Definition 1

Exoplanets are planets that are outside of our own solar system.

Terrestrial astronomers focus on the search for exoplanets in the so-called habitable zone.

habitable zone

Definition 2

The habitable zone is the optimal distance between the studied planet and its star, which allows the planet to have a temperature at which water can be in liquid form, which significantly increases the possibility of the origin of life.

The conditions under which life can arise are determined by factors such as:

• the presence of water in liquid form,
• an atmosphere with the required density,
• variety of chemical elements
• Availability greenhouse gases(water vapor, methane, ammonia, etc.)
• the presence of the sun required amount energy.

The boundaries of the habitable zone are established based on considerations of the possibility of water being in liquid form, since water in this state is a necessary component of many biochemical reactions.

If the planet is too far from its star, the water freezes; if it is too close, the water evaporates.

When exploring exoplanets in deep space, it is important to keep in mind that there is only a potential, possible habitable zone.

A potential habitable zone is a zone in which there are conditions for the formation of life, but they are not enough for this.

In this case, one should take into account such circumstances as the presence or absence of magnetic field, tectonic activity, duration of the day on the planet, etc.

The above points are dealt with in such a new scientific discipline like astrobiology, which is part of astronomy.

Search for exoplanets in the habitable zone

The problem with finding planets that are in a potential habitable zone is that they are located near stars very far from us.

In a broad sense, the search for life forms in the solar system and beyond is the search for biomarkers.

Remark 1

Biomarkers are chemical compounds that have a biological origin.

As an example, one can say that such a biomarker on Earth is the presence of oxygen in the atmosphere. However, the presence of oxygen in the atmosphere of an exoplanet does not mean the presence of life there. So, on a number of planets, oxygen in the atmosphere is a consequence of physical processes, such as the decomposition of water vapor under the influence of ultraviolet radiation, which emit stars.

Mission "Kepler"

One of the most productive space telescopes is the Kepler telescope, named after the famous mathematician Johannes Kepler. Another space telescope, the Hubble, also showed great results.

Thanks to work space telescope Kepler made a qualitative leap in the study of exoplanets.

Remark 2

The Kepler space telescope works with a photometer. This instrument tracks the change in the brightness of a star as the planet passes between it and the telescope. This way of discovering planets is called transit.

As a result of such observations, it was possible to obtain information about the orbit of the planet under study, the mass of the planet and its temperature.

Thus, in the first part of its study, the Kepler space telescope was able to detect about 4,500 potential planet candidates. In order to check the obtained data and make sure that the change in the brightness of the star is associated with the passage of the planet, and not with the peculiarities of the processes in the star itself, in particular, observation of the change in the radial velocity of the star is used.

As a result, on this moment there is a confirmed number of planets - there are about 3600 of them. And there are about 5000 possible candidates for planets.

Proxima Centauri

In August 2016, astronomers confirmed that the closest star to us, Proxima Centauri, has a planet. This planet is called Proxima b.

Proxima Centauri is 4.2 light years from our Sun. This distance means that the light from a given star takes 4.2 years to reach us.

Thus, it turns out that the star closest to us has a planet on which the emergence of life is possible.

The planet Proxima b itself was in the zone of potential habitability. And at the same time relatively close to our Earth.

Proxima b is 200 times closer to its star than the Earth is to the Sun. But since the star Proxima Centauri is a red dwarf, it is colder and weaker than our Sun.

It is noted that the planet Proxima b fell into the zone of tidal capture of a star and now revolves around it like the Earth's satellite - the Moon. As a result, one side of the planet turned out to be warm, and the other cold.

Thus, the possibility arises of the formation of suitable conditions for the origin of life at the boundaries of the dark and warm hemispheres. But for this life there is a problem associated with the fact that Proxima Centauri is a red dwarf, which is characterized by high activity. Flashes occur on such stars, there are coronal magma ejections, the level of ultraviolet radiation is 20-30 times higher than on Earth.

Thus, for the formation of favorable conditions that can lead to the emergence of life on such a planet, it is necessary to have enough dense atmosphere. Such an atmosphere is needed to protect against the radiation of a red dwarf.

Astronomical means of observation, developing, will make it possible to better study the planet closest to us. Earth specialists will be able to study the atmosphere of this planet and understand what is happening there, determine the presence or absence of greenhouse gases, study the climate, and also find or refute the presence of biomarkers on this planet.

For a more detailed and detailed study of it, it is planned to put into operation new space and ground-based telescopes.

So, in Russia, work is underway on the Spektr-UF space telescope project.

The launch of the James Webb Space Telescope, which should replace the almost legendary Hubble telescope, has been postponed to the early 2020s.

The new telescope will have a higher resolution, which will allow us to learn more about the composition of the atmospheres and the structure of exoplanets.

The boundaries of the habitable zone are established based on the requirement that the planets in it have water in liquid state, since it is a necessary solvent in many biomechanical reactions.

Beyond the outer edge of the habitable zone, the planet does not get enough solar radiation to compensate for radiation losses, and its temperature will drop below the freezing point of water. A planet closer to the sun than the inner edge of the habitable zone would be overheated by its radiation, causing the water to evaporate.

Calculating the position of the boundaries of the habitable zone and their displacement over time is rather complicated (in particular, due to negative feedbacks in the CNO cycle that can make the star more stable). Even for the solar system, estimates of the boundaries of the habitable zone vary widely. In addition, the possibility of the existence of liquid water on the planet strongly depends on physical parameters the planet itself.

The distance from the star where this phenomenon is possible is calculated from the size and luminosity of the star. The center of the habitable zone for a particular star is described by the equation:

Average habitable zone radius in astronomical units,

star luminosity,

Luminosity of the Sun.

Formulas for distances to the inner and outer boundaries of the habitable zone can be derived from the equations heat balance for planets that would be at these distances. We write the heat balance equation mathematically in differential form, that is, for a unit surface area of ​​the planet when the star is at its zenith.

Equilibrium flux of body radiation energy:

Absorbed energy from the star:

where E is the illumination, A is the albedo of the planet.

Then the heat balance equation in differential form has the form

Illumination is the amount of energy falling per unit area in 1 second.

Can be expressed in terms of the temperature of the star and the distance between the star and the planet:

where r is the distance between the star and the planet. Let's find this distance from the heat balance equation

You can also calculate the boundaries differently, using the illumination created by the star at each edge, . This illumination mainly depends on the luminosity, L, but to some extent also on the effective temperature, T e, stars. The lower the temperature, the greater the infrared part of the radiation. The greater the infrared radiation, the greater the thermal effect on the planet. Let us denote the critical illumination at the inner boundary of the habitable zone S bri (T e ) , the equation for it in units of the solar constant:

and the equation for illumination at the outer edge of the habitable zone:

where T e in degrees Kelvin. Distances from the star to the boundaries of the habitable zone in AU:

where L - star luminosity in solar units and S bri (T e ) and S Bro (T e ) in units of the solar constant.

Luminosity ,L, and effective temperature, T e , found from observations of the stars. L (in solar units) is obtained from the equation:

where V- apparent magnitude and Sun- bolometric correction. Visible bolometric magnitude is the sum (V + Sun).d is the distance to the star in parsecs.

Theoretical calculations have shown that the climate of planets near the outer boundary of the habitable zone can be unstable. It will fluctuate between long cold periods and occasional warm ones. As a result, apparently, highly developed life on such planets will not be able to arise. This can impose significant restrictions on the size of habitable zones in the direction of their reduction.

