The planets are similar in size to the earth. Earth and its "copies". There are billions of habitable planets in the Universe. Where are we looking

Are there planets similar to Earth? Astronomers have announced the discovery of eight new exoplanets in the so-called immediate "zone suitable for life", that is, distant from their stars at a distance at which water on their surface is able to exist in a direct liquid state.

Everything open planets belong to the type of "small planets" (class of planets, not more earth). The discovery doubled the number of known "small" exoplanets in the "zone suitable for life."

The most interesting thing, however, is that two of these planets turned out to be the most similar in their parameters to the Earth of all the planets that have so far been discovered outside Solar system.

"There is a high probability that most of the planets we have discovered are not gaseous, but rocky," says Gilgermo Torez, a scientist at the Harvard-Smithsonian Center for Astrophysics and author of the study.

The opening was announced during a meeting of the US Astronomical Society. The two exoplanets that are most similar to Earth are Kepler-438b and the Kepler-442b exoplanet. These exoplanets orbit directly around red dwarf stars (these stars are smaller and cooler than the Sun). Kepler-438b makes a complete revolution around its own star in 36 days, respectively, Kepler-442b - already in 112 days.

The diameter of Kepler-438b is only 11.5% larger than the diameter of our Earth, and the probability that it is rocky is 70%. As for Kepler-442b, this exoplanet is 1/3 larger than Earth, and the probability that it has a solid surface is 60%.

The main criterion for the "zone that is habitable" is the incoming amount of total light from the star that the planet receives. If there is a lot of it, the water on the planet's surface evaporates; little - it turns into ice.

According to astronomical calculations, Kepler-438b receives a total of 42% more light than the Earth can receive. This makes the planet, similar to Earth, chances of getting into the "habitable zone" at 70%. Kepler-442b, in turn, has 2/3 of the solar energy that the Earth receives. This increases the chances of an exoplanet entering this zone by up to 97%.

“It is not known for certain whether these planets, which are similar to Earth and resemble the Earth, or the conditions on these planets may contribute to the existence of life. We can only state that they are promising candidates, ”says study co-author David Kipping.

Until this time, the exoplanets most reminiscent of Earth were Kepler-186b, which is 1.1 times the size of Earth and has 32% sunlight, and Kepler-62f, which is 1.43 times the size of Earth, and receives 41 % sunlight.

All exoplanets were identified by the Kepler orbiting special telescope, which in May 2013 was out of order. They are too far from the Earth for their mass to be measured directly. Therefore, the astronomers calculated the data obtained statistically using a specialized computer program BLENDER, which runs on the Pleiades supercomputer at the Ames Research Center (California).

After the analysis carried out by the BLENDER program, the scientists collected data on the planets for another year using the methods of high-resolution spectroscopy, optical adaptive sampling, and speckle interferometry.

All these observations, in particular, established that 4 of the confirmed exoplanets are in the so-called. multiple star systems. However, the companion stars are located at a very large distance from them and in any way cannot seriously affect the planets similar to Earth.

As with many of Kepler's other discoveries, the Earth-like planets found are too distant from Earth, which greatly complicates their study. So, Kepler-438b is located at a distance of 476 light years, and Kepler-442b - as much as 1100 light years.

One can lose count of how many times we have heard the phrase that "scientists have found the first truly earth-like exoplanet." To date, astronomers have been able to determine the presence of more than 2,000 different exoplanets, so it is not surprising that among them there are those that, to one degree or another, are really similar to Earth. However, how many of these Earth-like exoplanets are actually habitable?

Similar statements were made in due time regarding Tau Ceti e and Kepler 186f, who were also baptized as twins of the Earth. Nevertheless, these exoplanets do not stand out in anything remarkable and do not at all look like Earth, as we would like it to be.

One way to determine how habitable a planet can be is through the so-called Earth Similarity Index (ESI). This indicator is calculated based on the data of the radius of the exoplanet, its density, surface temperature and data on the parabolic speed - the minimum speed that must be given to an object in order for it to overcome the gravitational attraction of a particular celestial body. The Earth-Similarity Index ranges from 0 to 1, and any planet with an index higher than 0.8 can be considered "Earth-like". In our solar system, for example, Mars has an ESI index of 0.64 (the same index for the exoplanet Kepler 186f), while the Venus index is 0.78 (the same index for Tau Ceti e).

