Potentially habitable planets. Our Earth can be used as a reference world for the existence of life. Yet scientists need to consider many different conditions that are very different from ours. In which life in the universe can be sustained in the long run.

How many years has life been in the universe?

The earth formed about 4.5 billion years ago. However, more than 9 billion years have passed since the Big Bang. It would be extremely presumptuous to assume that it took the universe all this time to create the necessary conditions for life. Inhabited worlds could have arisen much earlier. All the ingredients necessary for life are still unknown to scientists. But some are quite obvious. So what conditions must be met for a planet to emerge that can support life?

The first thing that will be needed is the correct star type. All kinds of scenarios can exist here. A planet can exist in orbit around an active, powerful star and remain habitable despite its hostility. Red dwarfs, such as, can emit powerful flares and rob the atmosphere of a potentially habitable planet. But it is clear that a magnetic field, a dense atmosphere, and life that was smart enough to take refuge during such intense events could very well combine to make such a world livable.

But if the lifespan of a star is not too long, then the development of biology in its orbit is impossible. The first generation of stars, known as Population III stars, had a 100 percent chance of no inhabited planets. The stars need at least some metals (heavier elements are heavier than helium). In addition, the first stars lived small enough for life to appear on the planet.

Requirements for planets

So, enough time has passed for the appearance of heavy elements. Stars have emerged whose lifespan is estimated at billions of years. The next ingredient we need is the correct planet type. As far as we understand life, this means that the planet must have the following characteristics:

• able to maintain a sufficiently dense atmosphere;
• maintains an uneven distribution of energy on its surface;
• has liquid water on the surface;
• possesses the necessary starting ingredients for the emergence of life;
• has a powerful magnetic field.

A rocky planet that is large enough, has a dense atmosphere, and orbits its star at the correct distance, has every chance. Considering that planetary systems are a fairly common phenomenon in space, and also the fact that there are a huge number of stars in each galaxy, the first three conditions are easy enough to fulfill.

The star of the system may well provide the energy gradient for its planet. It can occur when exposed to its gravity. Or such a generator could be a large satellite orbiting a planet. These factors can cause geological activity. Therefore, the condition of uneven energy distribution is easily fulfilled. The planet must also have a supply of all the necessary elements. Its dense atmosphere must allow liquid to exist on the surface.

Planets with similar conditions should have arisen by the time the universe was only 300 million years old.

Need more

But there is one nuance that needs to be taken into account. It consists in the fact that it is necessary to have enough heavy elements. And their synthesis takes longer than it takes for rocky planets with the correct physical conditions to appear.

These elements must provide the correct biochemical reactions that are essential for life. On the outskirts of large galaxies, this can take many billions of years and many generations of stars. Which will live and die in order to produce the required amount of the required substance.

In hearts, star formation occurs frequently and continuously. New stars are being born from recycled remnants of previous generations of supernovae and planetary nebulae. And the number of required elements can grow rapidly there.

The galactic center, however, is not a very favorable place for the origin of life. Gamma-ray bursts, supernovae, black hole formation, quasars and crumbling molecular clouds create an environment here that is unstable for life at best. It is unlikely that it will be able to arise and develop in such conditions.

To get the right conditions, this process must stop. It is imperative that star formation no longer occurs. That is why the very first planets most suitable for life arose, probably, not in such a galaxy as ours. Rather, in a red-dead galaxy that stopped forming stars billions of years ago.

When we study galaxies, we see that 99.9% of their composition is gas and dust. This is the reason for the emergence of new generations of stars and the continuous process of star formation. But some of them stopped forming new stars about 10 billion years ago or more. When their fuel runs out, which could happen after a catastrophic large galactic merger, star formation suddenly stops. Blue giants simply end their lives when they run out of fuel. And they remain to smolder slowly on.

Dead galaxies

As a result, these galaxies are today called "red dead" galaxies. All of their stars are stable, old, and safe with respect to the risks of active star-forming regions.

One of these, the galaxy NGC 1277, is located very close to us (by cosmic standards).

Therefore, it is obvious that the first planets on which life could arise appeared no later than 1 billion years after the birth of the Universe.

According to the most conservative estimates, there are two trillion galaxies. And so galaxies that are cosmic oddities and statistical outliers undoubtedly exist. Only a few questions remain: what is the prevalence of life, the likelihood of its occurrence and the time required for this? Life can arise in the Universe even before reaching the billionth year. But a stable, permanently inhabited world is a far greater achievement than life that has just arisen.

A rare person has not thought about whether there is another life in the Universe besides the earthly one. It would be naive and even selfish to believe that only planet Earth is intelligent life. The facts of the appearance of UFOs 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 discoveries made under the auspices of the government are classified as "Top Secret", which hides from ordinary people a lot of facts about the presence of other forms of life in the Universe. For example, several thousand images taken from the surface of Mars have disappeared, 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 touched, looked at.

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 of

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 are invisible to 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 hypothetically life could 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 orbiting 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 closest 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. Moreover, 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 of these phenomena are arguments that life on exoplanets is unlikely. But that was until recently. In July, researchers at the University of Chicago, USA, suggested that this is not entirely true. They compiled a climatic 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 currents 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 to help them capture 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 that, despite the most difficult, 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 that the amount of emitted radiation will significantly decrease after they have passed.

That is why many scientists share the opinion that if anywhere 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?

An interesting fact that emphasizes not only the uniqueness of life on our single planet, but also the existence of the entire solar system in general: over the past four years, thanks to the Kepler space telescope, we have learned that there are a lot of planets in our galaxy. But the most interesting fact, which Kepler obtained for us, is that among all these planets there is nothing like our solar system.

This fact is perfectly visible on the example of the animation "Kepler's Planetarium IV", created by a graduate student of the Department of Astronomy at the University of Washington, Ethan Kruse. In it, Kruse compares the orbits of hundreds of exoplanets from Kepler's database to our own solar system, which is shown on the right in the animation, and is immediately striking. The animation shows the relative size of the Keplerian planets (although, of course, not on a scale comparable to their stars), as well as the surface temperature.

In the animation, it is very easy to notice how strange the solar system seems compared to other systems. Prior to the Kepler mission in 2009, astronomers assumed that most exoplanetary systems would be arranged like ours: small rocky planets closer to the center, huge gas giants in the middle, and icy chunks of rock on the periphery. But it turned out that everything was arranged much more bizarre.

