Detection of planets near other stars. Scientists have estimated how many planets are in our galaxy and how many of them are potentially suitable for life

An exoplanet is a planet that is located outside our solar system. Thousands of similar objects have been discovered over the past two decades, mostly using NASA's Kepler space telescope.

Exoplanet - what is it?

These differ significantly in their sizes and orbits. Some of them are giant planets circling close to their stars. Some are covered with ice, others with rocks. NASA and other agencies are looking for a special kind of planet: They want an Earth-like exoplanet orbiting a Sun-like star located in the habitable zone.

The habitable zone is the range of distances from a star at which the planet's temperature allows for the existence of liquid oceans of water, which is critical for life. The earliest definition of the zone was based on simple thermal equilibrium, but modern calculations include many other factors, including the greenhouse effect of the planet's atmosphere. This makes the boundaries of the habitable zone blurry.

Theory of the origin of life

Although the exoplanet is a discovery from the 1990s, for years astronomers have been convinced of their existence. They not only believed, but based their conclusions on the slow rotation of our own Sun and other stars.

Astronomers have a theory about the origin of life in our solar system. In short, a rotating cloud of gas and dust (the so-called protosolar nebula) collapsed under the influence of its own gravity and formed our star and planets. After this, the conservation of angular momentum meant that the future star should rotate faster and faster. However, although it has 99.8% it has 96% of its angular momentum. Astronomers have wondered why our star rotates so slowly.

The young star had a very strong magnetic field, the lines of force of which penetrated the disk of swirling gas from which the planets were formed. These lines were associated with charged gas particles, and acted as anchors, slowing the formation of the Sun and spinning up the gas that eventually became planets. Most stars rotate slowly, so astronomers concluded that the same “magnetic braking” had occurred in them, meaning that planet formation must have occurred. Hence the logical conclusion: planets need to be looked for around stars similar to the Sun.

Early discoveries

For this and other reasons, scientists initially limited their search for exoplanets to stars similar to the Sun, but the first two discoveries in 1992 were of a pulsar (the rapidly spinning remnant of a star that died as a supernova) called PSR 1257+12. The first confirmed exoplanet orbiting a star (photo included in the article) that meets this requirement was discovered in 1995. It became 51 Pegasi b, whose mass is comparable to c and which is 20 times closer to its Sun than the Earth. This came as a surprise. But another strange thing happened seven years earlier, which made it clear that many exoplanets would be discovered.

In 1988, a group of Canadian scientists discovered a planet the size of Jupiter orbiting Gamma Cephei. But since its orbit was much smaller than that of Jupiter, scientists did not announce a definitive discovery. Astronomers did not dare to suggest that such planets exist. It was so different from our solar system that scientists were extremely cautious.

From big to small

Almost every exoplanet discovered at first is a huge Jupiter-like (or even larger) gas giant orbiting at a short distance from its parent star. This is explained by the fact that astronomers used a technique for measuring radial velocity, which determines the degree to which the star “swings” as the planets orbit around it. Large ones nearby had such a significant impact that it could be easily detected.

Before the era of exoplanet discoveries, instruments could only measure the movements of stars to within a kilometer per second, which was insufficient to detect their vibrations under the influence of planets. Modern instruments are capable of measuring speeds down to centimeters per second, partly due to improved precision of the equipment, but also because astronomers are more skilled at isolating faint signals from the data.

Kepler information explosion

To date, there are more than 1,000 confirmed exoplanets discovered by a single satellite. The Kepler space telescope was launched into orbit in 2009 and hunted for habitable planets for four years. It used a method called "transit" - measuring the dimming of a star while a cosmic object passed in front of it.

Kepler revealed an abundance of different types of planets. In addition to gas giants and terrestrial bodies, the telescope helped establish the existence of a new class of “super-Earths” whose sizes are within the range of the sizes of Earth and Neptune. Some of them are located in the habitable zones of their stars, but astrobiologists are still checking calculations to find out how life could develop on such worlds.

In 2014, Kepler astronomers introduced a method called “multiplicity testing” that would increase the rate at which planet candidates are promoted to confirmed status. The technique is based on orbital stability - many stars darkened at short intervals, which could only be caused by planets in small orbits, since if they were stars, they would gravitationally push each other out of the system within a few million years.

