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

Each discovered Earth-like exoplanet orbiting a solar-type star brings us one step closer to discovering a replica of our planet. The Kepler space telescope, the world's premier exoplanet hunter, 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 "life zones" - areas around stars where water can be in a liquid state, and, as a result, the temperature on a potential planet can also be favorable for maintaining life (as we know it).

In each star system, the "zone of life" has different sizes. Somewhere it is very extensive, somewhere narrower. 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 recall which worlds most similar to the Earth were discovered before the discovery of Kepler-452b.

Exoplanet Kepler-186f as seen by an 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 size of the planet Kepler-186f exceeds the earth's by only 10%.

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

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 surface of the planet, the star Kepler-186 shines in about the same way as our Sun an hour before its sunset. The composition of the atmosphere may be broadly similar to that 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, so the temperature on the planet will be much higher.

Kepler 62 system. NASA Ames/JPL-Caltech illustration

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 a circulation period of 267 Earth days. W the star of the system is "Kepler 62", 1200 light-years away from us in the constellation Lyra, 1/3 smaller than the Sun, colder than it and 5 times dimmer. However, the proximity of the exoplanet to the star makes the conditions on it more or less favorable for the development and maintenance of life.

Kepler 69 system. NASA Ames/JPL-Caltech illustration

At the same time (the first half of 2013), another interesting exoplanet was announced - Kepler-69c, 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 likely it is to find life on it. But there is also good data: the exoplanet is located in the zone of life, and its period of revolution is 242 Earth days.

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

Exoplanet Kepler-22b. NASA/Ames/JPL-Caltech illustration

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

The exoplanet is 2.4 times larger than Earth. It has not yet been established whether this planet has a rocky surface, or is covered with water, or maybe it consists of gas. The exoplanet was discovered almost immediately after the start of observations by Kepler 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 of earthlings was sent using the RT-70 radio telescope, but it will not come soon - the exoplanet is 600 light-years away from our planet.

Visual similarity of Earth (left) and Gliese 667Cc (right) - computer model.

Meanwhile, not all Earth-like exoplanets have been discovered using the "telescope-hunter". In 2011, astronomers announced the discovery of "Gliese 667Cc" using the 3.6-meter telescope owned by the European Southern Observatory.

The planet is only 22 light years away. It is about 4.5 times more massive than the Earth. Rotates in orbit around a red dwarf in the "life zone" at a small distance from the star - the period of revolution is 28 Earth days. Thus, the planet is strongly affected by the star's radiation. 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 is 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 what we started this material with: " Each discovered Earth-like exoplanet brings us one step closer to discovering a replica of our planet."

The planetary objects of the terrestrial group of the solar system are not the only ones in the Universe. There are other planets in space similar to Earth.

Planetary objects similar to the Earth. Credit: NASA Solar System Exploration.

What are called terrestrial exoplanets

Exoplanets are planetary objects located outside our solar system.

To date, more than 4,000 of them have been discovered, and about 1,000 more have already been discovered, but have not yet been included in astronomical catalogs.

Some of the exoplanets belong to the terrestrial type - these are bodies on the surface of which conditions similar to those familiar to us have developed:

• the presence of a solid surface;
• climate favorable for the development of life;
• dimensions and mass, guaranteeing the desired gravity;
• conditions of movement in outer space and rotation around its axis, ensuring sufficient supply of heat and light to the planet.

Discovery of exoplanets

Earth-like planets could be a potential home in the future. Credit: NASA Solar System Exploration.

The study of space is not limited to the study of our star system with its 8 planets. Today, mankind is aimed at discovering planetary objects revolving around other luminaries, if only because one of them could become a potential home for the population of the globe in the future.

Therefore, every discovered planet, at least a little similar to ours, is carefully studied. However, not only complete analogues of the Earth have not yet been found, but also such objects on the surface of which there would be conditions suitable for life.

The first attempts to see planets outside our star system were made by astronomers as early as the middle of the 19th century, but they were crowned with success only in 1988, when the first extrasolar planetary object similar to the Earth was discovered, orbiting the binary star Alrai (gamma constellation Cepheus). This discovery was confirmed and officially recognized by the scientific community only in the early 2000s.

