Just yesterday, NASA chief scientific adviser Ellen Stofan predicted that in the next 10 years, scientists will be able to find convincing signs of the existence of life outside the Earth. On this occasion, I offer the top most habitable planets known to us at the moment.

To support life (in the usual sense of the word), the planet must simultaneously boast the presence of an iron core, crust, atmosphere, and liquid water. Such planets in the space known to us are very rare, but they do exist.

Gliese 667 Cc.

Star System: Gliese 667
Constellation: Scorpio
Distance from the Sun: 22.7 light years
Earth similarity index: 0.84

The luminary around which the planet revolves belongs to a triple system of stars, and, in addition to the reddest dwarf Gliese 667C, the planet is also illuminated by its "sisters" - the orange dwarf Gliese 667A and Gliese 667B.

If the planet has an Earth-like atmosphere with a greenhouse effect due to the presence of 1% CO2, the effective temperature, according to calculations, will be -27 °C. For comparison: the effective temperature of the Earth is −24 °C. However, a sadder option is not ruled out: perhaps because of the proximity to the triple luminary, the planet's magnetic field suffered greatly, and the stellar wind tore off water and volatile gases from it long ago. In addition, there is a hypothesis that life in binary and triple star systems cannot originate in principle due to unstable conditions.

Kepler-62 f.

Star system: Kepler-62
Constellation: Lyra
Distance from the Sun: 1200 light years
Earth similarity index: 0.83

One of the most "livable" planets of all that we know. The index of similarity to the Earth is 0.83 out of 1.00. But that's not what scientists are most concerned about. The planet Kepler-62 f is 60% larger than the Earth, one and a half times older, and most likely completely covered in water.

The period of revolution of the planet around the parent star is 267 days. During the day, the temperature rises to + 30 ° - + 40 ° C, at night the temperature is + 20 ° - -10 ° C. The fact that we are separated from this planet by 1200 light years is also important. That is, today we see the Kepler-62 f, which he was in 815 according to the earth's chronology.

Gliese 832 c.

Star System: Gliese 832
Constellation: Crane
Distance from the Sun: 16 light years
Earth similarity index: 0.81

Gliese 832 s has a mass about 5.4 times that of the Earth. The period of revolution around the parent star is about 36 days. Its temperature is predicted to be fairly similar to Earth's, but fluctuates greatly as the planet rotates around its star. The average surface temperature is predicted to be -20°C. However, it could have a thick atmosphere, which could make it much hotter and more Venus-like.

The planet is a representative of "super-Earths" circulating in the habitable zone. Although the planet is much closer to its star than the Earth is from the Sun, it receives about the same amount of energy from the red dwarf as the Earth receives from our yellow dwarf.

Tau Ceti e.

Star system: Tau Ceti
Constellation: Whale
Distance from the Sun: 12 light years
Earth similarity index: 0.78

The planet receives about 60% more light than the Earth from the Sun. The stormy dense atmosphere, similar to the cloud cover of Venus, transmits light poorly, but warms up perfectly. The average temperature on the surface of Tau Ceti is about 70 °C. Under such conditions, only the simplest heat-loving organisms (bacteria) probably live in hot water and on the banks of reservoirs.

Unfortunately, at the moment, even using modern technology, it is impossible to send a mission to Tau Ceti. The fastest moving artificial space object is Voyager 1, whose speed relative to the Sun is currently about 17 km / s. But even for him, the journey to the planet Tau Ceti e will take 211,622 years, plus another 6 years needed for a new spacecraft to accelerate to such a speed.

Gliese 581 g.

Star System: Gliese 581
Constellation: Libra
Distance from the Sun: 20 light years
Earth similarity index: 0.76

Unofficially, this planet is called Zarmina - after the wife of the scientist who discovered it in 2010. It is assumed that Zarmin has rocks, liquid water and an atmosphere, but from the point of view of earthlings, even in this case, life here should be difficult.

Due to its proximity to the mother star, Zarmina most likely rotates around its axis in the same time it takes to complete a full circle in its orbit. As a result, Gliese 581g is always turned to its luminary on one side. On one side of it, a cold night constantly reigns with temperatures down to -34 ° C. The other half is shrouded in red twilight, since the luminosity of the star Gliese 581 is only 1% of that of the Sun. Nevertheless, it can be very hot on the day side of the planet: up to 71 ° C, as in hot springs in Kamchatka. Due to the temperature difference in Zarmina's atmosphere, hurricanes are likely to rage constantly.

Kepler 22b.

Star system: Kepler 22
Constellation: Cygnus
Distance from the Sun: 620 light years
Earth similarity index: 0.71

With a mass of the planet 35 times the mass of the Earth, the force of gravity on its surface is more than 6 times greater than the earth's. The combination of a shorter distance from the star and less light output suggests a moderate temperature on the planet's surface. Scientists estimate that in the absence of an atmosphere, the equilibrium temperature on the surface would be about -11 °C. If the greenhouse effect caused by the presence of the atmosphere is similar to that of the Earth, then this corresponds to an average surface temperature of about +22 °C.

However, some scientists believe that Kepler 22b is not like the Earth, but like a thawed Neptune. For a terrestrial planet, it is still too big. If such assumptions are correct, Kepler 22b is one continuous "ocean" with a small, solid core in the middle: a giant, shoreless expanse of water under a thick layer of atmospheric gases. However, this does not negate the viability of the planet: according to experts, the existence of life forms in the planetary ocean is "not beyond the bounds of the possible."

Kepler-186 f.

Star system: Kepler-186
Constellation: Cygnus
Distance from the Sun: 492 light years
Earth similarity index: 0.64

Kepler-186 f makes one revolution around its parent star in 130 days. The planet has an illumination of 32%, thus being inside the habitable zone, although closer to its outer edge, similar to the position of Mars in the solar system. Since Kepler-186 f was discovered only a year ago, the planet's mass, density, and composition are unknown.

According to the assumptions of scientists, the planet may well be viable, but only if it has retained its atmosphere. Red dwarfs, to which the planet's star belongs, emit a strong stream of high-energy ultraviolet radiation in the early stages of their existence. The planet could lose the primary atmosphere under the influence of this radiation.