Other missions

Although the satellites (Kepler and the French CoRoT) that hunted for exoplanets have completed their initial missions, scientists are still processing the data obtained with their help, making new discoveries. And they will not be left without work. The MOST and NASA TESS satellites continue to operate, and the Swiss CHEOPS and the ESA PLATO satellite will begin searching for transit from space in the near future. On Earth, the HARPS spectrograph on the European Southern Observatory's 3.6-meter telescope in Chile is conducting Doppler searches for stellar wobbles, but many other telescopes are in the hunt.

One example is NASA's Spitzer Space Telescope. Because it is sensitive in the infrared region of the spectrum, it is able to measure the exoplanet's temperature profile and provide insight into its atmosphere.

With over 3,000 known planets, it's hard to choose just a few. Small, rocky exoplanets in the habitable zone appear to be the best candidates, but astronomers have identified others that have expanded our understanding of the formation and development of other worlds.

The first swallows

51 Pegasi b. As mentioned above, it was the first proven exoplanet to orbit a solar-type star. With half the mass of Jupiter, it is removed from the center of the system at the distance of Mercury. The planet is so close to its star that, most likely, one side of it is tidally locked - it is constantly facing the star.

HD 209458 b. It was the first exoplanet discovered in 1999 (photo included in the article) to transit its star (albeit using the Doppler method), and was followed by other discoveries. It is the first planet outside the solar system to have the parameters of its atmosphere determined, including its temperature profile and absence of clouds.

Notable Worlds

55 Cancri e. This exoplanet is what is called a “super-Earth” that orbits a star bright enough to be seen with the naked eye. This way, astronomers can study the system in more detail than any other. Its “year” is only 17 hours and 41 minutes (this was determined when MOST observed the system for two weeks in 2011). Theorists suggest that 55 Cancri e may be rich in carbon and have a diamond core.

HD 80606 b. This exoplanet is the record holder (at the time of its discovery in 2001) for orbital eccentricity. It is likely that the path of its movement, similar to the orbit of Halley's comet, may be associated with the influence of another star. In addition, such an extreme orbit causes extreme variability in the planet's environment.

WASP-33b. It was discovered in 2011 and has a kind of sun protection layer - the stratosphere - that absorbs some of the visible and ultraviolet light from the parent star. The planet not only moves in orbit in the opposite direction, but also causes vibrations in the star, which are recorded by the MOST satellite.

Gemini of the Earth

Kepler-442b. This exoplanet is what is called “Earth’s twin.” With its size, mass and temperature regime, it is most similar to our planet. Discovered on January 6, 2015, it is located at a distance of 1,120 light years. The surface temperature of this rocky exoplanet is -40 °C. Its mass is 2.34 times the mass of the Earth, and its gravity is 30% greater. The planet is outside the zone where tidal locking is in effect. In a paper published in 2015, it was named, along with Kepler-186f and 62f, as the best candidate for potentially inhabited planets (see photo).

Exoplanet Kepler-78b. It orbits the star Kepler-78. At the time of its discovery in 2013, the planet was most similar to Earth in terms of mass, radius and average density. Not only was its transit against the background of the star detected, but also an eclipse and reflected light corresponding to the orbital phases. The “year” of the exoplanet lasts only 8.5 hours, because it is 40 times closer to the star than the distance from Mercury to the Sun.

Worlds that orbit other stars are called "exoplanets," and they range from giant gas giants larger than Jupiter to small, rocky planets like Earth or Mars. Distant planets can be hot enough that metal melts on their surfaces, or icy snow globes. Many of them orbit their stars so quickly and closely that their year lasts several Earth days. Some may have two suns. There are also wanderers expelled from their systems, those who wander the galaxy in the dark.

The Milky Way is a huge family of stars extending over approximately 100,000 light years. Its spiral structure contains about 400 billion inhabitants, and our Sun is among them. If each of these stars has not one planet in orbit, but several, as in the Solar System, then the number of worlds in the Milky Way is simply astronomical: the number goes into the trillions.

