For the evolution of living organisms from the simplest forms (viruses, bacteria) to intelligent beings, huge time intervals are required, since the "driving force" of such selection is mutations and natural selection - processes that are random. It is through a large number of random processes that the regular development from lower forms life to the higher. On the example of our planet Earth, we know that this time interval, apparently, exceeds a billion years. Therefore, only on planets orbiting sufficiently old stars, we can expect the presence of highly organized living beings. When current state astronomy, we can only talk about the arguments in favor of the hypothesis of multiplicity planetary systems and the possibility of life emerging on them. Astronomy does not yet have a rigorous proof of these most important statements. In order to talk about life, one must at least assume that sufficiently old stars have planetary systems. For the development of life on the planet, it is necessary that a number of general conditions be fulfilled. And it is quite obvious that not every planet can have life.
We can imagine around every star that has a planetary system, a zone where temperature conditions do not exclude the possibility of life development. It is unlikely that it is possible on planets like Mercury, the temperature of the part illuminated by the Sun is higher than the melting point of lead, or like Neptune, whose surface temperature is -200 ° C. However, one cannot underestimate the enormous adaptability of living organisms to unfavorable environmental conditions. It should also be noted that very high temperatures are much more “dangerous” for the vital activity of living organisms than low ones, since the simplest types of viruses and bacteria can, as is known, be in a state of suspended animation at temperatures close to absolute zero.
In addition, it is necessary that the radiation of the star remains approximately constant for many hundreds of millions and even billions of years. For example, the vast class of variable stars whose luminosities vary greatly with time (often periodically) should be excluded from consideration. However, most stars radiate with surprising consistency. For example, according to geological data, the luminosity of our Sun over the past several billion years has remained constant with an accuracy of several tens of percent.
For life to appear on the planet, its mass should not be too small. On the other hand, too large a mass is also an unfavorable factor, on such planets the probability of the formation of a solid surface is small, they usually represent gas balls with a rapidly growing density towards the center (for example, Jupiter and Saturn). One way or another, the masses of planets suitable for the development of life should be limited both from above and below. Apparently, the lower limit of the possibilities of the mass of such a planet is close to several hundredths of the Earth's mass, and the upper limit is ten times greater than the Earth's. The chemical composition of the surface and atmosphere is very important. As you can see, the limits of the parameters of the planets suitable for life are quite wide.
To study life, one must first of all define the concept of “living matter”. This question is far from simple. Many scientists, for example, define living matter as complex protein bodies with an orderly metabolism. This point of view was adhered to, in particular, by Academician A.I. Oparin, who was much involved in the problem of the origin of life on Earth. Of course, metabolism is an essential attribute of life, but the question of whether the essence of life can be reduced primarily to metabolism is controversial. Indeed, in the world of non-living, for example, in some solutions, metabolism is observed in its simplest forms. The question of defining the concept of "life" is very acute when we discuss the possibilities of life on other planetary systems.
Nowadays life is not defined through internal structure and the substances that are inherent in it, and through its functions: the "control system", which includes a mechanism for the transmission of hereditary information, ensuring the safety of subsequent generations. Thus, due to the inevitable hindrances in the transmission of such information, our molecular complex (organism) is capable of mutations, and hence of evolution.
The emergence of living matter on Earth (and, as can be judged by analogy, on other planets) was preceded by a rather long and complex evolution of the chemical composition of the atmosphere, which ultimately led to the formation of a number of organic molecules. These molecules subsequently served as "building blocks" for the formation of living matter.
According to modern data, the planets are formed from a primary gas-dust cloud, the chemical composition of which is similar chemical composition Suns and stars, their original atmosphere consisted mainly of the simplest compounds of hydrogen - the most common element in space. Most of them were molecules of hydrogen, ammonia, water and methane. In addition, the primary atmosphere should have been rich in inert gases - primarily helium and neon. At present, there are few noble gases on Earth, since at one time they dissipated (evaporated) into interplanetary space, like many hydrogen-containing compounds.
However, it seems that the decisive role in establishing the composition of the earth's atmosphere was played by plant photosynthesis, in which oxygen is released. It is possible that some, and maybe even a significant amount of organic matter was brought to Earth during the fall of meteorites and, possibly, even comets. Some meteorites are quite rich in organic compounds. It is estimated that over 2 billion years meteorites could have brought to Earth from 108 to 1012 tons of such substances. Also, organic compounds can arise in small quantities as a result of volcanic activity, meteorite strikes, lightning, due to the radioactive decay of some elements.
There are quite reliable geological data indicating that already 3.5 billion years ago the Earth's atmosphere was rich in oxygen. On the other hand, the age of the earth's crust is estimated by geologists at 4.5 billion years. Life should have originated on Earth before the atmosphere became rich in oxygen, since the latter is mainly a product of the vital activity of plants. According to a recent estimate by the American expert on planetary astronomy Sagan, life on Earth originated 4.0-4.4 billion years ago.
The mechanism of the complication of the structure of organic substances and the appearance in them of properties inherent in living matter is currently still insufficiently studied, although in recent times there are great advances in this area of \u200b\u200bbiology. But it is already clear that such processes have been going on for billions of years.
Any combination of amino acids and other organic compounds, however complex, is not yet a living organism. It is possible, of course, to assume that under some exceptional circumstances, somewhere on Earth, a kind of “praDNA” arose, which served as the beginning of all living things. It is unlikely, however, that this is so if the hypothetical “praDNA” was quite similar to the modern one. The fact is that modern DNA itself is completely helpless. It can only function with the presence of enzyme proteins. To think that purely by chance, by “shaking up” individual proteins - polyatomic molecules, such a complex machine as “pradDNA” and the complex of proteins-enzymes necessary for its functioning could arise - this means believing in miracles. However, it can be assumed that DNA and RNA molecules evolved from a more primitive molecule.