Kepler found "hot Jupiters," huge gas giants that almost touch the stars in the system. As Kruse himself explains, “Kepler's device dictates that it is much better at detecting planets with more compact orbits. In smaller systems, planets orbit faster, making it much easier for a telescope to spot them. "

Of course, the anomalousness of the solar system against the general background may be due to the fact that our knowledge of other systems is still insufficient, or because, as explained above, we mainly notice smaller systems with fast periodicity of motion. Nevertheless, Kepler has already found 685 star systems, and none of them are similar to ours.

Let's think about what extraterrestrial life could be?

Given the size of the universe, there are good reasons to assume the existence of life outside of the earth. And some scientists strongly believe that it will be discovered by 2040. But what do intelligent extraterrestrial life forms really look like (if they really exist)? For decades, science fiction has described aliens to us as short, gray humanoids with large heads and generally not very different from the human species. However, there are at least ten good reasons to believe that intelligent extraterrestrial life is not at all like us.

The planets have different gravity

Gravity is a key factor in the development of all organisms. In addition to limiting the size of land animals, gravity is also the reason organisms can adapt to various changes. environment... You don't have to go far for examples. All evidence is before us on Earth. According to evolutionary history, organisms that once decided to emerge from water onto land had to develop limbs and complex skeletons, as their bodies were no longer supported by the fluidity of water, which compensated for the effects of gravity. And although there is a certain range of how strong gravity can be in order to simultaneously support the atmosphere of a planet and at the same time not crush everything else on its surface, this range can vary, and, therefore, can vary. appearance organisms that have adapted to it (gravity).

Suppose the Earth's gravity is twice as strong as it is today. This, of course, does not mean that all complex living organisms will look like dwarf turtle-like creatures, but the likelihood of bipedal bipedal people will be drastically reduced. Even if we can maintain the mechanics of our movement, we will become much shorter and at the same time we will have denser and thicker bones of the skeleton, which will allow us to compensate for the increased force of gravity.

If the force of gravity is half the current level, then, most likely, the opposite effect will occur. Terrestrial animals no longer need powerful muscles and a strong skeleton. In general, everyone will get taller and larger.

We can endlessly theorize about the general characteristics and consequences of the presence of high and low gravity, but we are not yet able to predict the finer details of the organism's adaptation to certain conditions. However, this fitness will definitely be traced in extraterrestrial life (if, of course, we find it).

The planets have different atmospheres

Like gravity, the atmosphere also plays a key role in the development of life and its characteristics. For example, arthropods that lived during the Carboniferous period of the Paleozoic era (about 300 million years ago) were much larger than modern representatives. And all this is due to the higher concentration of oxygen in the air, which was up to 35 percent, compared to 21 percent, which is now. Some of the species of living organisms of that time, for example, are mega-neuras (ancestors of dragonflies), whose wingspan reached 75 centimeters, or the extinct species of giant scorpions, brontoscorpio, whose length reached 70 centimeters, not to mention arthropleura, giant relatives of modern millipedes. whose body length reached 2.6 meters.

If a 14 percent difference in the composition of the atmosphere has such a high impact on the size of arthropods, then imagine what unique creatures you can get if these differences in the volume of oxygen are much more significant.

But we have not even touched upon the question of the possibility of the existence of life, which does not require the presence of oxygen at all. All this gives us limitless possibilities of guessing what this life might look like. Interestingly, scientists have already discovered on Earth some types of multicellular organisms that do not require oxygen to exist, so the possibility of extraterrestrial life on planets without oxygen does not seem as crazy as it seemed before. Life on such planets will definitely be different from us.

Other chemical elements may serve as the basis for extraterrestrial life

All life on Earth has three identical biochemical characteristics: one of its main sources is carbon, it needs water, and it has DNA that allows it to transmit genetic information to future offspring. However, it would be a misconception to assume that all other possible life in the universe will follow the same rules. On the contrary, it can exist according to completely different principles.

The importance of carbon for all living organisms on Earth can be explained. First, carbon easily forms bonds with other atoms, it is relatively stable, available in large volumes, and complex biological molecules, which are required for the development of complex organisms, can appear on its basis.

However, the most likely alternative to the basic element of life is silicon. Scientists, including the famous Stephen Hawking and Carl Sagan, have discussed this possibility. Sagan even coined the term "carbon chauvinism" to describe our preconceptions that carbon is an integral part of life anywhere in the universe. If silicon-based life really exists somewhere, then it will look completely different from what life on Earth looks like. If only because silicon requires much higher temperatures to reach the reaction state.

Extraterrestrial life doesn't need water

As stated above, water is another essential requirement for life on Earth. Water is necessary because it can be in a liquid state even at a large temperature difference, it is an effective solvent, serves as a transport mechanism and is a trigger for various chemical reactions. But this does not mean that other liquids cannot replace it anywhere in the Universe. The most likely substitute for water as a source of life is liquid ammonia, since it shares many qualities with it.

Another possible alternative to water is liquid methane. Several scientific articles, based on information gathered by NASA's Cassini spacecraft, suggest that methane-based life may exist even within our solar system. Namely on one of Saturn's moons - Titan. Apart from the fact that ammonia and methane are completely different substances, which can nevertheless be present in water, scientists have proven that the two substances can be in a liquid state even at lower temperatures than water. Given this, it can be assumed that non-water-based life would look completely different.

Alternative to DNA

The third key puzzle of life on Earth is how genetic information is stored. For a very long time, scientists believed that only DNA was capable of this. However, it turned out that there are also alternative storage methods. Moreover, it is a proven fact. Scientists have recently created an artificial alternative to DNA - XNA (xenonucleic acid). Like DNA, XNA is capable of storing and transmitting genetic information during evolution.

In addition to having an alternative to DNA, extraterrestrial life is likely to produce other types of proteins (proteins) as well. All life on Earth uses a combination of just 22 amino acids to make proteins, but there are hundreds of other naturally occurring amino acids in nature, in addition to those we can create in laboratories. Therefore, extraterrestrial life can not only have "its own version of DNA", but also other amino acids for the production of other proteins.