The earth is a common home for more than 7 billion people. There will be enough food and resources for a long time to come, and overpopulation so far does not threaten us (not to mention individual countries). However, scientists are sure that such a relative idyll cannot last forever, and even if not in the near future, but someday our planet will no longer be habitable. This may be the result of a world war, a global cataclysm, or a cosmic impact. What is the way out for man? It would be nice to move to another habitable planet, of course, having prepared it in advance for this. Let's look at the TOP 7 planets that a person can colonize for future resettlement.

7th place. Mercury

Among other objects in the solar system, the planet Mercury is considered as a candidate for colonization. It is best to populate the region of the poles, because there are ice caps (so far, presumably) and daily temperature drops are minimal. On Mercury there will be no problems with energy due to its proximity to the Sun, and this planet is rich in useful resources, it’s a pity not in food ... The advantages of Mercury include the presence of a magnetic field that can cope with the solar wind and cosmic radiation, although not so efficient as the earth.

But the proximity to the Sun and the lack of a more or less dense atmosphere make Mercury not so attractive in terms of colonization. Well, a bonus disadvantage is the length of the day in 176 Earth. Terraforming in such conditions is simply impractical, so you will have to make do with a colony underground. In any case, organizing the possibility of human habitation on Mercury will be quite lengthy and labor intensive. Due to the gravity of the Sun, even the flight itself will be extremely energy-intensive and dangerous. That is why only 7th place.

6th place. Kepler-438b

For a change, consider two planets outside the solar system, but the most habitable. It is possible that in the distant future we will be able to overcome interstellar space in terms not exceeding a human life, therefore it is advisable to consider distant worlds as places of colonization.

Kepler-438 b is located in the constellation Lyra at a distance of 470 light years from Earth. Today it is considered the most similar to Earth in a number of ways., therefore, the presence of life on it is highly valued. This planet is slightly larger than ours, and its location from the star is optimal for the presence of liquid water and quite acceptable temperatures. In the catalog of habitable planets, Kepler-438 b is in second place after , and this is already saying something.

The only thing that calls into question the habitability of Kepler-438 b is the recently released results of observations of the star around which the planet revolves. Astronomers have noticed that this star very often produces strong emissions of radiation. So not everything is so rosy, and it’s far to fly to it. Therefore, 6th place.

5. place. Proxima Centauri b

The exoplanet Proxima Centauri b was discovered in early August 2016. It revolves around the nearest star to the Sun, Proxima Centauri. Among all the likely habitable planets outside our system, Proxima Centauri b is notable for its relatively small distance from Earth at 4.22 light years. The average temperature on it is about -40 ° C. So far, it is impossible to accurately declare the presence of life there, but the fact that the planet is located in a zone suitable for this is undeniable.

A year on this planet lasts only 11 Earth days. The star Proxima Centauri is small, which means that the habitable zone around it is closer than that of the Sun. And, consequently, the orbit of the planets will also be smaller, and therefore the revolution around the star is faster. By the way, like the Moon with the Earth, Proxima Centauri b always faces its star with only one side, so there is eternal night in one hemisphere, and constant day in the other.

On Proxima Centauri b, only one side is illuminated

Scientists seriously started talking that it would be nice to send probes there, or rather, nanoprobes weighing 1 gram, which could reach this planet in 20 years.

4th place. Moon

The moon (yes, it's not a planet) is most attractive in that the flight to it is only 3 days, and building a base there is not as costly as on other space objects. Water was found on the Earth's satellite, a small amount of which is concentrated at the poles. Strictly speaking, that's all - the Moon is no longer attractive as a place for resettlement.

Unfortunately, among all the options considered, terraforming the Moon will probably be the most difficult. It lacks both an atmosphere suitable for life and a significant magnetic field. So there is practically no protection from meteorites and radiation. In addition, it is necessary to solve the problem of all-pervading lunar dust, which not only spoils equipment, but also penetrates into human lungs. In general, to create terrestrial conditions on the moon, you will have to try hard. But its close location to the Earth is an undeniable advantage.

Today, the Moon is considered primarily as a place for scientific research and as a source of minerals. In particular, earthlings are attracted by the presence of helium-3 there, which we will need.

3rd place. Venus

Venus is a neighbor of the Earth and concurrently one of the hottest planets in our system. The reason for this is the densest clouds, which retain the resulting heat in the atmosphere. Because of this, the average temperature on the planet is 477 °C. Nevertheless, if you solve the problem with clouds, then it is quite possible to end up with conditions similar to those on Earth. In addition, getting to Venus is much easier than to any other planet.

Venus is deservedly called the twin of the Earth, because. their diameter and mass are very similar.

In addition to solving the problem of extreme heat, a person will have to solve the problem with water, which is not found on Venus, but there is still hope that somewhere in the bowels of the planet it is. Unpleasant is the fact that without clouds, Venus may be exposed to radiation due to a weak magnetic field.

Scientists already have an idea of ​​how to prepare Venus for active terraforming. You can install special screens between the planet and the Sun, which will reduce the flow of solar energy, which will significantly reduce the temperature. A less elegant way is to bombard Venus with comets and asteroids that carry ice. In addition, according to calculations, it is possible to spin the planet in this way and reduce the Venusian day, which now amounts to 58.5 Earth days. In the process of formation of the hydrosphere, it will already be possible to start throwing algae and terrestrial microorganisms into it.

The size of an asteroid needed to create a hydrosphere on Venus

Thus, the colonization of Venus is quite possible, albeit not in the near future, because now another planet has been chosen by mankind for these purposes ...

2nd place. Titanium

Yes, Titan, a satellite of Saturn, is not a planet, but it fits into our list very colorfully. This is one of the few places in the solar system where life is currently possible.(except the Earth of course) at least in the most primitive form. According to current research, Titan has carbon, hydrogen, nitrogen and oxygen - everything necessary for life. In addition, a sufficiently dense atmosphere provides reliable protection from cosmic radiation. On Titan there is everything necessary for the life of the colony: from water to the possibility of obtaining rocket fuel. Titanium is very attractive in economic terms, because. there are hundreds of times more liquid carbon than all the oil reserves on Earth. In addition, all these treasures are located directly on the surface of the satellite in the form of lakes.