For the first primitive living organisms formed on the planet, high doses of radiation can pose a mortal danger, since mutations will occur so quickly that natural selection will not keep pace with them.
Another question that deserves attention is: why does life on Earth not arise from inanimate matter in our time? This can only be explained by the fact that the life that has arisen earlier will not give an opportunity for a new birth of life. Microorganisms and viruses will literally eat up the first shoots of new life. The possibility that life on Earth arose by chance cannot be completely ruled out.
There is one more circumstance that may be worth paying attention to. It is well known that all "living" proteins consist of 22 amino acids, while over 100 amino acids are known in total. It is not entirely clear how these acids differ from their other "brothers". Is there some deep connection between the origin of life and this amazing phenomenon?
If life on Earth arose by chance, then life in the Universe is the rarest (although, of course, by no means an isolated) phenomenon. For a given planet (as, for example, our Earth), the occurrence of a special form of highly organized matter, which we call "life", is an accident. But in the vast expanses of the Universe, the life that arises in this way should be a natural phenomenon.
It should be noted once again that the central problem of the origin of life on Earth - the explanation of the qualitative leap from “inanimate” to “living” - is still far from clear. No wonder one of the founders of modern molecular biology Professor Crick said at the Byurakan Symposium on Extraterrestrial Civilizations in September 1971: “We do not see the path from primordial soup to natural selection. It can be concluded that the origin of life is a miracle, but this only testifies to our ignorance. "
The troubling question of life on other planets has occupied the minds of astronomers for centuries. The possibility of the very existence of planetary systems in other stars is only now becoming the subject of scientific research. Earlier, the question of life on other planets was the area of \u200b\u200bpurely speculative conclusions. Meanwhile, Mars, Venus and other planets of the solar system have long been known as non-self-luminous solid celestial bodies surrounded by atmospheres. It has long been clear that in general terms they resemble the Earth, and if so, why not have life on them, even highly organized, and, who knows, intelligent?
It is quite natural to believe that the physical conditions prevailing on the terrestrial planets (Mercury, Venus, Earth, Mars) that had just formed from the gas-dusty environment were very similar, in particular, their initial atmospheres were the same.
The main atoms that make up those molecular complexes from which living matter was formed are hydrogen, oxygen, nitrogen and carbon. The role of the latter is especially important. Carbon is a tetravalent element. Therefore, only carbon compounds lead to the formation of long molecular chains with rich and variable side branches. It is to this type that various protein molecules belong. Silicon is often referred to as a carbon substitute. Silicon is fairly abundant in space. In stellar atmospheres, its content is only 5-6 times less than carbon, that is, it is quite large. It is unlikely, however, that silicon can play the role of the "cornerstone" of life. For some reason, its compounds cannot provide such a wide variety of side branches in complex molecular chains as carbon compounds. Meanwhile, the richness and complexity of such lateral branches is precisely what provides a huge variety of properties of protein compounds, as well as the exceptional “information content” of DNA, which is absolutely necessary for the emergence and development of life.
The most important condition for the origin of life on the planet is the presence on its surface of a sufficiently large amount of liquid Medium. In such an environment, organic compounds are in a dissolved state and favorable conditions can be created for the synthesis of complex molecular complexes on their basis. In addition, newly formed living organisms need a liquid medium to protect themselves from the harmful effects of ultraviolet radiation, which at the initial stage of the planet's evolution can freely penetrate to its surface.
It can be expected that only water and liquid ammonia can be such a liquid shell, many compounds of which, by the way, are similar in structure organic compoundsm, due to which the possibility of the emergence of life on an ammonia basis is currently being considered. The formation of liquid ammonia requires a relatively low surface temperature of the planet. In general, the significance of the temperature of the original planet for the emergence of life on it is very great. If the temperature is high enough, for example, above 100 ° C, and the pressure of the atmosphere is not very high, a water shell cannot form on its surface, let alone an ammonia shell. In such conditions, there is no need to talk about the possibility of the origin of life on the planet.
Based on the foregoing, we can expect that the conditions for the emergence of life on Mars and Venus in the distant past could, generally speaking, be favorable. The liquid shell could only be water, not ammonia, which follows from the analysis of the physical conditions on these planets at the time of their formation. At present, these planets are quite well studied, and nothing indicates the presence of even the simplest forms of life on any of the planets of the solar system, let alone intelligent life. However, it is very difficult to obtain clear indications of the existence of life on a particular planet through astronomical observations, especially when it comes to a planet in another star system. Even in the most powerful telescopes, under the most favorable observation conditions, the dimensions of the details still distinguishable on the surface of Mars are equal to 100 km.
Before that, we only defined the most general conditions under which life can (not necessarily should) arise in the Universe. Such a complex form of matter as life depends on a large number of completely unrelated phenomena. But all this reasoning concerns only the simplest forms of life. When we move on to the possibility of certain manifestations of intelligent life in the Universe, we are faced with very great difficulties.
Life on a planet must undergo a tremendous evolution before becoming intelligent. The driving force behind this evolution is the ability of organisms to mutate and natural selection. In the process of such evolution, organisms become more and more complex, and their parts become specialized. Complication is going both in qualitative and quantitative directions. For example, a worm has only about 1000 nerve cells, while a human has about ten billion. Development nervous system significantly increases the ability of organisms to adapt, their plasticity. These properties of highly developed organisms are necessary, but, of course, not sufficient for the emergence of intelligence. The latter can be defined as the adaptation of organisms for their complex social behavior... The emergence of the mind should be closely related to the radical improvement and improvement of the methods of exchange of information between individuals. Therefore, for the history of the emergence of intelligent life on Earth, the emergence of language was of decisive importance. Can we, however, consider such a process as universal for the evolution of life in all corners of the Universe? Most probably not! Indeed, in principle, under completely different conditions, the means of information exchange between individuals could be not longitudinal vibrations of the atmosphere (or hydrosphere) in which these individuals live, but something completely different. Why not imagine a way of information exchange based not on acoustic effects, but, say, optical or magnetic ones? And in general - is it really necessary that life on any planet in the process of its evolution becomes intelligent?
