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 found in liquid state, and as a consequence, the temperature on a potential planet could also be favorable to support 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 about the same as our Sun an hour before its sunset. The composition of the atmosphere in in general terms 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, 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. Z 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 the bad news, because according to scientists, the larger the "super-Earth", the less chance of finding 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 exposed to the radiation of 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 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."

Since the 18th century, scientists have believed that life and intelligence are ubiquitous in the universe, and not only planets and moons, but even stars, including our Sun, are inhabited. Over time, such maximalism had to be abandoned, but there was hope for the habitability of Venus and Mars. Astronomers have even found "confirmation" of the existence of aliens: for example, "channels" on Mars.

In the 1960s, when research vehicles went to the planets, it turned out that the neighboring worlds were not adapted for life, and even if it is there, it is not in a developed form. In the history of mankind, a sad period of “cosmic loneliness” began: for twenty years, even the presence of planets around other stars was called into question.

Photo of the surface of Venus, transmitted by the Soviet probe Venera-13 (before the probe broke from high temperature). Happy colonization!

The first exoplanet, the existence of which was confirmed at once by two independent groups of researchers, was discovered in 1995. There was this "hot Jupiter" near the star 51st Pegasus, which recently received the official name Dimidius. Currently, 3518 planets have been discovered in 2635 planetary systems, and they are very diverse. However, both scientists and the public pay the most attention to the search for Earth-like planets located in the "habitable zone", because it is on them that there is a chance to find other life.

When searching for exoplanets, two main methods are used. First, they measure how the angular velocity of a star changes under the gravitational influence of its invisible satellites. Secondly, fluctuations in its brightness are recorded when the satellite passes against its background. Direct photographs of exoplanets can be counted on the fingers, so their physical characteristics have to be judged by indirect data, which implies a fairly wide range of options.

"Hot Jupiter" Demidius, 51 Pegasus, as imagined by the artist

The gas giant planets have the most significant influence on the angular velocity and brightness of a star, so for a long time scientists discovered only them. Because of this, there was even an opinion that giants are a typical phenomenon in the Universe, and Earth-like worlds are a rarity. For example, it was expressed by Stanislav Lem. For some reason, the great Polish science fiction writer forgot about instrument selection, which is determined by the resolution of the equipment.

The more perfect the instruments became, the more stone planets began to be found. First, super-Earths of enormous mass were discovered, and then came the turn of Earth-like planets, which are only slightly larger than our world. The search for Earth-2 began - a planet that would be close to ours in mass and would be in the "habitable zone", that is, at such a distance from the star at which there would be enough heat for liquid water to exist on the surface.

Why is it important? Because we know only one form of life - terrestrial, and it could not have arisen without liquid water, which serves as a universal solvent. Accordingly, scientists believe that the likelihood of a biosphere on a planet with water bodies is much higher than anywhere else.

Alpha Centauri system: α Centauri A, α Centauri B, Proxima Centauri. Sun - for comparison

Although Earth-like exoplanets are found in a variety of places, of particular interest are, of course, the worlds closest to us. They can become the main goal of astronautics in the future. In October 2012, the discovery of an exoplanet near Alpha Centauri B was announced. This star is the second component of a three-star system that is 4.3 light-years away.

The discovery made a lot of noise, but in 2015, after analyzing the accumulated data, astronomers “cancelled” it. Therefore, the study of the third component - Alpha Centauri C, better known as Proxima (Nearest) - was approached with extreme caution.

A star that is 4.22 light-years away but is not visible naked eye, was discovered relatively recently. In 1915, it was noticed and described by the Scottish astronomer Robert Innes; it took another two years to measure the distance to it.

Alpha Centauri C (aka Proxima), the closest star to us

Proxima is a red dwarf, and periodically flashing: its luminosity can increase six times at once! Studies have shown that the X-ray emission of Proxima is comparable to that of the sun, and during strong flares that occur eight times a year, it can increase by three to four orders of magnitude. All this makes the existence of habitable planets in the immediate vicinity of Proxima problematic, but science fiction writers have always believed that they are there.

