Types of exoplanets. Exoplanet - what is it? How are exoplanets discovered and studied? What are exoplanets broad explanation

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 close to 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 is naturally equal to 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

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 the 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.

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.

On a clear night, when light interference is not a major factor, the sky looks spectacular with a huge number of stars open to view. But, of course, we can only see a small part of the stars that actually exist in our Galaxy. What's even more amazing is that most of them have their own planetary system. The question arises, how many exoplanets are there? There must be billions of extraterrestrial worlds in our Galaxy alone!

So let's assume that the eight planets that exist within the solar system represent the average. The next step is to multiply this number by the number of stars that exist within the Milky Way. The actual number of stars in our Galaxy is a matter of some debate. Essentially, astronomers are forced to make rough estimates because we cannot view the Milky Way from the outside. And given that it is in the shape of a barred spiral, the galactic disk is the most difficult to study due to the interference of light from its many stars. As a result, the estimate is based on calculations of the mass of our Galaxy, as well as the mass fraction of stars in it. From this data, scientists estimate that the Milky Way contains between 100 and 400 billion stars.

Thus, the Milky Way galaxy could have between 800 billion and 3.2 trillion planets. However, in order to determine how many of them are habitable, we must consider the number of exoplanets studied so far.

As of October 13, 2016, astronomers have confirmed the presence of 3,397 exoplanets out of 4,696 potential candidates that were discovered between 2009 and 2015. Some of these planets were observed directly through direct imaging. However, the vast majority have been discovered indirectly using transit and radial velocity methods.

The histogram shows the dynamics of exoplanet discovery by year. Credit: NASA Ames/W. Stenzel, Princeton/T. Morton

During its initial 4-year mission, the Kepler space telescope observed about 150,000 stars, which were mostly M-class stars, also known as red dwarfs. When Kepler entered a new phase of the K2 mission in November 2013, it shifted its focus to studying K- and G-class stars, which are almost as bright and hot as the Sun.

According to a recent study conducted by NASA Ames Research Center, Kepler found that about 24% of M-class stars may have potentially habitable planets comparable in size to Earth (those that are no more than 1. 6 times the radius of the Earth). Based on the number of M-class stars, there may be about 10 billion potentially habitable, Earth-like worlds in our Galaxy.

In addition, analysis of the K2 results suggests that about one quarter of large stars may also have Earth-like planets orbiting within habitable zones. Thus, it can be estimated that there are literally tens of billions of planets potentially suitable for the development of life in the Milky Way alone.

In the coming years, the James Webb and TESS space telescope missions will be able to detect smaller planets orbiting dim stars, and perhaps even determine whether any of them harbor life. Once these new missions get underway, we will have more accurate estimates of the size and number of planets that exist in our Galaxy. Until then, their estimated number is encouraging: the chances of extraterrestrial intelligence are very high!

The total number of exoplanets in the Milky Way galaxy is more than 100 billion. An exoplanet is a planet that is outside our solar system. Currently, scientists have discovered only a small fraction of them. About the 10 most incredible planets in this post.

The darkest exoplanet is the distant, Jupiter-sized gas giant TrES-2b.

Measurements have shown that planet TrES-2b reflects less than one percent of light, making it blacker than coal and naturally darker than any planet in the solar system. The work on this planet was published in the journal of the Royal Astronomical Society Monthly Notices. Planet TrES-2b reflects less light even than black acrylic paint, so it is truly a dark world.

TrES-4

The largest planet found in the Universe is TrES-4. It was discovered in 2006 and is located in the constellation Hercules. The planet, called TrES-4, orbits a star that is about 1,400 light-years away from planet Earth.

Researchers claim that the diameter of the discovered planet is almost 2 times (more precisely 1.7) larger than the diameter of Jupiter (this is the largest planet in the solar system). The temperature of TrES-4 is about 1260 degrees Celsius.

COROT-7b

A year on COROT-7b lasts just over 20 hours. It is not surprising that the weather in this world is, to put it mildly, exotic.

Astronomers have suggested that the planet consists of cast and solid rock, and not of frozen gases, which will certainly boil away under such conditions. The temperature, according to scientists, drops from +2000 C on the illuminated surface to -200 C on the night.

WASP-12b

Astronomers saw a cosmic cataclysm: a star was consuming its own planet, which was in close proximity to it. We are talking about the exoplanet WASP-12b. It was discovered in 2008.

WASP-12b, like most known exoplanets discovered by astronomers, is a large gaseous world. However, unlike most other exoplanets, WASP-12b orbits its star at a very close distance - just over 1.5 million kilometers (75 times closer than Earth to the Sun).

The vast world of WASP-12b has already stared into the face of its death, researchers say. The most important problem of the planet is its size. It has grown to such an extent that it cannot hold its matter against the gravitational forces of its native star. WASP-12b is giving up its matter to the star at a tremendous rate: six billion tons every second. In this case, the planet will be completely destroyed by the star in about ten million years. By cosmic standards, this is quite a bit.

Kepler-10b

Using a space telescope, astronomers were able to discover the smallest rocky exoplanet, with a diameter of about 1.4 times the diameter of Earth.

The new planet was designated Kepler-10b. The star it orbits is located about 560 light-years from Earth in the constellation Draco and is similar to our Sun. Belonging to the class of “super-Earths,” Kepler-10b is in an orbit quite close to its star, orbiting it in just 0.84 Earth days, while the temperature on it reaches several thousand degrees Celsius. Scientists estimate that with a diameter of 1.4 times the diameter of the Earth, Kepler-10b has a mass of 4.5 times the Earth's.

HD 189733b

HD 189733b is a Jupiter-sized planet orbiting its star 63 light-years away. And although this planet is similar in size to Jupiter, due to its proximity to its star, it is significantly hotter than the dominant gas giant of our solar system. As with other hot Jupiters found, the rotation of this planet is synchronized with its orbital motion - the planet always faces the star with one side. The orbital period is 2.2 Earth days.

Kepler-16b

Analysis of data on the Kepler-16 system showed that the exoplanet Kepler-16b, discovered in it in June 2011, orbits two stars at once. If an observer could find himself on the surface of the planet, he would see two suns rising and setting, just like on the planet Tatooine from the fantastic Star Wars saga.

In June 2011, scientists announced that the system contained a planet, which they designated Kepler-16b. After conducting a further detailed study, they found that Kepler-16b revolves around a binary star system in an orbit approximately equal to the orbit of Venus, and completes one revolution every 229 days.

Thanks to the joint efforts of amateur astronomers participating in the Planet Hunters project and professional astronomers, a planet was discovered in a four-star system. The planet orbits two stars, which in turn orbit two more stars.

PSR 1257 b and PSR 1257 c

2 planets orbit a dying star.

Kepler-36b and Kepler-36c

Exoplanets Kepler-36b and Kepler-36c - these new planets were discovered by the Kepler telescope. These unusual exoplanets are strikingly close to each other.

Astronomers have discovered a pair of neighboring explanets with different densities orbiting very close to each other. Exoplanets are too close to their star and are not in the so-called "habitable zone" of the star system, that is, the zone where liquid water can exist on the surface, but that is not what makes them interesting. Astronomers were surprised by the very close proximity of these two completely different planets: the orbits of the planets are as close as any other orbits of previously discovered planets.