Planets are similar to the earth. Is there life in the Universe: Earth-like planets. Exoplanet hunting

Created on 07/30/2012 12:03 PM

Is there anything living outside of our planet? Astronomers and dreamers have wondered this question since the dawn of mankind, and yet the mystery remains unsolved to this day. Are we the only life form in the universe, or are there beings similar to us hiding just outside the solar system? NASA launched a mission to find out the truth. In March 2009, the space agency launched the Kepler project, which aims to find planets that can support life. In just 16 months of operation, the Kepler telescope discovered 2,326 potential planets. If confirmed by subsequent studies, these possible discoveries could significantly increase the number of known exoplanets (planets outside the solar system), of which there are currently 702. Below are 10 images of these alien worlds.

Above, you can see an artistic depiction of the planet Kepler 22, which was the first exoplanet discovered by a telescope to orbit a star in a habitable zone. This means that Kepler 22 could have liquid water like Earth, making it the closest sibling planet. As NASA experts write, “the planet is 2.4 times more earth and it is the smallest exoplanet discovered so far, located in the center of the habitable zone of a star similar to our sun. "

Where the sun sets twice

Why are we looking for exoplanets like Kepler 22? Experts say that the future of humanity may depend on this. The search for a planet capable of supporting life could ensure the survival of people, as our planet could become a victim of an asteroid, solar flare or our own unreasonable attitude towards her. However, not all planets discovered by NASA are habitable. Above is an artistic depiction of Kepler 16, the most Tatooine-like planet ever discovered. This refers to her two suns, reminiscent of the home planet of Luke Skywalker from " Star Wars". Although the planet revolves around two suns, it is obviously unusually cold and has a surface of gas.

Where are we looking?

Our galaxy is very large, and it is difficult even to imagine that the Kepler telescope can explore every centimeter of the firmament. The device focuses on a large area, including the constellations Cygnus and Lyra. This area can be seen in the photo. Each triangle points to a separate area of ​​the sky that is being processed by the Kepler telescope photometer. The Earth makes it difficult to study all parts of the sky all year round, because the device is located above the plane of the ecliptic. Kepler can observe 100,000 stars at a time. The region of Swan and Lyra was chosen because of the abundance of stars similar to our sun. What is final goal? Find planets similar to Earth.

Exotic atmospheres

Kepler is not the only spacecraft working with exoplanets. An artistic image of the hot gas-filled planet HD 209458b can be seen here, as reported by the Hubble and Spitzer Telescopes. The spacecraft found that the planet's atmosphere contains molecules of methane, water vapor, and carbon dioxide. HD 209458b orbits a 3.5-day orbit around a sun-like star in the constellation Pegasus, 150 light-years away. It is uninhabited, but experts say that the presence organic molecules may indicate the presence of life on similar planets but with a rocky surface.

Extreme planets

Have you ever wondered what will become of our solar system when the sun completes its life cycle in about 5 billion years? Above is an artistic depiction of a pulsar planetary system. A pulsar is a rapidly rotating neutron star with a destroyed core from a dead star. This pulsar, called PSR B1257 + 12, was discovered in 1992 by astronomer Alexander Volschan. In the image, we see at least two Earth-sized planets orbiting this star. Most likely, the radiation from the pulsar generously "waters" the surface of these planets, causing rainbow auroras throughout the atmosphere. They may be part of the second generation of planets that formed after the deadly outburst of a dying star.

Rocks of the planet Kepler-10b

2011 was a record year for the Kepler project, as thousands of potential exoplanets were discovered then. Earlier that year, NASA announced the discovery of Kepler 10b, the smallest and most mountainous planet ever discovered. Although Kepler 10b is too hot for life, it has demonstrated that the Kepler mission is capable of getting closer to its primary goal of finding a planet to support life, like Earth. Above you can see an artistic image of Kepler-10b hot rocks, the temperature of which is supposed to be up to 1,400 degrees Celsius. This means that the surface is hotter than the flow of lava on Earth, and the temperature of the planet is enough to melt iron.

