Friday, July 19, 2019

The Formation of Solar Systems

The basic outline of the formation of planetary systems is well-known. A cloud of mostly hydrogen gas is rotating, and subject to its own gravity, it starts to condense. It may not be spherical, but nonetheless, there will be a point of maximum condensation, caused not by gravity at first, but by the pressure generated by the overall gravity pulling everything together. This maximum point will start attracting gas near it and a steadily shrinking ball of gas forms. The center point of the ball will be the densest location, and temperature will mount due to compression happening faster than the ball can cool itself, which happens when the ball becomes dense enough to become opaque. Temperature and density continue to rise, and finally thermonuclear ignition thresholds are passed, and it begins to fuse at the center. Gravity doesn’t stop, and neither does condensation, and larger layers pass the ignition point. At this point, there is a star.

There is a direction of cloud angular momentum, meaning that in general, the cloud is rotating around this axis. Centrifugal force pushes the cloud out, especially near the plane intersecting the new star, while the lack of that force in axial directions leads to a compression there. A disk of gas forms, and it becomes thinner with time. On a tiny scale, condensation into molecules and dust particles happens in the disk, and if the star is large enough, a solar wind begins and blows lighter molecules out further, leading to a partial differentiation of materials in the disk.

The disk is unstable to ring formation, so instead of a smooth disk, with time some dust and gas rings develop, and they continue the condensation process. The particle size increases in the inner part of the disk, and in the outermost part, ices form into particles as well. These particles congeal, and in the middle region, blobs of gas start to form, as the rings are unstable to planetoid formation.

At this point, resonant interactions start to form, and the dominant gravity will be from the densest part of the disk, which is somewhere in the middle. The gas blobs may be in resonance with each other, or anti-resonance. If anti-resonance happens to be the situation in a solar system, the innermost gas blob, now turning into a planet, loses angular moment to the outermost one, and they drive in and out respectively. If a large gas giant planet is driven into near the star, passing by the planets and planetoids between its original formation radius and the star, they will be strongly perturbed and may wind up anywhere in the system. Similar things happen with a large gas giant which is driven outward. The ice giant planets will be scattered and can wind up anywhere. If they go inward far enough, they will lose some of their mass from thermal effects.

The alternate situation, where there is only one large gas giant or two of them fortunately in resonant orbits relative to one another, the solar system is divided into bands, being resonant or anti-resonant. Two gas giants in this situation will exchange angular momentum between each other, but not secularly, only with a to-and-fro situation which keeps both of them near their resonant band’s centers. Smaller planets inside and outside of this which are in antiresonant bands will be scattered out, winding up almost anywhere, while ones in resonant bands will simply engage in moving around within the resonant band. Two of them in the same resonant band will result in one expelling the other, or a violent merger will happen. These types of collisions occur with much less relative velocity than any other interaction in the solar system, as two planets in one resonant band are moving with close to the same orbital speed, not much eccentricity, and a seeming repellant effect. When one of the two planets comes close to the other, it speeds up, changing its orbital parameters, and may pass by the other without doing more than being distorted. This can continue to happen until the two of them get closer and closer in orbital parameters, when a merger finally happens with minimal velocity of impact.

The existence of resonant bands and antiresonant interactions helps to explain why the solar system zoo which we are gradually discovering is so diverse. Rings condense with no resonant interaction, just anywhere, depending on the radial structure of the gas and dust disk, but once they condense, they become subject to another instability leading to planetoid condensation. They might be in resonance with some other planet or anti-resonance, meaning they can travel in radius from the star, ending up in some strange place. This happening with many planets at once can lead to the lack of clear patterns of solar system planet location.

What does this mean about where to best look for aliens? The time scale for planetary rearrangement should be relatively short compared to the time needed for evolution of cells, so if a suitable planet, with the right gravity, atmosphere, and composition, shows up in a thermally favorable location, having other planets in the solar system in strange locations should not affect it. It might be that a solar system which has gone through a period where antiresonant effects took place would have many less planets, so the numbers might be against a planet holding an alien civilization, but if one exists, the other planets should not prevent origination and evolution of life. They will, of course, perturb the orbit over millions of years, but antiresonant effects should be over and the perturbation will be back-and-forth, simply creating a bit more interesting planet to evolve upon.

If there was a veryhot Jupiter and a very cold Saturn in some solar system, and one nice habitable planet in the middle with all the stuff needed to originate life, a civilization arising there might have no interest at all in interplanetary travel, which is the learning stage for interstellar travel, assuming it is possible at all. It is actually quite entertaining to try and think of what life might be like in an alien civilization in the variety of solar systems we are now discovering, bit by bit.

Wednesday, June 12, 2019

Rain and Life

When we are searching exoplanets for life, one of the premier signals is supposed to be the presence of oxygen. Oxygen typically is chemically combined unless it is renewed, and vegetative life provides this renewal. As all schoolchildren know, photosynthesis involves chlorophyll acting as a catalyst to break carbon dioxide into oxygen, which is released, and carbon which is utilized. But photosynthesis can be done in the oceans by near-surface plants, and while life in oceans would be tremendously interesting, life on land would be even more tremendously interesting. It is very hard to see how intelligent civilizations could evolve underwater, but on land, there is the possibility.

Thus, oxygen might be a great signature for life, vegetative specifically, but not so certain an indicator for alien civilizations. What might be used in addition?

It is certainly worth asking the question. Just consider that a hundred years from now we find ourselves in a galaxy with thousands of planets with life, but all of it wet. Now consider instead of that situation, we are in a galaxy with even hundreds of planets with alien civilizations. Orders of magnitude more interesting.

So, what is beyond oxygen as a signature of life on land? Trivially, there must be dry land, and that would have some reflective signature. Rock doesn't look like water when reflecting sunlight. But just having rock doesn't imply that there is anything living on it. There needs to be some preconditions before life can crawl out of the oceans and take up habitation on dry land. One is rain.

Life needs water. It doesn't need to be immersed in it, but it needs to have it to drink. Water evaporates, and water on land needs to be renewed. That means rain. Water evaporates from the oceans, drifts over the land, condenses into droplets and falls to the ground. There aren't too many other possible mechanisms. One could consider tidal flooding, which might produce wet areas, but if the ocean has dissolved some minerals from the rock, like salt, it might not be drinkable. If there was a lot of volcanic action, possibly someone could come up with a process that, on some suitable planet, might pump water, distill it in the volcanic heat, let it condense elsewhere, and expel it into a river. This complicated a mechanism doesn't seem likely, at least during the later life of the planet. So it is rain that is the mandatory precondition for an alien civilization and for animal life on land as well.