Thousands of star systems living in the Milky Way. Credit: ESO/M. Kornmesser

Humanity has been speculating for several centuries about the possibility of the existence of planets around distant stars, and now we can confidently say that extrasolar worlds do exist. Our closest neighbor, Proxima Centauri, recently had a discovery, and she's probably not alone. The distance to it is approximately 4.5 light years or 40 trillion kilometers. However, most of the exoplanets found are located hundreds or thousands of light years away.

The bad news is that we don't have a way to get to them yet. The good news is that we can look at them, measure their temperature, probe their atmosphere, and may soon discover signs of life hidden in the dim light coming from these distant worlds.

The first exoplanet to hit the world stage was 51 Pegasi b, 50 light-years away, which orbits its star once every 4 Earth days. The turning point after which extrasolar planets became commonplace occurred in 1995.

Artistic representation of hot Jupiter. Credit: ESO

Even before 51 Pegasi b there were several candidates. The exoplanet known today as Tadmor was discovered in 1988. Although its existence was called into question in 1992 due to insufficient evidence, ten years later additional observations confirmed that Gamma Cephei A was indeed orbited by a planet. Then, in 1992, a system of “pulsar planets” was discovered. These worlds orbit a dead star, PSR 1257+12, located 2,300 light-years from Earth.

We now live in a universe of exoplanets. Their number is constantly increasing, and at the moment the number of confirmed planets outside the solar system has crossed the threshold of 3,700, but in the next decade the graph could jump to tens of thousands.

How did we get here?

We stand on the threshold of great discoveries. The era of early exploration and the first confirmed exoplanets set the stage for the next phase: the hunt for distant worlds with sharper and more sophisticated telescopes in space and on the ground. Some of them were tasked with conducting an accurate census of the population, calculating the various sizes and types of exoplanets. Others carefully study individual worlds, their atmospheres and their potential to support life.

Direct imaging of exoplanets, that is, actual pictures of them, is playing an increasingly important role, although scientists have achieved the current level of knowledge mainly through indirect means. The two main methods rely on wobbles and eclipses.

"Hunter" for exoplanets TESS. Credit: NASA

Today, little is known about this class of extrasolar worlds, including whether they are habitable. The reason for this is the absence of super-Earth analogues in the Solar System. If we're lucky, one of them will show signs of oxygen, carbon dioxide and methane in its atmosphere. However, the hunt for the atmospheres of Earth-sized planets will have to wait until a future generation of space telescopes in the 2030s.

Thanks to the Kepler telescope, we now know that the stars above us are surrounded by planets. And we can be sure not only of a huge variety of exoplanet neighbors, but also that the adventure is just beginning.

– planets beyond the solar system: detection and characterization, first discoveries, classification, search methods, list, Kepler and James Webb.

Exoplanets called worlds located outside our solar system. Over the past 20 years, thousands of alien planets have been found using NASA's powerful Kepler space telescope. They all differ in size and orbit. Some are giants, orbiting very close, while others are icy or rocky. But space agencies are focused on a specific species. They are looking for exoplanets the size of Earth and located in the habitable zone.

The habitable zone is the ideal distance between a planet and a star to maintain the right temperature for the formation of liquid water. The first observations were based only on the heat balance, but now other factors, such as the greenhouse effect, are also taken into account. Of course, this “blurs” the boundaries of the zone.

In August 2016, scientists announced that they had found a suitable candidate for an Earth-like exoplanet near the star Proxima Centauri. The new world was named Proxima b. It is 1.3 times more massive than the Earth (rocky). It is distant from the star by 7.5 million km, and spends 11.2 days in orbit. This means that the planet is blocked - one side is always turned towards the star (as is the case with the Earth's satellite).

Early exoplanet discoveries

Although exoplanets weren't officially confirmed until the 1990s, astronomers knew they were out there. And it was not based on fantasies and strong desire. It was enough to look at the slow rotation of our star and planets.

Scientists owned the main mechanism - the history of the emergence of the solar system. They knew that there was a cloud of gas and dust that could not withstand the pressure of its own gravity and collapsed into itself. At the time of the crash, and appeared. Conservation of angular momentum provided acceleration for the future star. The Sun contains 99.8% of the mass of the entire system, and the planets contain 96% of the momentum. Therefore, researchers never tired of being surprised at the slowness of our star.