Meanwhile, this topic has worried mankind since time immemorial. Speaking about life in the Universe, they always, first of all, meant intelligent life. Are we alone in the endless expanses of space? Since ancient times, philosophers and scientists have always been convinced that there are many worlds where intelligent life exists. No scientifically substantiated arguments have been presented in favor of this statement. The reasoning, in essence, was conducted according to the following scheme: if there is life on the Earth, one of the planets of the solar system, then why should it not be on other planets? This method of reasoning, if developed logically, is not so bad. And in general it is scary to imagine that out of 1020 - 1022 planetary systems in the Universe, in an area with a radius of ten billion light years, the mind exists only on our tiny planet ... But maybe intelligent life is an extremely rare phenomenon. It may be, for example, that our planet as the abode of intelligent life is the only one in the Galaxy, and not all galaxies have intelligent life. Can any work on intelligent life in the Universe be considered scientific in general? Probably, after all, with the current level of technology development, it is possible and necessary to deal with this problem now, especially since it may suddenly turn out to be extremely important for the development of civilization ...
Finding any life, especially a sentient one, could make a huge difference. Therefore, attempts have been made for a long time to discover and establish contact with other civilizations. In 1974, an automatic interplanetary station "Pioneer-10". Several years later, she left the solar system, completing various scientific assignments. There is a negligible chance that someday, after many billions of years, highly civilized alien beings unknown to us will discover Pioneer-10 and meet it as a messenger of an alien, unknown to us, world. For this case, a steel plate is laid inside the station with a pattern and symbols engraved on it, which give minimal information about our earthly civilization. This image is compiled in such a way that the intelligent beings who found it could determine the position of the solar system in our Galaxy, would guess about our appearance and, possibly, intentions. But of course an extraterrestrial civilization has a much better chance of finding us on Earth than finding Pioneer 10.
The question of the possibility of communication with other worlds was first analyzed by Cocconi and Morris in 1959. They came to the conclusion that the most natural and feasible communication channel between any civilizations separated by interstellar distances can be established using electromagnetic waves. The obvious advantage of this type of communication is the propagation of a signal at the highest possible speed in nature, equal speed propagation of electromagnetic waves, and the concentration of energy within relatively small solid angles without any significant scattering. The main disadvantages of this method are the low power of the received signal and strong interference arising from the huge distances and cosmic radiation. Nature itself tells us that transmissions should go at a wavelength of 21 centimeters (the wavelength of radiation of free hydrogen), while the loss of signal energy will be minimal, and the probability of receiving a signal by an extraterrestrial civilization is much greater than at a randomly taken wavelength. Most likely, we should expect signals from space on the same wavelength.
But let's say we detected some strange signal. Now we must move on to the next, rather important question. How to recognize the artificial nature of the signal? Most likely, it should be modulated, that is, its power should change regularly over time. At first, it should, apparently, be fairly simple. After the signal is received (if, of course, this happens), two-way radio communication will be established between civilizations, and then you can begin to exchange more complex information. Of course, one should not forget that the answers can be received in this case no earlier than in a few tens or even hundreds of years. However, the exceptional importance and value of such negotiations must certainly compensate for their slowness.
Radio observations of several nearby stars have already been carried out several times within the framework of the large OMZA project in 1960 and with the telescope of the US National Radio Astronomy Laboratory in 1971. A large number of expensive projects of establishing contacts with other civilizations have been developed, but they are not funded, and so far very few real observations have been carried out.
Despite the obvious advantages of space radio communication, we should not lose sight of other types of communication, since it is impossible to say in advance what signals we can deal with. Firstly, it is optical communication, the main drawback of which is a very weak signal level, because, despite the fact that the angle of divergence of the light beam was brought to 10 -8 rad., Its width at a distance of several light years will be huge. Also, communication can be carried out using automatic probes. For obvious reasons, this type of communication is not yet available to earthlings, and will not become available even with the start of using controlled thermonuclear reactions. When launching such a probe, we would have encountered a huge number of problems, even if we consider the time of its flight to the target acceptable. In addition, there are already more than 50,000 stars less than 100 light-years from the solar system. Which one should the probe be sent to?
Thus, the establishment of direct contact with extraterrestrial civilization from our side is still impossible. But maybe we should just wait? Here it is impossible not to mention the very urgent problem of UFOs on Earth. So many different cases of "observation" of aliens and their activity have already been noticed that in no case it is impossible to unequivocally refute all these data. We can only say that many of them, as it turned out over time, were inventions or the result of an error. But this is already a topic for other studies.
If some form of life or civilization is found somewhere in space, then we absolutely, even approximately, cannot imagine how its representatives will look and how they will react to contact with us. What if this reaction will be, from our point of view, negative. Then it's good if the level of development of extraterrestrial beings is lower than ours. But it may turn out to be immeasurably higher. Such a contact, given the normal attitude towards us from another civilization, is of the greatest interest. But one can only guess about the level of development of aliens, and nothing at all can be said about their structure.