Extraterrestrial life evolved in a different habitat

While the planet's environment can be constant and versatile, it can and vary greatly depending on the surface of the planet. This, in turn, can lead to the formation of completely different habitats with specific unique characteristics. Such variations can lead to the emergence of different paths for the development of life on the planet. Based on this, five main biomes (ecosystems, if you will) can be distinguished on Earth. These are: tundra (and its variation), steppes (and their variation), deserts (and their variations), water and forest-steppe (and their variation). Each of these ecosystems is home to living organisms that had to adapt to certain environmental conditions in order to survive. Moreover, these organisms are very different from living organisms in other biomes.

The creatures of the deep oceans, for example, have several adaptive features that allow them to survive in cold water, without any source of light and still under high pressure. These organisms are not only not at all just unlike humans, they are unable to survive in our terrestrial habitats.

Based on all this, it is logical to assume that extraterrestrial life will not only radically differ from terrestrial life according to the general characteristics of the planet's environment, but will also differ according to each biome on the planet. Even on Earth, some of the smartest living organisms - dolphins and octopuses - do not live in the same habitat as humans.

They may be older than us

If you believe the opinion that intelligent extraterrestrial life forms can be more technologically advanced than the human race, then we could safely assume that these intelligent extraterrestrial life forms appeared before us. This assumption becomes even more likely if we consider that life as such in the entire Universe did not appear and develop at the same time. Even a difference of 100,000 years is nothing compared to billions of years.

In other words, all this means that extraterrestrial civilizations not only had more time to develop, but also more time for controlled evolution - a process that allows you to technologically change their own bodies depending on needs, instead of waiting for the natural course of evolution. For example, such forms of extraterrestrial intelligent life could adapt their bodies for long space travel, by increasing their lifespan and eliminating other biological restrictions and needs, for example, breathing and the need for food. This kind of bioengineering could definitely lead to a very peculiar state of the body's body and may even have led extraterrestrial life to replace their natural body parts with artificial ones.

If you think that all this sounds a little crazy, then know - humanity is moving towards the same thing. One striking example of this is that we are on the cusp of creating "ideal people." Through bioengineering, we can genetically alter embryos to acquire certain skills and characteristics of the future human, such as, for example, intelligence and growth.

Life on wandering planets

The sun is very important factor the presence of life on Earth. Without it, plants will not have the ability to photosynthesize, which will ultimately lead to the complete destruction of the food chain. Most life forms will die out within a few weeks. But we are not yet talking about one simple fact - without solar heat, the Earth will be covered with ice.

Fortunately, the Sun is not going to leave us in the near future. Nevertheless, in our own Milky Way galaxy alone, there are about 200 billion "roaming planets." These planets do not revolve around the stars, but only senselessly float through the impenetrable darkness of space.

Could life exist on such planets? Scientists put forward theories that under certain conditions, this is possible. The most important thing in this matter is what will be the source of energy for these planets? The most obvious and logical answer to this question may be the heat of your internal "engine", that is, the core. On Earth, internal heat is responsible for the movement of tectonic plates and volcanic activity. While this is likely to be far from sufficient for the development of complex life forms, there are other factors to consider as well.

One theory was proposed by planetary scientist David Stevenson, according to which wandering planets with a very dense and thick atmosphere could trap heat, which would allow the planet to keep the oceans in a liquid state. On such a planet, life could evolve to a fairly advanced level, similar to our ocean life, and perhaps even begin the transition from water to land.

Non-biological life forms

Another possibility that should also be considered is that extraterrestrial life may be non-biological forms. These can be both robots, which were created to replace biological bodies with artificial ones, and species created artificially by other species.

Seth Shostak, head of the program for the search for extraterrestrial civilizations (SETI), even believes that such an artificial life is more than likely, and humanity itself, thanks to the development of robotics, cybernetics and nanotechnology, will sooner or later come to this.

Moreover, we are getting as close as possible to the creation of artificial intelligence and advanced robotics. Who can say with certainty that humanity at some point in its history will not be replaced by robust robotic bodies? This transition is likely to be very painful. And such famous figures as Stephen Hawking and Elon Musk already realize this and believe that in the end, the AI ​​created can just rise up and take our place.

In this case, robots can only be the tip of the iceberg. But what if extraterrestrial life exists in the form of energetic entities? After all, this assumption also has some ground under it. Such life forms will not be constrained by any restrictions. physical bodies and ultimately, in theory, they will also be able to arrive at the aforementioned physical robotic shells. Energy entities, of course, without a doubt, will not at all look like people, since they will lack a physical form and, as a result, a completely different form of communication.

The random factor

Even after discussing all the possible factors described above, one should not rule out randomness in evolution. As far as we (humanity) know, there are no prerequisites to believe that any intelligent life must necessarily develop in the form of humanoid forms. What would have happened if dinosaurs had not become extinct? Would a humanoid intellect develop in them in the process of further evolution? What would happen if a completely different species evolved into the most intelligent form of life on Earth instead of us?

For the sake of fairness, it might be worth limiting the sample of potential candidates for the possibility of development among all species of animals to birds and mammals. Even so, however, there remain a myriad of possible species that could evolve to a level of intelligence comparable to that of a human. Representatives of their species, such as dolphins and crows, are indeed very intelligent creatures, and if evolution at some point turned to face them, then it is quite possible that they were the rulers of the Earth instead of us. The most important aspect is that life can develop in a variety of (almost endless) ways, so the chances that there is intelligent life in other parts of the universe, very similar to us humans, are astronomically very low.

Are we alone in the universe?

We are still looking for any signals from extraterrestrial civilizations. This intense and anxious listening to the airwaves has already generated a lot of speculation. Naturally, the most obvious explanation for the Great Silence is that there is simply no one besides us to “get in touch”. It is very unpleasant to admit this, but still there are sufficient grounds for such a conclusion.

Long before the time when the great physicist Enrico Fermi raised the question "Where is everyone?", People wondered why there were no signals from extraterrestrial civilizations. As Fermi correctly pointed out, mathematics cannot explain this. Our galaxy is about 13 billion years old, and this is more than enough for hypothetical other civilizations to have time to explore and colonize it. According to one of the works, this process can take from tens of millions to one billion years. In other words, in theory we should have met someone already.

but complete absence This confirmed contact led astronomer Michael Hart to speculate that a civilization capable of interstellar travel simply does not exist. However, this "absence" may be the result of any considerations on their part, including unwillingness to explore space, or unnecessary technological difficulties. Despite the recent discoveries of a number of potentially habitable exoplanets, as well as our feeling that the universe is simply intended for life, a number of considerations make us believe that we are still unique in every sense of the word.