They began to look exclusively for stars similar to ours. But early findings in 1992 unexpectedly led to a pulsar (a dead star spinning rapidly after a supernova explosion) - PSR 1257+12. In 1995, the first world was discovered - 51 Pegasi b. It was similar in size, but was located closer to its star. It was an amazing and shocking discovery. But 7 years have passed, and we have found a new planet, hinting that the Universe is rich in worlds.

In 1998, a team from Canada spotted a Jupiter-type world near Gamma Cepheus. But its orbital path was much smaller than that of Jupiter, and scientists did not pretend to study the find.

Exoplanet registration methods

Astrophysicist Sergei Popov about transiting planets, the phenomenon of gravitational lensing and the Gaia telescope:

Exoplanet data boom

The first discovered exoplanets were gas giants (like Jupiter). Then scientists used the radial velocity technique. She calculated the level of “sway” of the star. This effect was created if there were planets near it. Large specimens are more massive, and therefore their presence is easier to detect.

Before entering into active research on exoplanets, Earth-based instruments were able to measure the motion of stars up to km/s. This is too faint to pick up the wobble caused by the planet. There are now over a thousand discovered worlds discovered by the Kepler Space Telescope. He ended up in orbit in 2009 and hunted for 4 years. He adopted a new technique - “transit”. That is, it measures the level of decrease in the brightness of a star at the moment when a planet appears in front of it and obscures it. Below is a diagram that compares search methods and the number of discovered exoplanets.

In 2014, another technique appeared - the “multiplicity test”, which can speed up the process of confirming a candidacy for an exoplanet. Based on orbital stability. Most stellar transits are associated with the presence of minor planets in orbit. But repeatedly eclipsing stars could imitate this effect and force each other out of the system by gravity.

Hot Jupiters These are gas giants that resemble the mass of Jupiter, but orbit too close to their host star. Because of this, there is a sharp jump in temperature (7000°C). It was a real surprise for scientists to discover that this type is quite common, since it was previously believed that such planets should rotate in an outer line.

Pulsar planet Such objects make orbital passages around neutron stars - the residual cores of large stars, that is, everything that was preserved after a supernova explosion. There is no doubt that no planet will survive such an event, so they are formed after.

These objects resemble ours in parameters and chemical composition and rotate in the habitable zone (an ideal distance to the star that allows water to remain liquid). They are valuable for discovery because they can contain life.

Super Earth These are rocky planets, 10 times the mass of the Earth. The prefix “super” itself only hints at size characteristics, and not any planetary features. Therefore, gas dwarfs are also found among them. The first super-Earths found were two objects orbiting the pulsar PSR B1257+12. Super-Earths Astrophysicist Sergei Popov on the diversity of planets in the Solar System, the properties of super-Earths and the composition of exoplanets:

Eccentric planets In ours, the planets for the most part have fairly uniform circular orbits. However, the exoplanets found so far may have much more eccentric orbits, moving either close or far from the star. If a perfect circle has an eccentricity value of zero, then about half of the exoplanets have an eccentricity of 0.25 or more. These eccentric orbits can result in some pretty extreme heat waves. For example, HD 80606b, which is about four times the size of Jupiter and lies about 200 light-years from Earth, has an eccentricity of about 0.93. Thus, the orbital distance of HD 80606b varies between the orbital distance of the Earth and the orbital distance of Mercury.

Gas and ice giants Gas planets include those that resemble Jupiter and Saturn. The elements include hydrogen and helium, surrounding a rocky or metallic core. Ice ones, like Neptune and Uranus, have much less of these elements, but noticeably heavier ones. Approximately 2/3 of the exoplanets found belong to these types.

Planet-ocean These objects are completely covered by a layer of water. Most likely, from the very beginning these were icy worlds that appeared at a great distance from the star. But something made them come closer. The temperature rose and the ice transformed into water.

Chthonic planet They were originally gas giants that were unlucky enough to get too close to the star. Because of this, the atmosphere burned out, leaving only a metallic or rocky core. Lava may flow on the surface. Super-Earths and chthonic planets are similar, so they are sometimes confused.