Many scientists are of the opinion that civilization cannot develop beyond a certain limit, and then it either dies or no longer develops. For example, the German astronomer von Horner named six reasons, in his opinion, that could limit the duration of the existence of a technically advanced civilization:
- 1) complete destruction of all life on the planet;
- 2) the destruction of only highly organized beings;
- 3) physical or spiritual degeneration and extinction;
- 4) loss of interest in science and technology;
- 5) lack of energy for the development of a very highly developed civilization;
- 6) the lifetime is unlimited;
Von Horner considers this latter possibility quite incredible. Further, he believes that in the second and third cases, on the same planet, another civilization may develop on the basis (or on the debris) of the old one, and the time of such a “renewal” is relatively short.
From 5 to 11 September 1971, the first international conference on the problem of extraterrestrial civilizations and communication with them was held at the Byurakan Astrophysical Observatory in Armenia. The conference was attended by competent scientists working in various fields related to the complex problem under consideration - astronomers, physicists, radiophysics, cybernetics, biologists, chemists, archaeologists, linguists, anthropologists, historians, sociologists. The conference was organized jointly by the USSR Academy of Sciences and the US National Academy of Sciences with the involvement of scientists from other countries. Many aspects of the problem of extraterrestrial civilizations were discussed in detail at the conference. The questions of the plurality of planetary systems in the Universe, the origin of life on Earth and the possibility of the emergence of life on other space objects, the emergence and evolution of intelligent life, the emergence and development of a technological civilization, the problems of searching for signals from extraterrestrial civilizations and traces of their activities, problems of establishing communication with them, as well as the possible consequences of establishing contacts.
Last month, at the 223rd meeting of the American Astronomical Society, an important discovery was announced: Using equipment from the Kepler Space Observatory, researchers discovered a planet of approximately Earth's mass, orbiting a star outside the solar system. The new planet, GJ 1241b, is larger than our planet, but smaller than Neptune. But most importantly, the Hubble telescope showed that there are clouds in the atmosphere of the celestial body.
This, of course, is not enough to assert that there is life on this planet. In addition, GJ 1241b does not revolve around the massive and hot Sun, but around a small and cold (by cosmic standards) star - a red dwarf. Red dwarfs from Earth cannot be seen with the naked eye, although this type of star is the most common in our galaxy. And in the past few years, many studies have shown that these small stars are the best candidates for looking around them for so-called exoplanets, on which life could hypothetically exist.
The chances that such planets may have water temperatures that are optimal for living organisms are much higher than on planets orbiting super-hot stars. After all, the formation of the Earth is a unique case within the Universe, billions of different conditions and variables converged in such a way that life developed on it. In other cases known to mankind, planets revolving around stars like the Sun are not suitable for existence. Therefore, the researchers suggest that life forms on exoplanets, if any, are significantly different from those on Earth.
GJ 1214b (ESO)
Many scientists, however, believe that hopes of finding something living on exoplanets are still futile.
First, red dwarfs emit much less light and heat than many other stars in the universe. In addition, exoplanets do not rotate around their axis, so there will always be day and high temperature on its side close to the star, and eternal night and cold on the opposite side. Such a temperature difference creates strong disturbances in the planet's atmosphere: a very strong wind will blow from one side to the other and heavy torrential rains will go.
Radiation creates a lot of questions. Earth is reliably protected by magnetic fields, and terrestrial life forms are unlikely to survive under the brutal radiation of red dwarfs. In addition, these stars are very unstable. Due to powerful flares, the brightness of the star rises in a very short time and destroys all living things.
All these phenomena are arguments that life on exoplanets is unlikely. But that was until recently. In July, researchers from the University of Chicago, USA, suggested that this is not entirely true. They compiled a climate model, which explained that the very temperature difference makes the existence of life on these cosmic bodies possible. It was suggested that the clouds in the "daytime" part of the planet, being very dense, reflect a large amount of heat and radiation emanating from red dwarfs, while in the "nighttime" part, the opposite is true - the sky is cloudless.
GJ 1214b (ESO)
Thanks to this contrast, the streams of the wind created would carry heat evenly throughout the planet. As a result, the habitable area around the red dwarfs expands significantly. In some places on the planet, plants would be able to adapt to such conditions, but they would have to "grow" themselves a powerful root system to resist powerful air currents. Their foliage would be black, which would help them catch even the faintest rays of light streaming through the atmosphere. After all, it is light that is the basis of photosynthesis and the life of plants.
In addition, red dwarfs "live" for a very, very long time - trillions and trillions of years. In order for life to originate on Earth, it took "only" half a billion, so, despite the harshest, by our standards, conditions, living organisms on exoplanets have enough time to develop, evolve and adapt. The phase of active flares of red dwarfs lasts only the first one and a half billion years, so the amount of emitted radiation will be significantly reduced after they have passed.
That is why many scientists share the opinion that if where it is worth looking for life in the Universe, it is around red dwarfs. In 2017, NASA will launch an exoplanetary satellite specifically for this purpose. So who knows, maybe there, on the surface of an exoplanet, far beyond the solar system, for a long time a different and completely alien to us intelligent civilization is tormented by the same question: is there life elsewhere in the Universe?
A rare person has not thought about whether there is another life in the Universe besides earthly. It would be naive and even selfish to believe that only on planet Earth there is intelligent life. UFO appearance facts in different parts light, historical manuscripts, archaeological excavations suggest that people are not alone in the universe. Moreover, there are “contactees” who communicate with representatives of other civilizations. At least they say so.
Double standard
Unfortunately, most of the discoveries made under the auspices of the government are classified as "Top Secret", which hides from ordinary people a lot of facts about the existence of other forms of life in the Universe. For example, several thousand images taken from the surface of Mars have gone missing, which show channels, unusual structures and pyramids.
You can talk for a long time about the possible life within the solar system and beyond, but the scientific world needs evidence that can be felt, looked at.
The last interesting discovery
For several generations of scientists have been trying to find evidence of the existence of intelligent life in the Universe. Recently, a regular meeting of the American Astronomical Society took place, during which an important event was announced: with the help of the Kepler observatory equipment, it was possible to find a planet that is very similar to the Earth in both its parameters and astronomical position.