For example, Proxima is described as the target of "generation ships" in Robert Heinlein's Stepchildren of the Universe (1963) and Harry Harrison's The Captive Universe (1969). In Murray Leinster's story "Proxima Centauri" (1935), one of the two planets in the Proxima system is inhabited by carnivorous plants that are not averse to eating terrestrial astronauts. In Stanislav Lem's "Magellan Cloud" (1955), earthlings find there two rocky planets and an ancient dead starship of the "Atlantids". In Vladimir Savchenko's novel Over the Pass (1984), Proxima has desert planets where intelligent crystalline life has developed. In the novel by Vladimir Mikhanovsky "Steps in Infinity" (1973) in the vicinity of Proxima there is only one planet, Ruton, which does not have a biosphere, but is rich in minerals.

Scientists, like science fiction writers, were interested in finding planets around the nearest star. In 1998, the Hubble Space Telescope discovered a suspicious object at a distance of 0.5 AU. from Proxima, but more careful observations did not confirm the discovery. Further studies ruled out the possibility of the existence of brown dwarfs and gas giants in its orbits, then - super-Earths.

In 2013, astronomer Mikko Tuomi, studying data from many years of observations of Proxima, noticed a recurring anomaly and suggested that this indicates the presence of a small rocky exoplanet in orbit very close to the star. To verify the specialists of the European Southern Observatory, located in Chile, launched the Red Dot project in January 2016, and on August 24, the discovery of the world, which has so far received the code name Proxima Centauri b, was officially announced.

The exoplanet turned out to be relatively small: its mass is estimated at 1.27 Earth. It rotates so close to its star (0.05 AU) that the year on it is a little more than 11 Earth days, however, due to the low luminosity of Proxima, the conditions there are quite conducive to the emergence and development of life: it is believed that for this a new the planet fits better than Mars.

Proxima b (artist's view) compared to Earth

However, there are also problems. Due to its proximity to its star, the rotation of the exoplanet around its own axis must be synchronized with its circulation around Proxima, that is, it is always turned on one side towards the star. It must be very hot on this hemisphere, very cold on the other. Astrobiologists say that in this case, hypothetical reservoirs and life forms should be located in the transition zone between the hemispheres. At the same time, climatic parameters can vary within fairly wide limits: they depend on the density and composition of the atmosphere, as well as on what water reserves were on the planet after its formation.

Another problem is the radiation of Proxima, because the discovered planet, even in “quiet” times, receives from it 30 times more ultraviolet than the Earth from the Sun, and x-rays- 250 times more. And if we also remember periodic outbreaks and super outbreaks, then the situation for local life forms becomes completely unfavorable. Nevertheless, astrobiologists believe that the biosphere can adapt to such harsh conditions: from the deadly rays, local creatures can hide in caves or under water.

In addition, there are life forms on Earth (for example, coral polyps) that have learned to re-emit the energy of the Sun through biofluorescence. If the inhabitants of the exoplanet also mastered this technique, then they can be detected by radiation at certain wavelengths, which scientists are going to do in the future.

About what life might look like on an exoplanet like Proxima Centauri b, tells "Alien Worlds: Aurelia" (2005)

Another discovery, which was reported on August 27, was made on the Russian radio telescope RATAN-600, which is located in Karachay-Cherkessia. Scientists working on it caught a powerful point signal that came from the sun-like star HD 164595 - it is located in the constellation Hercules at a distance of 94.4 light years from us. By the way, a huge planet with a mass sixteen times greater than the earth's was discovered there a year earlier. The repetition of the signal has not yet been recorded, so astronomers avoid talking about its probable artificial origin.

In addition, calculations show that to generate such a signal, if it were directed exactly to the Earth, a whopping 50 trillion watts of energy would be required. This is more than all the energy generated by our civilization today, so the most plausible version looks like an accidental interception of radio emission from some natural source. In fact, the story is repeated with the “Wow!” signal, which was received in 1977 and the mystery of which has not yet been solved.

Telescope RATAN-600

Perhaps science is close to discovering alien life. Do we really have a chance for the first contact? Or will our hopes again, like half a century ago, turn into disappointment? ..

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 mass and density 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 this moment 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. AT solar system there is no second place 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 earth 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 largest moon 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 consists in the absence 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 aircrafts like airships.

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.

Image copyright PA Image caption This figure shows the comparative sizes of the Earth and the planet Kepler-452b (right)

NASA's Kepler Orbital Telescope has allowed scientists to peer into previously inaccessible depths of the universe. Among the discoveries made with his help is a planet that has a lot in common with the Earth.

The planet, named Kepler-452b, orbits its star at about the same distance as the Earth, although its diameter is 60% larger than Earth's.