A person on Titan can be harmed by low pressure, low temperature and the presence of hydrogen cyanide in the atmosphere. You can't do without special spacesuits in the first couple. An unpleasant factor is gravity, which is 7 times lower than ours. Because of this, our body can suffer. And there are often strong earthquakes.

There is a very high probability that Titan will become the 3rd space object after the Moon and Mars, on which a person will land. Today, it is primarily considered as a source of resources that are gradually running out on Earth.

1 place. Mars

It is Mars that lays claim to the planet that man colonizes first. The red planet is suitable for creating life-friendly conditions for humans, according to scientists, to the greatest extent today.

The indisputable advantage of Mars is the ability to produce food resources, oxygen and building materials on the spot. This is an undeniable plus over other options for the planets of the solar system. All this will allow the task of terraforming to be carried out, which will ultimately allow the creation of terrestrial conditions. It will be much easier for a person to get used to the Martian day, which is 24 hours and 39 minutes. And the plants will love it too.

There is definitely water on Mars. This is confirmed by the latest research guys from NASA. And water is life! True, it is in a frozen state, but there is an assumption that there are extensive underground reserves on Mars. The local soil, with additional cultivation, is suitable for growing terrestrial plants.

The Red Planet is seriously considered as a place to create the "Cradle of Humankind" in case a global catastrophe occurs on our planet. True, this is still a distant prospect, and now they look at the red planet rather as a place where it is possible to conduct interesting research and experiments that are dangerous to conduct on Earth.

By the way, there is an opinion that our civilization originated on Mars, but was forced to move to Earth.

Among the main problems that need to be addressed are the weak magnetic field of Mars, a rarefied atmosphere and gravity equal to 38% of the earth's.

To protect against radiation, it is necessary to create a normal magnetic field, which is still unrealistic with the current development of our science. With the current atmosphere, you will also have to decide something, because. it retains neither heat nor air. The average daily temperature on Mars is -55°C. In addition, the atmosphere of the red planet does not provide adequate protection against meteorites. So, until the problem with the optimal atmosphere is solved, you will have to live in special living quarters. The factor of lower gravity will subject the human body to great tests - it will have to rebuild. Another nuisance on Mars is its famous sandstorms, which are very poorly understood today. However, different methods of solving these problems are already being considered, when the organization of life on many other planets still looks like science fiction.

Today, the exploration of Mars is hampered by the high cost of flights. Of course, because the governments of all countries believe that it is better to spend billions on weapons than on conquering other worlds ... So let's hope that we will have time to organize at least cities with their own atmosphere on Mars before we finally pollute the Earth.

A flight to Mars takes about 9 months, but in the foreseeable future, new engines are being developed that can significantly reduce this time. If compared with a flight to Mercury, then the energy costs are simply miserable, not to mention the comparison with interstellar flights.

In general, Mars is the best option in terms of the ratio of habitability and distance from Earth.

Conclusion

In the next 20 years, humans will land on Mars. It will be a great useful experience in terms of exploring other planets. Today, there can be no talk of mass resettlement of earthlings, and there is no need yet. But on the other hand, we know for sure that there is more than one planet that can become our new home.

Yes! In other solar systems, there are also planets whose conditions allow life. With a small insert "maybe", because as such, they are called exoplanets, discovered recently and not yet sufficiently studied. Yes, and the environmental conditions on these planets, although close to Earth, are still different for a full-fledged life, like on Earth. Yes, and their location far from our solar system (in light years) for humans is still difficult to access and is considered only in theory.

So, the employees of the NASA space agency tried to understand the issue that may face humanity in the next thousand years - the colonization of other solar systems on the planets.

Consider the planets that fall under the so-called "habitable zone" (circumstellar habitable zone) - a conditional zone near a star, the conditions of which are suitable for life on the planet. It is in such a zone that there is at least some probability of the emergence of life on another planet, but first we will consider the planets closest to us from our solar system.

habitable planets in the solar system

Planet Earth

This is our home planet, which, of course, we do not want to leave under any circumstances. After all, the planet Earth is the most habitable planet of all known in the universe. There is a huge amount of oxygen here, like no other planet, nitrogen, hydrogen, helium, carbon and other important substances, thanks to which life exists in the form that we know.

The planet Mars

If they have to move under difficult circumstances, that is, the closest and only planet in our solar system more or less suitable for life is Mars. This planet has an atmosphere that protects from cosmic rays and the temperature is not so extreme for life. Unfortunately, the atmospheric pressure is too rarefied compared to the Earth's and although there is oxygen, it is very small, so it will be possible to stay on the planet only in protective suits or in hermetically sealed rooms. But there must be water on the planet! True, if there is, then it will be very, very small.

Planets of other stars suitable for life

Planet Gliese 581d

This amazing planet is located in the planetary system Gliese 581 of the constellation Libra, which is 20 light years from our Earth. This is a very large planet, 2 times the size of the Earth. The star Gliese, which is the sun for the planet, is somewhat dim because it is a red dwarf, but due to the close location of the planet to its sun, the temperature on it is slightly above 0 ° C, twilight reigns on the planet, and a huge red ball flickers in the sky.

Planet HD 85512 b

This is a planet that may already have life. After all, the temperature on the surface is about 25 ° C, despite the fact that the star is 8 times weaker than our Sun, but the planet is much closer to it. The planet is located in the constellation Sail, 36 light years from us.

Planet Kepler 22b

A very distant planet from us at a distance of 620 light years. The temperature on the planet is quite consistent with the average temperature at resorts in Greece, only in structure it is more like Neptune, it consists mainly of a huge ocean, so if there is life, then in water conditions. So you have to adapt to life afloat.

Planet Gliese 667cc

The second planet in the system of the red dwarf star Gliese. According to preliminary calculations, the temperature on the planet can be either -27 ° C, and if the atmosphere turns out to be similar in structure to the earth, then the temperature will already be +27 ° C, and both surface temperatures are already acceptable for life on another planet from Earth.