Detecting water vapor in the atmosphere might be the first surrogate for detecting rain. On Earth, water vapor is at a much lower concentration than oxygen, and therefore more difficult to detect; but it is not impossible to foresee that that would be a further step in astronomical capability, once oxygen was detectable. Carbon dioxide might be detectable first, or some other compound or element, such as argon, but eventually water vapor would succumb to astrophysical technology. These gases would likely first be detected for a transiting planet, where the light of the parent star shines through the atmosphere and gets spectrally absorbed. Later they might be detected from reflected light.

Rain would have to be either a local phenomenon, evaporating over most of the ocean area, and then precipitating on some region, or else a seasonal phenomenon, evaporating during one season of the year, and precipitating during another. Wet ground has little difference in albedo than dry ground, however, so even if telescopes grew sufficiently in aperture to see different parts of the exoplanet, seeing wet areas would be quite difficult. But if there was sufficient temperature range on the planet, and there was snow, then a significant albedo change might be detected. This would be even easier in the seasonal case, where evaporation occurred all summer and then all winter, snow happened. A planet with an elliptic orbit might produce this situation.

Another option is clouds. Rain and clouds are not the same thing, but there must be clouds to produce rain. Searching for clouds might be considerably easier that searching for rain. Clouds do change the global albedo, and monitoring for these changes would be an indicator of cloudiness, and by implication, rain.

Another variable which affects the detectability of atmospheric gases is the thickness of the atmosphere. Earth has a very thin atmosphere, about 10 km thick compared to 6000 km radius of the planet. This is to be compared to Venus, with approximately the same radius, but an atmospheric thickness of 250 km. Probably the components of Venus' atmosphere would be much easier to detect on a transiting planet. Clearly one must compare the loss of signal due to the longer transmission path with the larger cross-section of the atmosphere and the lengthened time for absorption. For a reflective signal, the loss of albedo may make the comparison go the opposite way, with thicker atmospheres being more difficult to break down into components.

One interesting question is, if there was an exoplanet with an atmosphere as thick as Venus' atmosphere but of the same composition as Earth's, would rain be possible? One might also make an assumption that the rotation rate was identical to Earth's as well. Similarly the average temperature would be assumed to be the same as Earth's. The vapor pressure of water is the same no matter where it is, so the amount of water in the atmosphere would be the same as Earth's, maybe a half percent on Earth on the average, with more of it at lower altitudes. On the exo-planet it would be a half a hundredth of a percent. Rain forms when the temperature of the atmosphere drops sufficiently that liquid water can form. Would the thermal inertia of a large atmosphere, with 100 times the atmospheric mass of Earth, prevent this temperature drop? Temperature drop comes from heating or cooling of the atmosphere, and a portion of the lower atmosphere gets a certain amount of heating from the solar energy passing through it, which is largely identical and a certain amount from the reflected heat from the planet. On the exoplanet, much more solar energy would be absorbed by the atmosphere, leaving the surface much darker and receiving less energy. Solar energy incident on the atmosphere would be largely identical for different longitudes, meaning much less opportunity for the temperature change that is required for rain. This possibly means that finding an exoplanet with a thick atmosphere would imply no rain, and no land lifeforms, and no alien civilization.

One hypothesis about the reason for the thinness of Earth's atmosphere is that atmospheric mass is almost unaffected by the aging of the planet, and once thin, it stays thin. If the formation of the Earth was mediated by the impact of a protoplanet, which led to the formation of our large moon, and the legacy atmospheric hypothesis is true, looking for a large moon might be the fastest way to find land life and the possibility of a civilization.

Friday, May 17, 2019

Imagining the Goals of an Alien Civilization

It is much easier to imagine some aspects of alien society, such as their energy sources, than other aspects, such as their goals, because we have on Earth made some progress in understanding the possible sources of energy and can make some good guesses as to what might exist in a more advanced society. But with respect to social goals, our technology is very primitive. We hardly understand anything about societies and their goals; even the basis for this technology or scientific knowledge is vague and undeveloped. We have some observations, but nothing equivalent of Newton's law has been figured out yet. Just to appreciate the difficulty involved, think of asking someone in Columbus' time about energy, after explaining the concept to him. He might answer there was wind power, and that's about all. A person who had some education involving ancient Greek science and who had heard of Hero of Alexandria's aeolipile might add steam power, which comes from fire. There would be no way that such a person could estimate what energy usage would look like five hundred years later, or a thousand.

On the other hand, we have some confidence now in understanding electromagnetic energy, kinetic energy, chemical energy, equation of state energy such as compression, and nuclear energy, along with the many ways they exist in nature and how they can be harnessed and converted. A person on Earth today might be able to do a good job in describing the use of energy, and might even be able to imagine how energy might be used in the far future. And if we subscribe to the concept of societal convergence, meaning technology drives society and since technology is the same no matter what planet you live on, all sufficiently advanced societies will have similar features, and therefore what this person imagines for Earth five hunderd years from now would be quite insightful as to what a similarly advanced alien civilization might be doing.

We are in the Columbus era stage of understanding neurology, politics, governance, societal arrangements and whatever else relate to the goals of an alien civilization. We would make grave mis-assumptions to try and use what we think are the goals of Earth's various societies, current and historical, as possible goals of an alien civilization.

Some goals that might pop up from the study of Earth societies' history include empire expansion, maintenance of the existing power structure and factionalization, development of profitable trade connections and routes, collection of items of universal value such as gold, the pursuit of scientific progress and technology, revenge or hatred directed toward some group, usage of a particular economic system, the spread of medical technology to various factions, and so on. These are goals which are appropriate, if at all, for a single planet. Ones which relate to multiple planets might be the expansion of life to dead planets, resettling on other planets as an insurance policy against catastrophes or other events which eliminate life on the home world, and a few others.

Our knowledge of energy and astronomy enable us to realize that some of the one-world goals are ineffectual for a multi-solar system civilization. Each planet of the civilization is almost totally isolated with respect to transportation and communication, not absolutely, but almost totally, by the distances between different solar systems and the huge amounts of energy needed to move anything from one civilization to another. Some minimal communication might be attempted between two solar systems which are not too far from one another, but little can be done with simple information transfer with no transport to implement any agreements, requests, or orders from one planet to another.

An alien civilization which is somehow frozen in its level of technology at something like what Earth has now might also have its goals be chosen from the ones listed above, but technology does not plateau easily. It proceeds forward to the asymptotic conclusion or the society degenerates. So at the very least, we can say that multi-planet civilizations do not have empire-building as their goal, nor the development of trade routes, collection of items to be brought from one solar system to another, and perhaps more.

After an alien civilization moves through its technological development of electronics, robotics, and artificial intelligence, the next area it encounters is genetics. The genetic revolution will overwhelm the electronics revolution, and the concept of factionalization, based on legacy concepts of genetics, local origins, language preferences and so on, will drift away as good genes are made available to all members of future generations beyond some point in time. Technology has shown cost reductions in the electronics phase of development, and when this wave passes genetics, there will be little reason to suspect that good genes would not be universally available.