In the right place at the right time

Astronomer Paul Davis once said: “For a planet to be populated, two conditions must be met: the planet must be suitable for this, and at one point there must be life on it” (thanks, Cap). The existence of life, from the point of view modern science depends on the presence of five critical chemical elements: sulfur, phosphorus, oxygen, nitrogen and carbon. These elements are synthesized in the course of thermonuclear reactions in the bowels of stars, and at the end of them life cycle spread through space. Therefore, over time, the concentration of these substances gradually increases.

But here's the point: the concentration of these substances in interstellar space has only relatively recently reached a level at which the emergence of life is possible. That is, the planets around older stars should be poor in these five elements. Our Sun is one of the fairly young stars. So we may be among the first civilizations to emerge, or even the most first.

Stephen Webb disagrees with this point of view. He believes that the role of the concentration of chemical elements in our appearance is exaggerated. For example, we do not know what their concentration must be in a star for life to arise on one of the surrounding planets. Moreover, the proportion of each element varies greatly depending on the class of the star. In other words, we simply have no reason to blame the lack of concentration of chemical elements.

Gamma Bursts: Evolutionary Reset Button

Another reason for the lack of signals from other civilizations may be that our galaxy is a source of frequent bursts of gamma radiation (GAM). Frequent means about one every few billion years. VGI is one of the most energetically powerful phenomena known to us today. They are believed to occur in supernova explosions that collapse into black holes, or in collisions of neutron stars. According to statistics, in the entire observable Universe, there is a daily burst of gamma radiation.

A sufficiently close emission of radiation from a supernova explosion is capable of destroying the biosphere of a terrestrial planet, instantly killing all life on the surface and at a certain depth (underwater and lithoautotrophic ecosystems must survive). Gamma radiation will also provoke chemical reactions, during which up to 90% of the ozone layer will be destroyed, as a result of which the planet will be burned out by the hard ultraviolet radiation of its star.

In 1999, a paper was published in which it was suggested that VGI could be the cause of mass extinction on any inhabited planet up to 10,000 light years away. For comparison, the diameter of the disk of the Milky Way is about 100,000 light years, and its thickness is about 1,000. Thus, a single flash can "sterilize" a significant part of our galaxy.

According to one study, the likelihood of such exposure depends on the location of the planet and the time. The closer a planet is to the galactic core, where the density of stars is highest, the more likely it is. According to the constructed model, the probability of falling under the deadly VGI every billion years, in the vicinity of the core, is 95%. At a distance of half the distance from the core to the solar system, the probability drops to 80%.

But there is a nuance. The frequency of IGR in the past was higher, which was due to the lower concentration of heavy elements in the Milky Way. In other galaxies rich in elements heavier than hydrogen and helium, less IRI was noted. And with the saturation of our galaxy with heavy elements, the VGI frequency decreased. And this may indicate that 5 billion years ago and earlier, the probability of the death of extraterrestrial life from VGI was more than high. Some scientists believe that the Earth was not spared this fate many billions of years ago. Taking into account the high estimated frequency of occurrence of VGI in the past, they can be called a kind of reset buttons, "dumping" inhabited planets, at best, into the state of the microbial biosphere.

So it can be assumed that, with a decrease in the frequency of VGI, our galaxy is now in a phase of equilibrium during the transition from a lifeless void to the ubiquitous emergence of extraterrestrial civilizations. So we may not be alone, but many more civilizations are actively developing with us.

The theory is fascinating, but still unconvincing for some scientists. For example, astronomer Milan Chirkovich believes that in this case, the VGI frequency should have changed very sharply in order to be able to speak of a noticeable boundary between the phases of the development of life in the Milky Way. He does not deny the very fact of a decrease in the amount of VGI, but this is clearly not enough to explain the Great Silence. Probably, their role is exaggerated, moreover, it is completely unknown how much time should pass from "sterilization" to the revival of life up to a sufficiently highly developed civilization.

Our unique Earth

Another possible reason for our loneliness is the Unique Earth Hypothesis. According to her, the conditions for the emergence of a civilization capable of space travel are extremely harsh. This idea originated in 1999 with the paleontologist Peter Ward and the astronomer Donald Brownlee as a result of a comparison of the latest research in astronomy, biology and paleontology. Scientists have compiled a list of parameters that, in their opinion, make our planet incredibly rare. So rare that we are unlikely to meet another civilization.

The mentioned list looks like this:

• Correct location in the correct galaxy type... In galaxies, there are desert zones that have arisen as a result of bursts of gamma and X-rays, changes in the concentration of heavy elements and the gravitational influence of stars on planets and planetesimals, which can lead to collisions celestial bodies.
• Rotating at the correct distance around a star of the correct type... Our planet is located in the so-called Goldilocks zone of our star system, in which the most favorable conditions for the emergence of complex life forms.
• Star system with the correct set of planets... Without the gas giants Jupiter and Saturn, life on Earth might not have arisen. By the way, planets like "hot Jupiter" are very common.
• Stable orbit... In binary star systems, the orbits of the planets are unstable, as a result, they periodically leave the habitable zones. And binary systems are very common in the Milky Way, almost half of the total.
• Correct size terrestrial planet... Sufficient land area, a stable atmosphere and a moderate level of gravity are required for evolutionary processes to take place.
• Plate tectonics... This process regulates the course of the change in the temperature of the earth's climate. Were it not for our tectonics, the average annual temperature would be very unstable.
• Large balancing companion... Our Moon helps the Earth to maintain a certain angle of inclination of the axis, which is the reason for the change of the seasons of the year.
• The trigger mechanism of the evolutionary process of the emergence of a complex life form... The transition from simple unicellular organisms (prokaryotes) to multicellular organisms (eukaryotes) can be one of the most difficult stages of evolution.
• The Right Time in Cosmic Evolution... The early periods of the existence of our galaxy and planet were not the best time for the birth of life, given the frequent fall of celestial bodies, off-scale volcanism, an unstable atmosphere and - outbreaks of gamma radiation.

Admittedly, the list is pretty discouraging. But many scientists consider him far-fetched. For example, according to calculations, there should be about 40 billion potentially habitable planets in our galaxy; life can arise in a rather extreme environment. And some parameters, such as the role of Jupiter and plate tectonics, are clearly overestimated.

