Extraterrestrial life causes a lot of controversy among scientists. Ordinary people often think about the existence of aliens. To date, many facts have been found that confirm that there is also life outside the Earth. Do aliens exist? You can find out this, and much more, in our article.

Space exploration

An exoplanet is a planetoid that is located outside the solar system. Scientists are actively exploring space. In 2010, more than 500 exoplanets were discovered. However, only one of them is similar to Earth. Small-sized cosmic bodies began to be discovered relatively recently. Most often, exoplanets are gas planetoids resembling Jupiter.

Astronomers are interested in “living” planets that are in a favorable zone for the development and origin of life. A planetoid on which there may be human-like creatures must have a solid surface. Another important factor is comfortable temperature.

“Living” planets should also be located away from sources of harmful radiation. According to scientists, clean water must be present on the planetoid. Only such an exoplanet can be suitable for the development of different forms of life. Researcher Andrew Howard is confident in the existence of a huge number of planets similar to Earth. He says he wouldn't be surprised if every 2nd or 8th star has a planetoid that is similar to ours.

Amazing Research

Many people are interested in whether extraterrestrial life forms exist. Scientists from California working in the Hawaiian Islands have discovered a new planet around the star It is located about 20 light years from us. The planetoid is located in a zone comfortable for living. None of the other planets have such a favorable location. It has a comfortable temperature for the development of life. Experts say that, most likely, there is clean drinking water there. Such However, experts do not know whether there are creatures similar to humans there.

The search for extraterrestrial life continues. Scientists have found that a planet similar to ours is about 3 times heavier than Earth. It circles around its axis in 37 Earth days. The average temperature ranges from 30 degrees Celsius to 12 degrees Celsius below zero. It is not yet possible to visit it. It will take several generations to reach it. Of course, there is definitely life there in some form. Scientists report that comfortable conditions do not guarantee the presence of intelligent creatures.

Other planets similar to Earth have been found. They are at the edges of the Gliese 5.81 comfort zone. One of them is 5 times heavier than the Earth, and the other is 7 times heavier. What would creatures of extraterrestrial origin look like? Scientists say that humanoids that may live on planets around Gliese 5.81 are likely to be short and broad-bodied.

They have already tried to establish contact with creatures that may live on these planets. Experts sent a radio signal there using a radio telescope located in Crimea. Surprisingly, it will be possible to find out whether aliens really exist around 2028. It is by this time that the message will reach the addressee. If extraterrestrial beings respond immediately, then we will be able to hear their answer around 2049.

Scientist Raghbir Batal claims that at the end of 2008 he received a strange signal from the region of Gliese 5. 81. It is possible that extraterrestrial beings tried to make themselves known even before habitable planets were discovered. Scientists promise to decipher the received signal.

About extraterrestrial life

Extraterrestrial life has always been of interest to scientists. Back in the 16th century, an Italian monk wrote that life exists not only on Earth, but also on other planets. He argued that creatures living on other planets may be different from humans. The monk believed that there was room in the Universe for different forms of development.

It was not only the monk who thought that we are not alone in the Universe. The scientist claims that life on Earth could have originated thanks to microorganisms that came from space. He suggests that the development of humanity can be observed by residents of other planetoids.

NASA experts were once asked to tell us how they imagine aliens. Scientists claim that planetoids that have a large mass should be home to flat, crawling creatures. It is still impossible to say whether aliens really exist and what they look like. The search for exoplanets continues today. 5 thousand of the most promising cosmic bodies favorable for life are already known.

Signal decoding

Another strange radio signal was received last year in the Russian Federation. Scientists claim that the message was sent from a planetoid located 94 light years from Earth. They believe the signal strength indicates an unnatural origin. Scientists suggest that extraterrestrial life cannot exist on this planetoid.

Where will alien life be found?

Some scientists suggest that the first planet on which extraterrestrial life will be found will be Earth. We are talking about meteorites. To date, it is officially known about 20 thousand alien bodies that have been found on Earth. Some of them contain organic substances. For example, 20 years ago the world learned about a meteorite in which fossilized microorganisms were found. The body is of Martian origin. It was in space for about three billion years. After many years of travel, the meteorite ended up on Earth. However, evidence that could make it possible to understand its origin has never been found.

Scientists believe that the best carrier of microorganisms is a comet. 15 years ago, the so-called “red rain” was observed in India. The Taurus found in the composition is of extraterrestrial origin. 6 years ago it was proven that the resulting microorganisms can carry out their life activities at 121 degrees Celsius. They do not develop at room temperature.

Alien Life and the Church

Many have repeatedly thought about the existence of alien life. However, the Bible denies that we are not alone in the Universe. According to scripture, the Earth is unique. God created it for life, and other planets are not intended for this. The Bible describes all stages of the creation of the Earth. Some believe that this is no coincidence, because, in their opinion, other planets were created for other purposes.

A huge number of science fiction films have been made. In them, anyone can see what aliens might look like. According to the Bible, an intelligent extraterrestrial being will not be able to receive redemption because it is only meant for humans.

Extraterrestrial life does not agree with the Bible. It is impossible to be confident in a scientific or church theory. There is no significant evidence that alien life exists. All planetoids are formed by chance. It is possible that some of them have favorable conditions for life.

UFO. Why does there be a belief in aliens?

Some believe that anything that cannot be recognized is a UFO. They claim that it is certainly possible to see something in the firmament that cannot be recognized. However, these can be flares, space stations, meteorites, lightning, false suns and much more. A person who is not familiar with all of the above may assume that he saw a UFO.

More than 20 years ago, a program about extraterrestrial life was shown on television. Some believe that belief in aliens is associated with a feeling of loneliness in space. Extraterrestrial beings could have medical knowledge that could cure the population of many diseases.

Alien emergence of life on Earth

It is no secret that there is a theory about the extraterrestrial origin of life on Earth. Scientists argue that this opinion arose because none of the theories of earthly origins have explained the appearance of RNA and DNA. Evidence in favor of the extraterrestrial theory was found by Chandra Wickramsingh and his colleagues. Scientists believe that radioactive substances in comets can retain water for up to a million years. A number of hydrocarbons provide another important condition for the emergence of life. The information received is confirmed by missions that took place in 2004 and 2005. Organic substances and clay particles were found in one of the comets, and a number of complex hydrocarbon molecules were found in the second.

According to Chandra, the entire Galaxy contains a huge amount of clay components. Their number significantly exceeds that contained on the young Earth. The chance of life arising in comets is more than 20 times higher than on our planet. These facts prove that life may have originated in space. At the moment, carbon dioxide, sucrose, hydrocarbons, molecular oxygen and much more have been found.

Pure aluminum in stock

Three years ago, a resident of one of the cities of the Russian Federation found a strange object. It resembled a piece of a gear wheel that had been inserted into a piece of coal. The man was going to light the stove with it, but changed his mind. The find seemed strange to him. He took it to the scientists. Experts examined the find. They found that the object was made of almost pure aluminum. In their opinion, the age of the find is about 300 million years. It is worth noting that the appearance of the object would not have occurred without the intervention of intelligent life. However, humanity learned to create such parts no earlier than in 1825. It was believed that the object was part of an alien ship.

Sandstone statue

Does extraterrestrial life exist? The facts cited by some scientists make us doubt that we are the only intelligent beings in the Universe. 100 years ago, archaeologists discovered an ancient sandstone statue in the jungles of Guatemala. The facial features were not similar to the appearance of the peoples who lived in this territory. Scientists believe that the statue depicted an ancient alien, whose civilization was more advanced than the locals. There is an assumption that the find previously had a torso. However, this has not been confirmed. Perhaps the statue was created later. However, the exact date of its origin is impossible to know, since it previously served as a target, and is now almost destroyed.

Mysterious stone object

18 years ago, computer genius John Williams discovered a strange stone object in the ground. He dug it up and cleared it of dirt. John discovered that the object had a strange electrical mechanism attached to it. In appearance, the device resembled an electric plug. The find is described in a large number of printed publications. Many argued that this was nothing more than a high-quality fake. At first, John refused to send the item for research. He tried to sell the find for 500 thousand dollars. Over time, William agreed to send the item for research. The first analysis showed that the object is about 100 thousand years old, and the mechanism located inside could not be created by man.

