Extraterrestrial Life: About Correcting the Drake Equation and the Great Filter
I also wanted to express my thoughts on this topic, especially after reading ideas for correcting the Drake equation. Although, it is rather a development of the idea of a great filter with a small amendment, that it is not one, but at each stage of evolution. But I’ll start with the methodology of the Drake equation, mentioning that I mean that the universe is probably teeming with life, but in the form of microbes, and intelligent beings may not meet in the whole cluster of galaxies.
According to current data, it turns out that indeed almost all stars have planets, even neutron stars. Probably, it was not possible to estimate only the presence of planets in black holes, but even then a question arises about the representativeness of the existing sample, because the distance is important for the detection and study of exoplanets, and for the most part the sample is around the solar system with a radius of about 1000 light years, which is an insignificant part of the galaxy.
But if we estimate the representativeness of the sample purely theoretically, it turns out a lot of reducing factors. Gravitational waves were discovered quite recently, and they are obviously extremely weak on earth, but in the center of the galaxy, where there are many black holes, gravitational storms are possible. Even if it does not interfere with the formation of planets, then they will be almost incessant earthquakes, volcanic eruptions, etc., that is, the existence of viable planets in the center of the galaxy is extremely unlikely. It is worth adding here the effect of intense X-rays from neutron stars and the vicinity of black holes, in front of which the planet’s atmosphere may not survive. The percentage of galaxy stars whose planets are in unfavorable conditions for any complex organisms turns out to be quite significant.
But if you roughly estimate what the planet can wait on the outskirts of the galaxy, the situation looms much better. First, the question arises whether they are there, especially, how many of them are rocky. The outskirts of the galaxy can have fewer heavy elements, and gas planets can hardly support life more complicated than microbial. But even if there is, it may lack elements for organic substances. Secondly, the outskirts of the galaxy may be more vulnerable to external influences, the presence of intergalactic asteroids, planets, neutron stars and black holes is very likely;
It turns out that a small fraction of the stars of the galaxy can have favorable for the complex life of the planet. But not every galaxy can have a "cozy periphery." In quasars, gravitational storms and high-energy radiation can cover the entire galaxy. In too small galaxies, larger galaxies can have a similar effect, besides, in small galaxies, there may also not be enough heavy elements to form rocky planets. As a result, the proportion of stars that have planets favorable for life in the observable universe is even lower.
Then you can go one step further and consider the probability of the birth of life under favorable conditions. Theoretically, it can be assumed that if panspermia is possible, it plays a complementary role to abiogenesis, that is, life on the planets can appear in both ways, depending on what happens before. Facts on this topic can add enceladus research. But while these facts are not, it can be assumed that panspermia is possible within certain distances, that is, bacteria can overcome some interstellar space, but not containing a large number of neutron stars and black holes. But then, if abiogenesis is a very unlikely event, and there are few favorable planets for life in some galaxy or their cluster, then life may not appear on them.
Returning to the assessment of the proportion of suitable for life of the planets, it is worth noting that there can be a lot of factors, and first of all they influence the fact that the planet is suitable for how complex life forms. It is very likely that the location of the giant planets in the solar system further from the sun provides protection from meteorites, and, most likely, it was the giant planets that caused the existence of an asteroid belt, and the distance from it to the earth is most favorable. fall more often. The current data on exoplanets can hardly be representative, because the current capabilities are much more suitable for finding large planets close to a star, which makes it difficult to estimate the proportion of planets that are favorable for development.
Another factor is probably the presence of the moon. Such an assumption arises at least from the fact that the moon is one of the largest satellites in the solar system, while the earth is in the second half of the list of planets ordered by size reduction. Moreover, it is likely that this ratio is close to the limit of a stable one. Regardless of the plausibility of the assumption that mercury could be a satellite of Venus, there is an assumption that such a system is unstable, in principle, the gravitational effect of a not very large asteroid or comet may be enough to tear too massive a satellite from the orbit of a too small planet.
At the expense of the mechanisms of the influence of the moon, you can build different assumptions, the reliability of which is difficult to assess now due to the lack of suitable data on other planets. As an example of a possible mechanism of influence, one can cite a variant on the effect of the gravity of the moon on volcanic activity. If the gravity of the moon periodically provokes small volcanic eruptions, this may prevent the increase of magmatic pressure and the onset of a period of very high volcanic activity observed on Venus. Probably, it is the moderate volcanic activity that provides the atmosphere density that is favorable for the existence of life, while extreme variants are observed on the neighboring planets on the earth.
Probably, the possibility of the formation of complex life forms is affected by the presence of certain elements. It is highly likely that phosphorus allowed complex organisms to develop on earth. It is worth noting that there may be other forms of life for which extreme temperatures may be favorable for terrestrial organisms, but probably not all of them, for some reason, can develop into complex forms. Even if the assumption about a different structure of cells of probable organisms on titanium is correct, then such forms cannot form complex organisms, otherwise the Huygens probe would find them b. A different basis than carbon, for which higher temperatures may be favorable, is unlikely due to the lower prevalence of alternative elements, so in this case the probability of abiogenesis becomes so low
Estimating according to the currently existing data the proportion of habitable planets, it is worth mentioning about probably widespread water worlds, which with some probability can be related to the closest known exoplanets proxiM-b. Of course, the start of the operation of the telescope named after J. Webb will be able to add a lot of facts about the prevalence of aquatic worlds and their suitability for life, but if we start from facts that are currently known, including the inhabitants of the Earth’s oceans, we can make an assumption that intelligent beings never or never appear on planets without continents. The composition of the oceans can also affect the complexity of organisms, some exoplanets can have oceans with high content of acids or salts, it is possible that most of them.
Thus, the prevalence of extraterrestrial life, most likely, can be represented in the form of a diagram. The number on the "top of the pyramid" is chosen arbitrarily, it only indicates the assumption that the absence of at least one planet with intelligent creatures in the whole galaxy is a very likely event, i.e. selected based on the approximate number of planets in the galaxy.
We should also mention the last factor of the Drake equation, that is, the share of technically advanced civilizations. The most notable known fact is the ratio of the period of existence of people on earth and the duration of the known history, and in particular the period of technical progress. The fact that the present technically developed civilization on earth is the first one can be sure that if a technically developed civilization had once appeared in some peoples or even in hypothetically previously existing rational beings, then the traces could not disappear completely. Polymers, like many other modern materials, are subject to natural decomposition substantially less than most natural, therefore, man-made traces could not disappear earlier than dinosaur skeletons. However, There is no doubt about the existence of non-technical civilizations among Maya Indians or in Ancient Egypt, and nothing is known about the disappearance of the first of these civilizations. Probably, the emergence of a technical civilization in Western Europe in the nineteenth century was caused by a rare coincidence of several factors, for example, the existence of previous ancient states and the subsequent period of the Middle Ages.
The second of them, which had a period of inquisition, most likely reduced the number of people with extrasensory and other abilities, which probably predetermined the technical path of development. Probably, these are by no means all the factors, the coincidental coincidence of which ensured the emergence of a technical civilization. It is highly likely that this is strongly influenced by the features of the planet itself - the location of the continents, oceans, islands, the force of gravity, the duration of a year and a day, the orbital period of satellites, and many more. Mechanisms of influence can be very different - through the characteristics of the climatic seasons, tides and ebb of coastal settlements, the preferred materials for the construction of dwellings, the ability to move around the planet and many other options. In view of this, if we assume the existence of a certain number of alien civilizations in the observable universe,