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 in the case of 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 larger than Earth's only 1.4 times, 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 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 index of 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 exoplanet has an approximate mass of 3.8 times that of Earth, but 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 allow us 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 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 times 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 sizes and surface temperatures from Earth. However, given the increased activity in recent years 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.
Humanity has long hoped to find a planet similar to our own in the sky. The first planet outside our solar system was
discovered back in 2009. However, according to all the characteristics available to us, it is completely unsuitable for the origin of life. There was a need for
apparatus that could constantly observe the starry sky, analyzing all changes. In addition, it was necessary to provide this device with the ability
constantly observe one section of the sky, which is impossible to do from the surface of the earth. All this led to the launch of the Kepler space telescope in 2009,
who should look for exoplanets.
Goals
The spacecraft launched by NASA was named Kepler. The planet, for the search of which it was created, can be located at any distance from our system.
Therefore, the transit method is used to search for exoplanets. It consists in observing a small area of the sky and measuring the brightness of the stars. When past the star
the planet passes, the brightness decreases slightly. It is on this basis that one can find out whether a luminary has a planetary type body. To set the period
circulation and number of planets, it is necessary to observe the star for at least three years. Only after this it can be argued that the brightness of the star decreases precisely by
the reason for the passing of an exoplanet.
In addition, there may not be so few planets on which life can be formed or once already formed. That is why Kepler has been operating for so many years and there is no need to stop this project at the present time.
Achievements
To date, through Kepler, more than 4 hundred exoplanets have been discovered. All newly discovered ones are given the names of the telescope, with the assignment of a serial number and a letter. The letter shows how many planets the star has.
Of the hundreds that have been discovered, several may well be habitable, Kepler showed. Planet 186f, for example, was at one time seriously considered the "twin" of the Earth. but
at the present time we cannot be sure of the real suitability of all discovered planets. After all, among other things, in order to be able to assert,
what is suitable for life, it is necessary to study the many that are really suitable. We have the opportunity to study only one planet, for sure
suitable for life - the Earth. This amount of material is extremely small. But based on known facts, scientists believe that for the emergence of any life
liquid water is required. This parameter made it possible to introduce such a concept as the "habitable zone" - there are planets on which, thanks to
favorable distance from the star, there may be liquid water. In this zone, the water has a chance not to evaporate or freeze. The presence of liquid also depends on the brightness
stars, and from the remoteness of the planet itself from the star.
Second earth
What needs to be further clarified in order to claim that Kepler has been discovered, be that as it may, we cannot give such information
maybe. It was created only to detect the very presence of an exoplanet. However, we know for sure that the characteristics of the planet can be completely different.
For example, even a discovered gas giant cannot be a guarantee that there is no water on it. After all, he may well have a companion with a suitable atmosphere.
Many factors are responsible for the likelihood of the emergence of life known to us: the presence of satellites, distance from the star, the activity of the star, the presence of an unstable
stars in the neighborhood, giant planets in a star system. Based on the data known to us, scientists suggest that life can arise, first of all, on those
planets that are as similar as possible to our own - revolving around a sun-like star in a similar orbit, having a similar mass, age,
radius and other parameters. Such a multitude of requirements for a "second Earth" leads to the fact that the discovery of planets that are similar to Earth, causes violent emotions
scientists and ordinary people. Currently, two exoplanets have been discovered that require more close attention, since they may well be the ones for which the Kepler astronomical satellite was created. Planet 186F and 452b.
Kepler 186f
186f Kepler - The planet was discovered in April 2014. Despite the considerable distance, it was possible to find out quite a lot about it: it revolves around a red dwarf with a periodicity of 130 Earth days, 10% larger than the Earth. It rotates in an orbit along the outer edge of the habitable zone. The astrophysicists' statement was greeted with enthusiasm, and there and then many ordinary people and even quite respected publications began to assume the appearance of the planet, its characteristics and the bonuses that the Earth could receive from such a "sister". However, over time, scientists have managed to bring the visionaries back to reality.