Planet Gliese 581g

This planet in the same planetary system Gliese 581 has a high probability of having both an atmosphere and water, and the terrain can be rocks, mountains and plains. An interesting feature of this planet is that it always faces its star on one side, that is, there is no change of day and night on it. On the day side, the temperature is quite hot, like in the Sahara desert on Earth (+71 ° C), and on the night side, it is cold, but tolerable, like a Russian winter in Siberia (-34 ° C)

Planet Gliese 163c

This is a very warm, even rather hot planet, where the temperature is +70 ° C, which casts doubt on the vegetation on the surface, but even at such temperatures, organisms can live on the planet. And a person can adapt with the help of special sun protection systems and lowering the temperature in enclosed spaces to life on this planet.

Planet HD 40307 g

The planet is around the star HD 40307 in the constellation Pictorus, which is the sixth in the planetary system and is tolerant of life conditions on the surface. A year on the planet is less than on Earth - 200 days and it is possible to have water on it.

P/S

(Dawn on the planet Earth and what the dawn would look like if our planet were in other star systems)

So there are planets outside the solar system where life is possible, but the most beautiful and kindest of them is our blue planet Earth!

Since ancient times, almost all peoples knew about the existence of parallel realities. This knowledge is reflected in the cosmogony, cosmology, mythology of these peoples. Almost all religions have ideas about the existence of various realities in which other beings live, as well as the reality where the souls of people go after the death of the physical body. And even "rational" science has come close to the concept of a multidimensional universe consisting of various parallel worlds.

One of such researchers of the "anomalous" activity of parallel worlds is the Russian physicist V. Rogozhkin, director of the research center "ENIO". And here is how he comments on this: “All mankind lives in the delusion as if we are in a three-dimensional space. In fact, we live in a multidimensional world and we perceive this multidimensional world at 3.14. Where 3 is the length, width, height , and 0.14 is time, a time constant, i.e. how much a person is able to go either into the past or into the future.

Physicists have long known that the world is multidimensional. Nowadays there are certain constants. What is a poltergeist - this is a violation of constants, i.e. when certain physical constants change and we encounter parallel worlds... Man is not only this physical shell. In fact, a person is multidimensional, as well as the Universe. And the projection of our multidimensional essence, it can be here on Earth and somewhere in another galaxy, but we are interconnected. At the same time, information is transmitted instantly, since our thought instantly spreads over any distance.

In higher dimensions there is no concept of distance, mass, time. These worlds function in a completely different way. But our civilization is still something "born in a cocoon" and the Higher Mind does not yet allow us to open this "cocoon". Because we have a colossal amount of aggression. You look, if you ask the question: "Who poses the greatest danger to a person in the night forest?", 70% on average around the world answered - a person ...

Aliens gave us magic. Ie, what is magic? Thoughtless, incomprehensible way out into multidimensionality... We had a real case. In Krymsk, the girl left the house and got on the bus. She had to drive a few stops to the library. No one remembers how she got off the bus. They saw that she sat down, how she left - they did not see. Parents came running to us in a panic that the child had disappeared. In this small town, everyone has been raised to their feet and cannot be found.

We made a correction, i.e. saw - yes, withdrawal. We forced them to return it. She returned to a locked hotel room in Novorossiysk on the same day. The maid was walking along the corridor and heard a knock on the door from inside. When the door was opened, this girl was there..."

So, maybe the numerous abductions of people are not the work of aliens, but aliens from other parallel worlds? It is no accident, because some ufologists adhere to just such a version. But why do they need all these kidnappings? Is it just to conduct genetic experiments?

There is such a version that by studying people, they create their "matrices" - clones that perform tasks unknown to us in our world, while outwardly not differing from ordinary people. It is they who often act as pseudo-skeptics, ridiculing and discrediting those areas of knowledge that are considered "forbidden" for humanity. Apparently, this is one of the tasks of at least some of them - by any means to keep humanity away from this knowledge that can "awaken" the possibilities of our consciousness.

The physicist V. Rogozhkin also supports the fact that most of the 7.5 billion people of the Earth are not actually people. Here is what he said about this: “The population of the Earth is 7.5 billion, and where do they come from? There may be 600 million people. And where did the rest come from? These are "matrices", empty shells. If you take a real "look", then they do not exist.

All these official statistics are invented for people and people think that there are really so many of us. But, if you look, there are very few people on Earth. Let the aliens take these "matrices" -duplicates from here. So that a real civilization remains on Earth."

So, on Earth, in our world, in addition to ordinary people, there are clone biorobots created by aliens. Surely those of the aliens who outwardly do not differ from us are also living. There are also reptilian hybrids that outwardly look like ordinary people, but have obvious genetic differences from us. They make up the clan of the ruling "black aristocracy", but they are not so numerous. To be honest, the figures given by V. Rogozhkin are amazing. But on the other hand, all this "herd" obsessed with material accumulation, predatory consumerism, the thirst for power and fame, "rams", really much more resemble clone biorobots than normal people.

Temperature

Although people can endure intense heat and bitter cold with clothing and other insulation, they still prefer a very specific range of temperatures for everyday life. One need only look at maps of isotherms and population density to see that people prefer to live in areas where the average annual temperature lies between 4 and 27 ° C. Of course, such a narrow temperature range is dictated not only by the desire of people to live in comfort, but also the important fact that crops and domestic animals feel best in this temperature range.

In general, many living beings are tolerant of very high or low temperatures. Here are just a few examples. Some species of blue-green algae (especially Oscyllatoria filiforms) live in almost boiling water, at a water temperature of 85°C. And ordinary ducks survived after they were kept for 16 days in forty-degree frost. Cold-blooded water snakes (Nadrix sipedon), of course, will not survive the frost, but the range of temperatures they tolerate is very impressive - from 0 to 43 ° C. This range is even wider in arctic pine, in which photosynthesis occurs both at -40°C and at +30°C.