Orphan Planet They are also called “orphans” because they do not have a main star. They are in isolation because for some reason they were thrown out of the system. Scientists have only found a few examples, but they believe this type is common.

Earth instruments are actively working on the search. We have NASA's MOST and TESS, CHEOPS (Switzerland) and the HARPS spectrograph. Don't forget about the Spitzer telescope. It is ideal because it is tuned to the infrared range and is capable of calculating exoplanets by temperature and even characterizing atmospheric parameters. Below is a list of exoplanets suitable for life.

Known exoplanets

With over two thousand planets outside our solar system, it's hard to pick just a few examples. Of course, small ones and those located in the habitat area stand out. But it is worth remembering 5 more objects that contribute to our understanding of the evolutionary planetary path.

- 51 Pegasus b- the first planet found with half the mass of Jupiter. Its orbital path is equivalent to that of Mercury. The distance from the star is small, so it is in a blocked state (one side is always turned towards the star).

- 55 Cancer e- a super-Earth near a star whose brightness allows it to be observed with the naked eye. This is very good, as it gives scientists the opportunity to study the details of someone else's system. One orbital pass takes 17 hours and 41 minutes. The object may have a diamond core and a large amount of carbon.

- WASP-33b- an interesting planet with a noticeable protective shell. We are talking about the stratosphere, which absorbs the visible and ultraviolet glow of the star. She was found in 2011. Orbital motion is opposite to stellar motion, which creates noticeable vibrations.

- HD 209458 b- the first to be found using stellar transit in 1999. It also became the first to have an atmospheric signature, along with temperature indicators and the absence of cloud formations.

- HD 80606 b- was considered the most unusual planet due to oddities in its orbit (as if the passage of Halley's comet around our star). Most likely, this is influenced by another star. Found in 2001. Explore a list of terrestrial exoplanets by host star and distance from the Sun.

List of nearby terrestrial exoplanets

Watch fascinating videos about exoplanets to explore their structure, internal composition, classification, atmospheric features, and location in the habitable zone.

Internal structure of exoplanets

Astrophysicist Sergei Popov about the substances of the planetary interior, types of exoplanets and the dependence of density on size:

Atmospheres of exoplanets

Astrophysicist Sergei Popov on methods of studying the atmosphere, the structure of the outer layers of the gaseous shell of planets and hot Jupiters:

Habitable zone

Astrophysicist Sergei Popov on the parameters of the habitable zone, the greenhouse effect and the prospects for searching for life on exoplanets:

How to look for exoplanets?

How is it possible to find a world similar in size to our planet if it is hidden dozens of light years away? And how difficult is it to find an Earth-like exoplanet with potential for life? The enormity of the problem posed becomes clearer if we remember that large stars appear to be just small bright points. Some cannot even be seen with powerful telescopes.

Planets reach only a small fraction of the stellar mass. Because of this, nuclear fusion is not activated. In this case, the worlds are very tiny and dark, which makes the work of researchers even more difficult. Add to this the fact that planets are found near bright stars, often covering them with their glow.

But for scientists nothing is impossible and they always find workarounds. If a planet cannot be seen directly, then noticeable stars remain that influence the planet's orbital path. At the beginning of the 20th century, astronomers identified specific search criteria, but only recently have telescopes reached the necessary sensitivity to put them into practice and not make mistakes. What methods are there? Let's list them:

With the development of technology, scientists are able to discover more and more exoplanets, whose number is beginning to number in the thousands. This is why it is important to be able to group objects in order to understand the characteristics. But we still have little information about distant planets, so the definition itself remains imprecise.

Astrophysicist Sergei Popov about the discovery of exoplanets, the Kepler astronomical satellite and spectral measurements

Exoplanet satellites

Astrophysicist Sergei Popov on the formation of the Moon, methods for registering satellites and the potential habitability of exomoons:

What is the planet like?