In order to say exactly how likely life is on the planet, you need to have much more data. For example, you need to find out the presence
atmosphere, its composition, composition and nature of the planet itself, surface temperature and many other characteristics. We do not currently have the equipment
capable of finding out all the factors of interest to us at such a huge distance. However, in the 2020s, it is planned to launch a similar mechanism into orbit,
for a detailed study of exoplanets.
How long is the 186f flight to Kepler? Well, she is practically next to us - before she is only some 400
Kepler 452b
Located a little further from us - at a distance of 1400 light years. The star around which this likely "twin" of the Earth revolves is similar to our Sun.
Kepler 452b's orbit is almost identical to Earth's. A day is equal to our 385 days. much larger than the Earth - the radius is 60% larger. Thus,
if the density of this planet is the same as that of the Earth, then it will weigh 4 times more, which will lead to greater gravity - 1.5 times. The age of the star system, in
which "lives" the planet of interest to us, 6 billion years, against 4.5 - the age of our Sun.
Could there be life on this planet? Maybe. But it may not be. Until accurate and modern equipment appears that will allow the study of the planets,
located at such huge distances, we will not be able to say exactly what this and others are, we will not be able to see a photo of the planet Kepler 452b and others like it.
Even Giordano Bruno believed that planets should exist around the stars. But the first exoplanet was discovered only in October 1995. It was then that astronomers Michel Mayor and Didier Kelos noticed the "wiggle" of the star. The wobble planet is close in mass to Jupiter, but much closer to its star. In honor of the 20th anniversary of the discovery of 51 Pegasus b, employees have compiled a list of 20 of the most amazing exoplanets.
Kepler-186 f
NASA Ames / SETI Institute / JPL-Caltech
Kepler-186 f is the first terrestrial exoplanet discovered in the habitable zone of a sun-like star. It is likely that the Kepler-186 f contains liquid water. The size of the alien planet resembles the Earth.
“So far we know only one planet on which life exists - this is the Earth. If we want to find life outside the solar system, we need to focus our observations on terrestrial planets. The fact that we have found an exoplanet resembling Earth in size and located in a habitable zone is a big step forward, "commented the discovery of Kepler-186 f, Eliza Quintana from the project on the search for extraterrestrial civilizations and possible contact with them, working at the research center. NASA named after Ames.
HD 209458 b
NASA, European Space Agency, Alfred Vidal-Madjar (Institut d'Astrophysique de Paris, CNRS)
HD 209458 b, also known as Osiris, is the first exoplanet to be discovered due to a slight decrease in star brightness caused by the planet's passage through its disk (transit). Thanks to these observations, scientists were able to determine the characteristics of HD 209458 b and began to apply this method to measure the parameters of other planets.
Scientists have noticed that due to the extremely small distance to the star, HD 209458 b is gradually evaporating under the influence of heat and stellar wind. For this reason, this exoplanet received the second name Osiris (an allusion to the ancient Egyptian myth, in which Set cut the body of his brother Osiris into pieces so that he could not return to life).
Planets of the star Kepler-11
NASA / JPL-Caltech
The six exoplanets orbiting the star Kepler-11 are the first planetary system detected by the NASA space observatory by the transit method. Scientists have found that the orbits of all six planets are very close to each other - so the orbits of the first five planets could fit inside the orbit of Mercury.
Thanks to the discovery of exoplanets in the star Kepler-11, astronomers realized that small planetary systems like ours could be common.
NASA / JPL-Caltech
Kepler-16 b is the first exoplanet found in a binary star. The planet is also unusual in that its orbit is less than the radius, which was considered the inner boundary for the formation of planets in the double star system.
Kepler-16 b is often compared to Tatooine, a Star Wars desert planet that also revolves around a binary star. In the epic, Tatooine was a gathering place for smugglers and gangsters of all stripes.