Unfortunately, most food grains require a temperature of 10 to 30°C during the growing season.

Light

That part of the visible electromagnetic spectrum, which we call light, lies between the wavelengths of 380 and 760 microns. Within this region lies the range of vision for most animals and, most importantly, the range of photosynthesis. If the illumination is too low, photosynthesis cannot proceed at a rate sufficient for the good of the cause, and if it is too high, then the growth of the plant is retarded due to the so-called solarization. These lower and upper illumination limits are 0.02 and 30 lumens/cm2, respectively. (By the way, the maximum illumination by direct and diffuse sunlight on the surface of the Earth is 15 lumens per square centimeter.)

A person can see well enough to move from one place to another even in such low light as 10~9 lumens/cm2. Light hurts us if the light level exceeds 50 lumens/cm2. But this refers to the illumination of the surface, and not to the radiation penetrating the eye. The endurance of a person looking directly at a point source of light is much lower - about 0.05 lumens / cm2.

We must not forget about the periodic change in lighting. Plant growth, especially in the temperate zones of the Earth, depends not only on the average annual temperature distribution, but also on the length of day and night. Therefore, most habitable planets should receive heat and light mainly from one source, similar to our Sun.

gravity

Biomedical experiments on large centrifuges have shown that some people can tolerate, without irreversible changes, an instantaneous acceleration of 5 g (five times the normal acceleration of gravity on the surface of the Earth). A sitting person, not dressed in a special suit, can withstand such an acceleration for only 2 minutes without loss of vision due to insufficient blood flow to the eyes. Acceleration in 4g can be sustained longer - as much as 8 minutes.

The participants in such experiments sat motionless, did not perform any actions. A small table gives an idea about the muscular fatigue of people, about the restrictions imposed by an increase in the gravitational field, from which it can be seen that life, or rather, work at 2g will be very difficult.

Time (in seconds) required to crawl 2.3 meters under varying gravity.

At the University of California, centrifuges have been raising chickens for quite some time that will lose weight if they live at an acceleration of 2.5g. The chickens had a faster heartbeat and their breathing rate dropped. Of course, experiments on centrifuges with their angular velocities do not accurately reproduce the linear gravitational field of massive planets, but still, based on the available information, we can conclude that few people would live on a planet where gravity would be more than 1.25-1.50g.

It is too early to talk about the lower gravitational limit for a person, since in fact there are no data * from which it would follow what minimum level of gravity is necessary for our body for normal physiological functioning. (* Expeditions into space have shown that a person, but at least for several months, can live in zero gravity. - Approx. ed.)

Composition of the atmosphere

It is clear that the planet must have a breathable atmosphere. The most essential parts of the atmosphere should be oxygen and a small amount of water vapor. Moreover, the partial pressure of oxygen should lie between two extreme values: the lower limit, beyond which hypoxia occurs, and the upper limit, above which oxygen poisoning occurs.

Somewhere near the lower limit of the partial pressure of oxygen live the inhabitants of the mining village of Aukankilcha in the Chilean Andes, which is located at an altitude of 5300 m. Apparently, this is the highest altitude at which people live settled. Here, the partial pressure of inhaled oxygen is only about 72 mmHg: nevertheless, the miners lead a very active life. To get into the mine, they climb another 450 m daily, that is, to a height at which the partial pressure of inhaled oxygen is only 68 mm Hg. see But even these conditions are probably still far from the lower limit. After all, climbers claim that you can live long and feel good at an altitude of 7000 m.

Well, what is the maximum concentration of oxygen we can endure? The upper limit of the partial pressure of inhaled oxygen lies near 400 mm Hg. Art., which is equivalent to 56% oxygen in the air at sea level. In medical institutions, the accepted oxygen ceiling is much lower - 40%.

So, the partial pressure of inhaled oxygen on a habitable planet must be greater than 60 mm Hg. Art., but less than 400 mm Hg. Art.

Therefore, oxygen must be diluted by gases, each of which has its own upper partial pressure limit, a limit that must not be exceeded. Otherwise, helium, nitrogen, argon, krypton and xenon can cause a state of anesthesia. This was even used during surgical operations: a mixture of 80% xenon and 20% oxygen generated an unconscious state for 2-5 minutes. The narcotic effect of carbon dioxide is even stronger. So, the argon pressure should not be more than 1220 mm Hg. Art., krypton - 350, xenon-160, and carbon dioxide - 7 mm Hg. Art. It is suggested that neon, and possibly hydrogen, may also be drugs.

Hydrogen occupies a special place: we can only talk about non-combustible mixtures of hydrogen and oxygen, but the simultaneous existence of large amounts of free hydrogen and oxygen in the planet's atmosphere is hardly possible.

Long-term experiments with the participation of people who would live in atmospheres that do not contain inert gases have not yet been carried out, so it cannot be categorically argued that inert gases are not needed. Human evolution took place in an atmosphere containing only 20% oxygen, and it is possible that at certain periods of life, some proportion of inert gases is necessary for the proper functioning of the respiratory system.

Since carbon dioxide is needed by plants, some lower limit of its partial pressure on a planet suitable for us must be established. The normal concentration of carbon dioxide in the earth's atmosphere is only 0.03%, which is equivalent to a partial pressure of 0.21 mm Hg. Art. The minimum value for maintaining the normal life of the plant is still unknown, but, apparently, it is close to 0.05-0.10 mm Hg. Art. Nitrogen is also necessary, because it enters the body of plants and animals. The minimum amount is probably small, but it is not known.

Other gases in a planet's atmosphere suitable for life (for example, NH3, H2S, SO2, CO) must be present in very small quantities, in millionths of the volume of the atmosphere. Otherwise the atmosphere will be poisonous.

Atmosphere pressure

The minimum atmospheric pressure on a planet suitable for life is quite simple to calculate: the pressure of an atmosphere of pure oxygen should be about 0.15 kg / cm2. The maximum barometric pressure endured by humans has not yet been determined. For example, an atmosphere of 2% oxygen and 98% helium at a total pressure of 10.5 kg / cm2 is theoretically acceptable, but the actual stay of people in such conditions has not been studied by anyone. Probably, the pressure of the atmosphere exceeds the limits of human endurance when a strong turbulent flow occurs in the air passing through the nasopharynx and the work of the respiratory organs becomes tiring. They say that under a pressure of 8 atmospheres, turbulence is so strong that when you inhale through the mouth, vortex air currents are felt.