The same wave of technology would also pass through the quasi-sciences of politics and economics, transforming them into fact-based sciences and enabling an alien society to have wise political structures and economic arrangements. The idea of an alien society having a goal of enforcing some legacy economic system on its members seems a little ridiculous; the optimal system would be known and used everywhere. Why would any region or goup want to use antiquated systems when better ones were instantly available?

For one-planet goals, the one which passes through the filter of advanced society might be the preservation of the civilization via wise use of resources, and the expansion of it to other appropriate planets. The other one is the preservation of life in general on the planet, but more importantly of spreading it to other planets. These are quite dissimilar goals in their effect on the civilization, even though they both originate from the abstraction of the goals of life across all species. There is no reason that both of them could not be accepted and acted upon by any particular alien civilization, except for the cost in resources they both have. If it is true that civilization can establish itself on a much different class of planets that life can evolve upon, it is fair to say that they operate almost independently.

It does not seem possible to extrapolate from goals of Earth societies, current and recent, to goals of a civilization with more advanced technology, by a few centuries of progress. The only way forward is to look for the simplest possible ones, those which derive from the nature of life. Perhaps some others can be found with a different approach, and that is certainly an interesting avenue to follow.

Thursday, April 4, 2019

Hunting for Life in the Milky Way

In earlier posts, there was some discussion of what would be the goals of an advanced alien civilization, assuming they had come together to choose one and then to work on it. In a different blog, some more thinking on this matter indicated that the most reasonable and likely goal of the civilization is that of life itself, which is best broken down into five separate goals, survival, reproduction, adaptation, evolution and dispersion. These goals imply many choices that the alien civilization would make, in order to further their alignment with these life goals. The last goal is dispersion, and that means first expansion all over the planet, then the solar system, and then outwards into the galaxy. Just think for a minute what this implies: all or most advanced alien civilizations are going to attempt colonization and seeding, both of which support the dispersion of life.

Neither of these tasks are easy, as has been noted in all the posts in this blog on these topics. Colonization means setting up some replica of the alien civilization on an exoplanet ,while seeding means starting out life with the alien version of DNA on some planet which doesn’t have the prerequisites to become an origin planet on its own, but can support life, being in the habitable zone plus all the other conditions. Current theory here on Earth indicate the cells that did that were cyanobacteria.

Looking for seeded planets would likely be the same as looking for origin planets. Seeding might put photosynthetic organisms into a planetary ocean, and then, after a few hundreds of millions of years, an oxygen atmosphere might exist, which is a tremendous benefit for evolution, allowing life to expand beyond chemotrophs and cyanobacteria cells to a food chain. The oxygen in a seeded planet’s atmosphere would look the same as in an origin planet’s atmosphere.

So, assuming most of the alien civilizations do both seeding of potential life-supporting planets and colonization of others, which are not able to support life, but which provide the resources necessary for the alien civilization to sustain itself for a long time. Which ones should be looked for?

Seeding a planet gets over the hump of life origination, which might be tremendously difficult, rare and improbable, at least according to one theory, mine. Is evolution fairly certain after that, or are there more highly improbable-to-overcome barriers along the way to intelligence? Suppose there aren’t. Suppose evolution is as easy as rolling down a hill. However, it takes a long time. Earth is our only example here, and life took about two and a half billion years after the atmosphere changed to partially oxygen to evolve to intelligence. This means that any alien civilization which evolved in the last two to three billion years has not had enough time yet for their first example of seeding to have led to a new alien civilization, evolved from cyanobacteria to tool-using creatures of one form or another.

This raises the obvious question of when, in the history of the galaxy, was life likely to originate? There are stars around which are ten or so billion years old. Could these have had planets soon after they formed, and perhaps one which met the prerequisites for life to originate? Unfortunately, current astronomical tools do not allow us to figure out much of the history of the galaxy. It likely started out as a gas blob, and condensed irregularly, with stars forming all over it, but more in the denser region in the center. Gas was more dense that now, as by now much has been consumed in star formation, and that implies that stars which formed early would be larger. Large stars live short lives, and end in a supernova explosion. There would not have been the neat division of the galaxy into the disk and the central bulge, so star motion would have been more random and Boltzmann-like. Neither of these two things bode well for planets. Supernovas going off near a planetary system sterilize it, but may also disturb planetary orbits, causing them to be ejected or rarely crash into the star. The passage of a nearby star does the same thing, pulling planets out of their orbit, leading to a planet-planet interaction where the smaller ones get ejected. So, while little definitive is known, it would seem likely that planetary formation in a system which perseveres long enough to originate and evolve life is more likely in the later stages of the galaxy and out in the disk. Finding planets to seed would also be more likely in these conditions.

Putting this together means that seeded planets might be around, but life on them is too young to have evolved into an advanced civilization. There really is a double time here. For life to originate and produce an alien civilization, capable of star travel, might take four billion years since the planet formed into a habitable world, with the right temperatures and everything else needed for life. Then if that civilization seeds another planet, we have another three billion years or so to wait. That is seven total, and seven billion years ago, there might have been so much turmoil in the galaxy that life couldn’t originate and evolve. So, planets which have been seeded might be common, and even many which have had the few hundred million years to produce an oxygen atmosphere. But if we are hunting for alien civilizations, seeded planets are not worth the effort. That leaves origin planets and colonized planets.

The previous post, on frozen worlds, indicates that colonized worlds, if the aliens choose worlds which are the easiest to colonize and which will sustain them for a long time, might look absolutely different from origin worlds. It also indicated, because of the very different time scales involved, that there could be very many of them all over the Milky Way, or at least out in the disk. The idea was simple: if there are sufficient resources on the planet, fusible and fissionable elements, plus all the other minerals necessary to supply the civilization with its raw materials, buried in the ground, they can simply build their civilization under the surface, on a frozen world and maybe some not so frozen. The ratio between colonized worlds and origin worlds might be a thousand to one. There would also be much larger numbers of previously colonized worlds where the alien civilization has used up the minerals and life on the planet was no longer sustainable for them.

How do you detect a mine shaft and a starship landing zone? Maybe there would have to be some surface transportation, if they needed to have mines in multiple locations. It might be possible, with a kilometer sized telescope, to see large oceans on an exoplanet in our vicinity, but even one ten times larger than that could not detect something as small as tens of meters or even a kilometer in size. Looking for a tiny heat source is conceivable, but unlikely as the resolution at deep infrared wavelengths is so much less than in the visible. If the concepts trotted out here and in the last post are viable, it means that alien civilizations are not detectable, and they would have no interest in coming to Earth, either for seeding as we are way past that, or colonizing as there are too many potential difficulties. It wouldn’t align with their goal of dispersing life at all to visit Earth. So the only thing we have any hope of doing is detecting an origin world, but if there is only a few of them,they might be on the other side of the Milky Way or in a different spiral arm. Perhaps a double hope of there being easy ways to originate life and our detecting oxygen in exo-planet atmospheres is the only possible salvation for the quest to find aliens.