Predictions from NASA

Scientists regularly find evidence of extraterrestrial life. However, they are not enough to verify the existence of aliens. NASA experts say we will know the truth about space by 2028. Ellen Stofan (head of NASA) believes that within the next ten years, humanity will receive evidence that will confirm that life exists beyond Earth. However, significant facts will be known in 20-30 years. The scientist claims that it is already clear where to look for evidence. He knows exactly what needs to be found. He reports that several planets are already known today on which there is drinking water. Ellen Stefan emphasizes that his group is looking for microorganisms, not aliens.

Let's sum it up

Extraterrestrial life raises many questions. Some believe that it exists, while others deny it. To believe in extraterrestrial life or not is a personal matter for everyone. However, today there is a large amount of evidence that forces everyone to assume that we are not alone in the Universe. It is possible that in a few years we will know the whole truth about space.

Search for life in the solar system Horowitz Norman H

Chapter 4. Is there life on other planets?

Nevertheless, most planets are undoubtedly inhabited, and the uninhabited ones will eventually be inhabited.

Thus, I can express everything stated above in the following general form: the substance from which the inhabitants of various planets are composed, including animals and plants from them, in general should be lighter and thinner... the further the planets are from the Sun. The perfection of thinking beings, the speed of their ideas... become more beautiful and perfect, the farther from the Sun the celestial body on which they live is located.

Since the degree of probability of this dependence is so great that it is close to complete reliability, then we have scope for interesting assumptions based on a comparison of the properties of the inhabitants of different planets.

Immanuel Kant. "General Natural History and Theory of the Sky"

In the XVII–XVIII centuries. people were convinced that the planets of the solar system were inhabited. Christiaan Huygens (1629–1695), who can rightfully be considered one of the founders of modern astronomy, believed that on Mercury, Mars, Jupiter and Saturn there are fields “warmed by the good warmth of the Sun and irrigated by fruitful dews and showers.” In the fields, Huygens thought, plants and animals live. Otherwise, these planets “would be worse than our Earth,” which he considered absolutely unacceptable. This argument, which sounds so strange these days, was based on the ideas about the surrounding world developed by Copernicus, according to which the Earth does not occupy a special place among the planets, and Huygens shared these views. For the same reason, he believed that intelligent beings should live on the planets, “perhaps not exactly people like ourselves, but living beings or some other creatures endowed with intelligence.” Such a conclusion seemed so indisputable to Huygens that he wrote: “If I am mistaken in this, then I no longer know when I can trust my reason, and I can only be content with the role of a pitiful judge in the true assessment of things.”

Although Huygens was mistaken on this issue (it turned out that other planets are still much “worse” than the Earth, at least as a place for life to exist), his reputation as a scientist did not suffer from this. His genius was all-encompassing, and his discoveries in mathematics, mechanics, astronomy and optics laid the foundations of modern science. For us, the lesson is that when it comes to the problem of the existence of extraterrestrial life, even the most talented scientists can follow the wrong path.

As can be judged from the epigraph to this chapter, little has changed in these ideas a century later. Immanuel Kant was not only convinced that life could and should exist on planets, but also believed that the level of organization of their inhabitants increases as the planet moves away from the Sun.

Of course, in the 17th–18th centuries. Little was known about the planets, and even less about the nature of life. Around the same time that Huygens was arguing for the possibility of extraterrestrial life, Francesco Redi proved that animals were not capable of spontaneous generation, and thus took another step towards understanding the essence of life. All this happened long before biologists and planetary scientists gained the ability to realistically assess the suitability of planets for life. As we learn from this and the next chapter, by 1975, the time of the flight of the Viking spacecraft, of all the planets known to Huygens and his contemporaries, only Mars continued to be considered a possible site for the existence of extraterrestrial life.

Criteria for habitability of planets

Temperature and pressure

If our assumption that life must be based on carbon chemistry is correct, then the limiting conditions for any environment capable of supporting life can be precisely established. First of all, the temperature should not exceed the stability limit of organic molecules. Determining the limiting temperature is not easy, but for our purpose exact numbers are not required. Because temperature and pressure effects are interdependent, they must be considered together. Assuming a pressure of approximately 1 atm (as on the surface of the Earth), one can estimate the upper temperature limit of life, given that many of the small molecules that make up the genetic system, such as amino acids, quickly break down at temperatures of 200–300 °C. Based on this, we can conclude. that areas with temperatures above 25 °C are uninhabited. (This does not mean, however, that life is determined only by amino acids; we have chosen them only as typical representatives of small organic molecules.) The actual temperature limit of life should almost certainly be lower than this, since large molecules with complex three-dimensional structures, in particular proteins , built from amino acids, are generally more sensitive to heat than small molecules. The upper temperature limit for life on the Earth's surface is close to 10 °C, and some species of bacteria can survive in hot springs under these conditions. However, the vast majority of organisms die at this temperature.

It may seem strange that the upper temperature limit of life is close to the boiling point of water. Is this coincidence due precisely to the fact that liquid water cannot exist at a temperature above its boiling point (10 °C on the earth’s surface), and not to some special properties of living matter itself?

Many years ago, Thomas D. Brock, an expert on thermophilic bacteria, suggested that life could be found wherever liquid water exists, regardless of its temperature. To raise the boiling point of water, you need to increase the pressure, as happens, for example, in a sealed pressure cooker. Increased heating causes water to boil faster without changing its temperature. Natural conditions in which liquid water exists at temperatures above its normal boiling point are found in areas of underwater geothermal activity, where superheated water pours out of the earth's interior under the combined action of atmospheric pressure and the pressure of a layer of ocean water. In 1982, K. O. Stetter discovered bacteria for which the optimal development temperature was 105 °C at a depth of up to 10 m in a zone of geothermal activity. Since the pressure under water at a depth of 10 m is 1 atm, the total pressure at this depth reached 2 atm. The boiling point of water at this pressure is 121 °C.

Indeed, measurements showed that the water temperature in this place was 103 °C. Therefore, life is possible at temperatures above the normal boiling point of water.

Obviously, bacteria that can exist at temperatures of about 10 °C have a “secret” that ordinary organisms lack. Since these thermophilic forms grow poorly or not at all at low temperatures, it is fair to assume that ordinary bacteria also have their own “secret”. A key property that determines the ability to survive at high temperatures is the ability to produce thermostable cellular components, especially proteins, nucleic acids and cell membranes. Proteins in ordinary organisms undergo rapid and irreversible changes in structure, or denaturation, at temperatures around 6 °C. An example is the coagulation of chicken egg albumin (egg white) during cooking. The proteins of bacteria living in hot springs do not experience such changes until a temperature of 9 °C. Nucleic acids are also subject to heat denaturation. The DNA molecule is then divided into its two constituent strands. This usually occurs in the temperature range of 85-100 °C, depending on the ratio of nucleotides in the DNA molecule.

Denaturation destroys the three-dimensional structure of proteins (unique to each protein), which is necessary for its functions such as catalysis. This structure is supported by a whole set of weak chemical bonds, as a result of which the linear sequence of amino acids that forms the primary structure of the protein molecule fits into a special conformation characteristic of a given protein. The bonds that support the three-dimensional structure are formed between amino acids located in different parts of the protein molecule. Mutations of the gene, which contains information about the amino acid sequence characteristic of a particular protein, can lead to changes in the composition of amino acids, which in turn often affects its thermal stability. This phenomenon opens the door for the evolution of thermostable proteins. The molecular structure that ensures the thermal stability of nucleic acids and cell membranes of bacteria living in hot springs also appears to be genetically determined.

Because increasing pressure prevents water from boiling at its normal boiling point, it can also prevent some of the damage to biological molecules associated with exposure to high temperatures. For example, pressure of several hundred atmospheres suppresses the thermal denaturation of proteins. This is explained by the fact that denaturation causes the helical structure of the protein molecule to unwind, accompanied by an increase in volume. By preventing volume expansion, pressure prevents denaturation. At much higher pressures, 5000 atm or more, it itself becomes the cause of denaturation. The mechanism of this phenomenon, which involves compression destruction of the protein molecule, is not yet clear. Exposure to very high pressure also increases the thermal stability of small molecules, since high pressure prevents the expansion of volume caused by the breaking of chemical bonds. For example, at atmospheric pressure, urea is rapidly destroyed at a temperature of 13 °C, but is stable, at least for an hour, at 20 °C and a pressure of 29 thousand atm.

Molecules in solution behave completely differently. When interacting with a solvent, they often disintegrate at high temperatures. The general name for such reactions is solvation; If the solvent is water, the reaction is called hydrolysis. (Reactions 1 and 2, shown on page 63, are typical examples of hydrolysis when traced from right to left.) Reaction 1, shown here as hydrolysis (3), reflects the fact that amino acids exist as electrically charged ions in solution .