Summarizing what has been said, we can draw the following conclusions: the atmosphere of a planet suitable for life must contain oxygen, the partial pressure of which, when inhaled, lies between 60 and 400 mm Hg. Art., and carbon dioxide, the partial pressure of which can vary between 0.05 and 7 mm Hg. Art. In addition, the partial pressure of any inert gas must not exceed a certain limit, and poison gases can only be present in traces. Among other things, nitrogen gas is needed so that it can find its way to plants in the form of compounds.

Water.

Man, with all his ecology, is very dependent on water, so it can be categorically argued that a habitable planet should have large open reservoirs. After all, without oceans there will be no abundant rainfall and, therefore, there will not be enough groundwater to replenish the stocks of flowing fresh water. Of course, it is rather difficult to accurately estimate the best ratio of ocean area to the total surface of the planet. If there is little water, if it is present only in the form of vapor or as water adsorbed on the surface or retained in cracks between solid particles of rocks, then such a planet is of little use for people. On the other hand, a planet entirely covered with water, an ocean planet, is hardly worth considering as suitable for human life.

The humidity of the atmosphere is also very important for people. The unpleasant consequences of high humidity and heat are hardly worth describing. The opposite physiological effects do not bode well either. Dry air quickly dehydrates the mucous membranes of the nose, mouth and throat; prolonged exposure to very low water vapor pressure may even be fatal.

So it turns out that open water bodies are obligatory on a habitable planet, but their area should not exceed 90% of the planet's surface.

Other requirements.

The definition "human habitable planet" means a planet that is not occupied by other thinking beings. We believe that a person can get along with lower forms of life, and without photosynthesis - the basis of the biological cycle of substances - he cannot even do without.

Wind speeds in habitable places on the planet should be moderate. It is impossible to live normally where a storm rages all the time (wind speed 23 m/sec). No more than 1.8-109 dust particles should fly in a cubic meter of air, and if there is a lot of silicic acid in it (over 50%), then there should be ten times less dust particles. Otherwise, the air will harm people.

Reservoirs are the main collectors of airborne dust. The formation of water droplets on dust nuclei is the main way to clean the atmosphere. It follows that on a planet with vast oceans, the atmosphere is not particularly dusty, but on a planet with a land dominated surface, it will indeed be very dusty. Radioactivity or ionizing radiation can also render a planet uninhabitable. For genetic reasons, a low dose of natural background radiation is desirable - less than one roentgen per year, or approximately 0.02 rem (the biological equivalent of a roentgen) per week. (The average intensity of natural background radiation on the Earth's surface is about 0.003 rems per week.) The planet can also be uninhabitable due to too many meteorite falls, too much volcanic activity, too many earthquakes, or excessive electrical activity.

The main signs of a planet suitable for life

What parameters should a planet have on which many people could live, without excessive protection from the environment and regardless of the delivery of materials from other planets?

The mass must be greater than 0.4 Earth masses, so that a breathable atmosphere can form and remain, but less than 2.35 Earth masses, so that the acceleration of gravity on the surface is less than l.5g.

The age of the planet (and the star around which it orbits) must be more than 3 billion years to give enough time for the emergence of complex life forms and the creation of a breathable atmosphere.

The rotation period should not exceed 96 hours (4 Earth days); this guarantees against excessively high temperatures during the day and extremely low temperatures at night.

The inclination of the axis of rotation (the inclination of the equator to the plane of the orbit) and the illumination of the planet are interrelated, and the distribution of temperature on its surface depends on this. The amount of illumination at low tilts should lie between 0.65 and 1.35 of the illumination on Earth, although the combination of high illumination (1.9 times greater than on Earth) and a large tilt of the equator (up to 81 °) is compatible with the requirements of life .

The orbital eccentricity must be less than 0.2, otherwise an unacceptable temperature distribution on the planet's surface will be created.

The mass of the main body (the star around which the planet revolves), on the one hand, should not exceed 1.43 solar masses, and on the other hand, it should be more than 0.72 solar masses, since only in this case are acceptable levels of illumination and tidal deceleration possible rotation of the planet. For special planets with extremely large or close satellites, the lower limit of the permissible mass of the main body can be reduced to 0.35 solar masses.

If a planet orbits in a binary star system, then the two stars must be either very close or very far apart. Only in these cases are stable planetary orbits and slight variability in illumination possible.

If all these conditions are met, then the probability that the planet is suitable for human life is very high.

Calculations say that around 0.47% of all stars there are planets suitable for life, and among the stars of the F2-KI classes, 3.7% have planets suitable for human life. We estimate that there is one habitable planet for every 2480 cubic meters. parsecs, if we consider that the properties of stars in regions of the Galaxy close to us are characteristic of the Galaxy as a whole. Since the volume of our Galaxy is about 1.6 x 1012 cubic meters. parsecs, the number of habitable planets is close to 600 million. And that's just in our galaxy!

At a distance of 100 light-years from Earth (a small distance, considering that the thickness of the Galaxy at the center exceeds 10,000 light-years, and the diameter is 80,000 light-years), there should be about 50 habitable planets. The average distance between a star with a habitable planet and its closest similar neighbor is about 24 light years.

Upcoming candidates

Of the 100 closest stars (plus eleven of their invisible companions) within 22 light-years of the Sun, formally 43 stars could have habitable planets. However, except for 14 stars, the rest are so small that they could have a planet suitable for life only in the very rare case that this planet has large and close satellites that help it maintain its rotational speed. The other 68 stars are not suitable for the following reasons: three of them (Sirius, Procyon and Altair) have too much mass, and therefore their life is too fleeting; seven are white dwarfs, and there can be no life around them; 57 stars are too small, they either slowed down the rotation of the planets, or generate tides of destructive force on those planets whose rotation is supported by a close satellite; one star (40 Eridani A), although acceptable from other points of view, is not suitable because it is a member of a binary system paired with a white dwarf.