It would seem, what's the big deal? It turns out that the atmosphere of the discovered planet has clouds formed by water! Of course, the presence of clouds does not mean anything if we consider the question of the existence of life on the planet. Although thirty years ago, scientists assured that the presence of water on the planet would mean that there is life on it. Clouds are direct evidence of the presence of water.
Although it has long been known that Venus also has clouds, they are composed of sulfuric acid. In such conditions, life cannot develop on the surface of the planet.
To answer a number of questions, scientists under the auspices of NASA decided to send a satellite in 2017, which will go beyond the solar system. He will have to find evidence of intelligent life outside of it.
Maybe it’s not worth looking for Earth?
According to many researchers, representatives of other civilizations periodically visit our Earth. It was they who left the Kerch catacombs, underground codes under the Ural Mountains, in Peru, in Antarctica, which are still used today. Very well written about them in the books of G. Sidorov "Chronological and esoteric analysis of the development of human civilization." There are many facts on its pages that confirm the existence of intelligent life outside the solar system.
Until now, experts cannot answer the question of how the pyramids were built in Egypt, Mexico and Peru. It is quite reasonable to assume that they were erected by representatives
In 2005, Heather Smith of the International Space University in Strasbourg and Chris McKay of NASA's Ames Research Center prepared a paper examining the possibility of life based on methane, the so-called methanogens. Such life forms could consume hydrogen, acetylene and ethane, exhaling methane instead of carbon dioxide.
This could make possible habitable zones for life in cold worlds like Saturn's moon Titan. Like Earth, Titan's atmosphere is mostly nitrogen, but mixed with methane. Titan is also the only place in our solar system, besides the Earth, where there are large liquid bodies of water - lakes and rivers of an ethane-methane mixture. (Underground bodies of water are also present on Titan, its sister moon Enceladus, and Jupiter's moon Europa.) Liquid is considered essential for molecular interactions in organic life and of course the focus will be on water, but ethane and methane also allow such interactions to occur.
NASA and ESA's Cassini-Huygens mission in 2004 observed a dirty world with a temperature of -179 degrees Celsius, where the water was rock-hard, and methane floated through river valleys and basins into polar lakes. In 2015, a team of chemical engineers and astronomers at Cornell University developed a theoretical cell membrane made of small organic nitrogen compounds that could function in Titan's liquid methane. They named their theoretical cell "nitrogenosome", which literally means "nitrogenous body", and it had the same stability and flexibility as the earth's liposome. The most interesting molecular compound was the acrylonitrile azotosome. Acrylonitrile, a colorless and toxic organic molecule, is used for acrylic paints, rubber and thermoplastics on Earth; it was also found in the atmosphere of Titan.
The implications of these experiments for the search for extraterrestrial life are difficult to overestimate. Life not only could potentially develop on Titan, but it can also be detected by hydrogen, acetylene and ethane traces on the surface. Methane-dominated planets and moons may not only be around Sun-like stars, but also around red dwarfs in a wider "". If NASA launches the Titan Mare Explorer in 2016, we will have detailed information about the possible life on nitrogen as early as 2023.
Silicon based life
Silicon-based life is perhaps the most common form of alternative biochemistry, beloved by popular science and fiction - remember the Horta from Star Trek. This idea is far from new, its roots go back to 1894: “What fantastic imagination could run out of such an assumption: imagine silicon-aluminum organisms - or, perhaps, silicon-aluminum people at once? - that travel through an atmosphere of gaseous sulfur, let's say, on seas of liquid iron with a temperature of several thousand degrees or something like that, just above the temperature of a blast furnace.
Silicon remains popular precisely because it is very similar to carbon and can form four bonds, like carbon, which opens up the possibility of creating a biochemical system completely dependent on silicon. This is the most common element in earth crustif you don't count oxygen. There are algae on earth that incorporate silicon into their growth process. Silicon plays a second role after carbon, because it can form more stable and diverse complex structures necessary for life. Carbon molecules include oxygen and nitrogen, which form incredibly strong bonds. Silicon-based complex molecules, unfortunately, tend to disintegrate. In addition, carbon is extremely abundant in the universe and has been around for billions of years.
Silicon-based life is unlikely to emerge in an earth-like environment, since most of the free silicon will be trapped in volcanic and igneous rocks of silicate materials. It is believed that in a high-temperature environment, everything may be different, but no evidence has yet been found. An extreme world like Titan could support silicon-based life, possibly coupled with methanogens, since silicon molecules like silanes and polysilanes can mimic Earth's organic chemistry. However, Titan's surface is dominated by carbon, while most of the silicon is located deep below the surface.
NASA astrochemist Max Bernstein suggested that silicon-based life could exist on a very hot planet, with an atmosphere rich in hydrogen and poor in oxygen, allowing complex silane chemistry with silicon reverse bonds to happen with selenium or tellurium, but this, according to Bernstein, is unlikely. On Earth, such organisms would multiply very slowly, and our biochemistry would not interfere with each other in any way. They, however, could slowly eat up our cities, but "a jackhammer could be applied to them."
Other biochemical options
Basically, there have been quite a few proposals for life systems based on anything other than carbon. Like carbon and silicon, boron also tends to form strong covalent molecular bonds, forming different structural hydride variants in which boron atoms are linked by hydrogen bridges. Like carbon, boron can bind with nitrogen, forming compounds, chemical and physical properties similar alkanes, the simplest organic compounds. The main problem with boron-based life is that it is a fairly rare element. Boron-based life will be most appropriate in an environment that is cold enough for liquid ammonia, then chemical reactions will be more controlled.