Detecting exoplanets is a difficult task: it is difficult to see them even with the help of the most powerful astronomical equipment, because, unlike stars, they do not glow.

Today, astronomers use several methods to discover such objects:

• direct observation through a telescope;
• spectrometric measurement of the radial velocity of a stellar object around which a planetary body can rotate;
• astrometric method, when an observer fixes a change in the motion of a star under the influence of the gravitational field of a neighboring planet;
• radio observation of pulsars - cosmic sources of any radiation (radioactive, optical, etc.);
• microlensing, when a stellar body is used as a telescope lens - it focuses the light emitted by the entire observed system with its gravitational field;
• transit method, which consists in detecting objects passing through the disk of luminous cosmic bodies.

Gliese 581 g is one of the top five exoplanets. Credit: NASA Solar System Exploration.

All exoplanets are named according to special rules.

The cosmonyms are made up of:

• the names of the star around which the objects revolve, and its numbers in the Gliese astronomical catalog;
• Latin letter (beginning with b), denoting the order in which the planet was discovered.

For example, Gliese 581 g is an exoplanet orbiting Gliese, stellar object No. 581 in the Gliese catalog, the sixth discovered in this system, and Kepler 438 b is a similar body orbiting Kepler's star (catalogue number 438), discovered first in this system.

Gliese 581g

This planet was born in the period from 7 to 11 billion years ago, revolves around one of the stellar objects in the constellation Libra - Gliese 581. It is located at a distance of 20 light years from Earth. The object was discovered in 2010 by spectrometric calculation of stellar velocity.

The body is controversial - since the first report of the discovery, its existence has been repeatedly confirmed and questioned. Nevertheless, Gliese 581 g is one of the top five exoplanets on which life can be detected in the form familiar to us.

It is similar to Earth in:

• size (1.3-2 earth radius);
• mass (3.1-4.3 of the weight of our planet);
• stability of the rotation period around the center of its star system (36.6 days);
• climate (on average -30 ... -10 ° С, according to some estimates, according to others, + 71 ° С on the illuminated side and -34 ° С on the shady one).

It is possible that the planet has an atmosphere and liquid water.

Kepler 438b

Kepler 438b is an exoplanet not suitable for human habitation. Credit: Calvin J. Hamilton.

This exoplanet was discovered using an orbiting telescope in 2015. It is located in the red dwarf system (the constellation Lyra). Recent observations have shown regular (every few hundred days) and powerful (tens of times greater than solar) emissions of radiation from Kepler 438, which can make the planet uninhabitable.

And yet the object is located in the habitable zone of its system, the existence of liquid water is possible on it.

Its parameters are:

• mass - presumably 1.4 of the earth;
• radius - 1.12 of the similar parameter of our planet;
• the period of a complete revolution around its own star is 35 days;
• the expected temperature on the surface is in the range of 0…+60°C.

Kepler 442b

The radius of the object is 1.3 times that of the earth. Discovered in 2015, Kepler 442b revolves around an orange dwarf in the constellation Lyra, making a full rotation in 112 days. On the planetary surface, the temperature can drop to -40°C, which is not critical for earthlings.

Kepler 62e and 62f

These 2 planets were discovered one after the other by the transit method in 2013 and therefore are almost always considered in pairs. They revolve around the star Kepler 62, an orange dwarf, a solitary object in the constellation Lyra.

The approximate age of Kepler 62 e is 7 billion years, the object is 1.5 times the diameter of the Earth.

Researchers suggest that the planet has an ocean, and the average ambient temperature is +15°C.

Whether there is an atmosphere here is not yet clear, but scientists estimate the probability of its presence as high, noting that the air layers should be 1.5-2 times denser than the earth's. The probability of the presence of life here, at least at the level of unicellular creatures, is 70-80%. Of all the extrasolar planets, Kepler 62 e is the closest to Earth.