Habitable zone (Goldilocks zone)

Once upon a time there was a solar system, and then one day - a long time ago, about four billion years ago - she realized that she was almost formed. Venus appeared near the Sun itself - and it was so close to the Sun that the energy of the sun's rays evaporated all of its water supply. And Mars was far from the Sun - and all its water froze. And only one planet - the Earth - turned out to be just at such a distance from the Sun - “just right” - that the water on it remained liquid, and therefore life could originate on the surface of the Earth. This belt around the Sun became known as the habitable zone. The tale of the three bears is told to children in many countries, and in England its heroine is called Goldilocks. She also liked everything to be “just right”. In the three bears' house, one bowl of porridge was too hot. The other is too cold. And only the third came to Goldilocks "just right." And in the house of the three bears there were three beds, and one was too hard, the other was too soft, and the third was “just right”, and Goldilocks fell asleep in it. When the three bears returned home, they found not only the loss of porridge from the third bowl, but also Goldilocks, who was sleeping sweetly in the little bear's bed. I don’t remember how it all ended there, but if I were three bears - omnivorous predators at the very top of the food chain - I would have eaten Goldilocks.

Goldilocks might be interested in the relative habitability of Venus, Earth, and Mars, but in fact, the plot of these planets is much more complicated than three bowls of porridge. Four billion years ago, water-rich comets and mineral-rich asteroids were still bombarding planetary surfaces, albeit much less frequently than before. During this game of space billiards, some planets migrated from their native places closer to the Sun, and some were knocked out into orbits of a larger diameter. And many of the dozens of formed planets ended up in unstable orbits and fell into the Sun or Jupiter. A few more planets were simply thrown out of the solar system. The remaining units in the end rotated precisely in those orbits that turned out to be “just right” in order to survive billions of years on them. The Earth settled in an orbit with an average distance from the Sun of about 150 million kilometers. At this distance, the Earth intercepts a very modest fraction of the total energy emitted by the Sun - only two billionths. If we assume that the Earth absorbs all this energy, then the average temperature of our planet is about 280 K, that is, 7 ° C - in the middle between winter and summer temperatures.

At normal atmospheric pressure, water freezes at 273 K and boils at 373 K, so to our great delight, almost all water on Earth is in a liquid state. However, there is no need to rush. Sometimes in science you get the right answers from the wrong premises. In fact, the Earth absorbs only two-thirds of the solar energy reaching it. The rest is reflected back into space by the earth's surface (especially the oceans) and cloud cover. If we add the reflection coefficient to the formula, then the average temperature of the Earth already drops to 255 K, which is much lower than the freezing point of water. There must be some other mechanism at work these days that keeps the average temperature at a more comfortable level. Again, take your time. All theories of stellar evolution tell us that four billion years ago, when life formed from the proverbial primordial soup on Earth, the Sun was a third dimmer than it is today, which means Earth's average temperature was below freezing. Maybe the Earth in the distant past was simply closer to the Sun? However, after a period of heavy bombardment that has long ended, we do not know of any mechanisms that would shift stable orbits within the solar system. Maybe the greenhouse effect was stronger in the past? We probably don't know. But we know that habitable zones in the original sense of these words have only a remote relation to whether life can exist on planets located within the boundaries of these zones.

The famous Drake equation, which is always referred to in the search for extraterrestrial intelligence, allows you to give a rough estimate of how many civilizations, in principle, can be found in the Milky Way galaxy. The equation was derived in the 1960s by the American astronomer Frank Drake, and at that time the concept of the habitable zone was limited to the idea that the planets should be at a distance from their star that is “just right” for the existence of life. The meaning of one version of the Drake equation is something like this: let's start with the number of stars in the galaxy (hundreds of billions). Multiply this huge number by the fraction of stars that have planets. The resulting number is multiplied by the fraction of planets that are in the habitable zone. Now we multiply the result by the fraction of planets on which life has developed. We multiply the result by the fraction of planets on which intelligent life has developed. The result is multiplied by the fraction of planets, where technical progress reached such a stage that it is possible to establish interstellar communication.

If we now take into account the rate of star formation and the life expectancy of a technologically advanced civilization, we get the number of advanced civilizations that, at this very minute, are probably waiting for our phone call. Small, cool, low-luminosity stars live hundreds of billions, maybe trillions of years, which means their planets have enough time to grow two or three types of living organisms on themselves, but their habitable zones are too close to the star. The planet that formed in this zone quickly falls into the so-called tidal capture of a star and always rotates with one side to it, which is why a strong distortion occurs in the heating of the planet - all the water on the "front" side of the planet will evaporate, and all the water on the "reverse" side will freeze . If Goldilocks lived on such a planet, we would find that she eats her porridge, spinning around her axis, like a grilled chicken - on the very border between eternal sunshine and eternal darkness. At habitable zones there is another drawback around long-lived stars - they are very narrow, so the planet has very little chance of accidentally being in orbit with a radius that is "just right".

But around hot, big, bright stars vast habitable zones spread out. However, these stars, unfortunately, are rare and live only a few million years, and then explode, so their planets can hardly be considered as candidates in the search for life in the form we are used to, unless there is some kind of very rapid evolution going on there. And it is unlikely that animals capable of inventing differential calculus. The Drake equation can be considered Goldilocks mathematics, a method by which one can estimate what the chances are that somewhere in the galaxy everything has worked out “just right”, as it should. However, the Drake equation in its original form does not include, for example, Mars, which is located far outside the habitable zone of the Sun. Meanwhile, Mars is full of winding dry rivers with deltas and floodplains, and this irrefutably proves that once in the past there was plenty of liquid water on Mars.

But what about Venus, the "sister" of the Earth? It falls right into the habitable zone of the sun. This planet, completely covered by a thick layer of clouds, has the highest reflectivity in the entire solar system. There are no obvious reasons why it can be bad and uncomfortable on Venus. However, there is a monstrous greenhouse effect on it. The thick Venusian atmosphere is mostly carbon dioxide and absorbs almost 100% of the small amount of radiation that reaches its surface. The temperature on Venus is 750 K, which is a record in the entire solar system, although the distance from the Sun to Venus is almost twice that to Mercury.

Since the Earth has sustained life throughout its evolution - billions of years of tumultuous vicissitudes - then life itself must provide some kind of feedback mechanism that keeps liquid water on the planet. This idea was developed by biologists James Lovelock and Lynn Margulis in the 1970s and is called the Gaia hypothesis. This rather popular but controversial hypothesis suggests that the set of biological species on Earth at any given time acts like a collective organism that continuously, albeit unintentionally, adjusts the composition of the Earth's atmosphere and climate in such a way that they contribute to the presence and development of life - that is, the presence of liquid water on the surface. I think it's very interesting and worthy of study. The Gaia Hypothesis is a favorite hypothesis of the proponents of New Age philosophy. But I'm willing to bet that some long-dead Martians and Venusians must have also championed this idea a billion years ago...