Thursday, March 21, 2019

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.

Friday, March 15, 2019

Momentum and Goals in an Advanced Alien Civilization

In this blog, the various eras of an alien civilization are described by the technology that is possessed. There is the early fire and stone era, then comes the age of metal, followed by the age of mechanical industry, followed by the age of electronics, then the age of genetics. It was convenient to divide these eras up by naming transition periods, 'grand transformations', when the knowledge and capability in one of these areas of technology was changing fast and leading the civilization into new directions and plateaus. All of the areas of technology continue changing at once, so there is necessarily overlapping of inventions in different fields, but the effect on society would seem to have peaks and valleys. In the peak, society is reorganizing itself to take advantage of the new technology. In the valleys, the reorganization is diffusing out but the main changes have passed in the part of the civilization that is at the forefront of technology change.

There are several possible catastrophes that could end an alien civilization and prevent it from ever traveling in space to visit Earth. Most of these are physical, such as a nearby supernova or a basalt flood or an asteroid impact. Some are social, such as idiocracy, which is the failure of the society to generate enough intelligent people to keep it running, or factionalism, where the civilization devotes itself to strife between factions, which again prevents it from pursuing higher technology or maintaining what has been achieved. A third one is resource exhaustion, where the cost of obtaining mineral or energy resources gets too high to maintain the standard of living necessary to keep technology going forward, and incidentally doing anything sufficient to prevent resource exhaustion. As noted in the posts on idiocracy, this happens when the culture ceases to value reproduction of intelligence, on the average, and might best be referred to as a situation of social momentum.

One way to think of social momentum is to think of a herd of herbivores outrunning some predators. They have no plan to follow, just speed to use to their advantage. So they run without thinking, most times to a successful escape, but sometimes into a cul-de-sac or over a cliff. The essence of social momentum is that the civilization has not reached the point where the goals of the civilization as a whole are discussed and clarified, but instead, they have not crystallized into any usable form. Goals are all personal and do not align. During a special period like a war, there will be a goal of at least a faction of the civilization, but other times, none exists.

For idiocracy, the social momentum is in the direction of differential breeding, with lower intelligence individuals breeding at a higher rate. For factionalism, there is a goal for each different faction, but they are opposite and pertain to the destruction of the other faction or factions. The social momentum is toward destruction of assets. For resource exhaustion, the social momentum is in the direction of individual consumption, and resources are not thought of as being needed for the successive generations, but only for the current one; otherwise they are thought of as being so huge that infinite is a good approximation in economic thinking.

Where does social momentum, in self-annihilating directions, arise? The nature of individual decision-making, in overview, is quite simple. Individuals make decisions for themselves or they copy the decisions made by others, which they obtain through individual contact or via media. Those controlling the media can filter such decisions, leading to a limited scope of choices for those individuals who prefer to copy the selections of others. Some number of individuals will make their own choices, depending on their feelings or using some amount of reasoning. If those who control the media make their choices in such as way as to have them fulfilled by spreading some particular set of goals, then the direction of the social momentum of society is determined by them. If in a particular alien civilization, there are divisions in choice among the media-controlling elements, then social goals will be diffuse, otherwise they might be more aligned.

Some economic systems have strong feedback loops which tend to concentrate wealth and power in the hands of a few individuals. Other systems might not have these loops. So one question to ask is, if factionalism is part of the social momentum of a particular alien civilization, will the economic system present on the planet allow power, in particular media control, to be concentrated. Technology might also push toward concentration, or rather, work via economics to do this.

Does technology and its understandable stages and steps tend to have economic changes along with the other social changes that it brings, and do those economic changes favor economic systems which concentrate power? One aspect of technology is a kind of communication range that individuals have. In the fire and stone era, there were only a small number of others who could communicate with any particular individual, maybe only one or a few families. In the metal era, there was surplus food at times, which allowed individuals to be used as travelers bearing communications. In the industrial era, communications begins to open up so that an individual might be in contact with thousands, via printing. Then electronics opens the gate even further, perhaps to the maximum possible, where any individual on an alien planet could without great difficulty communicate with any other one.

Is concentration of power also a social momentum artefact, so that if there at one time a high degree of it, does that continue for a long period, through technology changes? The feedback loop which promotes this might be the default condition of the civilization, and only by some unusual circumstances would there be a smaller concentration. The feedback loop works very simply. Someone with a large amount of power can use some of that to increase the amount of power he possesses, leading to a greater concentration. In the later stages of technology, transportation and communication are no longer hindrances to such concentration. So, the three social catastrophes, idiocracy, factionalism, and resource exhaustion might well be in the cards for many alien civilizations, as they will allow power to be concentrated to the point where the feedback loop begins to function, leaving the concentration to increase inevitably. The three catastrophes are not sudden, but very gradual, and the concentration of power effects will continue to push towards their final state, while power continues to concentrate even more.

Thursday, March 7, 2019

Later Stages of the Genetic Grand Transformation

In an older post, it was noted that the genetic revolution is likely to be, by a large margin, the most revolutionary of all, in the sense that an alien civilization will be wholly transformed when it happens. The different stages of this grand transformation can be laid out, as they are necessarily sequential. The knowledge gained at one stage is needed for the next stage.

The first stage is very simple, chromosomal selection for embryos. This is extremely old news here on Earth, and there has even been a movie produced about it, entitled GATTACA, from twenty years ago. A couple has twice as many of each chromosome as an embryo needs, so the best two of each type can be chosen. The second stage is what we hear in the news nowadays, which is when specific genes are chosen. Tools for that are just now being found here, and surely in any alien civilization reaching its maturity this would be as routine as antibiotics. Small amounts of changes are what we talk about now, as we don’t have confirmed technology for even that. The technology must exist, however, as inside the cell, genes are moved around during evolution all the time.

Right after that, industrial gestation would be the likely mechanism to be developed next. This particular invention will change an alien civilization more than the Internet has changed out, which is totally. No more parents and no more child-bearing, just new humans. Will parenting become a specialized business, just as has almost every other aspect of life? Why would it be any different? Parenting is extremely rewarding, perhaps more so than any other activity in life, but why not outsource the child-bearing to a machine? Yes, bonding between mother and child will be diminished, and in time, as an alien civilization ages, the role of mother might be also performed by specialists, either trained aliens or some robotics. It is almost trivial to be able to think up problems that might happen with this, but it will be just as trivial for an alien civilization to figure out how to avoid them or turn them into advantages.