Another possible life form that has received some attention is arsenic-based life. All life on Earth is made up of carbon, hydrogen, oxygen, phosphorus and sulfur, but in 2010 NASA announced that it had found the bacteria GFAJ-1, which could incorporate arsenic instead of phosphorus into the cellular structure without any consequences for itself. GFAJ-1 lives in the arsenic-rich waters of Lake Mono in California. Arsenic is poisonous to any living creature on the planet, except for a few microorganisms that normally carry it or breathe it. GFAJ-1 is the first time the body has incorporated this element as a biological building block. Independent experts diluted this claim a little when they found no evidence of arsenic included in DNA, or even any arsenates. Nevertheless, interest has flared up in possible biochemistry based on arsenic.
Ammonia has also been proposed as a possible alternative to water for building life forms. Scientists have hypothesized the existence of a biochemistry based on nitrogen-hydrogen compounds that use ammonia as a solvent; it could be used to create proteins, nucleic acids and polypeptides. Any ammonia-based life must exist at low temperatures, at which ammonia takes on a liquid form. Solid ammonia is denser than liquid ammonia, so there is no way to stop it freezing when it gets cold. For unicellular organisms, this would not be a problem, but it would cause chaos for multicellular organisms. Nevertheless, there is a possibility of the existence of unicellular ammonia organisms on the colder planets of the solar system, as well as on gas giants like Jupiter.
Sulfur is believed to be the basis for the beginning of metabolism on Earth, and known organisms that metabolize sulfur instead of oxygen exist in extreme conditions on Earth. Perhaps in another world, sulfur-based life forms could gain an evolutionary advantage. Some people think that nitrogen and phosphorus could also take the place of carbon under very specific conditions.
Memetic life
Richard Dawkins believes that the basic principle of life sounds like this: "All life develops thanks to the mechanisms of survival of reproducing creatures." Life should be able to reproduce (with some assumptions) and be in an environment where natural selection and evolution will be possible. In his book The Selfish Gene, Dawkins noted that concepts and ideas are generated in the brain and disseminated among people through communication. In many ways, this resembles the behavior and adaptation of genes, which is why he calls them "memes." Some people compare the songs, jokes and rituals of human society to the first stages of organic life - free radicals floating in the ancient seas of the Earth. The creations of the mind reproduce, evolve and struggle to survive in the realm of ideas.
Similar memes existed before humanity, in the social calls of birds and the learned behavior of primates. When humanity became able to think abstractly, memes received further development, governing tribal relations and forming the basis for early traditions, culture, and religion. The invention of writing further pushed the development of memes, as they were able to spread through space and time, transmitting memetic information in a similar way to how genes transmit biological information. For some, this is a pure analogy, but others believe that memes represent a unique, albeit slightly rudimentary and limited form of life.
Life on Earth is based on two information-carrying molecules, DNA and RNA, and scientists have long wondered if other similar molecules could be created. While any polymer can store information, RNA and DNA represent heredity, coding and transmission genetic information and are able to adapt over time in the process of evolution. DNA and RNA are chains of nucleotide molecules consisting of three chemical components - phosphate, a five-carbon sugar group (deoxyribose in DNA or ribose in RNA) and one of five standard bases (adenine, guanine, cytosine, thymine, or uracil).
In 2012, a group of scientists from England, Belgium and Denmark was the first in the world to develop xenonucleic acid (XNA, XNA), synthetic nucleotides that functionally and structurally resemble DNA and RNA. They were developed by replacing the sugar groups of deoxyribose and ribose with various substitutes. Such molecules have been made before, but for the first time in history they were able to reproduce and evolve. In DNA and RNA, replication occurs by polymerase molecules that can read, transcribe, and reverse transcribe normal nucleic acid sequences. The group developed synthetic polymerases that created six new genetic systems: HNA, CeNA, LNA, ANA, FANA, and TNA.
One of the new genetic systems, HNA, or hexitonucleic acid, was robust enough to store the right amount of genetic information that could serve as the basis for biological systems. Another, threosonucleic acid, or TNA, turned out to be a potential candidate for the mysterious primary biochemistry that reigned at the dawn of life.
There are many potential uses for these advances. Further research could help develop better models for the emergence of life on Earth and will have implications for biological inventions. XNA has therapeutic uses because it is possible to create nucleic acids to treat and bind to specific molecular targets that do not deteriorate as quickly as DNA or RNA. They can even form the basis molecular machines or even an artificial life form.
But before this is possible, other enzymes must be developed that are compatible with one of the XNAs. Some of them were already developed in the UK at the end of 2014. There is also the possibility that XNA can harm RNA / DNA organisms, so safety must come first.
Chromodynamics, Weak Nuclear Force, and Gravitational Life
In 1979, scientist and nanotechnologist Robert Freitas Jr. proposed a possible non-biological life. He stated that the possible metabolism of living systems is based on four fundamental forces - electromagnetism, strong nuclear force (or quantum chromodynamics), weak nuclear force, and gravity. Electromagnetic life is the standard biological life we \u200b\u200bhave on Earth.
Chromodynamic life could be based on a strong nuclear force, which is considered the strongest of the fundamental forces, but only over extremely short distances. Freitas theorized that such a medium might be possible in a neutron star, a heavy rotating object 10-20 kilometers in diameter with the mass of a star. With incredible density, the most powerful magnetic field and gravity 100 billion times stronger than on Earth, such a star would have a core with a 3-kilometer crust of crystalline iron. Beneath it there would be a sea with incredibly hot neutrons, various nuclear particles, protons and atomic nuclei, and possible neutron-rich "macro-nuclei". These macronuclei, in theory, could form large supernuclei, analogous to organic molecules, neutrons would act as the equivalent of water in a bizarre pseudobiological system.