Hydrolysis is the main process by which proteins, nucleic acids and many other complex biological molecules are destroyed in nature. Hydrolysis occurs, for example, during the digestion process in animals, but it also occurs outside living systems, spontaneously, especially at high temperatures. Electric fields arising during solvolytic reactions lead to a decrease in the volume of the solution through electrostriction, i.e., binding of neighboring solvent molecules. Therefore, it should be expected that high pressure should accelerate the process of solvolysis, and experiments confirm this.

Since we believe that vital processes can only occur in solutions, it follows that high pressure cannot raise the upper temperature limit of life, at least in such polar solvents as water and ammonia. A temperature of about 10 °C is probably a reasonable limit. As we will see, this excludes many planets in the solar system from consideration as possible habitats.

Atmosphere

The next condition necessary for the habitability of a planet is the presence of an atmosphere. Quite simple compounds of light elements, which, according to our assumptions, form the basis of living matter, are, as a rule, volatile, that is, they are in a gaseous state over a wide temperature range. Apparently, such compounds are necessarily produced in metabolic processes in living organisms, as well as during thermal and photochemical effects on dead organisms, which are accompanied by the release of gases into the atmosphere. These gases, the simplest examples of which on Earth are carbon dioxide (carbon dioxide), water vapor and oxygen, are eventually included in the cycle of substances that occurs in living nature. If the earth’s gravity could not hold them, they would evaporate into outer space, our planet would eventually exhaust its “reserves” of light elements and life on it would cease. Thus, if life arose on some cosmic body whose gravitational field was not strong enough to hold an atmosphere, it could not exist for long.

It has been suggested that life could exist beneath the surface of celestial bodies such as the Moon, which have either a very thin atmosphere or no atmosphere at all. This assumption is based on the fact that gases can be captured in the subsurface layer, which becomes the natural habitat of living organisms. But since any habitat that has arisen under the surface of the planet is deprived of the main biologically important source of energy - the Sun, such an assumption only replaces one problem with another. Life needs a constant influx of both matter and energy, but if matter participates in the circulation (this determines the need for an atmosphere), then energy, according to the fundamental laws of thermodynamics, behaves differently. The biosphere is able to function as long as it is supplied with energy, although its various sources are not equivalent. For example, the solar system is very rich in thermal energy - heat is generated in the depths of many planets, including the Earth. However, we do not know of organisms that would be able to use it as a source of energy for their life processes. To use heat as an energy source, the body must probably function like a heat engine, that is, transfer heat from an area of ​​high temperature (for example, from a gasoline engine cylinder) to an area of ​​low temperature (to the radiator). In this process, part of the transferred heat is converted into work. But in order for efficiency of such heat engines was quite high, a high temperature of the “heater” is required, and this immediately creates enormous difficulties for living systems, as it gives rise to many additional problems.

None of these problems are caused by sunlight. The sun is a constant, virtually inexhaustible source of energy, which is easily used in chemical processes at any temperature. Life on our planet is entirely dependent on solar energy, so it is natural to assume that nowhere else in the solar system could life develop without the direct or indirect consumption of this type of energy.

The fact that some bacteria are able to live in the dark, using only inorganic substances for nutrition, and carbon dioxide as the only source of carbon, does not change the essence of the matter. Such organisms, called chemolithoautotrophs (which literally means: feeding themselves on inorganic chemicals), obtain the energy needed to convert carbon dioxide into organic substances by oxidizing hydrogen, sulfur or other inorganic substances. But these energy sources, unlike the Sun, are depleted and after use cannot be restored without the participation of solar energy. Thus, hydrogen, an important source of energy for some chemolithoautotrophs, is formed under anaerobic conditions (for example, in swamps, at the bottom of lakes or in the gastrointestinal tract of animals) through the decomposition under the action of bacteria of plant material, which itself, of course, is formed during the process of photosynthesis. Chemolithoautotrophs use this hydrogen to produce methane and substances necessary for cell life from carbon dioxide. Methane enters the atmosphere, where it decomposes under the influence of sunlight to form hydrogen and other products. The Earth's atmosphere contains hydrogen at a concentration of 0.5 parts per million; almost all of it was formed from methane released by bacteria. Hydrogen and methane are also released into the atmosphere during volcanic eruptions, but in much smaller quantities. Another significant source of atmospheric hydrogen is the upper layers of the atmosphere, where, under the influence of solar UV radiation, water vapor decomposes, releasing hydrogen atoms that escape into outer space.

The numerous populations of various animals - fish, shellfish, mussels, giant worms, etc., which have been found to live near hot springs discovered at a depth of 2500 m in the Pacific Ocean, are sometimes credited with the ability to exist independently of solar energy. Several such zones are known: one near the Galapagos archipelago, the other at a distance of about 21 to the northwest, off the coast of Mexico. Food supplies are notoriously scarce in the deep ocean, and the discovery of the first such population in 1977 immediately raised the question of their food source. One possibility appears to be the use of organic matter that accumulates on the ocean floor, debris resulting from biological activity in the surface layer; they are transported to areas of geothermal activity by horizontal currents resulting from vertical emissions of hot water. The upward movement of superheated water causes the formation of bottom horizontal cold currents directed to the point of release. It is assumed that organic remains accumulate here in this way.

Another source of nutrients became known after it was discovered that thermal spring water contained hydrogen sulfide (H 2 S). It is possible that chemolithoautotrophic bacteria are located at the beginning of the food chain. As further studies have shown, chemolithoautotrophs are indeed the main source of organic matter in the ecosystem of thermal springs. The bacteria in question carry out the following reaction:

where CH 2 O means a carbohydrate or, in general, any cell substance.

Since the “fuel” for these deep-sea communities is hydrogen sulfide formed in the depths of the Earth, they are usually considered as living systems that can do without solar energy. However, this is not entirely true, since the oxygen they use to oxidize the “fuel” is a product of photochemical transformations. There are only two significant sources of free oxygen on Earth, and both are associated with solar activity. The main one is photosynthesis, which occurs in green plants (as well as in some bacteria):

where C 6 H 12 O 6 is the carbohydrate glucose. Another, less significant source of free oxygen is photolysis of water vapor in the upper atmosphere. If a microorganism could be discovered in a geothermal source that uses only gases formed in the depths of the Earth for life, this would mean that a type of metabolism has been discovered that is absolutely independent of solar energy.

It should be remembered that the ocean plays an important role in the life of the described deep-sea ecosystem, since it provides an environment for the thermal spring organisms, without which they could not exist. The ocean provides them not only with oxygen, but also with all the necessary nutrients, with the exception of hydrogen sulfide. It removes waste. And it also allows these organisms to move to new areas, which is necessary for their survival, since the sources are short-lived - according to estimates, their lifespan does not exceed 10 years. The distance between individual thermal springs in one area of ​​the ocean is 5-10 km.

Solvent

It is now generally accepted that a necessary condition for life is also the presence of a solvent of one type or another. Many chemical reactions occurring in living systems would be impossible without a solvent. On Earth, such a biological solvent is water. It is the main component of living cells and one of the most common compounds on the earth's surface. Due to the fact that the chemical elements that form water are widely distributed in outer space, water is undoubtedly one of the most abundant compounds in the Universe. But despite this abundance of water everywhere, the Earth is the only planet in the solar system that has an ocean on its surface: this is an important fact to which we will return later.

Water has a number of special and unexpected properties, thanks to which it can serve as a biological solvent - the natural habitat of living organisms. These properties determine its main role in stabilizing the Earth's temperature. These properties include: high melting (melting) and boiling temperatures: high heat capacity; a wide range of temperatures within which water remains in a liquid state; high dielectric constant (which is very important for a solvent); ability to expand near freezing point. These issues received comprehensive development, in particular, in the works of L.J. Henderson (1878–1942), professor of chemistry at Harvard University.

Modern research has shown that such unusual properties of water are due to the ability of its molecules to form hydrogen bonds with each other and with other molecules containing oxygen or nitrogen atoms. In reality, liquid water consists of aggregates in which individual molecules are joined together by hydrogen bonds. For this reason, when discussing what non-aqueous solvents might be used by living systems on other worlds, special attention is paid to ammonia (NH 3), which also forms hydrogen bonds and has many properties similar to water. Other substances capable of forming hydrogen bonds are also named, in particular hydrofluoric acid (HF) and hydrogen cyanide (HCN). However, the last two compounds are unlikely candidates for this role. Fluorine is a rare element: for every fluorine atom in the observable Universe there are 10,000 oxygen atoms, so it is difficult to imagine conditions on any planet that would favor the formation of an ocean consisting of HF rather than H 2 O. As for hydrogen cyanide (HCN ), its constituent elements are found in abundance in outer space, but this compound is not thermodynamically stable enough. It is therefore unlikely that it could ever accumulate in large quantities on any planet, although, as we said earlier, HCN represents an important (albeit temporary) intermediate in the prebiological synthesis of organic substances.