Our unique civilization

It is possible that life is actually very widespread in the universe. The very fact of the emergence of our civilization is simply unique. Where did we get the idea that using tools, technological progress, and creating a complex language are standard steps?

As far as we now know, a complex form of life appeared on Earth about two billion years ago, and terrestrial invertebrates - 500 million years ago. During all this huge period of time, not a single species of living creatures on the planet has reached any of the mentioned stages of development. Perhaps the same is happening throughout the galaxy, and for some reason we have become an exception.

Just for us

There is another hypothesis explaining our loneliness in the Universe, although it already refers to philosophy. It's called the Strong Anthropic Principle. In short, its essence lies in the fact that the Universe is not intended for the existence of life, but only for intelligent life, a person. A highly controversial theory that smacks of creationism and rejects a number of obvious evidence to the contrary.

Of course, we are not talking about the fact that the universe was created by some supernatural forces. Or that we are the product of a computer simulation of some highly developed civilization. This hypothesis only implies that we see the Universe just like that, because there are conditions here that only allow us to be observers.

Conclusion

There are many other theories explaining the Great Silence. Perhaps, for me personally, the theory of the parallel development of a large number of civilizations is closer to me than our complete loneliness. And if we are really in the group of leaders, then that would be great. This would mean that we have a lot of chances to create our own future.

The Fermi Paradox: Are We Alone in the Universe?

I think there is no person in the whole world who, finding himself in good location overlooking the stars on a good starry night and looking up, does not feel emotion at all. Some just experience a sense of rolling epic beauty, some think about the greatness of the universe. Someone plunges into the good old existential pool, feeling strange for at least half an hour. But everyone feels something.

Physicist Enrico Fermi also felt something: "Where is everyone?"

The starry sky looks huge, but everything we see is part of our small courtyard. In the best case, when there are absolutely no settlements nearby, we see about 2500 stars (that is, one hundred millionth part of the stars of our galaxy), and almost all of them are less than 1000 light years away (1% of the diameter of the Milky Way). In fact, we see this:

Faced with the theme of stars and galaxies, people inevitably begin to wonder, "Is there intelligent life there?" Let's take some numbers.

There are almost as many galaxies in the observable universe as there are stars in our galaxy (100 - 400 billion), so for every star in the Milky Way there is a galaxy outside it. Together they make up about 10 ^ 22 - 10 ^ 24 stars in total, that is, for every grain of sand on Earth, there are 10,000 stars there.

The scientific community has not yet come to a general agreement on what percentage of these stars are sun-like (similar in size, temperature and luminosity) - opinions are usually reduced to 5-20%. If we take the most conservative estimate (5%) and the lower limit of the total number of stars (10 ^ 22), there will be 500 quintillion, or 500 billion billion sun-like stars in the universe.

There is also controversy over what percentage of these sun-like stars will have an Earth-like planet (an Earth-like planet with similar temperature conditions allowing for liquid water and potential life support). Some say it could go up to 50%, but a conservative estimate from a recent PNAS study found that there will be no more and no less than 22%. This suggests that potentially habitable Earth-like planets revolve around at least 1% of the total number of stars in the Universe - a total of 100 billion billion Earth-like planets.

So, there are a hundred terrestrial planets for every grain of sand in our world. Think about it the next time you find yourself on the beach.

Moving on, we have no choice but to remain within the framework of pure theorization. Let's imagine that after billions of years of existence, 1% of terrestrial planets have developed life (if this is true, each grain of sand will represent one planet with life). And imagine that on 1% of these planets, life has managed to reach a level of intelligence similar to that of the earth. This would mean that there are 10 quadrillion, or 10 million million, intelligent civilizations in the observable universe.

Let's go back to our galaxy and do the same trick with the lower bound for stars in the Milky Way (100 billion). We get a billion terrestrial planets and 100,000 intelligent civilizations in our galaxy alone.

SETI (Search for Extraterrestrial Intelligence) is an organization dedicated to trying to hear signals from other intelligent life. If we are right and there are 100,000 or more intelligent civilizations in our galaxy, and at least some of them are sending radio waves or laser beams, trying to communicate with others, SETI should have caught these signals at least once.

But I didn't. No one. Never.

Where is everyone?

This is weird. Our Sun is relatively young by the standards of the Universe. There are stars much older with terrestrial planets that are also older, which in theory should speak of the existence of civilizations that are much more advanced than our own. For example, let's compare our 4.54 billion year old Earth to a hypothetical planet X 8 billion years old.

If Planet X has a history similar to Earth, let's take a look at where its civilization should be today (the orange gap will show how big the green is):

The technology and knowledge of a civilization that is a thousand years older than ours can shock us in the same way that our world is a person from the Middle Ages. A civilization that is a million years ahead of us may be incomprehensible to us, as human culture is to chimpanzees. And planet X is, let's say, 3.4 billion years ahead of us.

There is a so-called Kardashev scale that will help us categorize intelligent civilizations into three broad categories based on the amount of energy they use:

• Type I civilization uses all the energy of his planet. We have not yet reached a type I civilization, but we are approaching it (Carl Sagan called us a type 0.7 civilization).
• Type II civilization uses all the energy of his home star. Our weak brains can hardly imagine how it is, but we tried by drawing something like a Dyson Sphere. It absorbs the energy emitted by the Sun, and it can be redirected to the needs of civilization.

• Type III civilization blows off the previous two, using energy comparable to that produced by the entire Milky Way.

If this level of development is difficult to believe, remember that Planet X has a level of development 3.4 billion years higher than ours. If the civilization on planet X was similar to ours and was able to develop to a type III civilization, it is logical to assume that by now they have definitely reached interstellar travel, and maybe they have colonized the entire galaxy.

One hypothesis for how the colonization of the galaxy might occur is to build a machine that can fly to other planets, spend 500 years or so self-replicating using the raw materials of the planet, and then sending two replicas to do the same. Even without traveling at the speed of light, this process would colonize an entire galaxy in just 3.75 million years, an instant by the standards of billions of years of planetary existence.

We continue to reflect. If 1% of intelligent life survives long enough to become a potential galaxy-colonizing Type III civilization, our calculations above suggest that there should be at least 1000 Type III civilizations in our galaxy alone - and given the power of such civilizations, their presence is unlikely would go unnoticed. But there is nothing, we see nothing, we do not hear anything, no one visits us.

Where is everyone?

Welcome to the Fermi paradox.