The fourteen most promising candidates are listed in the table in order of increasing distance from Earth. The probability that at least one habitable planet is near these fourteen stars is 43%.

In the closest star system to us - Alpha Centauri - the probabilities for components A and B are 0.054 and 0.057, respectively; for the system, this probability rises to 0.107, which means that there is one in ten chances that a planet suitable for life can be found in the Alpha Centauri system.

Variants of habitable planets

If the ideas I am developing are correct, then the most common type of planets suitable for life should be planets like the Earth. Such a typical planet has a mass slightly less than that of the Earth, and a very similar atmosphere to the Earth, a similar change of day and night, a sun of similar size, as well as a moderate inclination of the orbital plane to the planet's equator and a small average orbital eccentricity. Seasons, rainbows, beaches, blue skies, starry nights, rain, lightning, clouds, and snow and ice in cold areas should be common. In short, most of the physical and meteorological phenomena we are accustomed to will also occur on many habitable planets.

It is hoped that the planets will contain both photosynthetic organisms and animal forms capable of surviving in any ecological niche: sea and land creatures, aerial life forms, etc. Despite the difference in details, it is likely that the main types of organisms will have common characteristic features, such as fast-swimming marine species will acquire a streamlined shape, land animals - limbs, and species flying in the air - wings.

Of course, we should not hope that on other planets we will find all the classes, orders, families or species of plants and animals to which we are accustomed on Earth. On the contrary, any planet on which the evolution of organisms took place must certainly have its own original classification (taxonomy). Nevertheless, there must be autotrophs (species that use only inorganic substances for food). You can expect to find heterotrophs (life forms that are used to feed autotrophs or other heterotrophs).

Among the half a billion habitable planets that exist in our Galaxy, there will also be unusual, rare ones. So, a planet might be habitable if it orbits another massive giant planet like Jupiter. On such a planet, there is an unusual change of light and dark. On the side facing the huge companion, eclipses of the sun occur daily, and a huge and bright "moon" shines in the night sky.

There may be twin planets: they revolve around a common center of mass, but their rotation relative to each other is stopped. A planet with two suns is also possible, orbiting around two stars very close to each other. These stars, separated by, say, millions of kilometers, create a complicated pattern of sunrises and sunsets and unusual changes in light intensity as the stars outshine each other. A habitable planet could also fly around one of the stars in a binary star system. This planet has very bright nights when it flies between the stars.

On a planet with an equator tilt of 75°, only a narrow strip between 14°N and 14°N is suitable for life. sh. and 14°S sh. At other latitudes, it is very cold there in winter. A planet with two habitable belts must be sought among those planets in which the inclination of the equator to the plane of the orbit is very small and which move close to their Sun. Such planets near the equator are very hot, and, therefore, you can live on them only in middle or high latitudes. On a planet whose axis is tilted the same as that of the Earth, but which receives 30% more heat, only two narrow belts between latitudes 51 and 66 are suitable for life. Marine animals and some inhabitants of the air can probably migrate between these two belts , but land migrations will be stopped by the unbearably hot thermal barrier of the equator.

And finally, another option for a habitable planet is a planet surrounded by rings. An important feature of the beautiful ring system of Saturn is that the rings are located within the Roche limit (at a distance of 2.45 planetary radii from its center). Of course, massive oblate planets are more likely to acquire a ring than planets suitable for human life. But still, some of the eligible planets may also have flat equatorial rings within their Roche limit. True, these rings should not be as densely filled with particles as the rings of Saturn.

It is believed that the oceans are generated by volcanic activity, which in turn depends on the mass of the planet. Therefore, planets with high gravity can be considered oceanic planets, and those with low gravity can be considered land planets. On a planet where 90% of the surface is occupied by water, the continents are probably distant from each other and not connected by isthmuses. With such isolation, the development of land life on its continents could follow almost independent evolutionary paths. Conversely, planets with oceans smaller than those on Earth, with oceans surrounded on all sides by land, will give a variety of marine fauna specific to each ocean-lake. On such planets, due to the lack of global oceanic circulation, temperature drops are more dramatic. Most of the land is probably occupied by desert, and habitable areas stretch along the coastline ...

Our Sun has settled in a star-poor sector of the Galaxy. Therefore, there are few stars in our night sky. On a clear night, twenty-five hundred stars can be seen with the naked eye from anywhere on Earth. Much more impressive is the night sky on a planet in globular clusters or near the center of the Galaxy. A: Asimov calculated that about 2 million stars are visible near the galactic center above the horizon of a habitable planet. They give as much light as the full moon. Asimov's assessment needs to be corrected - he did not take into account that scattered light will prevent us from seeing dim stars. However, there would still be thirty thousand such bright stars, about 10 times more than can be seen on the darkest night from Earth.

But in the night sky of planets in the dark nebulae of the Galaxy, there may be no stars at all - their light will trap dust. And the planets on the very periphery, on the very edge of the Galaxy, on one half of the celestial sphere will have stars, but not on the other. For a person looking "from the Galaxy", the night sky would be illuminated only by globular clusters that seem to border the Galaxy, or by distant island universes, among which only a very few are barely visible to the naked eye.

Changes in the human body.

Man is well adapted to those conditions that we are accustomed to call normal. And although the normal conditions for the Eskimos, the Aborigines of Australia, the African Pygmies or the Indians in the high Andes, it would seem quite different, they all belong to the same narrow range from an astronomical point of view.

In the future, when interstellar flights become a reality, a situation may arise when the expedition finds a planet suitable for life, and then, due to a coincidence of circumstances or in accordance with a plan for several hundred years, interrupts communication with humanity.

Imagine a colony landing on a planet where the acceleration due to gravity is 1.5 g. If the colony can survive and multiply, then people will certainly increase muscle strength, reduce the time of reactions to external influences and increase the accuracy of assessing the movement of surrounding objects. On such a planet, due to the greater gravity, even a simple fall is more dangerous than on Earth, since there would be more deaths or injuries. Dislocations, sprains, hemorrhoids, prolapse of internal organs, diseases of the back, feet and legs, varicose veins and additional hardships associated with pregnancy would be more noticeable than on Earth. Therefore, with inexorable constancy, selection would favor those individuals who are better adapted to life under increased gravity.