Consider for a moment what this point represents. It means that any organism that can be developed in a laboratory can be put through industrial gestation and be ‘born’. This refers to things on alien planets like mammals, but similar processes would be similarly possible for things like plants and insects and whatever else evolved on the planet. In other words, life becomes something like a recipe or a cookbook. AI will undoubtedly be very powerful by the time industrial gestation is well-developed, so the concoction of forms of life which can successfully pass from the egg stage to the real world and on to an adult animal or plant will be quite possible. A huge amount of data will have to be collected, about all the molecules that operate in a living organism, but huge data stores are just the media AI likes to live in.

Now, on Earth, to come up with a new species of plant or animal takes a lot of careful breeding and selection. On a planet with technology a few centuries past ours, it will be done from scratch, without experimentation, as ontology and growth can just be simulated. There can be as many new species as anyone wants to take the time and expense to come up with.

This is by no means the end of the genetic grand transformation. Since reproduction of anything will be economically done industrially, why would there be any species at all? Species are defined as groups of individuals capable of breeding with one another. There would be no need for this, so why have species? There could be a billion clones of some plant if it were desired, or none, meaning that organism was its own species.

Is DNA sacred, or whatever form of organic molecule evolved on an alien planet to serve as the template for genetics? We on Earth are far from knowing how many kinds of molecules can do this job, and if there are more than one, is there another which is more versatile, or more reliable, or easier to work with, or anything else which might mean that the alien technologists would start switching over to it for successive generations of organisms?

And whether DNA or XYZ is used, the legacy method of ontology might be changed. We don’t understand this process very well, but we have observed it in detail. The idea is that each successively evolved species keeps most of the ontology of its predecessor, and adds a little twist to it. Perhaps an alien civilization would rewrite the book, and have a completely different order of development of organs in some new organism they created. Just because something evolved does not mean it was the best that could exist, as there is a barrier posed by the need for evolutionary change to work gradually.

One point made in that earlier post is by the time of these later stages of the genetic grand transformation, it might be reasonable for aliens to switch over from mono-genetic organisms to multi-genetic organisms. We refer to these as chimeras, but that is only a tiny little glimpse of what might be possible. Any optimized genetic package can be used for any organ or part of an organ in a designed chimera. Aliens could choose to use just two or as many as desired. This would mean that an embryo would be fashioned by amalgamating cells of different genetic varieties, all of which were tuned so they could form a cooperative package of cells that could be gestated and have different genetic codes in different parts of the organism.

All the previous stages involve organic biochemistry. At some point, there could be a closer bond between organic and inorganic components in some hybrid object. We on Earth use certain types of microbes to sort out dilute liquids containing minerals, and of course that should be expected to expand far beyond these ideas. For example, technology may well allow communication between whatever passes for neurons on an alien planet, and some semiconductor gizmos of equally small size. The neurons would be tailored genetically for this, and the gizmos specifically designed and printed to be a good substrate. Then anything is possible.

Authors and screenwriters like to play with the idea of a person from some centuries ago being brought into the modern world and being astounded by what they see. Someone from before the genetic grand transformation being brought to a time after it would be immeasurably more confounded by what is seen. We on Earth would do well to simply contemplate these potential changes to better appreciate what an alien civilization of advanced technology really looks like. Then we can better ask the question of why haven’t they visited us here.

Sunday, January 27, 2019

Death by Erudition

When contemplating why an alien society might never reach its technological zenith, but instead get stuck at some lower point, there are many, many possibilities. If technology never reaches its finale in asymptotic technology, then space travel is impossible, the alien society lives and becomes extinct on its own planet, and we never get visited by them. One boondoggle that an advanced or middle-technology society can get in might be called 'Death by Erudition'.

Erudition is a nice English word which has the meaning of the accumulation of already known knowledge. In other words, it is the opposite of learning by experiment or by trial-and-error. The example that springs to mind is the old Chinese Empire, where opportunities for advancement and personal power were largely confined to the imperial government, and there were tests that were used to filter out the more qualified from the less qualified. The subject of the tests was Confucian learning and the derivations from it. Confucianism is something like a religion, but without any supernatural entities floating around, and a large behavioral code. Alien individuals would need, at that time and at all times, some basis for choosing how to behave in a multitude of situations, and what type of mandatory behavior would be necessary as well. If there was an alien civilization which developed a globe-spanning empire, and which put up a chokepoint to advancement as erudition in some subject like a behavioral code and all its trappings, then any alien who might have had a possible future in advancing technology would be steered away from that into the task of passing through the chokepoint.

Technology advances when there are some precursors to it. One is the scientific method, and we have Francis Bacon to thank for kicking off the theory of how to do good science. If an alien society took its Francis Bacons, meaning those aliens who had the equivalent of his mental abilities and freedom of thought, and induced a very large majority of them to instead work on following to the last detail some behavior code, “alien Confucianism” if it needs a title, there might be no one, between the time of the foundation of the empire and its collapse due to resource shortages or something else intrinsic to a colossal government, who invents the scientific method. With that, there would be no guidelines for interested aliens to follow in order to push the civilization up the technology ladder.

The alien empire does not have to be completely globe-spanning, but it does have to be large enough to dominate the globe and to set an example to all the outlying areas, where some minor kingdoms might be set up. It would seem quite logical that these outer regimes would try to imitate the globe's largest empire, and copy their focus on erudition and on having a chokepoint to advancement being the mis-directed competition on knowledge of some body of behavioral rules or some other religious category of knowledge. It is easy to imagine many ways such a competition could be organized and many sets of knowledge domains it could cover, without there being the slightest impetus to advancing technology.

It might be thought that some upstart kingdom on the periphery would want to be an alien Kublai Khan and conquer the empire, using some new technology. But technology provides an incremental advantage, and sheer numbers provides a different one. As long as the empire paid attention to the smaller kingdoms and maintained control over them, so they could not be amalgamated under one leader, their numbers could be sufficient to overwhelm any technology advantage, or for that matter, any inspirational leader or any secret cabal or so on. The key is that the empire has to pay attention to the details of what was going on in the periphery. With that in hand, an alien empire might easily prolong its existence, and the counter-technology chokepoint, until resource shortages or environmental effects or some natural catastrophe put an end to that civilization's window of opportunity to explore interstellar space.

There have been many examples of empires here on Earth, and three stand out as examples of humongous empires. One is the Chinese Empire, already mentioned, which had the chokepoint and which serves as a good example. Another is the Incan Empire, which was huge as well. The Incan Empire did not last long enough for such effects to be manifested, as it was swallowed up by the Spanish Empire after it had existed, as an empire, for only about a hundred years. The third is the venerable Roman Empire. Each of these three had suppressed or swallowed up the nearby competition. The Incan Empire had its own belief system, but it was so short-lived that it was still in the condition of having military leaders rule over it and take positions of power within it. The Roman Empire had passed that stage, but it was so diverse that it did not have any standard belief system to use in harnessing the ambition of young potential leaders. Thus the Chinese example is the only outstanding one, but it serves as an illustration of what might happen.