Below are five planets that best fit the description of the Earth's twin based on their ESI scores.

Exoplanet Kepler 438b has the highest ESI index among all exoplanets currently known. It is 0.88. Discovered in 2015, this planet orbits a red dwarf star (much smaller and colder than our Sun) and has a radius just 12 percent larger than Earth's. The star itself is located about 470 light years from Earth. The planet makes a complete revolution in 35 days. It is in the habitable zone - the space within its system where it is neither too hot nor too cold to maintain the presence of liquid water on the planet's surface.

As with other discovered exoplanets orbiting small stars, the mass of this exoplanet has not been studied. However, if this planet has a rocky surface, then its mass may be larger than the earth's only 1.4 times, and the temperature on the surface will vary from 0 to 60 degrees Celsius. Be that as it may, the ESI index is not the ultimate method for determining the habitability of planets. Scientists have recently observed and found that the planet's home star Kepler 438b has very powerful emissions of radiation on a fairly regular basis, which can ultimately make this planet completely uninhabitable.

The ESI index of planet Gliese 667Cc is 0.85. The planet was discovered in 2011. It orbits the red dwarf Gliese 667 in a triple star system "only" 24 light years from Earth. The exoplanet was discovered by measuring the radial velocity, as a result of which scientists found out that in the motion of the star there are some fluctuations caused by the gravitational effect of the planet located near it.

The approximate mass of the exoplanet is 3.8 times more mass Earth, however, scientists have no idea how big the Gliese 667Cc is. It is not possible to find out this because the planet does not pass in front of the star, which would allow us to calculate its radius. The orbital period of Gliese 667Cc is 28 days. It is located in the habitable zone of its cool star, which, in turn, allows scientists to assume that the temperature on its surface is about 5 degrees Celsius.

Kepler 442b

The planet Kepler 442b with a radius of 1.3 times the radius of the Earth and an ESI index of 0.84 was discovered in 2015. It orbits a star that is colder than the Sun and is about 1,100 light years away. Its orbital period is 112 days, which suggests that it is in the habitable zone of its star. However, the temperature on the planet's surface can drop to -40 degrees Celsius. For comparison: the temperature at the poles of Mars in winter can drop to -125 degrees. Again, the mass of this exoplanet is unknown. But if it has a rocky surface, then its mass can be 2.3 times the mass of the Earth.

The two planets with ESI indices of 0.83 and 0.67, respectively, were discovered by the Kepler space telescope in 2013, when they passed opposite their home star. The star itself is located about 1200 light years from us and somewhat colder than the Sun. With planetary radii 1.6 and 1.4 times the Earth's, their orbital periods are 122 and 267 days, respectively, which suggests that both are in the habitable zone.

Like most other planets discovered by the Kepler telescope, the mass of these exoplanets remains unknown, but scientists suggest that in both cases it is about 30 times larger than Earth. The temperature of each of the planets can support the presence of water in liquid form. True, everything will depend on the composition of the atmosphere that they possess.

Kepler 452b with ESI 0.84 was discovered in 2015 and became the first discovered potentially Earth-like planet, located in the habitable zone and orbiting a star similar to our Sun. The radius of the planet is about 1.6 times the radius of the Earth. The planet makes a complete revolution around its home star, which is about 1400 light years from us, in 385 days. Since the star is too far away, and its light is not too bright, scientists cannot measure the gravitational effect of Kepler 452b and, as a result, figure out the mass of the planet. There is only an assumption according to which the mass of the exoplanet is about 5 times the mass of the Earth. At the same time, the temperature on its surface, according to rough estimates, can vary from -20 to +10 degrees Celsius.

It follows from all this that even the most Earth-like planets, depending on the activity of their native stars, which can be very different from that of the sun, may be unable to support life. Other planets, in turn, have very different earthly dimensions and surface temperature. However, given the increased cost last years activity in the search for new exoplanets, one cannot exclude the possibility that among those found we will nevertheless meet a planet with a mass, size, orbit similar to the Earth, and a sun-like star around which it revolves.