If you expand the concept of the habitable zone, it turns out that it needs just any source of energy to melt the ice. One of Jupiter's moons icy europe, heated by tidal forces gravitational field Jupiter. Like a racquetball that heats up from frequent impacts, Europa heats up from a dynamic load difference due to the fact that Jupiter attracts one side of it more than the other. What is the result? Current observational data and theoretical calculations show that Europa has an ocean of liquid water or, possibly, snow slurry under a kilometer-thick crust of ice. Given the abundance of life in the ocean depths on Earth, Europa is the most tempting candidate for life in the Solar System outside Earth. Another recent breakthrough in our understanding of what a habitable zone is is living organisms, recently dubbed "extremophiles": organisms that not only survive, but even thrive in conditions of extreme cold or extreme heat. If there were biologists among extremophiles, they would probably think that they are normal, and extremophiles are all those who live well at room temperature. Among the extremophiles are heat-loving thermophiles who usually live near underwater mountain ranges in the middle of the oceans, where water, heated under enormous pressure to a temperature well above its normal boiling point, splashes out from under the earth's crust into the cold thickness of the ocean. The conditions there are similar to those in a kitchen pressure cooker: an especially strong pot with an airtight lid allows you to heat water under pressure to a temperature above boiling, while avoiding boiling as such.

Minerals rise from hot springs on the cold ocean floor, creating giant porous tubes ten stories high - it's hot in the middle, a little cooler at the edges, where they directly touch the ocean water. At all these temperatures, countless species of living beings live in the pipes who have never seen the Sun and who do not care if it exists or not. These tough nuts eat geothermal energy, which consists of what remains since the formation of the Earth, and the heat that constantly seeps into the earth's crust due to the radioactive decay of natural, but unstable isotopes of long-familiar chemical elements - including, for example, aluminum-26, which is enough for millions of years, and potassium-40, which lasts for billions. The ocean floor is probably one of the most stable ecosystems on Earth. What happens if the Earth collides giant asteroid and all life on its surface will die out? Ocean thermophiles will live on as if nothing had happened. Perhaps after each wave of extinction, they even evolve and repopulate the earth's land. And what will happen if the Sun, for mysterious reasons, disappears from the center of the solar system, and the Earth breaks out of orbit and drifts in outer space? This event will not even make it into the Thermophile papers. However, five billion years will pass, and the Sun will turn into a red giant, expand and absorb the entire inner part solar system. At the same time, the Earth's oceans will boil away, and the Earth itself will evaporate. This is going to be a sensation.

If thermophiles live everywhere on Earth, a serious question arises: what if life originated deep in the bowels of prodigal planets that were thrown out of the solar system during its formation? Their "geo" thermal reservoirs would last for billions of years. And what about the countless planets that were forcibly expelled from all other solar systems that had time to form in our Universe? Maybe interstellar space is teeming with life that originated and evolved in the depths of homeless planets? The habitable zone is not at all a neatly delineated area around a star where the ideal, "just right" amount of sunlight falls - in fact, it is everywhere. So the house of the three bears, perhaps, also does not take any special place in the world of fairy tales. A bowl of porridge, the temperature of which was “just right”, could be found in any dwelling, even in the houses of the three pigs. We found that the corresponding factor in the Drake equation - the one responsible for the existence of planets within the habitable zone - could well rise to almost 100%.

So our fairy tale has a very promising ending. Life is not necessarily rare and unique phenomenon, perhaps as common as the planets themselves. And thermophilic bacteria have lived happily ever after - about five billion years.

Water, water, all around water

Judging by the appearance of some of the driest and most inhospitable places in our solar system, one might think that water, which is abundant on Earth, is a rare luxury in the rest of the galaxy. However, of all triatomic molecules, water is the most common, and by a wide margin. And in the list of the most common elements in space, the components of water - hydrogen and oxygen - occupy the first and third places. So there is no need to ask where the water came from in this or that place - it is better to ask why it is still not available everywhere. Let's start with the solar system. If you are looking for a place without water and without air, you do not have to go far: you have the Moon at your disposal. With low atmospheric pressure on the Moon - it is almost zero - and two-week days when the temperature is close to 100 ° C, the water evaporates quickly. During the two-week night, the temperature drops to -155 °C: under such conditions, almost anything will freeze.

The Apollo astronauts took all the air, all the water, and all the air-conditioning systems they needed to the moon with them to travel there and back. However, in the distant future, expeditions will probably no longer need to carry water and various products from it with them. Data from the Clementine space probe put an end once and for all to the long-standing debate about whether there are deep craters at the bottom of the North and south poles The moons are frozen lakes. If we take into account the average number of collisions of the Moon with interplanetary debris per year, we have to assume that among the debris falling to the surface there should be quite large icy comets. What does "large enough" mean? There are enough comets in the solar system that, if melted, would leave a puddle the size of Lake Erie.

Of course, the new lake cannot be expected to survive many hot lunar days with temperatures close to 100 ° C, but any comet that fell on the surface of the Moon and evaporated dumps some of its water molecules into the bottom of deep craters near the poles. These molecules are absorbed into the lunar soil, where they remain forever and ever, since such places are the only corners on the Moon where, literally, "The sun does not shine." (If you were convinced that one side of the moon is always dark, then you were misled by a variety of authoritative sources, which undoubtedly included the Pink Floyd album The Dark Side of the Moon, released in 1973. ) As the inhabitants of the Arctic and Antarctic know, hungry for sunshine, in these places the Sun never rises high above the horizon - neither during the day, nor during the year. Now imagine that you live at the bottom of a crater whose rim is higher than the point in the sky where the sun rises. In such a crater, and even on the Moon, where there is no air and nothing to scatter light so that it gets into shady corners, one will have to live in eternal darkness.

It’s also cold and dark in your refrigerator, but the ice still evaporates there over time (do not believe it - look at what ice cubes look like when you return from a long absence), nevertheless, it is so cold at the bottom of these craters that evaporation, in essence, ceases (according to at least, within the framework of our conversation, we may well assume that it does not exist). There is no doubt that if we ever build a colony on the Moon, it will have to be located near such craters. In addition to the obvious advantages - the colonists will have plenty of ice, there will be something to melt, purify and drink - hydrogen can also be extracted from water molecules, separating it from oxygen. Hydrogen and part of oxygen will go to rocket fuel, and the rest of the oxygen the colonists will breathe. And in your free time from space expeditions, you can go skating on a frozen lake from the extracted water.

So, the ancient crater data tells us that comets hit the Moon, which means that this happened to the Earth as well. If we consider that the Earth is larger and its gravity is stronger, we can even conclude that comets fell to Earth much more often. So it is - from the very birth of the Earth to the present day. Moreover, the Earth did not emerge from the cosmic vacuum in the form of a ready-made spherical coma. It grew out of condensed protosolar gas, from which the Sun itself and all other planets were formed. The earth continued to grow as small solid particles stuck to it, and then - due to the constant bombardment of asteroids, which were rich in minerals, and comets, which were rich in water. In what sense is it permanent? It is suspected that the frequency of comets hitting the Earth in the early stages of its existence was enough to provide water for all of its oceans. However, certain questions remain (and room for debate). Compared to the water from the oceans, the water from the comets we are studying now has a lot of deuterium, a type of hydrogen that has an extra neutron in its nucleus. If the oceans were filled with comets, then the comets that fell to Earth at the beginning of the existence of the solar system had a slightly different chemical composition.