Ammonia is made up of fairly common elements and, although less stable than water, is still stable enough to be considered as a possible biological solvent. At a pressure of 1 atm, it is in a liquid state in the temperature range -78 -33 °C. This range (45°) is much narrower than the corresponding range for water (100 °C), but it covers the region of the temperature scale where water cannot function as a solvent. Considering ammonia, Henderson pointed out that this is the only known compound that, as a biological solvent, approaches water in its properties. But in the end, the scientist retracted his statement for the following reasons. First, ammonia cannot accumulate in sufficient quantities on the surface of any planet; secondly, unlike water, it does not expand at temperatures close to the freezing point (as a result of which its entire mass can remain entirely in a solid, frozen state), and finally, its choice as a solvent excludes the benefits of using oxygen as a biological reagent . Henderson did not express a definite opinion about the reasons that would prevent ammonia from accumulating on the surface of planets, but nevertheless he was right. Ammonia is destroyed by UV radiation from the sun more easily than water, i.e. its molecules are broken down by radiation of a longer wavelength, carrying less energy, which is widely represented in the solar spectrum. The hydrogen formed in this reaction evaporates from the planets (except for the largest) into outer space, while nitrogen remains. Water is also destroyed in the atmosphere under the influence of solar radiation, but only at a much shorter wavelength than that which destroys ammonia, and the oxygen (O 2) and ozone (O 3) released form a screen that very effectively protects the Earth from deadly UV radiation . In this way, self-limitation of photodestruction of atmospheric water vapor occurs. In the case of ammonia, a similar phenomenon is not observed.

These arguments do not apply to planets like Jupiter. Since hydrogen is present in abundance in the atmosphere of this planet, being its constant component, it is reasonable to assume the presence of ammonia there. These assumptions are confirmed by spectroscopic studies of Jupiter and Saturn. It is unlikely that there is liquid ammonia on these planets, but the existence of ammonia clouds consisting of frozen crystals is quite possible.

Considering the issue of water in a broad sense, we do not have the right to a priori assert or deny that water as a biological solvent can be replaced by other compounds. When discussing this problem, there is often a tendency to simplify it, since, as a rule, only the physical properties of alternative solvents are taken into account. At the same time, the fact that Henderson noted is downplayed or completely ignored, namely: water serves not only as a solvent, but also as an active participant in biochemical reactions. The elements that make up water are “incorporated” into the substances of living organisms through hydrolysis or photosynthesis in green plants (see reaction 4). The chemical structure of a living substance based on a different solvent, like the entire biological environment, must necessarily be different. In other words, changing the solvent inevitably entails extremely profound consequences. Nobody seriously tried to imagine them. Such an attempt is hardly reasonable, since it represents nothing more or less than a project for a new world, and this is a very dubious endeavor. So far we are not even able to answer the question about the possibility of life without water, and we will hardly know anything about this until we discover an example of anhydrous life.

So, since water is the only compound known to us that can act as a biological solvent, we will take the view that it is on this solvent that any form of extraterrestrial life appears to be based, unless there is another liquid capable of performing this role.

World without air

Thus, we come to the conclusion that life cannot exist either on the Moon, or on most of the satellites of other planets in the Solar System, or on Mercury, or on asteroids, since none of these objects is capable of retaining a significant atmosphere. (Asteroids are many small bodies - the largest of which are about 1000 km in diameter - orbiting the Sun; they form the so-called asteroid belt, located between the orbits of Mars and Jupiter. The asteroid belt "supplies" many of the meteorites bombarding the Earth.)

However, in the early 1960s, some NASA science advisers were not convinced that the Moon was lifeless. Believing that “harmful alien organisms” might be beneath the lunar surface, they convinced mission directors to quarantine returning astronauts, the spacecraft, and soil samples. Faced with conflicting opinions on this issue, NASA took the safest, if not the smartest, position by taking special measures to protect the Earth from what came to be called "backwash contamination." These measures included the creation of the Lunar Soil Reception Laboratory in Houston, where lunar samples were delivered. Astronauts returning from the Moon were subject to a three-week quarantine in order to prevent the possible introduction of an unknown infection to Earth. Some considered these measures necessary and in line with common sense, others perceived it as a comedy.

As the launch of Apollo 11, which was supposed to land the first man on the lunar surface, approached, doubts began to be expressed about the need for quarantine, since it placed an additional burden on the shoulders of the astronauts, who already had to endure a lot. The public acknowledgment that quarantine measures could be eased has sparked a national debate. The New York Times, for example, took a negative stance, declaring in its pages on May 18, 1969, that the easing of quarantine could lead to “unpredictable but likely disastrous consequences.” Experts such as Edward Anders of the University of Chicago and Philip Abelson, editor of Science magazine, responding to the newspaper, pointed out that unsterilized material from the Moon, thrown into outer space when meteorites struck its surface, fell on Earth over billions of years and millions of tons of it have accumulated here. Anders even expressed his intention to eat a sample of unsterilized lunar dust to prove its harmlessness. Joshua Lederberg of Stanford University wrote that if any of the responsible scientific advisers believed in the possibility of such a risk, NASA would have been ordered to cancel the human flight program. In general, NASA strictly adhered to quarantine procedures only on the first few Apollo flights, but later abandoned them.

The soil samples brought back from the Moon by the Apollo crews have been studied more thoroughly and comprehensively, by a larger number of specialists in different fields and with a higher level of organization of scientific research, than any other material in the past. Many tests were carried out to determine the presence of living organisms in the samples, and all of them gave negative results. The same result resulted in attempts to detect microfossils (microfossils) in the brought soil samples. According to chemical analysis, the concentration of carbon in the lunar soil was 100–200 parts per million, and it was mainly found in inorganic compounds (for example, carbides). There is reason to believe that the presence of carbon on the lunar surface is due to the action of the “solar wind” - a stream of high-energy charged particles emitted by the solar corona. Some simple organic compounds have been found in lunar samples in negligible (trace) quantities (on the order of a few parts per million). Of course, it was assumed that organic matter carried by meteorites may be present on the Moon, but it cannot be said with certainty whether the discovered “traces” of organic matter are of meteorite origin or they appeared as a result of pollution caused by rocket exhaust or the touch of human hands already on Earth. Since it is impossible to speak with sufficient certainty about the presence of organic matter from meteorites, it can be assumed that organic compounds on the surface of the Moon are destroyed. In any case, there is no doubt that the Moon is lifeless and probably always has been.

With the exception of Titan (a moon of Saturn) and possibly Triton (a moon of Neptune), all of the planetary moons in the Solar System are similar to the Moon in that they do not have any dense atmosphere. Of interest are Ganymede and Callisto, two satellites of Jupiter, close in size to the planet Mercury, since their low density (see Table 4) suggests the presence of a large amount of water on them. Current models suggest that both moons may have oceans beneath the surface, with some surface water in the form of rock-hard ice at -10°C.

Now let's turn to the objects of the Solar System, the masses of which (and in some cases low temperatures) are sufficient to retain an atmosphere.

Table 4. Planets and main satellites of the Solar System

Venus is the closest planet in the solar system to Earth, which is also most similar to it in mass, size and density (Table 4). Back in the 18th century. it was found to have an atmosphere. However, the continuous, highly reflective cloud cover of Venus makes its surface invisible from Earth. This also explains the great brightness of Venus (it is the third brightest object in our sky), which has long attracted the attention of observers to it (photo 2). It was originally assumed that the clouds on Venus, like those on Earth, were composed of water vapor and, therefore, there was an abundance of water on the planet's surface. Some scientists imagined Venus as a planet covered with a huge swamp, above which evaporation constantly rises, others suggested that its entire surface was occupied by a giant ocean. In any case, it seemed that there were excellent conditions for the existence of life.

Photo 2. An image of Venus in the UV range obtained by the Mariner 10 spacecraft reveals the structure of the cloud layer. The blue color is artificially created. (NASA and Jet Propulsion Laboratory.)