The Scorching World of Kepler-10b

it appearance Planet Kepler 10b by NASA artist. On it, the planet literally boils, apparently because it revolves around its star at a distance of 20 times closer than the orbit of Mercury in relation to our sun. How did NASA find planets like Kepler 10b? The telescope scans the brightness of over 100,000 stars every 30 minutes. It is measured by a built-in photometer. The device looks for tiny changes in the brightness of a star that happen when an exoplanet passes in front of it.

On a dark, dark night

For all its fame, Kepler-10b is not the hottest exoplent we have found. Above is the planet HD 149026b - "hot Jupiter" with a terrifying temperature of 2,000 degrees Celsius, which is three times hotter than our hottest planet Venus. How Hot Is It? So much so that, according to astronomers, the planet absorbs almost all the heat from its star and practically does not reflect light. This makes it the blackest, or darkest planet in the entire studied universe. The planet discovered by the Spitzer telescope is believed to be much colder on the dark side, which does not turn towards the star.

New world

Does a planet have to be exactly the same as Earth in order to support life? NASA experts are not sure. Above is an artistic depiction of a planet orbiting a star colder than our sun. These stars are called red and brown dwarfs. It's unclear if a cooler star can support young planets with the same chemical mix that gave birth to life on Earth. For a planet to support life, it must keep water below its boiling point, but above its freezing point. In addition, it should have enough air, but not too much. This precarious balance depends on the proximity of the planet to the star.

Future discoveries

Above is an artistic image of the two-star system HD 113766, where, as NASA experts hope, a rocky planet like Earth is forming at a distance of 424 light years. The brown ring of stones in the future will merge into a sphere, giving rise to a young planet. The age of the star is supposedly 10-16 million years, and this is exactly the period when planets begin to form. But can she

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

NASA's Kepler Orbiting Telescope has allowed scientists to look into the depths of the Universe that were previously inaccessible for study. Among the discoveries made with its 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 Earth, although its diameter is 60% larger than Earth's.

Scientists claim that this planet has more terrestrial features than other terrestrial counterparts previously discovered.

Such planets are of great interest to astronomers for the reason that they are compact and cool enough that water can be kept in a liquid state on their surface. This means that they can have conditions favorable to sustain life.

The Kepler-452 star system is located 1400 light-years from Earth in the constellation Cygnus.

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

The neighborhood is relative: at the maximum speed of removal from the solar system, reached today by any of the man-made spacecraft, it would take over 25 million years to reach this planet.

Exoplanet

The new planet has joined the list of exoplanets discovered by Kepler - celestial bodies that revolve, like the Earth, around their sun.

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

They are among the 4,175 planetary candidates identified with this telescope, excluding the current find. Until now, most of these candidates have subsequently received the status of proven exoplanets.

Image copyright Thinkstock Image caption Scientists have found thousands of exoplanets in space, but getting to them is not so easy

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

At the moment, 12 planets have been found in different star systems, presumably meeting 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 Earth than others depends largely on which characteristics are taken into account in the first place.

Image copyright NASA Image caption In the artist's imagination, Kepler-452b looks something like this

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

Kepler-452b orbits a star of 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 that its "year" or, more precisely, its orbital period is only 5% longer than that of the Earth.

The mass of the planet Kepler-452b is still impossible to measure, so astronomers have to rely on computer simulations to estimate various options for its approximate mass. It is most likely that Kepler-452b has a mass of about five times that of Earth.

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

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.

Image copyright Thinkstock Image caption Not all exoplanets, even of the "terrestrial" type, may be suitable for life

"If Kepler-452b is actually rocky, its location relative to the star means that it has entered the greenhouse phase of its climatic history," says Kepler scientist Doug Caldwell.