First, the Earth was displaced from the center of the universe, proving that it revolves around the Sun, and not vice versa. Then it turned out that the solar system itself is just a formation at the periphery of its galaxy.

Now the uniqueness of the Earth as such is questioned. More recently, a number of scientists believed that perhaps our planet is an exceptional case and the conditions that have arisen here and are suitable for the origin of life are not repeated anywhere else.

However, American space researchers believe that life is possible on almost every one of them.

Such conclusions of specialists are contained in the material published in the scientific journal "Trudy national academy Sciences of the USA ".

This work was based on the analysis of the results of the Kepler space telescope.

The Kepler telescope was named after the German scientist Johannes Kepler, the discoverer of the laws of motion of the planets of the solar system. Launched in 2009, the apparatus was entrusted with a mission to search for the so-called exoplanets, that is, planets orbiting not around the Sun, but around other stars. Moreover, the Kepler mission included the task of detecting exoplanets with parameters similar to Earth.

Exoplanet hunting

The first exoplanets were discovered at the turn of the 1980s and 1990s. The search for such objects is extremely difficult due to their extreme remoteness from the Earth, their small size and dimness - after all, the planets themselves do not shine, but only reflect the light of the star.

The Kepler telescope was engaged in the detection of exoplanets using the so-called "transit method", that is, by measuring the fluctuations in the brightness of stars as the planet passes through its disk.

Kepler, which has been in orbit for four years, has discovered more than 3,500 planets during that time, on which, in theory, life could exist. There are 647 of them that are similar in size and mass to the Earth, and about 104 of them are located at such a distance from the star that makes it possible for the existence of water.

In the work of "Kepler" malfunctions were discovered in mid-2012, and at the end of spring 2013, it finally went out of order. Currently, engineers are working on plans for a possible modification of Kepler, but when they will be implemented and whether they will be implemented at all remains unknown.

Nevertheless, the data that Kepler collected during its work will be analyzed for several more years.

Was Giordano Bruno right?

Based on the data already studied, American scientists have come to the conclusion that there are a huge number of planets in the Universe that are suitable for the origin of life and are similar to the Earth.

Based on known information, astronomers believe that Earth-like planets exist in 22 percent of all stars. That is, every fifth star can rotate its own "Earth".

In the Milky Way galaxy alone, there are possibly 8.8 billion planets similar to Earth in size, mass and surface temperature. This means that some life forms can be found on them.

As for the Universe as a whole, then, as the famous cat Matroskin used to say, “we have heaps of shoe polish” - we are talking about tens and hundreds of billions of “copies” of the Earth.

Of course, under these conditions, the probability of the existence of brothers in mind among earthlings is extremely high.

By the way, American astronomers with their conclusions actually confirm the idea of ​​"multiple worlds", for which Giordano Bruno ascended the fire more than four hundred years ago. By the way, in the year of the 400th anniversary of Bruno's execution, the Catholic Church refused to consider the issue of the scientist's rehabilitation.

To knock on neighbors

The closest "copy" of the Earth from the "original" Earth is located relatively close - about 15 light years. True, with the current level of technology in order to get to the neighbors, it will take earthlings millions of years.

However, supporters of the uniqueness of the Earth revolving around the Sun do not give up - now they rely on the original geometry of our system, where the planets have almost regular circular orbits. They also point to the influence exerted on the development of the Earth by the Moon, without which "everything could be different."

The theoretical calculations of American astronomers, of course, look more weighty. It is quite possible that among the billions of "copies" of the Earth, there are also many that have their own "copies" of the Moon.

However, it is practically impossible to verify this so far - this requires something stronger than the Kepler telescope. Perhaps such a technique will appear in the not so distant future, because human curiosity is a great engine of progress.

What planets are similar to Earth? The answer to this question can be approached in different ways. If we take, for example, diameter and mass as the main criterion, then in the solar system, Venus is closest to our cosmic home. However, it is much more interesting to consider the question "Which planet is more like Earth?" in terms of the suitability of objects for life. In this case, we will not find a suitable candidate within the solar system - we will have to take a closer look at the endless expanses of outer space.