Spectroscopic results obtained in the 1930s showed the presence of significant amounts of carbon dioxide in the atmosphere of Venus and the complete absence of water vapor. However, the possibility of detecting water vapor above the cloud top seemed doubtful even with the presence of an ocean at the surface; therefore the idea of ​​a moist Venus was not abandoned. Other suggestions have been made about the nature of the cloud cover, ranging from inorganic dust to hydrocarbon smog. It was not until 1973 that several researchers independently concluded that the properties of the clouds of Venus are best explained by assuming that they consist of tiny droplets of concentrated (70–80%) sulfuric acid; this view is now generally accepted. Meanwhile, studies using modern radio astronomy methods and automatic interplanetary spacecraft have shown that the average surface temperature of Venus reaches approximately 45 ° C, the atmosphere under the cloud cover is almost entirely (96%) carbon dioxide, and the pressure at the surface is 90 atm. At this temperature, liquid water cannot exist on the surface of Venus.

The high temperature of Venus is due to the so-called greenhouse effect: sunlight, reaching the surface, heats the ground and is re-radiated as heat, but due to the opacity of the atmosphere for infrared (thermal) radiation, heat cannot dissipate into outer space. According to some considerations, Venus may once have had an ocean, which later evaporated as the planet warmed up. Under the influence of the sun's ultraviolet light, the water vapor was largely destroyed, the hydrogen evaporated, and the remaining oxygen oxidized the carbon and sulfur on the surface to carbon dioxide (carbon dioxide) and sulfur oxides. Apparently, the same thing would happen on Earth if it were as close to the Sun as Venus. The same scenario could explain why carbon dioxide on Venus is found in the atmosphere, whereas on Earth it exists primarily in the form of carbonates that make up rocks. On our planet, carbon dioxide dissolves in the oceans, then precipitates as the carbonate minerals calcite (limestone) and dolomite; on Venus, where there are no oceans, it remains in the atmosphere. It is estimated that if all the carbon on the Earth's surface and crust were converted into carbon dioxide, the mass of this gas would be close to that found on Venus.

Although in the distant past conditions on Venus may have been more favorable for life than now, it is clear that the existence of life there has been impossible for a long time.

Giant planets

Jupiter, Saturn, Uranus and Neptune, often called the giant planets, are much larger than Earth (see Table 4). Among these giants, Jupiter and Saturn are supergiants: they account for over 90% of the total mass of the planets in the solar system. The low density of these four celestial bodies means that they are composed mainly of gases and ice, and since hydrogen and helium are unable to overcome their gravitational fields, it is assumed that their elemental composition should be more similar to the Sun (see table . 3) than on the terrestrial planets. Observations of Jupiter and Saturn made from Earth and from the Pioneer and Voyager spacecraft have shown that both planets are indeed composed primarily of hydrogen and helium. Due to their great distance, Uranus and Neptune are poorly studied, but hydrogen and the hydrogen-containing gas methane (CH 3) have been detected in their atmospheres using spectrometric observations from Earth. It is assumed that helium may also be present in their atmospheres, but so far it has not been detected due to the lack of spectrometers with the required sensitivity. For this reason, the information presented in this chapter relates mainly to Jupiter and Saturn.

Much of what is known about the structure of the giant planets is based on theoretical models, which, thanks to the simple composition of the planets, can be calculated quite accurately. The results obtained from the models indicate that at the center of both Jupiter and Saturn there is a solid core (larger than the Earth’s), the pressure in which reaches millions of atmospheres, and the temperature is 12000-2500 °C. These high temperatures are consistent with observations: they indicate that both planets emit about twice as much heat as they receive from the Sun. Heat comes to the surface of the planets from the interior regions. Therefore, the temperature decreases with distance from the core. At the top of the cloud cover, the visible "surface" of the planet, temperatures are -150 and -18 °C on Jupiter and Saturn, respectively. The zone surrounding the central core is a thick layer consisting primarily of metallic hydrogen, a special electrically conductive form that forms at very high pressures. This is followed by a layer of molecular hydrogen mixed with helium and small amounts of other gases. Near the upper boundary of the hydrogen-helium shell there are layers of clouds, the composition of which is determined by local values ​​of temperature and pressure. Clouds consisting of crystals of water ice, and in places, perhaps, droplets of liquid water, form where the temperature approaches 0 C. Somewhat higher are clouds of ammonium hydrosulfide, and above them (at temperatures around -115 C) are clouds consisting from ammonia ice.

The structure of the described model assumes that Jupiter and Saturn are close in composition to the Sun: the hydrogen content both in volume and in the molecular composition of the atmosphere reaches 90% or higher. Apparently, in atmospheres of this type, carbon, oxygen and nitrogen are present almost exclusively in the composition of methane, water and ammonia, respectively. These gases, like hydrogen, were found on Jupiter, all except water, in quantities characteristic of solar-type atmospheres. When studying the spectra of atmospheres, water is not detected in sufficient concentrations - perhaps because its vapors condense in relatively deep atmospheric layers. In addition to these gases, carbon monoxide and traces of simple organic molecules have been recorded in Jupiter’s atmosphere: ethane (C 2 H 6), acetylene (C 2 H 2) and hydrogen cyanide (HCN). The reason for the bright colors of Jupiter's clouds - red, yellow, blue, brown - has not yet been fully elucidated, but both theoretical and laboratory studies lead to the conclusion that sulfur, its compounds and, possibly, red phosphorus are responsible for this.

The presence of water vapor and simple organic compounds in the upper layers of Jupiter's atmosphere, as well as the likelihood of the formation of clouds consisting of droplets of liquid water in deeper layers, suggests the possibility of chemical evolution on the planet. At first glance, it seems that in the reducing atmosphere of Jupiter we should expect the presence of complex organic compounds similar to those formed in experiments simulating prebiological conditions on primitive Earth (see Chapter 3), and perhaps even life forms characteristic of this planet. Indeed, even before water vapor and organic molecules were discovered in Jupiter’s atmosphere, Carl Sagan suggested that “of all the planets in the solar system, Jupiter is a priori the most interesting from a biological point of view.”

However, the actual conditions on Jupiter did not live up to these hopes.

Jupiter's atmosphere is not conducive to the formation of complex organic compounds for a number of reasons. First, at the high temperatures and pressures that characterize the planet's highly reduced environment, hydrogen breaks down organic molecules, turning them into methane, ammonia and water. As Urey pointed out many years ago, moderately reduced, i.e., partially oxidized, gas mixtures are more favorable for carrying out the most important organic syntheses than highly reduced ones. For example, the synthesis of glycine, the simplest amino acid, cannot occur spontaneously in the gas mixture of water, methane and ammonia present in the atmosphere of Jupiter. It is impossible without the supply of free energy (6). On the other hand, without access to energy, synthesis can occur in a less strongly reduced gas mixture consisting of carbon monoxide, ammonia and hydrogen (7):

In the presence of free hydrogen, which is typical for the atmospheres of planets like Jupiter, according to equation (6), the reaction can proceed from right to left, which means that glycine will spontaneously convert into methane, water and ammonia. So far, no experiments have been carried out with real gas mixtures that would make it possible to find out how many different organic synthesis reactions can occur in the atmosphere of Jupiter. Such experiments are difficult to perform because they require very high concentrations of hydrogen and helium. However, a decrease in the concentration of one of the components (in some publications on the results of experiments on the synthesis of organic substances in gas mixtures simulating the atmosphere of Jupiter, it is reported that hydrogen was not used at all) casts doubt on the value of the results obtained.

Jupiter and the other giant planets do not have suitable surfaces on which organic products formed in the atmosphere could accumulate and interact, and this is an important factor that must be taken into account when considering the possibility of chemical evolution. Therefore, evolution must take place in the atmosphere, presumably in clouds of water vapor. But Jupiter's atmosphere is not a stable environment, like the oceans on Earth. It is more like a giant furnace, where vertical flows constantly move hot gases from the lower (internal) regions to the periphery: there these gases give up their heat into outer space, while cooled gases move down to deeper layers, where they are heated again. The turbulence observed in the clouds of Jupiter is a sign of such convection (see photo 3). How intensely can chemical evolution proceed under conditions in which organic molecules formed by sunlight in the upper atmosphere move to hotter areas where they are destroyed? Apparently, almost imperceptibly. Calculations show that the movement of gases located in the atmosphere at the level of a layer of water clouds to an area where the temperature is 20 °C takes several days. Consequently, after a short time, organic compounds will begin to break down, and the carbon, nitrogen and oxygen released will again turn into methane, ammonia and water.