Are there any features we could observe on distant planets that would have an effect on the rise of such an empire? Is there anything unique about Earth which means we don't have such features and therefore escaped from that collapse mode?

Empires grow because they have a central granary, a large area where foodstuffs can be grown and where villages and cities can be formed. Rome had the Italian peninsula, the Incans had the terraced mountains up and down the Andean mountain chain, the Chinese had central China. They also had to have transportation, and that consisted of one spine of roads plus branches for the Incas, a network of roads emanating from the capital for China, and the Mediterranean Sea plus roads for the Romans. To have a globe-spanning empire would means there would have to be a large continent, all fertile, without barriers to transportation. Alternatively, an archipelago with all the fertile land might do. There would have to be no obstacles such as mountain ranges dividing the sole continent, or multiple fertile continents at large distances. Thus, once we have constructed a telescope of kilometer size or greater, we can look at exo-planets which are otherwise likely to have originated life, and see if they might have had a civilization which collapsed early in their technological progress, owing to 'Death by Erudition'. 

Monday, December 31, 2018

The Approach to Arcologies in Alien Civilizations

Arcologies and massive recycling go hand-in-hand. An alien civilization which reaches the stage where it is aware of resource constraints on their home planet will gradually improve recycling, and work to decrease the fraction of materials used in production that come from resource extraction, using recycling instead. Having the population concentrated in arcologies makes high-level recycling easier and more efficient.

An alien civilization cannot just decide that on some date everyone will move into an arcology. It must be a gradual process. But just what might that process look like? Are there any stumbling blocks along the way that might interfere with the civilization's eventual decision to leave their solar system and travel to another?

Recycling itself grows bit by bit. On Earth we are familiar with collection of a few materials which can be reprocessed and re-submitted to manufacturing. There is also other forms of recycling going on here that we do not necessarily categorize as recycling, but which would be a major feature of life on any advanced planet that had decided it wanted to survive for eons. One is re-use. If an item is not discarded while still being useful, but instead is transferred to a new user, this is a form of recycling. Not much is recycled here, perhaps clothing and children's toys, a small amount of furniture and a few other things are simply sold or transferred to new owners, such as family members or friends. Housing is the other large component of goods which are transferred from owner to owner, along with vehicles.

Refurbishing of goods prior to resale also occurs in a few instances here on Earth. Recycling of organic materials in compost is used on Earth and has been for thousands of years, being perhaps the first of all recycling that humans have done. All of these techniques and several others would be needed to push the level of recycling in an alien civilization up to 80%, 90%, 95% or higher. These high levels translate into large increases in longevity for the alien civilization, provided catastrophes do not occur. A long duration alien civilization is needed to prepare for and conduct space flight between stars.

Recycling, to reach the high levels that might be mandatory for longevity, needs to increase both in degree and in extent. The increase in degree means that, if copper is being recycled, as time passes, the percentage that is mined dropped, and the percentage that is lost and unrecoverable diminishes. This limits the type of usage that can be done. Losses occur when a substance is too completely mixed with diverse other substances to be economically separated, or when it is used in consumption, such as the liner of rocket nozzles, where ablation would remove it and irretrievably disperse it. A mixed material that can be simply treated and reused in the same or similar function is certainly categorizable as recycling, and it is only if the material is dispersed would it be lost. The combination of mixing and dispersal might remove some substance that either one of them would not.  The expansion of extent means more and more substances are submitted to recycling, eventually approaching 100%.

There will certainly be a preference for making all items in the civilization out of parts which can be recycled, and in increasing the lifetime of all parts as well. A bearing which lasts for fifty years cuts losses by 80% over a similar bearing which only lasts for ten. Such longevity increases might come from simple design changes, not involving any different materials. It is not clear immediately how the selection of design will be made and by whom in any particular alien civilization, but it is clear that one of the strongest constraints on design will include reliability and the possibility to remove all or most of the materials for recycling as a materials or as parts.

If the population of the alien planet is spread out everywhere, with low density, the transportation costs of recycling will be larger, and it will be more difficult to collect waste. To get to very high levels of recycling, it might be necessary to collect dust from manufacturing areas or perhaps elsewhere, or even to filter the atmosphere. Thus, one of the pressures in the alien society is to bring everyone who consumes resources into one of the locales where collection and reprocessing can be done. This means more population in large cities and less in non-urban areas.

Another aspect of resource usage minimization is the introduction of efficiency in every process that occurs in the alien civilization. Earthlings know a little about this, as we understand that reducing gasoline per distance helps cut losses of resource, as does home insulation. Efficiency becomes another strong design driver in an advanced alien civilization on its pathway to the stars. Transportation efficiency comes not just in fuel usage, but in mode of transport and distance between sites as well. In an arcology, elevators and the horizontal equivalents can be used as the distances are smaller, and this is yet another factor that will tend to make arcologies the only viable choice for a long-term alien civilization.

Not only will distances that are mandatory for transportation be reduced in an arcology, but so also will the mass involved in transportation. If something universal, such as food, needed by all aliens, has to be transported, having an apparatus within the arcology to do it is likely many times more efficient in transportation costs than any other options.

It would seem reasonable, after recycling technology reaches a certain point, that large buildings would be built in cities, not like the small ones we have today, but ones which occupy much more space and house much more population, thus making this type of transportation apparatus sufficiently economical to replace other types of transportation. Then, recycling centers can be constructed at short distances from other components of the system, such as refurbishing facilites, collection of materials for preprocessing facilities, waste handling facilities and all the other needed to bring the civilization up to a high level of recycling and cut resource usage down to a small fraction of what it was before these sequential changes take place.

Saturday, November 17, 2018

Technology Can Outrun Economics

One question which can be posed about the ascent to space travel in an alien civilization is: Are there barriers to the achievement of asymptotic technology by an alien society in the realm of economics? In other words, as we try to hypothesize how alien civilizations develop, are there pitfalls within their economic systems which might lead to a halt in progress or a descent from a high standard of living to one which cannot support space travel? Thinking through economic systems and their evolution, in parallel with technology, might provide some insights.

All alien civilizations start out when a species evolves, because of elementary tool use, into something which can accumulate knowledge of a technology nature. Perhaps the first tool use is fire, or stone, or something else on some exo-planet. But after some use of this, the species starts to live in groups, and then to live in fixed sites.

An economic system that works very well for a village, with a clan living within it, may not be the best system for a society where technology has advanced beyond the handiwork stage. First consider how village economics works, or at least might work. There would be a village boss, whose role was to make decisions, along with some other influential people, and to ensure the whole clan was taken care of. He needed to make sure the food supply was adequate, in all seasons of the planet's year, and that everyone received a sufficient share. He was also responsible for safety, from invasion or physical catastrophe, for making the largest decisions such as the choice to migrate to a more favorable location, for regulating trade, for encouraging skill improvement in whatever handicrafts were present, for following the rituals of the clan, such as might be related to death and burial, and more. The economic system was not communism, as some people were rewarded with significantly more than others, and was not capitalism, as there was a strong current of compassion, meaning those too old, infirm, disabled, young, or whatever were taken care of.