Freitas saw life forms based on weak nuclear interactions as unlikely, since weak forces operate only in the subnuclear range and are not particularly strong. As beta radioactive decay and free decay of neutrons often show, weak interactions life forms could exist with careful control of weak interactions in their environment. Freitas envisioned creatures made up of atoms with excess neutrons that become radioactive when they die. He also suggested that there are regions of the Universe where a weak nuclear force is stronger, which means that the chances of such life emerging are higher.
Gravitational beings can exist too, since gravity is the most abundant and effective fundamental force in the universe. Such creatures could receive energy from gravity itself, receiving unlimited power from collisions of black holes, galaxies, and other celestial objects; smaller creatures from the rotation of the planets; the smallest - from the energy of waterfalls, wind, tides and ocean currentspossibly earthquakes.
Dust and Plasma Life Forms
Organic life on Earth is based on molecules with carbon compounds, and we have already figured out possible compounds for alternative forms. But in 2007 international group scientists headed by V.N.Tsytovich from the Institute general physics Of the Russian Academy Sci. has documented that under the right conditions, inorganic dust particles can collect in spiral structures, which will then interact with each other in a manner inherent to organic chemistry... This behavior is also born in the plasma state, the fourth state of matter after solid, liquid and gaseous, when electrons are detached from atoms, leaving a mass of charged particles.
Tsytovich's group found that when electron charges are separated and the plasma is polarized, the particles in the plasma self-organize into spiral structures like a corkscrew, electrically charged, and are attracted to each other. They can also divide by making copies of original structures, like DNA, and induce charges in their neighbors. According to Tsytovich, “these complex, self-organizing plasma structures meet all the necessary requirements to be considered as candidates for inorganic living matter. They are autonomous, they reproduce and they evolve. "
Some skeptics believe such claims are more attention grabbing than serious scientific claims. Although helical structures in plasma may resemble DNA, similarity in shape does not necessarily imply similarity in function. Moreover, the fact that the spirals reproduce does not mean the potential for life; clouds do it too. Even more disheartening, much of the research has been done on computer models.
One of the participants in the experiment also reported that although the results did resemble life, in the end they were "just a special form of plasma crystal." And yet, if inorganic particles in plasma can grow into self-replicating, evolving life forms, they could be the most abundant form of life in the universe, thanks to the ubiquitous plasma and interstellar dust clouds throughout the cosmos.
Inorganic chemical cells
Professor Lee Cronin, a chemist at the College of Science and Engineering at the University of Glasgow, dreams of creating living cells from metal. He uses polyoxometallates, a series of metal atoms bonded to oxygen and phosphorus, to create cell-like bubbles, which he calls "inorganic chemical cells," or iCHELLs (an acronym that can be translated as "neocheleta").
Cronin's group began by creating salts from negatively charged ions of large metal oxides bound to a small positively charged ion like hydrogen or sodium. A solution of these salts is then injected into another saline solution full of large positively charged organic ions bound to small negatively charged ones. The two salts meet and exchange parts, so that the large metal oxides become partners with the large organic ions, forming a kind of bubble that is impervious to water. By modifying the backbone of the metal oxide, the bubbles can acquire the properties of biological cell membranes that selectively pass and release chemicals from the cell, which could potentially allow the same type of controlled chemical reactions that occurs in living cells.
The team has also made bubbles within bubbles by mimicking the internal structures of biological cells and has made progress in creating an artificial form of photosynthesis that could potentially be used to create artificial plant cells. Other synthetic biologists point out that such cells may never become alive until they have a system of replication and evolution like DNA. Cronin does not lose hope that further development will bear fruit. Possible applications of this technology also include the development of materials for solar fuel devices and, of course, medicine.
According to Cronin, “the main goal is to create comprehensive chemical cells with living properties that can help us understand the development of life and follow the same path to bring new technologies based on evolution into the material world - a kind of inorganic living technologies. "
Von Neumann probes
Machine-based artificial life is a fairly common idea, almost trivial, so let's just look at von Neumann probes so as not to bypass it. They were first invented in the middle of the 20th century by the Hungarian mathematician and futurist John von Neumann, who believed that in order to reproduce the functions of the human brain, a machine must have mechanisms of self-control and self-healing. So he came up with the idea of \u200b\u200bcreating self-reproducing machines, based on observations of the increasing complexity of life in the process of reproduction. He believed that such machines could become a kind of universal constructor, which could allow not only creating complete replicas of itself, but also improving or changing versions, thereby carrying out evolution and increasing complexity over time.
Other futurists like Freeman Dyson and Eric Drexler quickly applied these ideas to space exploration and created the von Neumann probe. Sending a self-replicating robot into space may be the most efficient way to colonize a galaxy, as it can capture everything in less than one million years, even at the speed of light.
As Michio Kaku explained:
“The von Neumann probe is a robot designed to reach distant stellar systems and create factories that will build thousands of copies of themselves. A dead moon, not even a planet, could be an ideal destination for von Neumann probes, as it will make it easier to land and take off from those moons, and also because the moons do not have erosion. The probes could live off the land, mining iron, nickel and other raw materials to build robotic factories. They would create thousands of copies of themselves, which would then disperse in search of other star systems. "
Over the years, various versions of the basic idea of \u200b\u200bthe von Neumann probe have been devised, including exploration and exploration probes for quietly exploring and observing extraterrestrial civilizations; communication probes scattered throughout space to better pick up alien radio signals; working probes for the construction of supermassive space structures; colonizing probes that will conquer other worlds. There may even be guiding probes that will take young civilizations into space. Alas, there may be berserker probes, whose task will be to destroy traces of any organic matter in space, followed by the construction of police probes that will reflect these attacks. Given that von Neumann probes can become a kind of space virus, we should be careful when developing them.