Kepler 62 f is 40% larger than Earth and was born about 7.5 billion years ago. The climate on it is reminiscent of the earth, the axis is tilted stably, the conditions for the emergence of life are assessed by astrophysicists as favorable.

Kepler 452b

This terrestrial exoplanet orbits its star, a yellow dwarf in the constellation Cygnus, about the same distance as the Earth from the Sun. It is 60% larger in diameter than ours, and 5 times heavier in weight. It completes a complete orbit around the center of its system in 385 days. In the ranking of planetary objects similar in conditions to the Earth, the planet Kepler 452 b is sixth.

The celestial body was discovered in 2015 in a transit way, in 2018 its existence was called into question by scientists. So far, the dispute on this topic has not been finally resolved.

Gliese 667 Cc

The planet orbits Gliese 667 C. This red dwarf is located in the constellation Scorpius and is one of the elements of the triple star object Gliese 667. The planetary object was discovered in 2011 after a detailed spectrometric analysis of the speed parameters of the star. It is 3.5-4 times heavier than the Earth, the body travels around the center of its system in 28-29 Earth days. The average temperature here is +27°C, which suggests the existence of life on Gliese 667 Cc.

Kepler 22b

It is an exoplanet from the constellation Cygnus. It was opened in 2011 by the transit method. Around the center of its system - Kepler 22 - turns around in about 290 days.

The exact dimensions and mass of the object have not yet been studied.

Presumably, it belongs to the type of minineptune - this is an intermediate class between gas giants (Uranus, Neptune) and planets such as Earth, that is, with a solid surface.

Using the example of Kepler 22 b, the scientist M. Hippke substantiated why hypothetical living beings living on it cannot leave their home planet. With a large mass, it has a gravity superior to that of the Earth, and in order for the spacecraft to break away from the surface, hundreds of tons of rocket fuel will be required.

Kepler 78b

This planet is called one of the most similar to Earth in size and composition, but it is too hot for the emergence and development of life - the local temperature can reach + 2100 ... + 2800 ° С. The celestial body is located in the constellation Cygnus, at a distance of 1.5 million km from its star, making 1 complete revolution in 8.5 hours.

The mass of the object is 1.7 (according to other sources - 1.86) of the earth, the radius is 1.2 of the same parameter of our planet. The density of the local solid is 5.3-5.57 g / cm³ - this is comparable to the density of the Earth (5.5 g / cm³), which allows us to speak of a similar composition of these 2 objects.

Proxima Centauri b is the closest exoplanet to us.

The star closest to the Sun, Proxima Centauri, is invisible to the naked eye from Earth due to its low luminosity. Thus, Proxima Centauri b, discovered in 2016, is the closest exoplanet to the solar system. It is only 4.22 light years from us.

Proxima b (this object is most often called by such an abbreviated name) is 1.27 times heavier than the globe and 1.1 times larger in radius. The planet moves at a distance of 7.3 million km from its star, 1 complete orbital revolution lasts 11 days.

The presence of life is not excluded here - the exoplanet receives a lot of heat, so water on its surface can exist without freezing into eternal ice, but the radiation background is high.

The temperature here is expected to be -39°C.

Colonization of nearby exoplanets

Today, scientists are still only discussing which Earth-like planet to choose for future colonization.

Obstacles to the implementation of the plan can be called:

• long distances - modern spacecraft at the maximum possible speed will fly to some of these objects for 25 million years);
• unknown conditions in the new habitat of earthlings (presence or absence of atmosphere, water, background radiation, climate);
• the complexity of calculating the flight parameters (time spent on the road, reaching the desired orbit, landing).

Even the fusion-powered spaceships that exist today only on paper will fly to the nearest exoplanet for at least 10 years, during which time dust and asteroids from interstellar space will damage them. Obstacles in this case will also be destructive loads on the human body during acceleration or deceleration, the risk of exposure to cosmic radiation and psychological problems for the crew associated with such a long stay in an enclosed space.

The science

Scientists have discovered a mysterious planet outside our solar system, which is most similar in size and composition to the Earth, but on it too hot to sustain life.