NASA / JPL-Caltech
51 Pegasus b is the very first exoplanet discovered. 51 Pegasus b has a nickname - "Bellerophon", received in honor of the ancient Greek hero who tamed the horse of Pegasus (an allusion to the constellation Pegasus, in which the exoplanet's parent star is located).
CoRoT 7 b
ESO / L. Calçada
CoRoT 7 b is the first rocky exoplanet to be discovered. Super-Earths include planets whose mass exceeds the mass of the Earth, but much less than the mass of gas giants - large planets with a low density and a short period of daily rotation (in the solar system, such planets include Jupiter, Saturn, Uranus and Neptune).
The discovery of CoRoT 7 b showed that outside our system there are planets that resemble Earth in characteristics. It is possible that some super-earths will be inhabited.
NASA / Ames / JPL-Caltech
According to scientists from NASA, Kepler-22 b is an exoplanet that has no analogues in our solar system. The gas giant is in the habitable zone, and there may be water on its surface. The radius of Kepler-22 b is 2.4 times the radius of the Earth. Astronomers do not exclude that life may exist on the exoplanet.
NASA / Kepler Mission / Dana Berry
Kepler-10 b is one of the smallest exoplanets, as well as the first known "iron exoplanet", consisting primarily of an iron-rich core followed by a thin layer of the mantle, or without a mantle.
Scientists believe there may be an ocean of lava on the surface of Kepler-10 b.
Planets of the star Kepler-444
Tiago Campante / Peter Devine
Kepler-444 and the planets orbiting it are the oldest known system of planets similar to Earth. This system is about twice as old as the Solar system. According to scientists, to form almost immediately after the Big Bang.
When the Sun was first born, the Kepler-444 system was already older than our solar system is now.
55 Cancer e
NASA / JPL-Caltech
55 Cancer e is a super-earth that orbits its star in 17 hours 41 minutes. The planet is 8 times heavier than the Earth and is located closer to the star than Mercury is located to the Sun. When rotating 55 Cancer e is always turned to its "sun" with only one side.
Astronomers say that 55 Cancer e is the first rocky exoplanet to experience sudden temperature changes. The planet's surface is most likely anhydrous.
HD 189733 b
NASA / ESA / G. Bacon (STScI)
HD 189733 b is one of the most studied exoplanets. It is close in size to Jupiter and belongs to the class. It was for HD 189733 b that the surface temperature map was first compiled.
HD 189733 b is one of the hottest exoplanets discovered to date.
PSR B1257 + 12 system
NASA / JPL-Caltech
PSR B1257 + 12 is surprising in that the planets in this system revolve around a neutron star - stellar remnants that are the result of the gravitational collapse of a massive star during a supernova explosion. The PSR B1257 + 12 system proves that planets can be found anywhere - even around the "debris" of a star.
Planets of the star K2-3
ESO / M. Kornmesser / Nick Risinger / L. Calcada
K2-3 is a red dwarf star around which three super-earth planets revolve. Scientists from NASA believe that the conditions on these exoplanets may be suitable for the existence of life.
Planets of the star HR 8799
NRC-HIA, Christian Marois, Keck Observatory
HR 8799 is the first star in which several exoplanets have been discovered at once by direct observation. At least three planets revolve around the star. The orbits of the distant planets HR 8799 are within the protoplanetary disk - the circumstellar disk, from which the planets are subsequently formed. It is one of the most massive discs discovered around a star within 300 sv. years from us.
Planets of the star Kepler-36
The two planets orbiting the star Kepler-36 have the largest orbits recorded to date. Moreover, their orbits are located abnormally close to each other.
It is likely that Kepler-36 is a subgiant - a star whose core has run out of hydrogen fuel.
NASA / JPL-Caltech
HD 114762 b was discovered back in 1989 - 6 years before the discovery of the first "official" exoplanet. But the object was considered a brown dwarf - an infrared star with a mass less than 8% of the mass of the Sun, in the depths of which thermonuclear combustion of ordinary hydrogen is impossible.