Even with allowance for inaccuracy in calculations, it is clear that conditions in the atmosphere of Jupiter are not favorable for chemical evolution. In addition, Jupiter is not only a “furnace”, but also, as we have seen, a reaction vessel, and this excludes any possibility of stabilization of organic molecules by high pressure under thermal influence. Thus, it must be concluded that the lifetime of organic compounds on Jupiter is too short for any complex organic synthesis to be possible. Similar reasoning applies to Saturn (see photo 4); they are probably also true for Neptune. Uranus is still a mystery, but there is every reason to believe that it is no more habitable than other giant planets.

Titan, Triton and Pluto

Titan, Saturn's largest moon, is the only moon in the Solar System known to have a dense atmosphere. The flight of the automatic station Voyager 1, which in 1980 approached within a distance of about 5000 km to the surface of Titan and transmitted to Earth a large amount of data on the chemical and physical conditions on this unusual cosmic body the size of the planet Mercury, put an end to numerous speculations. (For a complete summary of data and research on this moon by many scientists, see articles by Stone and Miner, as well as Pollack.)

author Euvelmans Bernard

Chapter 2. IS THERE STILL HOPE TO FIND UNKNOWN SPECIES OF BIRDS AND ANIMALS? Once delivering a “Speech on the Theory of the Earth,” Baron Georges Cuvier, who then used it as a preface to the book “In Search of the Remains of Fossil Animals,” made an extremely reckless

From the book Wolf [Questions of ontogenesis of behavior, problems and method of reintroduction] author Badridze Yason Konstantinovich

Chapter 2.2. Formation of predatory and hunting behavior in captive-bred wolves and some other predatory animals Material and methods To establish the age at which a reaction to a potential prey appears in the process of postnatal ontogenesis,

From the book How Life Came to Earth author Keller Boris Alexandrovich

Is there life on other worlds? There are a great many different worlds in the universe. Is it really possible that among these worlds only life arose on our Earth? Of course, this is completely incredible. And there, at enormous distances from us, hundreds of millions of kilometers from the earth, there must be

From the book Searches for Life in the Solar System author Horowitz Norman H

Chapter 1. What is life? Not much time has passed since genetics and biochemistry became independent sciences, each of which... is trying to find the key to the phenomenon of life. Biochemists discovered enzymes, and geneticists discovered genes. William Hesch, "Genetics of Bacteria and

From the book Traces of Indian Herbs author Meyen Sergey Viktorovich

Chapter IX WHAT IS THE TRUTH IN THE HISTORY OF THE EARTH? In previous chapters we talked about the distant past of the Earth, about the history of plant life on it. It has been said more than once that there were some ideas about the past, and then they turned out to be erroneous. In some cases the error was

From the book The Greatest Show on Earth [Evidence of Evolution] author Dawkins Clinton Richard

CHAPTER 13 There is greatness in this view of life Unlike his evolutionist grandfather Erasmus, whose scientific poems (somewhat surprisingly, I might say) were admired by Wordsworth and Coleridge, Charles Darwin was not known as a poet, but he created a lyrical culmination V

From the book The Greatest Show on Earth [Evidence of Evolution] author Dawkins Clinton Richard

CHAPTER 13 THERE IS GREATNESS IN THIS VIEW OF LIFE Unlike his evolutionary grandfather Erasmus, whose scientific poetry (somewhat unexpectedly, I might say) was admired by Wordsworth and Coleridge, Charles Darwin was not known as a poet, but he created a lyrical culmination in

From the book Conversations about Life author Galaktionov Stanislav Gennadievich

Chapter 6. Life in a caricature A few half-joking lines preceding each chapter of our narrative have already become, it seems to us, a kind of tradition: whether good or bad is for the reader to judge. But, honestly, preparing for the story about the functional role of protein

From the book The Prevalence of Life and the Uniqueness of Mind? author Mosevitsky Mark Isaakovich

Chapter VIII. Does humanity have a future? This question is of interest to many contemporaries. It is touched upon in a number of recent monographs (Nazaretyan, 2001; Glad, 2005; Arutyunov and Strekova, 2006; Zubov, 2002). First of all, it is necessary to decide what is meant by

From the book The Power of Genes [beautiful like Monroe, smart like Einstein] author Hengstschläger Markus

Short life for humans, but long life for humanity Bacteria and humans are different in many ways. If one generation of bacteria lives for twenty minutes, then many years pass between one human generation and the next. If a person is born through the fusion of an egg and

From the book Energy of Life [From spark to photosynthesis] by Isaac Asimov

Chapter 23. LIFE WITH AIR When considering reactions that take place with the participation of atmospheric oxygen, a natural desire arises to understand the very process of oxygen absorption by living tissue (well, it fills the lungs, and then what?). From such different creatures as potatoes and

From the book The Brain in Electromagnetic Fields author Kholodov Yuri Andreevich

Chapter 3. Is there electromagnetic disease? Just as humans do not have specific electromagnetic sensations, there are also no specific clinical manifestations of EMF exposure, which makes it difficult to diagnose the changes observed in people working in EMFs. That such changes

From the book We are immortal! Scientific Evidence of the Soul author Mukhin Yuri Ignatievich

What is life? Now let's turn to man - the most complex structure that we know. The achievements of chemical science are such that almost everything is known about the material that makes up the body of a living being and a person - it is known from which atoms and molecules.

From the book The Paganini Syndrome [and other true stories of genius written in our genetic code] by Keen Sam

Chapter 14: Three Billion Little Pieces Why don't humans have more genes than other species? Scale, scope, ambition, decades of work and tens of billions of dollars are the reasons why the Human Genome Project, an attempt to decipher the entire DNA chain, is rightly

In recent years, there has been a lot of discussion in astronomical circles about the search for life on other planets, so much so that a new term has been coined for this research - astrobiology, since there is no evidence yet that life exists elsewhere.

Astrobiology is the science of the origins of evolution and the spread of life for which there is as yet no data, or at least no data to support the science.

Search for life in the solar system

Since there is no support for the claim that life exists on other planets, much attention has been devoted to finding planetary conditions favorable to life.

Mars has been the focus of attention for a very long time and is now being targeted for Martian soil samples. The Red Planet is about half the size of Earth, and it has at least a thin atmosphere. Water exists on Mars, although it is probably not abundant in vapor or solid form. The temperature and atmospheric pressure on Mars are too low to support liquid water.

The rovers that have explored the surface of Mars since 1976 have contained three very reliable experiments to detect signs of life. Two experiments showed no signs of living organisms, the third experiment had weak but ambiguous data. Even the most optimistic searchers for extraterrestrial life agree that these slight positive signs were likely the result of inorganic chemical reactions in the soil. In addition to the terrible cold and the rarity of water, there are other obstacles to life on Mars today. For example, the thin Martian atmosphere does not provide protection from the sun's ultraviolet radiation, which is lethal to living things.

With these concerns, interest in life on Mars has waned, although some hopes still hold out and many think that life may have existed on Mars in the past.

Mars exploration

In recent years, the orbiter has detected methane in the Martian atmosphere. Methane is a gas often produced by living things, although it can also form inorganically. A gamma-ray spectrometer aboard the Mars Odyssey orbiter detected significant amounts of hydrogen in the upper surfaces, likely indicating an abundance of ice. The iconic Spirit and Opportunity rovers provided compelling evidence that liquid water existed on the surface of Mars. This latest point is confirmation of what we have known for decades: photographs from the orbiter have shown numerous features that are best interpreted as having a lot of liquid water on Mars in the past. It's possible the Red Planet once had a much more substantial atmosphere than it does now, an atmosphere that provided enough pressure and heat to support liquid water.

This holds exciting promise for pessimists of life on other planets.

• First, scientists have concluded that Mars, a planet without liquid water, once experienced a near-global flood, all the while denying that such a thing could happen on Earth, a planet with abundant water.
• Secondly, many believe that the earth's atmosphere underwent enormous changes during the Flood. It is believed that the Earth has experienced catastrophic changes in its atmosphere.

Please note that in the study of astrobiology, water indicators occupy a prominent place.

As a universal solvent, water is absolutely essential to life, making up the majority of the mass of many organisms. And water is one of the most abundant molecules in the Universe. While water has been directly detected throughout the universe (even in the outer layers of cool stars!), we have never found liquid water anywhere in the universe. Liquid water is the main standard for living beings, since it seems that life is impossible without it. However, while water is a necessary condition for life, it is far from being a sufficient condition for life—much more is required.