Let's figure out what a planet is. In 2006, a document was released by the International Astronomical Union (IAU), which stated that an object must meet several criteria for planetary status:

• makes revolutions around the Sun;
• has the necessary mass to secure the round shape;
• removed debris and foreign objects from orbit;

These conditions only appeared after Mike Brown turned his attention to several worlds on the outskirts of the solar system. They were similar in size. The definition had to be revised and Pluto was automatically moved to the category of dwarf planets.

It is important to note that this decision was not received with enthusiasm or approval. Not only scientists, but also ordinary people stood up for Pluto. Alan Stern protested especially strongly. He was the principal investigator of the New Horizons mission that visited Pluto in 2015. He has stated many times that “eliminate foreign objects” is too vague a requirement. After all, there are asteroids in Earth's orbit. And the photos showed a complex and interesting world, in which mountains, frozen lakes and other planetary attributes are visible.

But the IAU refused to change anything and said that dwarf planets are of the same scientific interest. They also mentioned such large bodies as and, on which many interesting features are noticeable.

In 2017, Stern and several other scientists proposed a more refined definition: “A planet is a substellar massive object that lacks nuclear fusion and has sufficient gravity of its own to form a spheroid.”

The first exoplanet was noticed in 1992 near PSR B1257+12 (pulsar). But a planet around a main sequence star (51 Pegasi b) was discovered in 1995. Since then, the Kepler telescope has been able to find thousands of “terrestrial” planets and those living in the habitable zone (there are necessary conditions for water to persist as a liquid).

But it also revealed a wide variety of planets. For example, hot Jupiters were common. Some were incredibly ancient. Suffice it to recall PSR 1620-26 b, which is only a billion years younger than the Universe. There are those who are unlucky enough to live too close to the star, and their atmosphere resembles the hell on Venus. Instances have been found that manage to orbit two or even three stars at once.

Of course, it becomes clear that with such planetary diversity it is very difficult to follow a single classification system. First of all, researchers take into account the predisposition to the presence of life. These are included in the list of habitable exoplanets.

But for this you need to know two parameters: mass and orbit. Unfortunately, modern technology still does not have the necessary power to study foreign atmospheres, unless the object is close and large enough. But that could all change with the arrival of the James Webb Telescope in 2018.

Variety of planets

Astrophysicist Sergei Popov about gas and ice giants, double star systems and single planets:

Exoplanet classification

What types of exoplanets are there and what is the classification? Probably the most popular is the one used in Star Trek: an inhabited planet - class M. Following this scheme, we have:

• D – planetoid or satellite without an atmosphere.
• H – unsuitable for life.
• J is a gas giant.
• K – there is life or dome cameras are used.
• L – there is vegetation, but no animals.
• M – ground.
• N – sulfuric.
• R is an outcast.
• T – gas giant.
• Y – toxic atmosphere and high temperature.

If we take scientific schemes, then the mass or variety of elements is used for distribution. The mass is obtained from telescope observations. It is calculated from the radial velocity detected by spectrographs. In this case, the classification looks like this:

Minor planets, satellites and comets:

• asteroid: less than 0.00001 Earth mass.
• Mercurian type: from 0.00001 to 0.1 Earth mass.

Terrestrial group (rocky):

• subterran: 0.1-0.5 Earth mass.
• Terran (Earth): 0.5-2 Earth masses.
• Super Terran: 2-10 Earth masses.

Gas giants:

• Neptune: 10-50 Earth masses.
• Jupiter: 50-5000 Earth masses.

Evolution of exoplanets

Astrophysicist Sergei Popov about changes in the orbits of planets, a super-Earth in the Solar System and the transformation of a star into a red giant:

Modern methods for studying exoplanets

Astrophysicist Sergei Popov on the discovery of exoplanets, the Kepler astronomical satellite and spectral measurements:

28.03.2018 18:47 1024

Many of you guys are interested in astronomy, read various books and watch films about space. You may have ever heard that scientists call some planets exoplanets. But we will now find out what exoplanets are.

The word "exo" in Greek means "outside" or "outside." From these words it follows that exoplanets are planets that are located outside our solar system.

Scientists began to notice such planets in the late 1980s, when powerful devices appeared that made it possible to do this. Astronomers have been greatly assisted in studying exoplanets by space telescopes - artificial satellites that were invented to discover new planets. Many exoplanets have been discovered by scientists using powerful optical telescopes installed at various observatories.