We have no answer to the Fermi paradox - the best we can do is "possible explanations." And if you ask ten different scientists, you get ten different answers. What would you think of the people of the past who discuss whether the Earth is round or flat, the Sun revolves around it or is it around it, does the almighty Zeus give lightning? They seem so primitive and dense. The same can be said about us discussing the Fermi paradox.

Looking at the most discussed possible explanations of the Fermi paradox, it is worth dividing them into two broad categories - those explanations that suggest that there are no signs of civilizations of type II and III, because they simply do not exist, and those that assume that we do not see and we don't hear them for some reason:

I group of explanations: there are no signs of higher civilizations (types II and III), because there are no higher civilizations

Those who adhere to Group I explanations point to what is called the problem of non-exclusiveness. She rejects any theory that states: "There are higher civilizations, but none of them tried to contact us, because they all ...". Group I people look at mathematics, which says that there must be thousands or millions of higher civilizations, so at least one must be an exception to the rule. Even if the theory supports the existence of 99.9% of higher civilizations, the remaining 0.01% will be different, and we will definitely know about it.

Thus, supporters of the explanations of the first group say, super-developed civilizations do not exist. And since the calculations speak of thousands of such in our galaxy alone, there must be something else. And this something else is called the Great Filter.

The theory of the Great Filter says that at a certain point from the very beginning of life to a type III civilization there is a certain wall that almost all life attempts hit. This is a certain step in a long evolutionary process, through which life practically cannot pass. And it's called the Great Filter.

If this theory is correct, the big question remains: at what length of time does the Great Filter arise?

It turns out that when it comes to the fate of humanity, this issue becomes very important. Depending on where the Great Filter arises, we are left with three possible realities: we are rare, we are the first, or we are lost.

1. We Are Rare (The Great Filter Behind)

There is a hope that the Great Filter remained behind us - we managed to pass it, and this will mean that it is extremely difficult for life to develop to the intellect of our level, and this happens extremely rarely. The diagram below shows that only two species have done this in the past, and we are one of them.

This scenario could explain why there are no Type III civilizations ... but it would also mean that we might be one of several exceptions. That is, we have hope. At first glance, it looks the same as people believed that the Earth was at the center of the universe 500 years ago - they thought they were special, and we may think so today too. But the so-called "selective observation effect" says that regardless of whether our situation is rare or fairly common, we will tend to see the former. This leads to the fact that we admit the possibility that we are special.

And if we are special, when exactly did we become special - that is, what step did we take where others get stuck?

One possibility: The Great Filter could be at the very beginning - thus, the very beginning of life was an extremely unusual event. This option is good because it took billions of years for life to finally appear, and we tried to repeat this event in the laboratory, but we failed. If the Great Filter is to blame, this will mean not only that there may not be intelligent life in the Universe, it will mean that life may not exist outside our planet at all.

Another possibility: The Great Filter could be a transition from simple prokaryotic cells to complex eukaryotic cells. After prokaryotes are born, they need at least two billion years before they can make an evolutionary leap, become complex and get a nucleus. If this is the whole Great Filter, this may indicate that the Universe is teeming with simple eukaryotic cells and that's it.

There are a number of other possibilities - some even believe that even our last leap to our current intelligence may be a sign of the Great Filter. Although the leap from semi-intelligent life (chimpanzees) to intelligent life (humans) does not seem like a miraculous step, Stephen Pinker rejects the idea of ​​an inevitable 'uplift' in the process of evolution: “Since evolution does not set a goal, but simply happens, it uses adaptations that will a specific ecological niche, and the fact that it has led to technological intelligence on Earth, in itself may indicate that such a result of natural selection is very rare and is not a habitual consequence of the evolution of the tree of life. "

Most jumps are not considered Grand Filter candidates. Any possible Great Filter has to be a one-in-a-billion thing, when something incredibly weird is about to happen to provide a crazy exception - for this reason, the transition from single-celled to multicellular life is not taken into account, because it happened only on our planet 46 times as isolated events. For the same reason, if we find fossilized eukaryotic cells on Mars, they will not be a sign of the Great Filter (like nothing else that happened up to this point in the evolutionary chain), because if this happened on Earth and Mars, then it will happen where something else.

If we are truly rare, it could be due to a strange biological event, and also due to what is called the "rare earth" hypothesis, which says that there may be many terrestrial planets with similar conditions on Earth, but separate conditions on Earth - the specificity of the solar system, the connection with the moon (a large moon is rare for such small planets) or something in the planet itself can make it extremely friendly for life.

2. We are the first

The adherents of group I believe that if the Great Filter is not behind us, there is hope that the conditions in the Universe quite recently, for the first time since the Big Bang, became such that they allowed intelligent life to develop. In this case, we and many other species may be on the path to superintelligence, and just before that no one got there. We were in the right place at the right time to become one of the first superintelligent civilizations.

One example of a phenomenon that could make this explanation possible is the prevalence of gamma-ray bursts, giant explosions that we see in distant galaxies. Just as it took the young Earth several hundred million years before asteroids and volcanoes subsided, opening the way for life, the Universe could be filled with cataclysms like gamma-ray bursts that burned out everything that could become life from time to time, up to a certain point. ... Now, perhaps, we are in the middle of the third astrobiological stage of the transition, when life is able to develop for such a long time and nothing interferes with it.

3. We have a cover (Great filter in front)

If we are not rare and not the first, among the possible explanations of the 1st group there is also the fact that the Great Filter is still waiting for us. Perhaps life regularly develops to the threshold at which we stand, but something prevents it from developing further and growing to a higher intelligence in almost all cases - and we are unlikely to become an exception.

One of the possible Great Filters is a regularly occurring catastrophic natural event like the aforementioned gamma-ray bursts. Perhaps they are not over yet, and it is only a matter of time before all life on Earth suddenly divides to zero. Another candidate is the possible inevitability of self-destruction of all advanced civilizations after reaching a certain level of technology.

This is why Oxford University philosopher Nick Bostrom says "no news is good news." The discovery of even the simplest life on Mars would be devastating because it would trim a number of possible Great Filters behind us. And if we find fossils of complex life on Mars, according to Bostrom, "it will be the worst news in human history, printed in a newspaper," because it would mean that the Great Filter will almost certainly be ahead. Bostrom believes that when it comes to the Fermi paradox, "the silence of the night sky is gold."