The exoplanet was named Kepler-78b. Its orbit has puzzled astronomers - it is 20% wider, and the mass is 80% more than the earth, despite the fact that its density is the same as that of our planet.

The exoplanet is at a distance of about 1.5 million kilometers from the star. Kepler-78b orbits its star in about 8.5 hours. The temperature on the planet is about 2000 degrees Celsius, according to scientists.

The discovery was mentioned in two studies, the results of which were in turn published in the journal Nature.

Thanks to telescope Kepler astronomers have learned of thousands of exoplanets in our galaxy, many of them the same size as our planet. These planets revolve around stars like our Sun.

Although it is easy to measure the size of an exoplanet, it was quite difficult to find out its mass. Mass is an important parameter, since it allows you to find out the density of the planet, and therefore find out what this planet is made of.

Earth-like exoplanets

Kepler-78b is very interesting because this smallest exoplanet, in which scientists were able to find out the radius and mass with great accuracy.

By astronomical standards, this planet can be called a virtual twin of the Earth.

Scientists learn the size of an exoplanet, as well as the time it takes to orbit its star, by measuring the amount of light the planet blocks as it passes in front of the star.

After scientists measured the brightness of the planet Kepler-78b for 4 years at 30-minute intervals, the scientists found that the star's brightness dropped by .02% every 8.5 hours as the planet passed in front of its star.

secret planet

The planet Kepler-78b was discovered in September 2013 when it orbited a star similar to our Sun in the constellation Cygnus, approximately at a distance 400 light years from Earth.

Since its launch (March 2009), the Kepler space telescope has been able to detect nearly 3,600 potential exoplanets.

Two teams of scientists studied the mass and density of the new planet. Team Andrew Howard (Andrew Howard) from University of Hawaii, calculated that the mass of the planet Kepler-78b is 1.69 times that of the Earth, while the data of the team of Francesco Pepe (Francesco Pepe) from University of Geneva, showed that the exoplanet has a mass of 1.86 times more.

The density that the first team calculated is 5.57 grams per cubic centimeter, while the second team came up with a density of 5.3 grams per cubic centimeter.

Since each team recognizes certain errors, it can be said with certainty that scientists are right in their calculations. It is worth noting that the density of the Earth is 5.5 grams per cubic centimeter. This means that the new exoplanet may have the same composition as the Earth.

new planet

The new planet circles around its sun, gradually approaching it, and, approximately in 3 billion years her days will be numbered- the colossal gravity of the star will tear it to pieces.

By astronomical standards, the planet will become part of a star very soon. On Kepler-78b it will not be possible find alien life, due to too high a temperature on its surface.

And yet, the mass and density of the new planet, similar to the Earth, allow us to hope that somewhere there is a twin planet of our Earth, which has a similar size, composition and temperature on its surface.

According to Drake Deming of University of Maryland, the existence of Kepler-78b proves that, outside our solar system, planets similar in composition to Earth are not uncommon.

Deming hints at a new NASA program called TESS (Transiting Exoplanet Survey Satellite). It will be a space telescope currently being developed by the Massachusetts Institute of Technology. For two years, his mission will be to find and study of unknown transiting exoplanets revolving around bright stars.

* The mass of the Sun is equal to 99.86% of the mass of our entire solar system. Everything else, including planets and asteroids, is only 0.14%.

* Jupiter boasts such a powerful magnetic field that every day it enriches the Earth's magnetic field with billions of watts.

* One day on Venus lasts 243 Earth days, despite the fact that the year lasts only 225.

* Mars boasts the largest volcano in our solar system. It is called "Olympus" and it stretches for more than 600 km, having a height of 27 km. It is worth noting that the peak of Mount Everest is at an altitude of 8.5 km.

* Our planet does not have a constant weight. According to scientists, every year the Earth becomes heavier by 40,000 -160,000 tons, but manages to drop about 96,600 tons, which means a loss of about 56,440 tons.

> > The most Earth-like planet

Second Earth: is there a twin of the Earth and what will be Earth-like planets systems? Description of candidates for the role of the second world with life and resettlement.

Tired of living on Earth? Do you want to pack a backpack and move to another world? Well, we have bad news. There is no second place in the solar system that doesn't kill you in a second.