Habitable zone

People started searching for a long time. At first, these were only guesses, assumptions and conjectures, but as the technical capabilities improved, things began to move from the category of theoretical problems to the field of practice and scientific knowledge.

Criteria were identified by which a space object can be classified as potentially viable. Any planet similar to Earth must be located in the so-called habitable zone. This term refers to a specific area around the star. Its main characteristic is the possibility of the existence of liquid water on the planet within its boundaries. Depending on the characteristics of the star, the habitable zone can be located closer to it or a little further, have a greater or lesser extent.

Luminary properties

Studies show that a planet similar to Earth and potentially suitable for life should revolve around a star of spectral class from G to K and a surface temperature from 7000 to 4000 K. Such luminaries emit a sufficient amount of energy, are stable for a long time, their life cycle ends in several billion years.

It is important that the star does not exhibit significant variability. Stability both on Earth and in space is a guarantee of a more or less calm life. Sudden flares or long-term attenuation of the luminary can lead to the disappearance of organisms on the surface of the candidate for the twin of our planet.

Metallicity, that is, the presence of elements other than hydrogen and helium in a star's matter, is another important property. At low values ​​of this sign, the probability of the formation of planets is extremely small. Relatively young stars have a higher metallicity.

Properties of planets

And why, in fact, only a planet similar to the Earth can be potentially habitable? Why are objects similar in size to Jupiter not included in this list? The answer lies in the optimal conditions for the development of living organisms. They are created precisely on planets similar to ours. The properties of earth-like planets on which life can exist include:

mass close to the Earth: such planets are able to hold the atmosphere, with plates on their surface not as high as that of the "giants";

dominance in the composition of silicate rocks;

the absence of a dense atmosphere of helium and hydrogen, typical, for example, of Jupiter and Neptune;

not too large an eccentricity of the orbit, otherwise the planet from time to time will be too far from the star or too close to it;

a certain ratio of the tilt of the axis and the speed of rotation required for the change of seasons, the average length of the day and night.

These and other parameters affect the climate on the planet's surface, geological processes in its bowels. It should be noted that the necessary conditions may differ for different living organisms. Bacteria are much more likely to be found in space than mammals.

Assessing all of these parameters requires high-precision equipment capable of not only calculating the location of the planet, but also specifying its characteristics. Fortunately, modern equipment already "knows how" a lot, and unceasing research and development allow us to hope that in the near future people will be able to look even further into space.

Since the beginning of the century, a fairly large number of objects have been discovered that, to one degree or another, are suitable for life. True, it is not possible to answer the question of which planet is more similar to Earth than others, since this requires even more accurate data.

Controversial exoplanet

On September 29, 2010, scientists announced the discovery of the planet Gliese 581 g, orbiting a star.It is located at a distance of 20 light-years from the Sun. To date, the existence of the planet has not been confirmed. Over the five years since its discovery, it has been corroborated several times by additional research data, and then refuted.

If this planet exists, then, according to calculations, it has an atmosphere, liquid water and a rocky surface. In radius, it is close enough to our space home. It is 1.2-1.5 times the earth. The mass of the object is estimated at 3.1-4.3 Earth. The likelihood of the existence of life on it is as controversial as its very discovery.

First confirmed

Kepler-22 b is an Earth-like planet discovered by the Kepler telescope in 2011 (December 5). She is an object whose existence has been confirmed. Characteristics of the planet:

Comparative sizes of the Earth (right) and exoplanets (left to right): Kepler-22b, Kepler-69c, Kepler-452b, Kepler-62f and Kepler-186f. Illustration: NASA

Every Earth-like exoplanet discovered orbiting a solar-type star takes us one step closer to discovering a replica of our planet. The Kepler space telescope - the main "hunter" for exoplanets, has already discovered many potentially habitable worlds in our galaxy.To narrow down the search for a potentially habitable planet, Kepler searches for new objects in the so-called "zones of life" - areas around stars where water can be in a liquid state, and as a result, the temperature on a potential planet may also be favorable for maintaining life (the one we know).

In each star system, the "zone of life" has different sizes. Somewhere it is quite extensive, somewhere more narrow. In one system, the "zone" of life is located closer to the star, in the other further. The main factor, of course, is the star itself and its physical characteristics.