II group of explanations: civilizations of II and III types exist, but there are logical reasons that we do not hear them

The second group of explanations gets rid of any mention of our rarity or uniqueness - on the contrary, its followers believe in the principle of mediocrity, the starting point of which is that there is nothing rare in our galaxy, solar system, planet, level of intelligence, until the evidence proves otherwise. They are also in no hurry to say that the lack of evidence of higher intelligence indicates their absence as such - and emphasize the fact that our search for signals stretched only 100 light years from us (0.1% of the galaxy). Here are ten possible Group II explanations for the Fermi paradox.

1. Superintelligent Life Has Been Visiting Earth, long before we appeared. In this scheme of things, living people have existed for about 50,000 years, which is relatively short. If the contact occurred before that, our guests simply plunged into the water alone, and that's all. In addition, the recorded history is only 5,500 years old - perhaps a group of ancient tribes of hunter-gatherers encountered unknown extraterrestrial bullshit, but did not find a way to remember or capture this event for future descendants.

2. Galaxy colonized but we just live in some desolate countryside. Americans may have been colonized by Europeans long before the small Inuit tribe in northern Canada realized this was happening. There may be an urban moment in the colonization of a galaxy, where species gather in the neighborhood for convenience, and it would be impractical and pointless to try to contact someone in that part of the spiral galaxy we are in.

3. All concept physical colonization - funny idea of ​​antiquity for more advanced views. Remember the image of a Type II civilization in the sphere around its star? With all this energy, they could create the perfect place for themselves that would satisfy all needs. They could incredibly reduce the need for resources and live in their happy utopia, instead of exploring a cold, empty and undeveloped universe.

An even more advanced civilization could see the entire physical world as a terribly primitive place, having long ago conquered its own biology and loaded its brains into virtual reality, a paradise for eternal life. Life in the physical world of biology, mortality, desires and needs might seem primitive for such creatures, as it seems to us primitive life in a cold dark ocean.

4. Somewhere out there there are predatory terrible civilizations, and the most intelligent life knows that broadcast any outgoing signal, thereby giving away their location, extremely unreasonable... This unpleasant moment could explain the absence of any signal received by the SETI satellites. It could also mean that we are just naive newbies who foolishly give out their location in a risky way. There is a debate over whether we should try to contact an extraterrestrial civilization, and most people conclude that no, it is not. Stephen Hawking warns: "If aliens visit us, the consequences will be worse than when Columbus landed in America, which was clearly not very good for Native Americans." Even Carly Sagan (who firmly believed that any advanced civilization that mastered interstellar travel would be altruistic and not hostile) called the METI practice “extremely unreasonable and immature” and recommended “newborns in a strange and incomprehensible space to sit and listen quietly for a long time, patiently learning and absorbing before screaming into the unknown we don't understand. "

5. There is only one representative of the highest intellectual life - predator civilization(like people here on Earth) - which is much more advanced than everyone else, and is kept afloat by destroying any intelligent civilization once it reaches a certain level of development. That would be extremely bad. It would be extremely unreasonable to destroy civilizations, spending resources on it, because most of them would die out by themselves. But after a certain point, intelligent species can begin to multiply like a virus and soon populate the entire galaxy. This theory implies that whoever populates the galaxy first will win, and no one else has a chance. This could explain the lack of activity, because it would reduce the number of superintelligent civilizations to one.

6. Somewhere out there there is both activity and noise, but our technology is too primitive and we're trying to hear the wrong thing. You walk into a modern building, turn on your walkie-talkie and try to hear something, but everyone sends text messages and you decide the building is empty. Or, as Carl Sagan said, our minds can work many times slower or faster than the minds of other intelligent forms: they need 12 years to say "Hello", but when we hear it, it is white noise for us.

7. We are in contact with intelligent life, but the authorities are hiding it... This theory is completely idiotic, but we must mention it.

8. Higher civilizations know about us and watching us("The zoo hypothesis"). As far as we know, superintelligent civilizations exist in a tightly regulated galaxy, and our Earth is considered to be something like a national reserve, protected and large, with a sign “watch but do not touch”. We do not notice them, because if an intelligent species wanted to watch us, it would know how to hide from us with ease. Perhaps there really is some "first directive" from Star Trek that prohibits superintelligent beings from making any contact with younger species until they reach a certain level of intelligence.

9. Higher civilizations are here around us. But we are too primitive to perceive them... Michio Kaku explains it this way:

“Let's say we have an anthill in the center of the forest. A ten-lane expressway has been built next to the anthill. The question is: “Will ants understand what a ten-lane freeway is? Will the ants be able to understand the technology and intentions of the creatures that build the highway next to them? "

Thus, not only can we not pick up signals from planet X using our technology, we cannot even understand what the creatures from planet X are doing. On their part, trying to enlighten us would be like trying to train ants to use the Internet.

It could also answer the question, "Well, if there are so many incredible Type III civilizations, why haven't they contacted us yet?" To answer that question, let's ask ourselves: When Pizarro was heading to Peru, did he stop in front of the anthills to mingle? Was he generous in trying to help the ants in their difficult affairs? Was he hostile and stopped from time to time to burn the hated ant hills? Or was he deeply on the drum? That's the same.

10. We are completely deluded in their ideas about reality. There are a lot of options that could completely divide our ideas by zero. The universe can be something like a hologram. Or we are aliens, and we were placed here as an experiment or fertilizer. There is even a chance that we are all part of a computer simulation of some scientists from another world, and other life forms were simply not programmed to appear.

As our journey continues, we continue to search for extraterrestrial intelligence, it is not entirely clear what to expect. If we find out that we are alone in the universe, or officially enter the galactic community, both options are equally creepy and equally mind-blowing.

Aside from its shocking fantasy component, the Fermi Paradox leaves people with a deep sense of humility. This is not the usual "I am a microbe and live for three seconds" that arises when thinking about the Universe. The Fermi Paradox leaves behind a clearer, personal resignation that can only appear after hours spent studying the most incredible theories presented by the best scientists who constantly turn their minds over and contradict one another. He reminds us that future generations will look at us in the same way as we look at the people of antiquity, who thought that the stars were bolted to a wooden firmament, and wonder: "Wow, they really had no idea what was going on."

All this hits our self-esteem, together with conversations about civilizations of type II and III. Here on Earth, we are the kings of our little castle, proudly reigning over a handful of fools who share the planet with us. And in this bubble there is no competition and no one will condemn us, we generally have no one to discuss the problem of being with, except ourselves.