Think you can safely go outside? Here and there: recent studies of water content in the upper layers earth's atmosphere showed that pieces of ice the size of a house regularly fall to Earth. These interplanetary snowballs, when in contact with air, quickly evaporate, but manage to contribute to the Earth's water budget. If the frequency of falls has been constant throughout the Earth's history of 4.6 billion years, then these snowballs may also have replenished Earth's oceans. Add to this the water vapor that we know is released into the atmosphere by volcanic eruptions, and it turns out that the Earth got its water supply on the surface in a variety of ways. Now our majestic oceans occupy two-thirds earth's surface, but they are only one five thousandth of the earth's mass. It would seem that a very small fraction, but it is still as much as one and a half quintillion tons, 2% of which at any given time are in the form of ice. If the Earth ever experiences a period of extreme greenhouse effect, as on Venus, then our atmosphere will absorb excess solar energy, the air temperature will rise, and the oceans will boil and quickly evaporate into the atmosphere. It will be bad. Not only will the flora and fauna of the Earth die out - this is obvious - one of the compelling (literally) reasons for the general death will be that the atmosphere, saturated with water vapor, will become three hundred times more massive. It will crush us all.

Venus differs from other planets in the solar system in many ways, including its thick, dense, heavy atmosphere of carbon dioxide, which is a hundred times more pressure earth's atmosphere. We would have been flattened there. However, in my ranking of the most amazing features of Venus, the presence of craters, which all formed relatively recently and are distributed evenly over the entire surface, occupies the first place. This seemingly innocuous feature suggests a single catastrophe on a planetary scale, which restarted the cratering clock and erased all evidence of impacts in the past. This is within the power, for example, of an erosive climatic phenomenon like the global flood. And also - large-scale geological (not venereal) activity, say, lava flows, which turned the entire surface of Venus into the dream of an American motorist - an entirely paved planet. Whatever restarted the clock happened suddenly and abruptly. However, not everything is clear here. If there really was a worldwide flood on Venus, where did all the water go now? Gone below the surface? Evaporated into the atmosphere? Or was it not water at all that flooded Venus, but some other substance?

Our curiosity and ignorance is not limited to one Venus - they extend to other planets. Mars was once a real swamp - with meandering rivers, floodplains, deltas, a network of small streams and huge canyons, carved by running water. We already have enough evidence that if anywhere in the solar system there were abundant sources of water, it is on Mars. However, today the surface of Mars is completely dry, and why is not clear. Looking at Mars and Venus - the brother and sister of our planet - I look at the Earth in a new way and think about how unreliable our sources of water on the earth's surface may be. As we already know, Percival Lowell's imagination led him to assume that colonies of resourceful Martians built an ingenious network of canals on Mars to bring water from the polar glaciers to the more populated mid-latitudes. To explain what he saw (or thought he saw), Lowell invented a dying civilization that somehow lost water. In his detailed but marvelously misleading treatise Mars as the Abode of Life (1909), Lowell laments the imminent decline of the Martian civilization born of his fantasy:

The drying up of the planet will continue, no doubt, until its surface is no longer capable of supporting all life. Time will surely blow it away like dust. However, when its last spark goes out, the dead planet will rush through space like a ghost, and its evolutionary career will end forever.

(Lowell, 1908, p. 216)

Something Lowell got right. If there was once a civilization (or any living organisms) on the Martian surface that needed water, then at some unknown stage in Martian history and for some unknown reason, all the water on the surface really dried up, which led exactly to an ending such as Lowell describes. Possibly missing martian water just went underground and was captured by permafrost. How can this be proven? Large craters on the surface of Mars have more streaks of dried mud overflowing than small craters. Assuming the permafrost lies deep enough, it would take a violent impact to get to it. The release of energy from such a collision should have melted the ice below the surface on contact, and the dirt splashed out. Craters with these features are more common in cold subpolar latitudes, exactly where you would expect a layer of permafrost to lie closer to the surface. According to some estimates, if all the water, which, as we suspect, hid in the permafrost on Mars and, as we know for sure, is enclosed in glaciers at the poles, melted and evenly distributed over its surface, Mars would turn into a continuous ocean in tens of meters deep. The search plan for life on Mars, both modern and fossil, should include looking at a wide variety of places, especially under the surface of Mars.

When astrophysicists began to think about where to find liquid water, and by association, life, they were at first inclined to take into account planets that orbit at a certain distance from their star - at such a distance that water remained on their surface liquid, not too far and not too close. This zone is commonly referred to as the habitable zone, or the Goldilocks zone (see the previous chapter), and for a start it was quite an acceptable estimate. However, she did not take into account the possibility of the emergence of life in places where there were other sources of energy, due to which water, where it should have turned into ice, remained in a liquid state. This could provide a slight greenhouse effect. As well as internal source energy, such as residual heat after the formation of a planet or radioactive decay unstable heavy elements, each of which contributes to the internal heating of the Earth and, consequently, to its geological activity. In addition, planetary tides also serve as a source of energy - this is a more general concept than just a billowing ocean dancing with the moon. As we have seen, Jupiter's moon Io is subjected to constant stresses from shifting tidal forces as its orbit is not perfectly circular and Io moves in and out of Jupiter. Io is located at such a distance from the Sun that under other conditions it would have to freeze forever, but due to constant tidal changes, it has earned the title of a celestial body with the most violent geological activity in the entire solar system - everything is there: and volcanoes spewing lava , and fiery crevices, and tectonic shifts. Sometimes modern Io is likened to the young Earth, when our planet has not yet cooled down after birth.

Europa is no less interesting - another satellite of Jupiter, which also draws heat from tidal forces. Scientists have long suspected, and recently confirmed (based on images from the Galileo space probe) that Europa is covered in thick, migrating layers of ice, beneath which lies an ocean of slush or liquid water. A whole ocean of water! Just imagine what kind of ice fishing there is. Indeed, engineers and scientists from the Jet Propulsion Laboratory are already considering sending a space probe to Europa, which will land on the ice, find an opening in it (or cut or stomp it itself), lower a deep-sea video camera into it, and we Let's see what's there and how. Since life on Earth most likely originated in the ocean, the existence of life in the oceans of Europe is by no means an empty fantasy, it may well be. In my opinion, the most amazing quality of water is not the well-deserved "universal solvent" label we all learned about in chemistry class at school, nor is it extraordinary wide range temperature at which water remains liquid. The most amazing feature of water is that although almost all substances, including water itself, become denser when cooled, water, when cooled below 4 ° C, becomes less and less dense. When it freezes at zero degrees, it becomes less dense than in a liquid state at any temperature, and this is annoying for water pipes, but very fortunate for fish. In winter, when the air temperature drops below zero, water at a temperature of 4 degrees sinks to the bottom and remains there, and a floating layer of ice builds up very slowly on the surface and isolates the warmer water from the cold air.

If this density inversion did not occur with water at a temperature below 4 degrees, then at an air temperature below the freezing point, the outer surface of the reservoir would cool down and sink to the bottom, and more warm water would go up. Such forced convection would quickly cool the entire mass of water to zero, after which the surface would begin to freeze. More dense ice would sink - and the entire water column would freeze from the bottom to the surface. In such a world, there would be no ice fishing, because all the fish would be frozen - frozen alive. And lovers of ice fishing would either sit under the thickness of the water that has not yet frozen, or on a block of a completely frozen reservoir. There would be no need for icebreakers to travel across the frozen Arctic: the Arctic Ocean would either freeze to the bottom or remain open to normal navigation, since a layer of ice would lie below. And you could walk on the ice as much as you want and not be afraid to fail. In such a parallel world, ice floes and icebergs would sink, and in 1912 the Titanic would have safely sailed to its destination - New York.