You will encounter hellish heat, ice age, poisonous fumes and other inhospitable worlds. Almost the entire solar system is negatively opposed to the life that is found on Earth. But if you look for options, which place would be the best? And are there planets similar to Earth?

We need to find a world with similar gravity, composition, temperature and weather conditions. In general, the second Earth. Let's take a look at the contenders.

How is the planet most similar to Earth? Luna comes to mind first. Of course, this is not a planet, but an earthly satellite. But the celestial body is located close. The moon is devoid of air, so you can not do without a spacesuit. Your bones will not be happy with low gravity because they will lose mass and become brittle. The temperature also jumps between hot and cold and there is no protection from cosmic rays.

If we consider satellites, then why not Titan?

It is the largest moon of Saturn. Reaches 15% of Earth's gravity, and the temperature can drop to -173°C. The pressure is higher than the earth, so you don’t have to equip the suit with special protection.

And what about Mars? The gravity of the Red Planet reaches 38% of the Earth's (terrestrial planet). So far we have no data on how this will affect the human body during a long visit. The Martian atmosphere is made up of poisonous carbon dioxide and low pressure. The temperature mark varies from 35°C to -143°C. But the main problem is the lack of a magnetosphere, which means we will have to create protection from radiation.

Let's go to Venus! It seems like a real suicide. It is as if you are flying into an oven with a temperature of 462 ° C and a pressure 92 times higher than the earth (the hottest planet in the solar system). Around you there is a massive accumulation of carbon dioxide and clouds of sulfuric acid. However, gravity and the atmospheric layer protect from radiation.

Despite all the horror, there is one cozy place to live. In the clouds of Venus.

Yes, you just need to climb to a height of 50-60 km and you will find yourself in the usual conditions for the Earth. Carbon dioxide will still be concentrated around, but special aircraft, such as airships, can be equipped.

As you can see, it is extremely difficult to find planets similar to the Earth. So far, opinions about colonization differ. Most are focused on Mars, but thoughts of Venus also haunt. It remains only to observe where we go first.

While working with the high-precision HARPS spectrograph installed at the European Southern Observatory (ESO), a team of researchers discovered a small exoplanet orbiting the red dwarf Ross 128. Astronomers believe that its size and surface temperature are very close to Earth. More interestingly, the planet Ross 128 b is located only 11 light-years from the solar system, making it the second closest exoplanet to us after Proxima b.

Silent star and promising planet

“This discovery was made possible by a decade of monitoring HARPS (High Accuracy Radial velocity Planet Searcher) data, coupled with state-of-the-art information analysis methods,” says Nicola Astudillo-Defrou from the University of Geneva, co-author of a paper on the new discovery. “Until now, only HARPS has demonstrated such measurement accuracy, and for 15 years it has been the best planet hunter in the world,” he assures.

The team notes that most red dwarfs experience intense solar flares, which usually literally blow planets off the atmosphere and irradiate them with solar radiation. However, Ross 128 is an unexpectedly "quiet" star that does not have such activity. As a result, its planets may be the closest point to our planet for the colonization of other star systems. This is the special importance of the discovery: if in the case of the well-known Proxima b, an aggressive star could destroy the planet's atmosphere and turn it into a rocky desert, then Ross 128 b gives humanity hope for space expansion.

Opening value

The orbit of Ross 128b is 20 times closer to the star than the distance between the Earth and the Sun, but the planet receives only 1.38 times more solar radiation. As a result, the temperature on its surface does not differ much from our planet: in the coldest points it does not fall below -60 ° C, and in the hottest it does not rise above 20 ° C. However, scientists are not yet sure whether the planet is included in such called " the goldilocks zone"- the region around the star, the conditions of which allow water on the planets to exist in a liquid state.

“Thanks to powerful modern telescopes, in 10 years we will be able to see a new planet and characterize its atmosphere. Currently, we only have theoretical models, and therefore we cannot say with certainty whether liquid water exists on the surface of Ross 128 b, ”explains Nicola in an interview with Futurism.