The last discovered "sister" of the Earth is the exoplanet "Kepler-452b", about which we are. Now, according to scientists, this exoplanet is the most similar to our planet. But there are other Earth-like exoplanets discovered earlier. And now, together we will remember which worlds most similar to Earth were discovered before the discovery of Kepler-452b.

Exoplanet Kepler-186f as seen by the artist. Illustration: NASA Ames / SETI Institute / JPL-Caltech

The second most Earth-like exoplanet is Kepler-186f in the Kepler-186 system, located 500 light-years from Earth in the constellation Cygnus. The planet Kepler-186f is only 10% larger than Earth.

The planet is located at a relatively small distance from the star: its period of revolution around the parent star, which is a red dwarf of spectral class M, is 130 Earth days. And at the same time, the exoplanet is on the far border of the "zone of life".

The energy received by Kepler-186f from its star is one third of the energy received by our planet from the Sun. At noon on the planet's surface, the star Kepler-186 shines about the same as our Sun an hour before its sunset. The composition of the atmosphere in general outline may be similar to the composition of the Earth's atmosphere; the temperature on Kepler-186f is probably the same as on our planet. But astronomers do not exclude the similarity with the atmosphere of Venus, hence the temperature on the planet will be much higher.

Kepler 62 system. Illustration by NASA Ames / JPL-Caltech

Before the discovery of Kepler-186f, the exoplanet Kepler-62f occupied the leading place in the list of Earth's "twins". Calculations show that it is 40% larger than the Earth and has an orbital period of 267 Earth days. Z star system - "Kepler 62", distant from us at 1200 light years in the constellation Lyra, 1/3 smaller than the Sun, colder and 5 times dimmer. However, the proximity of an exoplanet to a star makes the conditions on it more or less favorable for the development and maintenance of life.

Kepler 69 system. Illustration by NASA Ames / JPL-Caltech

At the same time (the first half of 2013), another interesting exoplanet, Kepler-69c, was announced, but it is 70% larger than our planet! In a sense, this is bad news, because according to scientists, the larger the "super-Earth", the less chances of finding life on it. But there is also good data: the exoplanet is located in the life zone, and its orbital period is 242 Earth days.

In addition, the parent star of the Kepler 69 system belongs to spectral type G. It is very similar to the Sun: 93% of the mass of the Sun, and luminosity - 80% of the Sun.

Exoplanet Kepler-22b. Illustration by NASA / Ames / JPL-Caltech

Even earlier, the exoplanet Kepler-22b was considered the ideal twin of the Earth. It was the first exoplanet discovered in the "zone of life" as part of the Kepler telescope mission. And among the planets sounded, "Kepler-22b" is the real "sumo".

The exoplanet's diameter is 2.4 times larger than that of Earth. It has not yet been established whether this planet has a rocky surface, or is covered with water, and perhaps consists of gas. The exoplanet was discovered almost immediately after Kepler began observing in 2009.

And one more interesting fact about "Kepler-22b": December 21, 2012 to this planet, containing information about the world around us and greetings to potential extraterrestrial civilizations. The message from earthlings was sent using the RT-70 radio telescope, but it will not reach soon - the exoplanet is 600 light-years away from our planet.

Visual similarities between Earth (left) and Gliese 667Cc (right) - computer model.

Meanwhile, not all Earth-like exoplanets have been discovered with the help of the "telescope-hunter". In 2011, astronomers announced the discovery of "Gliese 667Cc" with a 3.6-meter telescope belonging to the European Southern Observatory.

The planet is located just 22 light years from us. It is about 4.5 times more massive than the Earth. It revolves in orbit around a red dwarf in the "life zone" at a short distance from the star - the orbital period is 28 Earth days. Thus, the planet is highly exposed to radiation from the star. And at the same time, it receives only about 90% of the energy that we receive from our Sun. Unfortunately, the diameter and density of the exoplanet are still a mystery to astronomers.

Thus, the following chain is well traced - each discovered Earth-like exoplanet is the closest "double" of our planet, which in turn confirms where we started this material: " Every Earth-like exoplanet discovered takes us one step closer to discovering an exact replica of our planet. "