The existence of water in the galaxy is not limited to the planets and their moons. Molecules of water, as well as several other familiar household chemicals such as ammonia, methane and ethyl alcohol, are constantly registered in interstellar gas clouds. Under certain conditions - low temperature and high density - a group of water molecules can re-emit the energy of the nearest star into space in the form of amplified high-intensity directional microwave radiation. The physics of this phenomenon strongly resembles everything that happens to visible light in a laser. But in this case it is better to talk not about a laser, but about a maser - this is how the phrase "Microwave amplification by the stimulated emission of radiation" is shortened. So water is not just everywhere and everywhere in the galaxy - sometimes it also smiles radiantly at you from the depths of space.

We know that water is essential for life on Earth, but we can only assume that it is necessary condition the emergence of life anywhere in the galaxy. However, chemically illiterate people often believe that water is a deadly substance that is better not to encounter. In 1997, Nathan Zoner, a fourteen-year-old high school student in Eagle Rock, Idaho, objective research anti-technological prejudices and the associated “chemophobia”, which has gained well-deserved fame. Nathan invited passers-by on the street to sign a petition demanding strict control or even a ban on the use of dihydrogen monoxide. The young experimenter gave a list of nightmarish properties of this substance, devoid of taste and smell:

Dihydrogen monoxide is the main constituent of acid rain;

Sooner or later this substance dissolves everything it comes into contact with;

If accidentally inhaled, it can be fatal;

In the gaseous state, it leaves severe burns;

It is found in the tumors of terminal cancer patients.

Forty-three of the fifty that Zoner approached signed the petition, six hesitated, and one turned out to be an ardent supporter of dihydrogen monoxide and refused to put his signature.

Living space

If you ask a person where he is from, in response you will usually hear the name of the city where he was born, or some place on the earth's surface where he spent his childhood. And this is absolutely correct. However

the astrochemically accurate answer should sound differently: “I come from the remains of the explosions of many massive stars that died more than five billion years ago." Outer space is the main chemical factory. It was launched by the Big Bang, which supplied the Universe with hydrogen, helium and a drop of lithium - the three lightest elements. The remaining ninety-two naturally occurring elements created the stars, including every single carbon, calcium, and phosphorus in every single living organism on Earth, human and otherwise. Who would need all this richest assortment of raw materials if it remained locked up in the stars? But when stars die, they return the lion's share of their mass to space and season the nearest gas clouds with a whole set of atoms, which subsequently enrich the next generation of stars.

If the right conditions are created—the right temperature and the right pressure—many atoms combine to form simple molecules. After that, many molecules become larger and more complex, and the mechanisms for this are both intricate and inventive. Ultimately, complex molecules self-organize into living organisms of one kind or another, and this is certainly happening in billions of corners of the universe. In at least one of these, the molecules became so complex that they developed intelligence and then the ability to formulate and communicate to each other the ideas expressed in the icons on this page.

Yes, yes, not only people, but also all other living organisms in space, as well as the planets and moons on which they live, would not exist if it were not for the remains of spent stars. Basically, you are trash. This will have to be dealt with. Better to be happy. After all, what could be nobler than the idea that the Universe lives in all of us? You don't need rare ingredients to concoct life. Recall which elements occupy the top five places in terms of abundance in space: hydrogen, helium, oxygen, carbon and nitrogen. With the exception of the chemically inert helium, which does not like to create molecules with anyone, we get the four main components of life on Earth. They wait in the wings in the massive clouds that envelop the stars in the galaxy, and begin to create molecules as soon as the temperature drops below a couple of thousand degrees Kelvin. Molecules from two atoms are formed at once: this carbon monoxide and a hydrogen molecule (two hydrogen atoms bonded to each other). Lower the temperature a little more and you get stable three- or four-atomic molecules like water (H2O), carbon dioxide (CO2) and ammonia (NH3) - simple but high-quality products of biological cuisine. If the temperature drops a little more, there will be a whole host of molecules of five and six atoms. And since carbon is not only widely distributed, but also very active from a chemical point of view, it is included in most molecules - in fact, in three-quarters of all "kinds" of molecules observed in interstellar medium contains at least one carbon atom. Promising. However, space for molecules is a rather dangerous place. If they are not destroyed by the energy of supernova explosions, then ultraviolet radiation from nearby ultra-bright stars completes the matter.

How more molecules and, the worse it withstands attacks. If the molecules are lucky and they live in relatively calm or sheltered areas from extraneous influences, they can live to the point that they will become part of the grains. space dust, and eventually into asteroids, comets, planets and people. But even if the stellar onslaught does not leave any of the original molecules alive, there will be enough atoms and time to create complex molecules - not only during the formation of this or that planet, but also on and under the pliable surface of the planet. Among the most common complex molecules, adenine (this is such a nucleotide, or "base", an integral part of DNA), glycine (a protein precursor) and glycoaldehyde (hydrocarbon) are especially distinguished. All these and similar ingredients are necessary for the emergence of life in the form familiar to us and, of course, are not found only on Earth.

However, all this bacchanalia of organic molecules is not yet life, just like flour, water, yeast and salt are not yet bread. While the actual transition from raw material to living being remains a mystery, it is clear that several conditions are required for this to happen. The environment should encourage molecules to experiment with each other and at the same time protect against unnecessary injury. Liquids are especially good for this, as they provide both close contact and great mobility. The more opportunities for chemical reactions the environment provides, the more inventive the experiments of its inhabitants. It is important to take into account another factor that the laws of physics speak of: chemical reactions require an uninterrupted source of energy.

When one considers the wide range of temperatures, pressures, acidity, and radiations under which life on Earth can thrive, and remembering that what is a cozy corner for one microbe is a torture chamber for another, it becomes clear why scientists no longer have the right to put forward additional conditions for life elsewhere. An excellent illustration of the limitations of such conclusions is given in the charming book "Cosmotheoros" by the 17th century Dutch astronomer Christian Huygens: the author is convinced that hemp should be cultivated on other planets - otherwise what would ship ropes be made of to control ships and navigate the seas? Three hundred years have passed, and we are content with just a handful of molecules. If you mix them well and put them in a warm place, you can expect that it will take only a few hundred million years - and we will have thriving colonies of microorganisms. Life on earth is extraordinarily fruitful, there is no doubt about it. And what about the rest of the universe? If somewhere else there is a celestial body that is at least somewhat similar to our planet, it is possible that it did similar experiments with similar chemical reagents and these experiments were staged by the same physical laws, which are the same throughout the universe.

Let's take carbon, for example. He knows how to create the most different connections both with itself and with other elements, and therefore it is included in an incredible number of chemical compounds - in this it has no equal in the entire periodic table. Carbon creates more molecules than all the other elements combined (10 million - what do you think?). Usually, to create a molecule, atoms share one or more outer electrons, trapping each other like cam joints between freight cars. Each carbon atom is able to create such bonds with one, two, three or four other atoms - but a hydrogen atom, say, with only one, oxygen - with one or two, nitrogen - with three.