All this suggests that we humans are probably not so smart, sitting on a tiny rock in the middle of a desert universe and even have no idea that we can be wrong. But we may be wrong, let's not forget about it in attempts to justify our own greatness. We do not even have a clue that somewhere there is a story in which we do not even represent the letters - a period, a comma, a page number, a bookmark.

Searching for life beyond Earth. Are we alone? (documentary film)

Are we alone in this universe? Until now, this issue remains unresolved. But UFO sightings and mysterious space images make one believe in the existence of aliens. Let's see where else, besides our planet, the existence of life is possible.

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7

The Orion Nebula is one of the brightest nebulae in the sky visible to the naked eye. This nebula is located one and a half thousand light years from us. Scientists have discovered many particles in the nebula, from which life can form in our understanding. The nebula contains substances such as methanol, water, carbon monoxide, and hydrogen cyanide.

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6

There are billions of exoplanets in the universe. And some of them contain a huge amount organic matter... The planets also revolve around their stars, like our Earth around the Sun. And if you're lucky, some of them rotate at such an optimal distance from their star, at which they receive enough heat so that the water present on the planet is in liquid form, and not in solid or gaseous.

Kepler 62e is the exoplanet most widely suited to support life. It orbits the star Kepler-62 (in the constellation Lyra) and is 1200 light years distant from us. It is believed that the planet is one and a half times heavier than Earth, and its surface is completely covered with a 100-kilometer layer of water. In addition, the average temperature of the planet's surface, according to calculations, is slightly higher than the Earth's and is 17 ° C, and ice caps at the poles may be completely absent. Scientists say there is a 70-80% probability that some form of life is possible on this planet.

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5

Enceladus is one of the moons of Saturn. It was discovered back in the 18th century, but interest in it increased a little later, after the Voyager 2 spacecraft discovered that the satellite's surface has a complex structure. It is completely covered in ice, has ridges, areas with many craters, and very young areas flooded with water and frozen. This makes Enceladus one of three geologically active objects in the outer Solar System.

The interplanetary probe Cassini studied the surface of Enceladus in 2005 and made many interesting discoveries. Cassini discovered carbon, hydrogen and oxygen on the moon's surface, and these are key components for the formation of life. Methane and organic matter have also been found in some areas of Enceladus. In addition, the probe detected the presence of liquid water beneath the satellite's surface.

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4

Titanium

Titan is Saturn's largest moon. Its diameter is 5150 km, which is 50% more than the diameter of our Moon. In size, Titan is even larger than the planet Mercury, slightly inferior in mass.

Titan is considered to be the only satellite of the planet in the solar system that has its own dense atmosphere, consisting mainly of nitrogen. The temperature on the satellite's surface is minus 170-180 ° C. And while it is considered too cold an environment for life to arise, the large amount of organic matter on Titan may indicate otherwise. The role of water in the construction of life here can be played by liquid methane and ethane, which are here in several states of aggregation. Titan's surface is made up of methane-ethane rivers and lakes, water ice, and sedimentary organic matter.

In addition, it is possible that there are more comfortable living conditions under the surface of Titan. Perhaps there are warm thermal springs rich in life. Therefore, this satellite is the subject of future research.

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3

Callisto is the second largest natural satellite of Jupiter. Its diameter is 4820 km, which is 99% of the diameter of the planet Mercury.

This satellite is one of the most distant from Jupiter. This means that the deadly radiation of the planet affects him to a lesser extent. The satellite always faces Jupiter on one side. All this makes it one of the most likely candidates for the creation of a habitable base there in the future for the study of the Jupiter system.

And although Callisto does not have a dense atmosphere, its geological activity is zero, it is one of the candidates for the detection of living forms of organisms. This is because amino acids and other organics were found on the satellite, which are necessary for the emergence of life. In addition, there may be an underground ocean under the planet's surface that is rich in minerals and other organic compounds.

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2

Europa is one of the moons of Jupiter. It has a diameter of 3120 km, which is slightly inferior to the Moon. The surface of the satellite is composed of ice, under which there is a liquid ocean. Beneath the ocean, the surface is composed of silicate rocks, and an iron core is located in the center of the moon. Europe has a thin oxygen atmosphere. The ice surface is rather smooth, which indicates geological activity.

You ask, where from at such a distance from the Sun can a liquid ocean arise? Jupiter's tidal interactions are to blame. The planet has a huge mass, its gravity strongly affects the surfaces of the satellites. Just as the Moon influences the ebb and flow of the earth, Jupiter does the same with its satellites, only to a much greater extent.

The surface of Europa is strongly deformed by Jupiter's gravity, friction forms inside the satellite, which heats up the bowels, making this process something similar to the earth's movements of lithospheric plates.

Thus, we see that Europe has oxygen, a weak atmosphere, liquid water, and many different minerals that are the building blocks of life.

The European Space Agency is planning a landing mission across Europe, which is scheduled for 2022. She can reveal many secrets of this moon of Jupiter.

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1

Mars

Mars is by far the most accessible planet to find evidence of extraterrestrial life. The position of the planet in the Solar System, its size and composition indicate the possibility of the existence of life on it. And, if now Mars is lifeless, then perhaps he had life earlier.

There are many facts about the existence of life on Mars:

Most of the Martian asteroids found on Earth contain micro-fossils of life. The only question is whether these fossils could have got to the asteroids after landing.

The presence of dry riverbeds, volcanoes, ice caps and various minerals testifies to the possibility of life on the planet.

Short-term increases in the amount of methane in the atmosphere of Mars have been documented. In the absence of geological activity on the planet, such emissions can be caused only by the presence of microorganisms on the planet.

Research has shown that Mars in the past had significantly more comfortable conditions than it does now. Rough streams of rivers flowed on the planet's surface, Mars had its seas and lakes. Unfortunately, the planet does not have its own magnetic field and it is much lighter than the Earth (its mass is about 10% of the Earth's). All this prevents Mars from holding a dense atmosphere. If the planet were heavier, and perhaps we would now see life on it, which would be as beautiful and diverse as on Earth.

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Conclusion

Science explores space by leaps and bounds. Everything that we know today will help us find answers to many questions tomorrow.

Hopefully in this century, humanity will find extraterrestrial life. It was the article "TOP-7 places in the Universe where the existence of life is possible." Thank you for the attention.