Researchers divide exoplanets into two types: terrestrial exoplanets and gas exoplanets. Terrestrial planets are composed of iron, aluminum, magnesium and oxygen. Due to this, they have a high density and a hard surface. Gas giants consist of various gases: hydrogen, methane, helium. You will not be able to walk on such planets, since they do not have a solid surface. If you go down to such a planet, you can fall into it, as if you were flying through the clouds. But the deeper you go, the more the pressure increases, which can simply crush an object. In our solar system, the terrestrial planets include Mercury, Venus, Earth and Mars, and the gas giants include Jupiter, Saturn, Uranus and Neptune.

Terrestrial exoplanets are divided into different classes, such as super-Earth, ocean planet, iron planet and many others.

Super-Earths are planets whose mass is greater than the mass of the Earth, but less than the mass of gas giants. Among the super-Earths, one can highlight the planet Gliese 581c. It orbits the star Gliese 581 (its sun) in the constellation Libra. This planet was discovered in 2007 at the La Silla Observatory, which is located in Chile. The exoplanet Gliese 581c is similar in size to our planet. It is located approximately 20 light years from Earth. Thanks to various calculations, astronomers were able to find out that an atmosphere can exist on this planet, the surface temperature is about 100 0 C, and one year lasts only 13 Earth days. Scientists suggest that water may exist on this exoplanet.

An ocean planet is an exoplanet that is completely covered in water. Astronomers have so far discovered only one such planet with the complex name GJ 1214 b, which fits this name. It is located in the constellation Ophiuchus.

Iron planets are a type of planet that has a large amount of metal in its core. An example of such a planet is the exoplanet Kepler-10 b in the constellation Draco.

Gas exoplanets are also divided into different classes: hot Neptune, super-Jupiter and others.

Hot Neptune is a class of exoplanets that are similar in size and mass to Neptune and Uranus and are very close to their star (distance less than one astronomical unit). Planet Gliese 436 b belongs to just such a class of exoplanets. It is located in the constellation Leo, 33 light years from our Earth. This planet consists mainly of water. Due to its close location to its star (its Sun), the temperature on the planet is about 300 0 C! However, water at this temperature does not evaporate, but rather is in a solid state (ice). This is all due to the enormous force of gravity on this planet. It creates very high pressure, which compresses the water molecules, turning them into hot ice. Gravity forces prevent this ice from melting.

Super-Jupiter is a type of exoplanet whose size and mass exceed the size of the largest planet in our solar system, Jupiter. An example of such an exoplanet is the planet Kepler-419 c. It is located in the constellation Cygnus, at a distance of 2544 light years from Earth.

As you guys have already noticed, all the exoplanets listed above have very strange and complex names that are difficult to remember. The fact is that in recent years, scientists have managed to discover several thousand new exoplanets, and it was difficult to come up with a name for each. Therefore, they decided to name exoplanets after the stars (their Sun) around which they revolve. And astronomers began to add one letter to the name of the star. For example, the planet Kepler-419 c orbits the star (its Sun) Kepler-419.

What is an exoplanet? This is a planet that is located outside the solar system and revolves around a star. In addition to this definition, there is also such a concept as habitable zone(Goldilocks zone). It refers to a conditional region in outer space where liquid water can exist on the planet located in it. If this characteristic is present, then it means that there are conditions for the emergence of life.

Johannes Kepler

How are exoplanets discovered?

Unlike the stars that shine brightly in Earth's night sky, exoplanets are so dim and small that they are almost impossible to see. Their existence in outer space began to be discussed only in 1885, when Captain Jacob of the Madras Observatory reported the presence of a planetary body in the 70 Ophiuchi system (a double star system in the constellation Ophiuchus). However, the existence of this non-luminous body was subsequently questioned.

Many years passed before another extrasolar planet was discovered by three Canadian astronomers. It was found near the double star Gamma Cephei in the constellation Cepheus. This happened in 1988, but official science confirmed this discovery only in 2002.

