated invitation.

It would be a safe assumption to think that any alien species that can build a space ship breathes oxygen, as methane breathers or about anything else don't produce enough energy to support big creatures. That means an alpha-habitable planet has to have oxygen, and to have oxygen, it has to have something to make it on a continuous basis. Oxygen is chemically reactive enough that it doesn't typically stay around long if it is not being renewed. This means life. So, an alpha-habitable planet can be an origin planet, with its own intelligent alien species there, or a plateau planet, where life didn't get far enough to produce intelligence. The hundred years might be the amount of time needed to subdue or otherwise deal with a native intelligent species, or to remove some toxicity present on the planet, in the atmosphere or perhaps somewhere else. It is also a short time to figure out the planet and build the first habitat there, and then occupy it. Occupying a habitat does not mean living inside a hermetically sealed container, but living in the habitat and interacting with the planet by going outside, not inside a hermetically sealed suit. In short, it means a planet with a tolerable atmosphere.

What's a bit worse than a alpha-habitable planet? Of course, it's a beta-habitable planet, which we will use to denote a planet which can be inhabited in ten thousand years. There aren't too many classes of problems which cannot be solved in a hundred years but can be in ten thousand years. One is temperature adjustment. If the planet is too hot because of greenhouse gases, they can be removed by some process known to aliens, and the planet will gradually cool down. The same holds for a too-cold planet. Doctoring the atmosphere and then waiting for the planet to adjust to a more comfortable temperature is a slow process, and ten thousand years seems to be a wide enough range to make sure it can be done.

This is a multi-step process, as it would be too costly to truck all the chemicals needed to doctor up an atmosphere over tens or hundreds of light years. Instead, technology to generate the chemicals locally would have to be used. Perhaps some resources from another planet in the target solar system would have to be dragged over to the target planet. Perhaps something would need to be done to the lifeforms on the planet to induce them to produce more of whatever was needed, or less perhaps.

Gamma-habitable planets need a million years to convert them to a place where the aliens can set down on the surface and survive and sustain themselves there. These are likely planets with genetics problems, where the lifeforms on the planet do not produce the right atmospheric gases. A million years is a short time for the evolution of the right lifeforms and the gradual replacement of the atmosphere with the exhaust of these new organisms, but it doesn't seem so short if there can be massive seeding of lifeforms, perhaps in many different generations of changing organisms, to do what is necessary to produce a decent atmosphere. This probably means making oxygen, but it might also mean taking out hydrogen sulfide or some other bad actor.

Delta-habitable planets raise the timespan another factor of a hundred, up to a hundred million years. Probably no alien civilization could be involved in this, but it serves as the end of the parametric range. These would be planets where geology hasn't settled down yet, and some civilization, if it had staying power beyond all belief and imagination, would simply wait it out. Young planets go through a stage of geological unsettledness and a hundred million years is probably a good ballpark for how long it would take for the major upheavals to come to an end and a nice steady crust to form and remain constant over long periods.

The astute reader of this blog knows that underground habitats have been considered. A planet with no atmosphere would be just fine for aliens seeking this type of home. Let's call such a planet U-habitable, meaning that mining of resources produces enough net energy to run the habitat there, and also enough resources of all minimally necessary types can be found to support life. Obviously this can be largely mechanical, but not necessarily.

If there are shortages of energy, and something has to be done on the surface to take advantage of the photons, or maybe just to gaze at the galaxy, we call this a D-habitable planet, meaning life under domes is possible, from an energy and resource sustainability point of view.

If alien life on the surface is not sustainable by the end of the geo-engineering period, the planet does not qualify as alpha through delta habitable; similarly if alien life cannot be sustained underground or in domes, or a combination, it is also not U or D-habitable. Clearly it is possible to have some group of aliens touch down, and live on the supplies sent from the home planet. These aliens have not established a habitable planet, simply a colony of the home world. All a colony like this does is drain resources from the home planet, running down the supplies there even faster. This would not satisfy the goals of any alien civilization that was bent on surviving the exhaustion of their home planet or home solar system.

To wax philosophical, life is both entities but also a means of extracting energy and resources from whatever environment exists so that the entities can be preserved and regenerated. So, perhaps the terms X-habitable are really appropriate here. And there is one more coda to put at the end of this story: delta-habitable planets are ones that alien civilizations with the meme for spreading life around would seek out, provided there is a way to properly seed the planet. Recall this category of alien is enamored of life itself, and is not trying to preserve its civilization. Instead, they recognize, perhaps because they understand that the origination of life without help is a very, very rare event, and they want to be the godfathers of life all over the place. Back in the posts on the early evolution of life it was noted that just perhaps, the origination of life takes a very unusual impact of a planetesimal on a proto-Earth. if this or some other very rare process was required, those alien civilizations that liked life would have many planets just waiting to be seeded.

Wouldn't it be absolutely hilarious if we eventually found out that life could only originate in a very unusual situation, which we had a great deal of difficulty figuring out because it didn't happen on our planet. We were seeded, and all those hours that curious people spent trying to figure out the origin of life were all for naught, going in the wrong direction, so to speak. I can't stop chuckling.

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