In a few generations, the colonists will probably have shorter arms and legs, a more compact body, and heavier bones. Due to the constant burden of gravity, the tendency to develop musculature and less deposition of fatty tissues will prevail. During pregnancy, a smaller child will be a clear advantage, so the average adult weight will gradually decrease to some optimal level. If the isolation from the Earth is long and continuous, genetic shifts in as yet unpredictable directions are inevitable. If a fund of genetic changes accumulates, then during subsequent contacts of the colonists with the population of the Earth, genetic incompatibility is possible. It turns out that as a result of interstellar travel, a new species of the human race may appear.

Different conditions on another planet will lead to different changes. Colonists on a planet with, say, 3/4 of the force of gravity would experience less stress from gravity than on Earth. And they could live at a low partial pressure of oxygen. Natural selection there will favor individuals with a more efficient respiratory system, with greater chest capacity. Strong-bodied humans would not have major genetic advantages here, and the colonists' age-old physique changes would depend on other factors.

On a small planet with a thin atmosphere and a weak magnetic field, the level of background radiation may be higher than on Earth. There are two reasons for this. First, due to the poor gravitational stratification of rocks during the formation of the planet, the proportion of heavy minerals, including radioactive ones, in the crust may be high. Secondly, with less atmospheric protection from proton flares, from primary solar and galactic particles and cosmic rays, many more energetic particles will reach the surface. This means that we should expect the acceleration of mutations and, possibly, the acceleration of evolution.

Praise for the Earth.

We live on Earth and treat it as something inalienable. We love to complain about the weather, do not pay attention to the splendor of sunsets, and even cease to be surprised at the diversity of wildlife. This is natural, because we ourselves are a product of the Earth. And since the Earth is our home, everything that surrounds us seems to be the most ordinary. Well, how different would the familiar world be if its astronomical parameters changed a little?

Suppose (or maybe there is such a planet somewhere) that the original mass of the Earth was twice as much and, therefore, the acceleration of gravity is 1.38 times higher than it is now. How fast would the animals then get out of the sea onto land? Most likely, the evolution of marine species would not have undergone significant changes, but in land animals and plants the body structure would have been stronger, and the center of mass would have been located lower. The trees would be lower and the trunks would have strong support. Land animals would develop heavier leg bones, stronger muscles. Birds and insects would have to adjust to denser air (greater aerodynamic drag) and increased acceleration due to gravity (more lifting surface required). Mountain-building activity would go faster, but mountains would not become as tall with the same structural strength to support their own weight; erosion under the influence of rains and surface waters would be stronger, and a different density of the atmosphere would change the pattern of weather changes.

The waves in the oceans would be lower and the spray path would be shorter, which would worsen evaporation. The atmosphere would become drier and the clouds thinner and lower. The ratio of land to sea would also change. The magnetic field of the Earth, the thickness of its crust and the size of the core, and the distribution of minerals in the crust and their chemical composition, and the level of radioactivity would be different. And of course, the double of a person (if he did appear under such conditions) would look different.

Now suppose the Earth had half its current mass. Then the acceleration due to gravity would be 0.73 of normal. Weaker gravity, a thinner atmosphere, reduced erosion, and likely increased background radiation would have made the evolutionary and geological history of the planet different. Would evolution go faster? How quickly would animals master land and air? It is not yet possible to answer. But there is no doubt that the skeletons would be lighter, and the trees, generally speaking, would be tall, but frail; and, of course, an analogue of man on such a planet would not be like us in many respects.

But what if the tilt of the earth's axis was not 23.5, but 60 °? Seasonal meteorological changes would persist, but the only climatic region suitable for the kind of life we ​​know would be a narrow belt within ±5° of the equator. The rest of the planet would be scorching heat or bitter cold. And if the equator were in the plane of the orbit, then the seasons would not change, but it would be much easier to predict the weather, and it would be more constant. It would be impossible to live within ±12° of the equator due to the heat, but this reduction in usable area would be partially offset by an improvement in the climate in the circumpolar regions.

Suppose now that the average distance of the Earth from the Sun is only 10% less than it really is. Less than 20% of the surface is then suitable for life (the belt between latitudes 45 and 64 °). Consequently, life would occupy only two narrow strips of land, separated by an unbearably hot barrier. Polar ice would not exist, which would raise ocean levels and reduce land area.

If the speed of the Earth's rotation slowed down and the day lengthened, for example, to 100 hours, then temperature fluctuations from day to night would become very sharp. The sun would barely crawl across the sky, and few forms of life would have survived the heat of a long day and the cold of an equally long night.

Suppose now that the mass of the Sun has increased by 20% (the average radius of the Earth's orbit must be increased to 1.408 AU to keep the solar constant at the current level). This would lengthen the circulation period to 1.54 years. If the mass of the Sun were less by 20%, then the radius of the Earth's orbit (this time it should be reduced to compensate) would be 0.654 AU. e. A year in this case would last only 215 days. The main body would be of spectral type G8 (that is, slightly yellower than the Sun now), and its lifespan would increase to 20 billion years. The ocean tides generated by the main body would be about the same as those generated by the Moon now.

Planets for people
In general, the Earth is a wonderful planet for life on it, just what a person needs. Almost any change in its physical properties, position or orientation would worsen our lives. Apparently, we will not be able to find a planet at all that would suit us better, although some of the people of the future may prefer to live on other planets. For the time being, however, the Earth is our only home, and we would do well to guard her riches and use her resources wisely.

If a person learns to move in outer space at a speed close to a quarter or half the speed of light, then even with long stops near the planets, the entire Galaxy can be examined and populated in some million years. True, it will be a long time before technology advances so far that the speed of movement of people in the Galaxy will become much greater than at present. And yet the history of mankind can be written among the stars.

Dole S.