When carbon combines with itself, it creates many molecules from all sorts of combinations of long chains, closed rings, or branched structures. These complex organic molecules are capable of feats that small molecules can only dream of. For example, they are able to perform one task at one end and another at the other, twist, curl, intertwine with other molecules, create substances with more and more new properties and qualities - they have no barriers. Perhaps the most striking carbon-based molecule is DNA, the double helix that encodes the individual appearance of every living organism. But what about water? If a we are talking about ensuring life, water has a very useful quality- it remains liquid at a very wide, according to most biologists, temperature range. Unfortunately, most biologists only consider Earth, where water remains liquid within 100 degrees Celsius. Meanwhile, somewhere on Mars Atmosphere pressure so low that water is not liquid at all - as soon as you pour yourself a glass of H2O, all the water will boil and freeze at the same time! However, no matter how unfortunate current situation the atmosphere of Mars, in the past it allowed the existence of huge reserves of liquid water. If once life existed on the surface of the red planet, then only at that time.

As for the Earth, it is very well placed on the surface with water, sometimes even too well and even deadly. Where did she come from? As we have already seen, it is logical to assume that comets brought it here in part: they can be said to be saturated with water (frozen, of course), there are billions of them in the solar system, there are quite large ones among them, and when the solar system was just being formed, they constantly bombarded young Earth. Volcanoes erupt not only because the magma is very hot, but also because the heaving hot magma turns The groundwater into steam, and the steam expands rapidly, resulting in an explosion. The steam no longer fits into underground voids, and rips the lid off the volcano, causing H2O to come to the surface. Given all this, it should not be surprising that the surface of our planet is full of water. With all the diversity of living organisms on Earth, they all have common parts of DNA. The biologist, who has never seen anything but the Earth in his life, only rejoices at the versatility of life, but the astrobiologist dreams of diversity on a larger scale: about life based on DNA completely alien to us, or on something else altogether.

Unfortunately, so far our planet is the only biological sample. However, an astrobiologist can afford to collect hypotheses about living organisms that live somewhere in the depths of space by studying organisms that live in extreme environments here on Earth. It is worth starting to look for these extremophiles, and it turns out that they live almost everywhere: in nuclear waste dumps, in acid geysers, in acidic rivers saturated with iron, in deep-sea springs spewing chemical suspensions, and near underwater volcanoes, in permafrost , in piles of scale, in industrial salt ponds and in all sorts of places where you probably wouldn't go on your honeymoon, but which are probably quite typical of most other planets and moons. Biologists once believed that life originated in some kind of "warm pool," as Darwin wrote (Darwin 1959, p. 202); however, accumulated over recent times evidence tends to incline to the idea that extremophiles were the first living organisms on Earth.

As we will see in the next part, for the first half a billion years of its existence, the solar system was most like a shooting range. Large and small blocks constantly fell on the surface of the Earth, which left behind craters and were crushed into dust. rocks. Any attempt to launch Project Life would have been immediately thwarted. However, about four billion years ago, the bombardment waned and the temperature of the earth's surface began to drop, which allowed the results of complex chemical experiments to survive and flourish. In old textbooks, time is counted from the birth of the solar system, and their authors usually state that it took the Earth 700-800 million years to form. But this is not so: experiments in chemical laboratory planets could not begin until the celestial bombardment subsided. Feel free to subtract 600 million years of "warfare" - and it turns out that unicellular mechanisms got out of the primitive slurry in just 200 million years. While scientists still can't figure out exactly how life began, nature doesn't seem to have any problem with it.

Astrochemists have come a long way in just a few decades: until recently they knew nothing at all about molecules in space, and by now they have already discovered many different compounds almost everywhere. Moreover, in the past decade, astrophysicists have confirmed that planets also orbit other stars, and that every star system, not just the solar system, is full of the same four essential ingredients of life as our own cosmic home. Of course, no one expects to find life on a star, even on a “cold” one, where it is only a thousand degrees, but life on Earth is often found in places where the temperature reaches several hundred degrees. All these discoveries together lead to the conclusion that in fact the Universe is by no means alien and unknown to us - in fact, we are already familiar with it on fundamental level. But how closely do we know each other? What is the probability that any living organisms are similar to terrestrial - based on carbon and prefer water to all other liquids? Consider, for example, silicon, one of the most abundant elements in the universe. In the periodic table, silicon is directly below carbon, which means that they have the same electron configuration on external level. Silicon, like carbon, can form bonds with one, two, three or four other atoms. At right conditions it can also form chain molecules. Since the possibilities for creating chemical compounds for silicon are about the same as for carbon, it is reasonable to assume that life can also arise on its basis.

However, there is one difficulty with silicon: in addition to being ten times rarer than carbon, it also creates very strong bonds. In particular, if you combine silicon and hydrogen, you will get not the beginnings of organic chemistry, but stones. On Earth, these chemical compounds have a long shelf life. And for a chemical compound to be favorable to a living organism, you need bonds that are strong enough to withstand not too strong attacks. environment, but not so indestructible as to cut off the possibility for further experiments. How important is liquid water? Is this the only environment suitable for chemical experiments, the only environment capable of delivering nutrients from one part of a living organism to another? Maybe living organisms just need any liquid. In nature, ammonia is quite common, for example. And ethyl alcohol. Both are derived from the most abundant elements in the universe. Ammonia mixed with water freezes at a temperature much lower than just water (-73°C, not 0°C), which widens the temperature range at which it is possible to detect living organisms that love liquid. There is another option: on a planet where there are few sources internal heat, for example, it rotates far from its star and is frozen to the bone, methane, which is usually in a gaseous state, can also play the role of a necessary liquid. Such compounds have a long shelf life. And for a chemical compound to be favorable to a living organism, bonds are needed that are strong enough to withstand not too strong environmental attacks, but not so indestructible as to cut off the possibility for further experiments.

How important is liquid water? Is it really the only environment suitable for chemical experiments, the only environment capable of delivering nutrients from one part of a living organism to another? Maybe living organisms just need any liquid. In nature, ammonia is quite common, for example. And ethyl alcohol. Both are derived from the most abundant elements in the universe. Ammonia mixed with water freezes at a temperature much lower than just water (-73°C, not 0°C), which widens the temperature range at which it is possible to detect living organisms that love liquid. There is another option: on a planet where there are few sources of internal heat, for example, it rotates far from its star and is frozen to the bone, methane, which is usually in a gaseous state, can also play the role of a necessary liquid.

In 2005, the Huygens space probe (named after you-know-who) landed on Titan, the most large satellite Saturn, where there are many organic compounds and the atmosphere is ten times thicker than the earth. Aside from the planets Jupiter, Saturn, Uranus, and Neptune, all of which are composed entirely of gas and have no solid surface, only four celestial bodies in our solar system have a noteworthy atmosphere: Venus, Earth, Mars, and Titan. Titanium is not random object research. The list of molecules that can be found there inspires respect: these are water, and ammonia, and methane, and ethane, as well as the so-called polycyclic aromatic hydrocarbons - molecules from many rings. The water ice on Titan is so cold that it has become as hard as cement. However, a combination of temperature and pressure liquefies methane, and the first Huygens images show streams, rivers, and lakes of liquid methane. The chemical environment on Titan's surface is in some ways similar to that of a young Earth, which is why so many astrobiologists consider Titan a "living" laboratory for studying Earth's distant past. Indeed, experiments two decades ago showed that if you add water and a little acid to the organic suspension that results from irradiating the gases that make up Titan's cloudy atmosphere, this will give us sixteen amino acids.