Work motivation is a critical requirement for a large village or larger urban region. There are only two ways in which individuals can be motivated to work, and one is for personal gain or the gain for those closely associated with the individual, and the other is for altruistic reasons, for the benefits of all clan members. In a small village, where everyone knows everyone, these two reasons partially merge.

In general, individuals of any intelligent species can be happy and content either from two causes, one, because they produce a large amount, or with a high degree of skill or, two, because they consume a large amount, or consume things of higher value or quality than others. It doesn't seem it would be too common that a single individual has both sources of happiness in high degree. The productive individual is often somewhat indifferent to the distribution of his production, as long as it is appreciated by the whole clan. This type of personality is what is encouraged by the clan and its leaders.

Those who care mostly about consumption find themselves without much support in a small clan. They certainly can exist, and serve some role in the clan by creating a demand for better quality products, more carefully done, and with attributes which might be unique. A productive individual can also create such demand, however, so there is a little utility within a village for a solely consumption-oriented individual. When the size of the habitation increases, however, from the level allowed by improvements in technology, things can change.

One of the first results is factionalization. A brain, in any creature, is not infinite and not uniform. Some sort of division of other individuals must occur, and there would be a preference relating to them. This translates into a preference for some to have benefits more than others. Contact frequency might affect this, of which the strongest is familial relationships. The alien civilization in each small town would gradual factionate, and at least at first, into families. Members of one family would seek benefits for their family, at the expense of others. There are a great many benefits possible in this division, both tangible and intangible ones, such as opportunities to take positions, learn skills, occupy areas, and so on.

Factionalization can expand beyond families, either in such a way that the population of the town is divided into sub-clans, or in different directions, that is, based on different types of divisions, like profession or something even more arbitrary, like groups formed in regions of the town. The point to be made is that the village economic system had universal compassion as a component, and as growth in population continues, this becomes stretched beyond its limits and breaks down. We have instead compassion and benefit-seeking divided into competing factions.

As this continues and becomes more rigid, one might have castes or classes forming, and furthermore, the rules or customs which controlled the village are rewritten so that the more powerful factions can create even larger discrepancies between benefits for individuals. The village boss role is fractured into multiple heads of family and other groups. Possessions are not freely divided and shared with those in need, partially because the level of production is higher and fewer individuals are near minimal sustenance level, but also because the feelings inside each individual no longer tend to compel this. We have a different economic system.

Production fractures as well among the factions, so that any technology items are made by one or more of the factions, and there is no conduit for an individual to become expert in a technology if he does not belong to the appropriate faction. Professions are likewise divided. The skills needed for defense of the town are concentrated, as well as the equipment for this, and this may be turned inward instead of outward, meaning force now can replace volunteerism. The rules by which trade is conducted can be changed. There is little left of village economics in a larger town, although there may be facsimiles within some factions.

This 'town economics', as it might be called, is something that can linger as technology continues onward and onward. The principal derivation from this is that factions become an integral part of an alien civilization, and it would be important to see if they can also be a limiting factor in the progress of the civilization up to the level needed for space travel. A little more subtly, the goals that individuals gain in their upbringing under town economics is different that those in village economics. In town economics the goal is to get a larger share of the benefits for your faction. In village economics, the goal is to increase the overall amount of benefits to be shared within the village. Factionalism may or may not lead to technology progress and utilization, and this question needs to be explored further.

Tuesday, October 9, 2018

The Origins of Moons

There are a lot of moons in our solar system, and it has been impossible to detect whether there are similar numbers in any of the distant solar systems which have been detected or even if there are any at all, with one possible exception. The existence of Earth's moon may have played a large role in the origin of life here, and so it is an interesting question to ask where they might come from. It is certainly not necessary to assume that all moons originate in the same way.

Let's try to imagine the various ways a moon could originate. It could originate in place, in other words, form as a binary planet. A rotating cloud of gas and dust might be spinning too fast to simply condense directly into a single planet, and, similar to the formation of a binary star, the condensation starts in two places and continues to draw in the gas cloud, winding up with a planet and a moon. This would leave both planet and moon spinning rapidly, as the angular momentum of the whole cloud gets collected in the planet and moon, which must spin faster and faster as they condense. Tidal effects take over at this point, and begin to slow down the rotation of the planet and moon, while moving them closer together. If there was differential motion in the gas cloud that they condensed from, so the remainder is not following the same orbit as the planet-moon system, they will move into other regions of cloud and then accrete more mass, which may also affect the rotation and orbital rates over very long periods of time. The moon is smaller, and so it would intercept and accrete directly less gas, but since it is orbiting the planet, it sweeps out a much larger volume that would be swept by the cross-section of the moon. It sweeps out a volume corresponding to the cross-section of the swept volume of the moon's orbit, which can be huge compared to the moon itself. So the moon would grow in mass faster than the planet in this situation. Possibly the Pluto-Charon pair might have this origin.

If not formed in place, there must be a capture event. If the planet, already existing, has a large atmosphere, a smaller object could approach the planet and penetrate the atmosphere, losing relative speed. If its relative velocity was not too different from the planet, this might be enough to put it into an orbit around the planet, and then more passes would tend to circularize the orbit enough to stop the repeated interceptions of the planet's atmosphere, and the usual tidal effects could start their slow process to further circularize the moon's orbit. Both atmospheric drag and tidal pull tend to reduce angular momentum of the orbiting moon relative to the planet, which increases the major axis of the orbit. Tidal pull is stronger at the peri-planet part of the moon's orbit than at the apo-planet, reducing the eccentricity of the orbit. Tidal pull from a rotating planet also serves to reduce the axial tilt of the orbit. Likewise it affects the axial rotation of the moon, meaning it would tend to slow down any large rotation, relative to the planet, that it might have started with.

The reduction of angular momentum by the planet's atmosphere is proportional to the cross-section of the moon, meaning it goes as the square of the moon's mean radius. Angular momentum, however, goes as the mass of the moon, which varies as the third power of the moon's mean radius. This means that the chance of slowing a larger moon is less than that of slowing a smaller one with approximately the same orbit. Some of the moons around our solar system's four large gas giants might have come from this mode of capture. None of the moons is large in mass compared to the planet it orbits.

The likeliness of capture also depends on the relative velocity at the time of atmospheric entry. Too much speed, and the smallest of the impacting objects will burn up. Larger ones will go through the atmosphere and leave with sufficient remaining velocity to stay uncaptured. Gas giants have very deep atmospheres, and so there is also the chance that the impacting object will enter at an angle more steep than just grazing, and go so deep that the drag will overcome all of its velocity. Then its mass would simply be absorbed by the planet. For any giant planet-moon combination, there is probably a very sharp difference between nearby angles of entry, where one leaves the planet forever, another leads to absorption, and the gap between them, capture.