“The increasing energy release from this aging sun could heat the surface and vaporize any oceans. Water could evaporate and the planet could lose it forever," Caldwell says. The sun will get older and brighter. "

Super-earth

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

They really have no idea what this planet is made of. It could be a stone, or it could be 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 its surface is rocky, you need to measure the mass of the planet, and this is much more difficult to do, since they are too far away. to take such measurements. "

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

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

Image copyright Thinkstock Image caption So far, the Earth remains the only object in the Universe about which we can confidently say that it is possible to live here.

"In fact, at 1.6 Earth's diameter, Kepler-452b falls into a category called Super-Earth." Solar system there is not a single planet of this type. For this reason, super-earths are very interesting, but can we say that they are similar to the Earth? "Asks Dr. Chris Watson from Queen's University Belfast.

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

"So it could potentially be a rocky Super Earth in an orbit similar to Earth. It is this combination of star and orbit that makes this planet stand out, in my opinion," the scientist said in an interview with the BBC.

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

Search alien life people have been engaged for quite a long time. At first, these were only hypotheses, assumptions and conjectures, but as technical abilities improved, things began to move from the category of theoretical problems to the field of practice and scientific knowledge.

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

Luminary properties

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

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

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

Properties of planets

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

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

predominance in the composition of silicate rocks;

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

not too large eccentricity of the orbit, otherwise the planet will at times move too far from the star or come too close to it;

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

These and other parameters affect the climate on the planet's surface, geological processes in its bowels. It should be seen that the necessary conditions may differ for different living organisms. The possibility of encountering microbes in space is even higher than that of mammals.

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

Since the beginning of the century, a fairly huge number of objects have been discovered, in one way or another, suitable for life. True, it does not seem likely to answer the question of which planet is more similar to Earth than others, since this requires even more accurate data.

Controversial exoplanet

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

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

First confirmed

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

Characteristics of the planet:

• revolves around a G5 star with a period of 290 Earth days;
• mass - 34.92 earth;
• the composition of the surface is unknown;
• radius - 2.4 terrestrial;
• receives about 25% less energy from the star than the Earth from the Sun;
• the distance to the star is about 15% less than from the Sun to the Earth.

The shorter distance-to-energy ratio makes Kepler-22 b a candidate for habitable planet. If it is surrounded by a fairly dense atmosphere, the surface temperature can reach +22 ºС. At the same time, there is an assumption that the planet is similar in composition, rather, to Neptune.

Recent discoveries

The "newest" Earth-like planets were discovered this year, 2015. This is Kepler-442 b, located 1,120 light-years from the Sun. It is 1.3 times larger than the Earth and is located in the habitable zone of its star.

In the same year, the planet Kepler-438 b was discovered in the constellation Lyra (470 light years from Earth). It is also close in size to the Earth and is located in the habitable zone.

Finally, on July 23, 2015, the discovery of Kepler-452 b was announced. The planet is located in the habitable zone of a star, very similar to our star. It is about 63% larger than the Earth. The mass of Kepler-452 b is, according to scientists, 5 times the mass of our planet. Its age is also more - by 1.5 billion years. The surface temperature is estimated at -8 ºС.

The existence of these three planets has been confirmed. They are considered potentially habitable. However, it does not seem likely to confirm or deny their habitability.

The upcoming improvement of technology will allow astrologers to study these worlds in more detail, and, therefore, to answer the question of which planet is more similar to Earth.

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

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

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

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

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

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

Exoplanet hunting

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

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

Kepler, which has worked in orbit for four years, has discovered over 3,500 planets during this time, on which, in theory, life could exist. 647 of them are similar in size and mass to the Earth, and about 104 of them are located at such a distance from the star, which makes the possibility of the existence of water real.

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

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

Was Giordano Bruno right?

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

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

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

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

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

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

To knock on neighbors

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

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

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

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

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

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

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

Below we will consider five planets that best fit the description of the "twin of the Earth" based on their ESI scores.

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

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

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

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

Kepler 442b

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

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

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

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

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