Not so long ago, biologists learned that the total biomass below the surface of planet Earth is possibly greater than on the surface. The current studies of especially hardy living organisms show time after time that life knows no barriers and boundaries. Researchers studying the conditions for the emergence of life are no longer "crazy professors" who are looking for little green men on the nearest planets, they are generalist scientists who own a variety of tools: they must be specialists not only in astrophysics, chemistry and biology, but also in geology and planetology, because they have to look for life anywhere.

An example of a system for finding the habitable zone depending on the type of stars.

in astronomy, habitable zone, habitable zone, life zone (habitable zone, HZ) - this is conditional area in space, determined on the basis that the conditions on the surface of those in it will be close to the conditions on and will ensure the existence of water in liquid phase. Accordingly, such planets (or their) will be favorable for the emergence of life similar to the earth. The likelihood of life occurring is greatest in the habitable zone in the vicinity ( circumstellar habitable zone, CHZ ) located in the habitable zone ( galactic habitable zone, GHZ), although research on the latter is still in its infancy.

It should be noted that the presence of a planet in the habitable zone and its favorable for life are not necessarily related: the first characteristic describes the conditions in the planetary system as a whole, and the second - directly on the surface of a celestial body.

In English-language literature, the habitable zone is also called goldilocks zone (Goldilocks Zone). This name is a reference to the English fairy tale Goldilocks and the Three Bears, in Russian known as "Three Bears". In the fairy tale, Goldilocks tries to use several sets of three homogeneous objects, in each of which one of the objects turns out to be too large (hard, hot, etc.), the other is too small (soft, cold ...), and the third, intermediate between them , the item turns out to be “just right”. Similarly, in order to be in the habitable zone, the planet must be neither too far from the star nor too close to it, but at the "right" distance.

Habitable zone of a star

The boundaries of the habitable zone are established based on the requirement that the planets in it have water in a liquid state, since it is a necessary solvent in many biochemical reactions.

Beyond the outer edge of the habitable zone, the planet does not receive enough solar radiation to compensate for radiation losses, and its temperature will drop below the freezing point of water. A planet closer to the sun than the inner edge of the habitable zone would be overheated by its radiation, causing the water to evaporate.

The distance from the star where this phenomenon is possible is calculated from the size and luminosity of the star. The center of the habitable zone for a particular star is described by the equation:

(\displaystyle d_(AU)=(\sqrt (L_(star)/L_(sun)))), where: - average radius habitable zone in , - bolometric index (luminosity) of the star, - bolometric index (luminosity) .

Habitable zone in the solar system

There are various estimates of where the habitable zone extends in:

Inner boundary, a.e.	Outer border a. e.	Source	Notes
0,725	1,24	Dole 1964	Estimation under the assumption of optically transparent and fixed albedo.
0,95	1,01	Hart et al. 1978, 1979	K0 stars and beyond cannot have a habitable zone
0,95	3,0	Fogg 1992	Valuation using carbon cycles
0,95	1,37	Casting et al. 1993
-	1-2% further...	Budyko 1969, Sellers 1969, North 1975	… leads to global glaciation.
4-7% closer...	-	Rasool & DeBurgh 1970	…and the oceans won't condense.
-	-	Schneider and Thompson 1980	Criticism of Hart.
-	-	1991
-	-	1988	Water clouds can narrow the habitable zone as they increase the albedo and thus counteract the greenhouse effect.
-	-	Ramanathan and Collins 1991	Greenhouse effect for infrared radiation has a stronger influence than the increased albedo due to clouds, and Venus should have been dry.
-	-	Lovelock 1991
-	-	Whitemire et al. 1991

Galactic habitable zone

Considerations about the fact that the location of the planetary system, located within the galaxy, should have an impact on the possibility of the development of life, led to the concept of the so-called. "galactic habitable zone" ( GHZ, galactic habitable zone ). Concept developed in 1995 Guillermo Gonzalez despite being challenged.

The galactic habitable zone is, according to currently available ideas, a ring-shaped region located in the plane of the galactic disk. The habitable zone is estimated to be located in a region 7 to 9 kpc from the center of the galaxy, expanding with time and containing stars 4 to 8 billion years old. Of these stars, 75% are older than the Sun.

In 2008, a group of scientists published extensive computer simulations that, at least in galaxies like the Milky Way, stars like the Sun can migrate long distances. This goes against the concept that some areas of the galaxy are more suitable for life than others.

Search for planets in the habitable zone

Planets in habitable zones are of great interest to scientists who are looking for both extraterrestrial life and future homes for humanity.

The Drake Equation, which attempts to determine the probability of an extraterrestrial intelligent life, includes the variable ( ne) as the number of habitable planets in star systems with planets. Finding Goldilocks helps refine the values ​​for this variable. Extremely low values ​​may support the hypothesis unique earth, which claims that a series of extremely unlikely events and occurrences led to the origin of life on . High values ​​can reinforce the Copernican mediocrity principle in the position: a large number of Goldilocks planets means that the Earth is not unique.

Searching for Earth-sized planets in the habitable zones of stars is a key part of the mission, which uses (launched March 7, 2009, UTC) to survey and collect characteristics of planets in the habitable zones. As of April 2011, 1235 possible planets have been discovered, of which 54 are located in habitable zones.

The first confirmed exoplanet in the habitable zone, Kepler-22 b, was discovered in 2011. As of February 3, 2012, four reliably confirmed planets are known to be in the habitable zones of their stars.



With a discussion about the translation of the astrophysical term “habitable zone”, we open a new section “A false friend of a translator”, in which the correctness and adequacy of the translation will be discussed. Send examples of terms that, in your opinion, are incorrectly translated into Russian, explaining why your proposed translation is better and more accurate than others.

The introduction of new scientific terms is a responsible matter. You use a ringing word without thinking, and then people will suffer for centuries. Ideal for every new scientific concept it would be desirable to invent a new word that did not have a stable meaning before. But this rarely happens. A good example is the “quark” of physicists. Related concepts are usually called single-root words, which is quite convenient (geology, geography, geomagnetic). But often scientists act contrary to these traditions, giving names according to the principle “what came to mind”. An example from astronomy is “planetary nebulae”, which have nothing to do with planets, which every time has to be explained to non-specialists.

No less careful consideration should be given to the translation of English terms into native language. This has always been a problem: for example, star clusters ( star cluster) at the beginning of the 20th century were called star heaps. I’m not even talking about the transliteration of the names of scientists: for example, the astronomer H. N. Russell is presented in Russian-language literature in six versions - Russell, Russell, Ressel, Ressell, Ressel and Russell. For modern search engines, these are different people.

AT last years The problem of terminology has become aggravated for several reasons: illiterate journalists and non-professional authors publish their translations on the Web, not bothering to get acquainted with the already existing Russian terminology, but simply transliterating English words. So, the word “transit” began to appear more and more often, meaning the passage of the planet against the background of the disk of a star. For professional astronomers, the terms "passage", "occultation", "eclipse" have their own specific meanings, which are not reflected in the single word "transit".

Unfortunately, most online publications lack scientific editing, and even paper publishers rarely allow themselves this “luxury”. It would seem that there is a "Wikipedia", in which the terminology should be clarified by common efforts. Sometimes this really succeeds, but still professionals prefer to invest in one common platform called Wikipedia, leaving the content of Wikipedia (Russian-language) on the conscience of amateur enthusiasts.

When a new and, moreover, unsuccessful term begins to come into circulation, there is time to consider the problem and democratically come to a common opinion. Therefore - as an initiative - I propose to discuss the translation English term “circumstellar habitable zone”, or, in short, “ habitable zone”, which has recently become very popular among researchers of exoplanetary systems.