For rocky planets with minimally thick atmospheres, the possibility of capture by atmospheric drag must be very small. The only analog is impacting trajectories. If an object comes in and impacts a rocky planet's surface, it might lose some angular momentum and become a moon. Again there is likely a small gap between an angle of impact where the impactor is simply absorbed by the planet, possibly with some shedding of debris, and an angle of impact where the impactor simply leaves the region of the planet, and there would be a small range of angles where it stays on as a moon. The size of this gap may be negligible for large impactors, with one exception. If the incoming relative velocity is not much more than the additional velocity caused by mutual gravitational pull, the gap might be large enough so that some probability of retention of the moon is possible.

How could this velocity match happen? The first thing to come to mind might be some variation of the gravitational slingshot idea very frequently used in the trajectories of probes heading either toward the sun or toward the outer planets. These are used to augment or decrement the velocity of the probe by using the gravity of the planet and sun. Regrettably, these do not lead to orbital capture, much less low impact velocity. Another possibility is for the planet and impactor to have the same velocity almost exactly, as they would if they were in the same orbit around the sun. If a ring of gas around the sun did not condense into simply one single planet, but into two, at co-Lagrangian points, they would have nearly identical velocities, and if a slow migration started bringing them closer together, their relative velocity at impact would be only that provided by mutual gravity.

The L4 and L5 Lagrangian points are stable, and could conceivably collect mass from a gas ring simultaneously. Currently, there are a few asteroids at these points, but nothing large compared to the planet owning the orbit. Over time, the effect of other planets would probably make the two planets drift out of mutual Lagrangian stability, and thus an impact at slow relative velocity might happen, leading to a moon around a rocky planet. Like the Earth and Luna, for example.

In exo-solar planetary systems, there are often smaller planets at larger distances from the star, so there is no reason to immediately suspect that there would be radius bands for moon capture, mimicing what we have in our own solar system. Here we can hypothesize an inner band where Lagrangian impact might happen, then a band where large gas giants can capture relatively small moons, and then a band where icy planets condense in binary fashion. These bands might not correspond to anything relevant in other systems. However, the same mechanisms might exist, and can potentially serve as a guide for where to search. 

Friday, September 14, 2018

Latitude, Seasonality and Evolution

When we are scanning planets for signs of life, there are levels of priorities based on what attributes the planet has – some planets are more likely to harbor life, as far as we know, than others, and therefore the largest effort should be put into extracting information from these planets.

These parameters are mostly very obvious. We don't want one that is too hot or too cold, as life is an organic process and its molecules are destroyed by heat and inactivated by cold. We don't want one that is too big or too small, as the big ones have to be gas giants as they can hold onto their hydrogen, and the little ones can't hold onto any atmosphere at all. Earthlings think having a small atmosphere is a requirement for life, and it probably is a requirement for the origination of life. An advanced alien civilization might find living on an airless planet not very difficult.

There are two planetary parameters in play here. One is rotation rate and the other is axial tilt. If they are both zero, there is no seasonality. Every minute is the same, provided the ellipticity of the orbit is also small. Unless the atmosphere had some type of difficult-to-imagine instability, then the weather would be the same from one minute to the next and one year to the next as well. It would be possible to define sidereal months, but they would be inconsequential. Nothing would ever change. The assumptions in this extreme case include no moon of significant mass.

Rotation rate goes to zero from the effects of solar tidal forces on the planet. The moon has suffered this and so have other moons in our solar system. No planets have, but Mercury comes close, with a 3:2 phase locking. Venus also has a very low rotation rate. An alien planet with this situation would place life on the planet in a strange situation: nothing every changes about the environment.

This is a different type of fitness test than was present on Earth. There shouldn't be variation in the winds, which would be driven by constant convection forces. Things are about as constant as they can possibly be, and life on such a planet would evolve to a very stable arrangement as well. On a planet such as this, latitude certainly plays a role as it does on every planet, but here longitude is like a variation of latitude. A rotating planet averages over longitude, so that only latitude makes a difference, but on a non-rotator, walking around the equator is very similar to walking to the north pole. There are simply circles of constant illumination, dependent on the angle the sun makes. It keeps the same angle and same position in the sky perpetually. The substellar point would likely be the hottest, and once one passed to the dark side, everything would be cold, except for heating done by winds and the ground.

Winds would likely flow inward on the surface toward the substellar point, driven by the heating of the atmosphere there. That means the flow of air at upper altitudes would be away from the substellar point, and where it would descend is somewhat indeterminate. Likely, descent would be in the circular band near the perimeter where the star is just on the horizon, although it could be a bit inside this. The atmosphere would be too thin to support the toroidal flows that are seen on our solar system's larger planets.

With no tectonics going on, as this needs to be driven by rotation interacting with tidal forces, if there is water, it would be in a circular ring. If the planet were hot enough, no surface water would exist at the substellar point, but as one moved away, there would be a place where water could exist, and perhaps it would create a tremendous moat. On the other side of the moat might be ice, which could continue onto the dark side.

Evolution takes place in a locality, as a huge gene pool takes too long to modify genes by fitness testing. So, in each radial band, circumscribing the substellar point, there would be optimized life forms. Each life form must have some form of mobility, although it might be quite different than here on Earth. With a constant surface wind blowing away from the substellar point, wind-blown seeds would only move outward, and reseeding at the location where a plant was already rooted would not happen. Thus, heavy seeds, such as in a fruit, would be likely in all the various bands.

Evolution likes to migrate, however, so plants would likely have something like rhizomes to move inward toward the substellar point, up to the ring where there is no longer any rain. Animals have no such constraints and could move freely toward and away from the substellar point, as their capabilities to compete in adjacent bands developed.

The other two possibilities, bring closer in or farther out from the star, would provide different bull's eye patterns. Too far out and there would be ice everywhere, with only snow falling near the substellar point and nothing beyond a certain radius. Too far in and there would be no liquid water on the lighted side, and perhaps some chemotropes living in the dark but wet band just past the light boundary.

Whether or not life could originate on such a planet depends on how it originates. If the theory expounded in this blog, the organic oceans theory, where life only could originate in an early Earth-like setting, would rule out life originating on a phase-locked planet, unless some very unusual planetary movements had taken place. Maybe if there was a moon, but it eventually drifted so far out that it could detach from its planet, and then the planet became phase-locked, something might be possible. If some other theory is the correct one, such as the sea-vent concept, this planet would would be a loser, as without continents and oceans, there would be no sea vents. Perhaps life would find a completely unique way of originating on such a planet however, but out preoccupation with life here on Earth inhibits our realizing how it might happen.