Jupiter exploration

A few years ago, a stir in scientific circles was caused by the announcement of the possibility of a small ocean of liquid water beneath the surface of Europa, one of Jupiter's larger moons. Most of the cases for this water depend on the surface features of Europa - there are large cracked segments that resemble features of the polar ice pack that are the result of upwelling frozen between the cracks. Additionally, if the water were salty, this could explain the magnetic field of Jupiter's moon. It has since been suggested that a similar argument was made on the moon Ganymede, another large moon of Jupiter.

Many scientists are now considering a possible undersea ocean on the Europa moon as the most likely place in the solar system to find life beyond where we live. This ocean, if it exists, is very dark and probably very cold. A few decades ago, living organisms in such a place would have been unthinkable. However, scientists have found that organisms live in very hostile environments, such as hydrothermal vents deep in the Earth's oceans. In addition, underground lakes exist far beneath the Antarctic ice sheet. The largest and most famous of them is Lake Vostok, located 4 kilometers under the ice. Although we don't know if life exists in these lakes, many scientists want to find out. They believe that if life could exist in these terrestrial lakes, why wouldn't life exist inside Jupiter's moon?

The search for life outside the solar system

Whether there is life on other planets outside the solar system has always worried humanity. Therefore, in our time, scientists, astronomers, and astrobiologists are constantly looking for the presence of life on other celestial bodies. The National Aeronautics and Space Administration (NASA) has specially developed an astronomical satellite, on which the Kepler space telescope is located, designed to search for planets outside the solar system around other stars.

Kepler Space Telescope

Kepler is a space observatory launched by NASA in 2009. The observatory is equipped with an ultrasensitive photometer capable of analyzing signals in the light region of the spectrum and transmitting data to Earth. Thanks to its high resolution, it is able to distinguish not only exoplanets, but also their satellites with a size of 0.2 the size of the Earth. During operation there were several emergency situations, but it still operates and transmits information. Placed into a circular heliocentric orbit

A planet similar to Earth where extraterrestrial existence is possible in size is named Kepler 186f. Kepler's discovery of 186f confirms that in the study area there are stars with planets other than our Sun where life on another planet is possible.
While celestial bodies in the habitable zone have previously been found, they are all at least 40 percent larger in size than Earth and are less likely to harbor life on larger planets. Kepler-186f looks more like Earth.
"The discovery of Kepler 186f represents a significant step toward the search for worlds like our planet Earth," say NASA astrophysicists at the agency's headquarters in Washington. Although Kepler-186f's size is known, its mass and composition have not yet been determined.

Now we know of only one planet where life exists - Earth.

When we search for life beyond our solar system, we focus on finding celestial bodies with characteristics that are similar to Earth. WITH whether life exists on another planet will, of course, be revealed over time.

• Planet Kepler-186f is located in the Kepler-186 system, about 500 light years from Earth in the constellation Cygnus.
• The system is also home to four planetary satellites that orbit a star half the size and mass of our Sun.
• The star is classified as an M dwarf or red dwarf, a class of stars that makes up 70% of the stars in the Milky Way galaxy. M dwarfs are the most numerous stars. Possible signs of life in the galaxy could also come from planets orbiting the M dwarf.
• Kepler-186f orbits its star every 130 days and receives one-third the energy from its star that Earth receives from the Sun, closer to the edges of the habitable zone.
• On the surface of Kepler-186f, the star's brightness matches the brightness when our Sun shines about an hour before sunset.

Being in the habitable zone does not mean that we know that this celestial body is suitable for life. The temperature on a planet is highly dependent on the planet's atmosphere. Kepler-186f can be thought of as Earth's cousin, with many properties that resemble our planet, rather than a twin.

The planet's four moons Kepler 186b, Kepler 186c, Kepler 186d and Kepler-186e orbit their sun every four, seven, 13 and 22 days, respectively, making them too hot for life.
The next steps to determine whether there is life on other planets include measuring their chemical composition, determining atmospheric conditions, and continuing humanity's quest to find truly Earth-like worlds.

conclusions

For a long time, scientists believed that life on Earth first evolved in warm, highly hospitable pools and then colonized more complex environments. Many people now think that life began on the outskirts, in very hostile places, and then migrated in the other direction to better places.

Much of the motivation for this complete reversal of thinking stems from the need to find life on other planets. Scientists should welcome the search for extraterrestrial life, although many experiments will continue to yield null results, disproving the evolutionary theory of origin.

The question of whether there is life on other planets and bodies in the solar system has worried humanity since the dawn of civilization. This topic gave rise to the development of an entire genre of literature and art - science fiction. The desire to discover living organisms on other planets has contributed to enormous progress in space technology and has helped to study many objects in the solar system and beyond. But the question of the existence of life on other planets still remains open. Is it possible that there is someone else in the solar system besides earthlings?

Water is the source of life

Life in the Solar System

Just a couple of centuries ago, the existence of various forms of life on other planets and satellites was considered quite plausible. Before the invention of powerful telescopes and spacecraft in the 20th century, it was believed that there were intelligent organisms on Mars, and that a tropical forest was hidden under the dense clouds of Venus. Naturally, these assumptions were erroneous, which was repeatedly confirmed by the study of outer space using probes and orbital observatories.

But still, the prerequisites for the emergence of life are possible on some objects of our star system. Planets and small bodies that are potentially suitable for life are those that have certain properties:

• presence of liquid water;
• close to earth mass;
• proximity to a central star or hot gas giant;
• the presence of metals, carbon, oxygen, silicon salts, nitrogen, sulfur and hydrogen;
• low orbital eccentricity;
• the angle of inclination of the rotation axis to the orbital plane is similar to that on Earth (mild change of seasons);
• quick change of day and night.

Let's consider what celestial bodies are included in the hypothetical belt of life in the Solar System.

artistic image

Mars

Mars is similar in physical parameters to Earth. It also belongs to the solid planets, its mass is 10 times less than that of the Earth, and its diameter is only 2 times. The red planet's orbit is not highly eccentric, and the inclination of its axis to its plane is 25°, which causes the change of seasons. A day on Mars lasts 39 minutes longer than on our planet.

Mars

The surface of the fourth planet of the solar system is dotted with many formations that resemble the beds of dried rivers and lakes. The study of Martian soil by planetary rovers confirmed the presence of ice in the subsurface layer, as well as minerals, the formation of which requires water. It remains a mystery what happened to Mars in the past that could deplete all the water reserves on the planet.

The atmosphere significantly reduces the chances of life existing on Mars. It is extremely rarefied and consists of carbon dioxide with admixtures of nitrogen and inert gases. Such an atmosphere cannot withstand the rapid cooling of the planet’s surface, so the temperature on Mars in the mid-latitude region ranges from -50°C to 0°C. In such conditions, only one form of life can survive - anaerobic extremophile microorganisms. But these were not found in soil samples from the fourth planet of the solar system.

Methane on the planet

The discovery of methane in the atmosphere of Mars in 2004 became a real mystery for space researchers. It should have easily evaporated from the surface of the planet under the influence of the solar wind. But its concentration remained relatively constant. It has been suggested that reserves of the simplest hydrocarbon are constantly replenished through the decomposition of organic matter by life forms such as methane-producing bacteria. However, when studying the atmosphere of the fourth planet of the solar system in 2018, no traces of gas were found.

Europe

Europa is a satellite of Jupiter, the largest planet in the solar system. In size it is slightly smaller than the Moon. Its atmosphere is rich in molecular oxygen, and its surface is a huge shell of ice, under which is hidden an ocean of liquid water. It is thanks to this that we consider Europa as an object in the solar system potentially suitable for life.

Europe

Oxygen in the gaseous shell of the Jupiterian satellite appeared due to the splitting of the icy crust by solar radiation. Most of it evaporates from the surface of the planet, but a small percentage still remains on the satellite. For life to arise on Europa, molecular oxygen needs to penetrate into the ocean under the icy shell. This is not easy to do, because... its thickness is more than 30 km.

According to scientists, several million years must pass before the oxygen concentration in Europa's ocean becomes optimal for the emergence of life. Under such conditions, microorganisms similar to bacteria and protozoa that inhabit the depths of the Earth's oceans can arise.

Enceladus

Enceladus is a satellite of Saturn. This is one of the coldest places in the solar system - its surface temperature is -200°C. How is life possible under such conditions?

Enceladus

Under the icy crust of Enceladus hides an ocean of water, in which active hydrothermal processes constantly occur. This constant source of heat heats the depths of Enceladus's ocean to a temperature of +1°C. In addition, many salts are dissolved in water, as well as some organic compounds. Such a “broth” could become the source of life on the Saturnian satellite, as it once was on Earth.