Scientists claim that this planet has more terrestrial features than other terrestrial analogues discovered earlier.

Such planets are of great interest to astronomers because they are compact and cool enough to hold liquid water on their surface. And this means that they may have conditions favorable for sustaining life.

The Kepler-452 star system is located 1,400 light-years from Earth in the constellation Cygnus.

NASA lead scientist John Grunsfeld, presenting this discovery, called the planet Kepler-452b so far the most similar to Earth.

Neighborhood is relative: at the maximum speed of removal from the solar system, achieved today by any of the man-made spacecraft, it would take more than 25 million years to reach this planet.

exoplanet

New planet joins the list of exoplanets discovered by Kepler celestial bodies, revolving, like the Earth, around its sun.

At the moment, the attention of scientists is riveted on about 500 alleged planets located near distant stars.

They are among 4,175 planet candidates identified with this telescope, excluding the current find. So far, most of these candidates have subsequently been granted the status of proven exoplanets.

A small part of these planets is not much larger than the Earth and is located within the so-called "habitable zone" in the vicinity of their star, similar in structure to the Sun - that is, where, in principle, water can be in a liquid state, which is considered a prerequisite sustaining life.

At the moment, 12 planets have been found in different star systems that presumably meet these requirements. Kepler-452b is the first "habitable" planet whose existence is considered proven.

The answer to the question of which of these planets is more similar to the Earth than others depends largely on what characteristics are taken into account in the first place.

Smaller than Kepler-452b, but orbiting a "red dwarf" - a star that is much dimmer and cooler than the Sun.

Kepler-452b orbits a star in the same class as the Sun. This star is only 4% more massive and 10% brighter than the Sun. Kepler-452B flies around it in 385 days, so its "year" or, more precisely, its orbital period is only 5% longer than the Earth's.

The mass of the planet Kepler-452b cannot yet be measured, so astronomers have to rely on computer simulations to estimate different versions of its approximate mass. It is most likely that the mass of Kepler-452b is about five times that of the earth.

If its surface is rocky, the planet should continue active volcanic activity, and the force of gravity on it should be about twice as strong as on Earth.

The star around which Kepler-452b orbits is 1.5 billion years older than the Sun. Scientists believe that she can tell what awaits the Earth in the future.

The age of the planet itself is estimated at 6 billion years, that is, if these data are correct, it is also 1.5 billion years older than the Earth.

"If Kepler-452b does indeed have a rocky surface, its location relative to the star means it has entered the greenhouse phase of its climatic history," says Kepler scientist Doug Caldwell.

“The increasing release of energy from this aging sun could heat the surface and evaporate any oceans. Water could evaporate and the planet could lose it forever,” says Caldwell. “Kepler-452b can experience now what the Earth will experience in more than a billion years The sun will age and become brighter."

super earth

University of Warwick scientist Don Pollacco, who is not involved in the project, told the BBC that the data collected by the Kepler telescope allows an estimate of the size of the planet relative to the star it orbits.

They really have no idea what this planet is made of. It could be a stone, or maybe a small ball of gas, or maybe something more exotic Don Pollacco

“If you know the size of a star, you know the size of the planet,” the scientist says. “But to go further, for example, to find out if it has a rocky surface, you need to measure the mass of the planet, and this is much more difficult to do, since they are too far away, to make such measurements.

"So they really have no idea what this planet is made of. It could be rock, or it could be a small ball of gas, or maybe something more exotic," says Don Pollacco.

"Other Kepler planets that are in the" zone of life "may be even more similar to the Earth. For example, Kepler-186f is about 1.17 larger than the Earth, and Kepler-438b is about 1.12 from the Earth" , - points out the scientist.

"Actually, at 1.6 Earth's diameter, Kepler-452b falls into a category called 'Super-Earth'. There is not a single planet of this type in our solar system. For this reason, Super-Earths are very interesting, but can we say that they are similar to Earth?" asks Dr Chris Watson of Queen's University Belfast.

“If we look at the type of star that Kepler-452b orbits, it becomes clear that this star is similar to the Sun,” says Chris Watson. “Other Kepler planets found in “life zones” revolve around “red dwarfs” Stars that are much less hot than the Sun, so the planets must orbit much closer to them to receive the same level of heat.

"So it could potentially be a rocky Super-Earth in an Earth-like orbit. It's this combination of star and orbit that makes this planet stand out, in my opinion," the scientist told the BBC.