Gaia's hypothesis
In 1975, James Lovelock and Sidney Upton co-wrote an article for the New Scientist entitled "Finding Gaia." Adhering to the traditional view that life originated on Earth and flourished due to the right material conditions, Lovelock and Upton suggested that life thus took an active role in maintaining and determining the conditions for its survival. They suggested that all living matter on Earth, in the air, oceans and on the surface is part of a single system that behaves like a superorganism that is able to adjust the temperature on the surface and the composition of the atmosphere in a way necessary for survival. They named this system Gaia, after the Greek earth goddess. It exists to maintain homeostasis, thanks to which the biosphere can exist on earth.
Lovelock has been working on the Gaia hypothesis since the mid-1960s. The basic idea is that the Earth's biosphere has a number of natural cycles, and when one goes awry, others compensate for it in a way that maintains vital capacity. This could explain why the atmosphere is not made entirely of carbon dioxide or why the seas are not too salty. Although volcanic eruptions made the early atmosphere predominantly carbon dioxide, nitrogen-producing bacteria and plants emerged that produce oxygen through photosynthesis. Millions of years later, the atmosphere has changed in our favor. While rivers carry salt to the oceans from rocks, the salinity of the oceans remains stable at 3.4% as salt seeps through cracks in the ocean floor. These are not conscious processes, but the result feedbackthat keeps the planets in habitable equilibrium.
Other evidence includes that if it weren't for biotic activity, methane and hydrogen would disappear from the atmosphere in just a few decades. In addition, despite a 30% increase in the Sun's temperature over the past 3.5 billion years, the average global temperature has staggered by only 5 degrees Celsius, thanks to a regulatory mechanism that removes carbon dioxide from the atmosphere and traps it in fossilized organic matter.
Initially, Lovelock's ideas were met with ridicule and accusations. Over time, however, Gaia's hypothesis influenced the ideas about the Earth's biosphere, helping to form their integral perception in the scientific world. Today, Gaia's hypothesis is respected rather than accepted by scientists. Rather, it is a positive cultural framework within which scientific research on the Earth as a global ecosystem should be conducted.
Paleontologist Peter Ward developed the competitive Medea hypothesis, named after the mother who killed her children, in Greek mythology, the main idea of \u200b\u200bwhich is that life is inherently self-destructive and suicidal. He points out that historically most mass extinctions have been caused by life forms such as microorganisms or hominids in pants, which severely injure the Earth's atmosphere.
Based on materials from listverse.com
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"Are we alone in the universe?" - one of the eternal questions of humanity, which forces us to build giant telescopes, launch satellites to distant planets and come up with the most incredible theories. For many decades, people have been tirelessly searching for extraterrestrial life, and, as scientists say, we have found something.
website collected for you 7 most that neither is scientific evidence that we are not alone in the universe.
1. Tiny bacteria on meteorites
Over the millions of years of our planet's existence, tens of thousands of meteorites have fallen on it. Some of them belong to the Martian class. Namely, those in which at least hints of the existence of extraterrestrial life were found.
One such meteorite is Nakhla, which fell in Egypt in 1911. But they began to study it only 80 years later, in 1999. Inside a piece of meteorite, filamentous structures were found, which usually leave behind bacteria. Terrestrial organisms could not get into the center of the millennial stone in any way, so it is possible that the bacteria that left behind these traces were not from the Earth.
Another meteorite, Shergotti, was found in India in 1865. When they finally tackled it, they discovered deep within it the presence of certain elements that could only form in water. The age of these elements is several tens of thousands of years. Scientists concluded: "This meteorite spent most of its life submerged in water."
2. Signal "WoW!"
Researchers at Ohio State University on August 15, 1977, while working on the Big Ear radio telescope, was caught strong and strange signal , the source of which was outside the solar system. The sound was so unexpected to cameraman Dr. Jerry Eiman that he circled the corresponding group of symbols on the printout and signed the side "Wow!" ("Wow!").
There are many theories and supposed transcripts of these sounds, but none have been found to be reliable. Subsequently, scientists have repeatedly tried to catch a similar radio signal, but no matter how long they listened to space, this could not be done.
3. Evidence in history
Egyptian hieroglyphs found in the temple of Seti I at Abydos have a very strange appearance. They depict something similar to a helicopter, an airship and a submarine. This find caused a lot of controversy among Egyptologists and archaeologists, who still have not found a scientific explanation.
The painting, painted by Domenico Ghirlandaio in the 15th century, depicts the Virgin Mary, and behind her you can see a man looking at some kind of luminous ball in the sky that looks like a flying ship.
Another artifact of antiquity that haunts scientists is Enigmalite. This is a stone containing a built-in element, the purpose of which is not clear, but in appearance it resembles a plug from electrical appliances. The approximate age of this stone is 100,000 years.
4. Living atmosphere of Mars
More recently, data from the Curiosity rover have confirmed that the Red Planet has a fairly high methane content. On Earth, 95% of this gas is produced by living organisms, and the remaining 5% is released as a result of volcanic activity.
Scientists say that Martian methane in such concentrations should be renewable, as it actively decays under ultraviolet light and radiation. This means that it most likely appeared not from volcanoes, but as a result of living processes.
5. Life can exist everywhere
Open space is destructive for living beings, but some are able to survive in it for long periods of time.
For example, a moth walker can survive temperatures ranging from -273 to +151 ° C and exposure to radiation 1,000 times the lethal dose for any other creature on the planet. Can live in an atmosphere of hydrogen sulfide and carbon dioxide. And it is also capable of losing almost 100% of all its liquid.
Swedish scientists conducted an experiment and placed the tardigrade on the surface space station... After 10 days in outer space, the organisms were dried up, but upon returning to the ISS, they came to life again.
If life from our planet can exist in the most extreme conditions, then why not be outside the Earth.