Titanium

Saturn's largest moon is also a candidate for the emergence of life in the solar system. Titan is slightly larger in diameter than Mercury, and twice as heavy as the Moon. Its atmosphere contains a high concentration of nitrogen, and its surface is pockmarked with ethane and methane rivers, lakes and even oceans.

Titanium

Such an abundance of organic matter, located under a dense nitrogen atmosphere, can become the impetus for the prebiotic revolution - the emergence of nitrogenous bases, which are the building material for RNA and DNA. These acids are the precursors of life on Earth.

Conditions for life on the satellite will become more favorable in 6 billion years, when the Sun transforms into a red giant. The surface temperature will rise from -180° C to -70° C, which is enough for an ocean of water and ammonia to form in the subsurface layer and life to arise.

Exoplanets

There is a whole list of planets outside the solar system, the conditions on which may be similar to those on Earth. With such parameters, the existence of life or its emergence in the near future is possible on them.

Potentially habitable planets outside the solar system are:

• Kepler-438 b. This planet orbits the red dwarf star of the same name in the constellation Lyra. It is distant from the solar system at a distance of 470 light years. It is a solid planet with an average surface temperature in the range of 0-50°C. Probably has an atmosphere.
• Proxima b. Orbits the dwarf of the same name in the constellation Centaurus at a distance of 4.3 light years from the Sun. It is a hot rocky planet with a weak atmosphere.
• Kepler-296 e. Located in the single star system Kepler-296 in the constellation Cygnus. The average surface temperature is no more than 50°C. A dense hydrogen atmosphere, the composition of the surface is close to that of Earth.
• Gliese 667 C p. It is located 24 light years away from the Solar System and is located in the constellation Scorpio. It has an atmosphere potentially suitable for life in composition and humidity. The average temperature does not exceed 50° C. The structure of the surface layer is ferruginous-stone.
• Kepler-62 e. Orbits the star of the same name in the constellation Lyra. An iron-rock planet with a dense atmosphere and optimal temperature for the existence of life. Its mass is one and a half times that of the Earth.

The list shows the most habitable planets outside the solar system. In total, there are currently 34 exoplanets whose conditions are similar to those on Earth and could be suitable for the origin of life.

Is there life on other planets? This question has two sides: applied and fundamental. The fundamental question interests those who study biology, astronomy, those who want to find life as such and see how different it is from earthly life, how widespread it is in the Universe. The rest of humanity is interested in the applied side of this issue.

We still have only one point in the Universe where life exists - this is our planet Earth. This is a reliable spacecraft, it has existed for 4.5 billion years, of which 4 billion years it has supported life. But this does not mean that it will always be like this. The Earth is threatened by cosmic dangers in the form of asteroids, comets, supernova explosions, and so on, not to mention our own man-made problems. Therefore, for future generations, it would be very nice to find a spare planet, resettle part of humanity and transfer there everything that our civilization has gained over the millennia of its development.

The main thing is the information accumulated by previous generations. Everything has disappeared, everything has decayed: the bones of people and animals, buildings that were erected in past centuries. The only thing that has been preserved from our ancestors to this day is the knowledge they accumulated. First of all, we are obliged to preserve knowledge for future generations. Therefore, a spare planet is needed; now a separate field between astronomy and biology, called astrobiology or bioastronomy, is searching for it.

Moon, Mars and giant planets

Where could such a spare planet be found near us? I must say that it is quite close to us - only three days of flight on a spaceship. This is the Moon. The lack of an atmosphere on the Moon limits our capabilities, but it is suitable as a repository of information for humanity. For now, we are creating such storage facilities on Earth - for example, on Svalbard there is a storage facility for cereal seeds in case of some agricultural disasters. But on the Moon we could create a base and preserve knowledge there for future generations, all the giga-giga-gigabytes of information that have been accumulated by humanity, and thus pass it on to descendants. For human settlement, the Moon is not an easy option, since artificial cities can only be created under the surface of the Moon, and this will be very expensive and will not happen in the coming centuries.

More attractive are bodies located even further away: Mars, satellites of the giant planets. In previous decades, only astronomers could use telescopes to study these attractive bodies. Today, that is, for the last several decades, space probes have been flying towards them. Mars is especially well explored - several satellites are constantly operating around it. In recent decades, landing probes and rovers have constantly been located on its surface.

There is an atmosphere on Mars, although it is, of course, rarefied and not suitable for us, but we can try to improve it, and there is also the main resource there - water, without which not a single living creature, or humans, can do. Today on Mars it is frozen, in the form of permafrost and polar ice caps. However, it can be melted, purified and used for drinking, for technical needs, to produce oxygen, hydrogen - and this is rocket fuel and generally good fuel.

Unfortunately, we have not yet explored the most interesting thing that is on Mars - its depths. There is quite high radiation on the surface of Mars, it will be difficult to live there. But in the Martian caves, which have already been discovered from orbit, it should be much better. And we see the entrances to them, but so far not a single automatic device has penetrated there - this is a matter of the next few years. Literally at the end of this year or at the beginning of next year, a new Russian-European project will begin to drill the Martian surface and study the shallow Martian subsoil to a depth of 1.5–2 meters. There is hope that in the coming years we will launch robots into Martian caves that will scout out life there or report to us that these caves are ready to receive our astronauts.

Even more attractive are the satellites of the giant planets, such as Europa near Jupiter or Enceladus near Saturn. There are giant oceans there. Under the icy crust of the satellites, normal, liquid, brackish, as we now know, water splashes. And the ocean is where life was born and where it thrives today on Earth. And, eventually, a person could adapt to live in the ocean or on its surface. Such satellites have not yet been explored, unlike Mars. Spacecraft only flew past them, but none landed. But in the coming years this will happen, and we will explore them, firstly, to search for life itself - this is an interesting problem for biology, and perhaps it will be solved, and we will see new options for life; and secondly, to explore them as reserve sites for human settlement.

There is another aspect why these distant bodies are especially attractive. The fact is that the solar radiation power is constantly increasing and in the future it will begin to increase faster and faster. The earth will overheat and become unsuitable for life. It will lose its atmosphere, lose its liquid shell. And those distant satellites will become, on the contrary, warmer than today. Today it’s a little cold there - -150, -180 °C. But in the era when the Sun warms up properly, they will become favorable for life. They must be kept in mind and studied as future backup planets.

Exoplanets

Of course, someday engineers will invent a way to travel between the stars - there is no such method yet, but if it appears, a boundless number of planets similar to Earth in size, presence of an atmosphere, and climate will open before us. Such planets have already been practically discovered, but only with the help of telescopes. These are Earth-like exoplanets, and there are relatively few of them. Among others, exoplanets make up maybe 1–2%. But today astronomers know thousands of exoplanets. Among them are dozens that are quite reminiscent of our Earth. We don’t yet know whether there is life there. But if it doesn’t exist, then we have the right to colonize these planets and use them to develop our civilization. The main thing is to learn how to travel to them. The interstellar distance is colossal, and our modern rockets will never cover them. This takes hundreds of thousands of years. But in the end, a way to quickly fly across the expanses of our Galaxy will probably be discovered, fast spacecraft will be made, and then these exoplanets will truly become copies of the Earth and spare planets for people.

Extraterrestrial civilizations

In the search for life beyond the Earth, there is one method that, as it seemed to us, should bring very quick results. We are talking about the search for not just life, but intelligent life, capable of communicating its existence using some means of communication. Particular hopes were placed on radio communications, because they are capable of covering enormous distances. We maintain radio contact with spacecraft that fly hundreds of millions of kilometers away from Earth, and our modern technology gives us the ability to communicate with the civilizations of neighboring stars. The opportunity is there, but it has not been possible to establish a connection or notice other people’s signals for half a century. Since 1960, attempts have been made to receive such signals from intelligent inhabitants of other planets and other star systems, but so far they have led nowhere. And in this sense, pessimism is growing more and more, and we are increasingly convinced that our civilization, if not unique at all, is so rare that there are no other intelligent beings or planets inhabited by them near us. This once again emphasizes the need to preserve our civilization as a unique fact, a unique phenomenon in the Universe. In this sense, it is important to find a place for settlement, to guarantee the preservation of our biosphere and especially its highest representative - man, our civilization. So far we have not been able to discover brothers in mind, although considerable efforts have been made for this and we have opportunities today. We could see them on the other side of the galaxy. But the Universe is silent.