In 1995, Swiss astronomers Didier Queloz and Michel Mayor discovered an extrasolar planet near the star 51 Pegasus in the constellation Pegasus. It was similar in size to Jupiter, but was very close to the star and made a full revolution around it in 4.23 days. They called it Planet b.

On March 6, 2009, NASA launched the Kepler telescope, whose mission was to detect exoplanets. This device was named after the German astronomer and mathematician Johannes Kepler. It was he who discovered the laws of planetary motion.

The telescope was equipped with the most advanced instruments capable of observing the light of stars. When a non-luminous cosmic body passes in front of a star, it obscures its light. The telescope records this phenomenon, and astronomers identify new extraterrestrial planets.

In addition to Kepler, there is the COROT orbital telescope. It records the light curves of stars. This device was launched on December 27, 2006. The Gaia space observatory was also launched on December 19, 2013. Its main task is to create a three-dimensional map of the Milky Way and discover extrasolar planets. There are also ground-based observatories that monitor space.

Besides transit method, which identifies non-luminous bodies against the background of a star, there are other ways to search for exoplanets. Here it is necessary to name Doppler method, with the help of which you can detect very large planets, which in their mass significantly exceed the Earth. They, acting on the star, seem to rock it. As a result, a shift in the spectrum of the star is observed.

This is what an exoplanet might look like

Also used gravitational microlensing. Its essence is that between the astronomer on Earth and the star he is observing, there must be another star. It takes on the role of a lens, that is, it focuses the scattered light of the observed star with its gravitational field. There may be a planet near such a lens star. Its presence is manifested in an asymmetrical light curve and lack of color tone. Using this method, it is possible to identify planets with a small mass corresponding to the Earth's.

In addition to those mentioned, there are astrometric method. It is based on recording changes in the motion of a star under the influence of the gravitational forces of the planet. Thanks to astrometry, it is possible to determine the masses of such cosmic bodies.

It is also carried out from Earth radio observation of pulsars. If there are planets near the pulsar, then its radiation creates conical shapes in outer space, which indicate the presence of planetary bodies.

And, of course, exoplanets can be discovered by direct observation, isolating them from the light of the stars. This method is good in cases where planetary bodies are located at a considerable distance from the star. They have residual heat retained after their formation. This method gives a good effect when observing young stars.

How many exoplanets have been discovered?

Currently, 10% of the stars included in the search program have planets discovered. At the same time, their number is steadily increasing. As of July 2015, there were 1935 planetary bodies. But there are more candidates that could become exoplanets. There are 4695 of them.

There should be at least 100 billion such cosmic bodies in the Milky Way. At the same time, about 20 billion may turn out to be similar to the Earth. According to modern estimates, 34% of stars similar to the Sun have planets in their habitable zones that are comparable in many characteristics to ours.

Experts have developed a similarity index. It characterizes the suitability of a particular planet or satellite for life. The index takes into account such characteristics as mass, size, density, distance to the star, and surface temperature.

For our blue planet, the index, naturally, is 1. For Mars, it is 0.64, but for some exoplanets it reaches 0.8. So, for the recently discovered Kepler-452b, this figure is 0.862.

Earth-like exoplanets, from left to right:
Earth, Kepler-186f, Kepler-62f, Kepler-452b, Kepler-69c, Kepler-22b

Is life possible on exoplanets?

Planets located outside the solar system and having characteristics close to those of Earth may have life. But it can be radically different from the earthly one. For example, consider the already mentioned Kepler-452b. This celestial body orbits the star Kepler-452, which is located in the constellation Cygnus and is 1,400 light years away from Earth. The age of the star is 6 billion years, that is, it is 1.5 billion years older than the Sun, exceeds it in brightness by 20% and is 10% larger in diameter.

As for Kepler-452b, this exoplanet has a diameter 1.6 times larger than Earth's. Its orbital period around the star is 385 days. It is assumed that there are active volcanoes on its surface, and the heat received from the star does not exclude the possibility of photosynthesis.

There are extremely many such cosmic bodies in the Universe. This leads to a very simple conclusion: life outside the solar system is possible. And since life is possible, it means that the existence of intelligence cannot be ruled out. But for now these are only assumptions and conjectures, but it is unknown when the moment of truth will come.

Yuri Syromyatnikov