We are talking about the range of distances from the star, within which the temperature on the surface of the planet lies in the range from 0 to 100°C. Under normal atmospheric pressure, this opens up the possibility of the existence of liquid water, and hence life in its current sense. In domestic publications on this topic, three variants of the translation of the term “ habitable zone” - life zone, habitable zone and habitable zone. Let's try to figure it out.

The complete unsuitability of the term is immediately obvious habitable zone, indicating the presence of living beings in this zone and even hinting at the presence of a person there. "Dictionary of the Russian language" S. I. Ozhegov (1987) defines: inhabited- inhabited by people, having a population; an example is an inhabited island.

Indeed, "uninhabited island" does not mean at all that it is sterile; there are just no people there.

The broader meaning is Dictionary Russian language” by S. I. Ozhegov and N. Yu. Shvedova (1992): inhabited- inhabited by people, having a population; generally such, where there are living beings. Examples - inhabited earth , island inhabited by seagulls. Anyway, inhabited means inhabited, a " habitable zone"- a populated area in which SOMEONE LIVES. In reality, we are talking about the presence of CONDITIONS FOR LIFE, and not at all about the presence of creatures in it. Obviously, authors who use the term habitable zone are the least sensitive to the meanings of their native language.

What is habitable zone? Word habitability in Russian is. But what is it?

1. Explanatory Dictionary of Ushakov: habitability - the degree of population (about the area).
2. Naval historical reference book (A. Loparev, D. Loparev): habitability of the ship - a set of factors that characterize the conditions of stay of people on the ship. Elements of habitability: dimensions of cabins, utility rooms, walkways; composition, dimensions and location of cabin equipment; indicators of vessel roll, vibration, noise, ease of maintenance of ship equipment, instruments, systems, etc.
3. Glossary of terms of the Ministry of Emergency Situations (2010): habitability - a set of factors that characterize the conditions of human life.
4. River Dictionary of A. A. Lapin (2012): habitability of the ship - the duration of the voyage without resupply. Usually applied to tourist ships; calculated in days.

As you can see, the common denominator of these somewhat different interpretations is the person whose presence is assumed.

Direct transfer habitable according to the dictionary gives the following options - habitable, habitable. We have already dealt with habitability, but habitability, for life, accurately reflects the meaning of the term habitable zone. In general, in English -able speaks of possibility, not availability. The most appropriate translation would be the long expression "livable zone" or the somewhat pretentious "livable zone". A simpler and shorter "zone of life", in my opinion, accurately conveys the meaning English expression. Not the last role is played by the ease of pronunciation. Compare: life zone or habitable zone. I am for the zone of life. And you?

Comments

,
doc. Phys.-Math. sciences, head. Department of Physics and Evolution of Stars, Institute of Astronomy, Russian Academy of Sciences

In my practice, I use the variant "habitable zone", although I undoubtedly admit that Vladimir Surdin is right in the sense that this term does not give an adequate understanding of its essence. But the "livable" zone in this respect is no better, if not worse!

After all, what is habitable zone? This is some rather conventionally defined interval of distances within which the existence of liquid water is possible. Not life, but only water! At the same time, it must be remembered that the possibility of the existence of water does not mean that water exists, and the presence of water does not guarantee viability.

In other words, in this case(as in many others) we are trying to describe in two words a very complex concept. It will not be possible to do this adequately, so it is quite acceptable to use an established translation. Moreover, it is almost always necessary to explain what it means anyway.

In astronomy, this happens all the time, and the examples are endless. From the recent one, one can, for example, recall "near-Earth asteroids", which may not be near-Earth at all in literally this word. We also use another, slightly more accurate term - near-Earth asteroids - but it is also not ideal in terms of conveying meaning. There have been attempts to introduce the correct term "near-Earth asteroids" - but try to put it into practice! A third of the lecture or report will be spent on delivering it.

In general, I also adhere to a rather conformist position in this respect. When I say "planetary nebula," I don't worry about it not having to do with planets. The main thing is that both I and my interlocutor understand what is meant.

In astronomy, there are two-thirds of such controversial terms. Who can guess the meaning of the words "right ascension"? Who would guess that “metallicity” is often referred to as the oxygen content? What about new and supernova stars?

,
translator of M. S. Gorbachev, now the head of the press service of the Gorbachev Foundation

In this matter, of course, Vladimir Surdin is right. The fact is that English language in this case clearly separates the possibility and its implementation: habitable- a place to live inhabited- the place where they live. In most cases, the suffix - able and Russian suffix - received- are quite equivalent ( renewable- renewable), and in the case when there is a negation in the definition, they are completely equivalent (since the possibility cannot be realized: impenetrable- impenetrable, unsinkable- unsinkable, etc.)

But in the case of the word "uninhabited" in Russian, there was some "failure" (which is quite normal in natural languages), and it does not mean "a place where one cannot live", but "a place where one does not live". In English- uninhabited. That's why habitable it is desirable to translate so that the meaning of the English suffix - able was preserved and there was no possibility of misinterpretation. So “zone suitable for life” or “zone of possible life” is correct in meaning and correct in Russian. And the word "habitability" is artificial and unnecessary (although some artificial words may be needed, see the "inventive" experience of Karamzin and his contemporaries).

, science journalist

So far, in Russian there is no unambiguously rigidly fixed translation of the term for habitable zone. Well, actually not in English. They also use the "Goldilocks zone" ( Goldilocks Zone), which allows us to abstract from descriptiveness, but it will be clearly incomprehensible to our reader (our analogue is the fairy tale about Masha and the three bears). We have many uses; “life zone” and “habitable zone” are the most common and, in my opinion, never “erroneous”. A term is a term, it does not have to be supported by a verbal construction that is ideal from all points of view. There is where worst cases, already rigidly fixed; say, the same "planetary nebula" ... Well, what to do - you have to live with it, do not arrange "holivars" every time ...

We had a similar discussion in the Science in Focus magazine. In the end, they chose the "habitable zone" with the ability to sometimes commemorate the "life zone". I was neutral. So be it, although I am not at all against the “life zone” with an appropriate explanation. Nothing worse. The remaining options - "habitable zone", "habitat zone" - were decided to be excluded. “The zone where the existence of water in liquid form in open reservoirs is possible” is, of course, super-cumbersome, it is possible only as an explanation once, and even then in the case when the reader is supposed to be completely ignorant ...

The option proposed by Pavel Palazhchenko (“the zone of possible life”) is also cumbersome and does not explain everything, not to mention the prevalence (the term should be ALREADY widespread if possible, so as not to fall into the margins with the old options, when it finally finally get fixed).

In addition to being cumbersome and not as widespread as possible, the "zone of possible life" is not good because it creates only the illusion of correctness. After all, firstly, we are only talking about water, and secondly, about life in the forms known to us (theoretically, life can arise on a different basis ...).

Out of curiosity, I looked up what term we used earlier in the Trinity Variant. There is a complete mess here. Aleksey Paevsky wrote about the "habitable zone" and "habitable zone" (less often). Boris Stern - about the "habitat zone". Sergey Popov - "terrestrial planets in habitable zones". And only I used to write about the "life zone" (but now in the magazine I correct for the "habitable zone").

I also forgot to say that instead of "zone of life" you can also write "belt of life", that is, the first word in this term can also be argued for a long time and with taste.