NASA / Ames / JPL-Caltech
Kepler-452 b is an exoplanet sometimes referred to as "Earth 2.0" due to its resemblance to Earth. Kepler-452 b is the first near-Earth planet found in the habitable zone of a Sun-like G2 star.
According to scientists, "Earth's twin" is included in the list of potentially viable exoplanets.
NASA / JPL-Caltech / UCSC
Astrophysicists believe that HD 80606 b "is not shy about his emotions" - storms constantly arise on it and strong winds blow.
The exoplanet is located in the constellation Ursa Major and revolves around its star in 111 days in a highly elongated orbit.
Planets of the star WASP-47
NASA / JPL-Caltech
The planetary system WASP-47 is unique in that only it contains "hot Jupiter" with planetary companions located close to it.
Planet of the star OGLE-2005-BLG-390
NASA, ESA and G. Bacon (STScI)
The planet of the star OGLE-2005-BLG-390 is considered by scientists as the first super-earth, consisting mainly of ice.
An exoplanet orbits its parent star in 3,500 days.
Sources:
- 20 Intriguing Exoplanets
- 20 Intriguing Exoplanets - Part 2 // NASA Jet Propulsion Laboratory
Illustration: NASA Ames / SETI Institute / JPL-CalTech
This week it became known about the discovery of a planet similar in climate and structure to the Earth. Slightly larger, somewhat colder, and located in our galaxy 500 light-years from Earth. Its diameter is approximately 14,000 kilometers, which is only 10% larger than the Earth. This name Kepler 186f received from the name of the Kepler orbiting telescope, with which the planet was discovered.
Kepler 186f lies within the Goldilocks zone (zone of life) of its star. And this means that on this planet there may be liquid water - the basis for life.
It is difficult to study Kepler 186f in more detail, since the mass is small, and the planet is too close to its star. Finding it is already a great success.
Kepler 186f is located in the constellation Cygnus in the Kepler186 system.
Constellation Cygnus. Astrobobo / Astrobobo
The letter "f" denotes the order of location from the star, that is, it is 5 in a row. On four other planets, temperatures are too high for life. But the last, fifth planet, has almost ideal conditions, similar to the Earth.
Researchers believe Kepler 186f is composed of iron, rock, ice, liquid water, but the relative amounts may differ from those on Earth.
Kepler 186f makes one complete revolution around the star not in 365 days, like the Earth, but in 130 days. In addition, the outer edge of the habitable zone receives less heat, so it is possible that this surface will freeze.
Because of its greater mass, Kepler 186f likely has a denser atmosphere. This makes it possible for the planet to absorb energy from its star more efficiently, avoiding freezing.
Astronomers can't tell the exact age of a star, but dwarfs like Kepler 186 are the longest-lived stars in the universe. If Kepler 186f is inhabited, life could have appeared there billions of years ago.
However, such dwarfs are the most common types of stars in the galaxy. Astronomers hope that Earth's twins are numerous, and that some of them are close enough to determine the temperature, mass, and composition of the atmosphere.
* Video playback is available with Russian subtitles
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 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 to hold water 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.
Lead scientist on this NASA project, John Grunsfeld, presenting this discovery, called the planet Kepler-452b so far the most similar to Earth.
The neighborhood is relative: with the maximum speed of removal from the solar system, achieved by any of the man-made spacecraft today, it would take more than 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 easyA small part of these planets are not much larger than 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 thisSmaller 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 not yet measurable, 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 two times greater than 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 in relation 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,” says the scientist. “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 in diameter than Earth, and Kepler-438b is about 1.12 of Earth's diameter." , - 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 you can live here"In fact, with a diameter of 1.6 Earth's Kepler-452b falls into the category called 'Super-Earth'. There is not a single planet of this type in our solar system. For this reason, super-Earths are very interesting, but can we say that they are similar to Earth? " asks Dr. Chris Watson of Queen's University Belfast.
"If we look at the type of star that Kepler-452b orbits 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 orbit 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.
