Could Proxima Centauri b be habitable? Astronomers have found the closest Earth-like planet. It won’t be any closer Planet proxima b where it is

The red dwarf Proxima Centauri, which belongs to the Alpha Centauri star system and is located at a distance of 4.25 light years from us, has discovered the planet Proxima Centauri b, and liquid water and other conditions for supporting life may exist on it. Of the 3.5 thousand exoplanets that have been discovered outside the solar system since 1995, it is the closest to Earth.

Its mass is close to that of Earth, while its year is tens of times shorter. Despite the fact that it is separated from the star by only a few million kilometers, it is potentially suitable for the existence of life. The discovery was announced at a press conference by the European Southern Observatory in August 2016 in Germany.

The planet was discovered by the radial velocity method using the European Southern Observatory's HARPS spectrograph. A large body, revolving around a star, seems to rock it with its gravity - the star either slightly accelerates towards the earthly observer, or, on the contrary, moves away from him. At the same time, in the radiation of the star reaching astronomers, a Doppler shift of the spectrum is observed, which is different for the moments of approaching and moving away. By determining the period of such oscillations of a star, astronomers learn the periodicity of rotation and the minimum mass of the body influencing it with its gravity.

For the planet Proxima Centauri b, the rotation period around the star (year) is 11.2 days, and the minimum mass is 1.3 Earth masses. A year of 11.2 days means that the planet is closer to the center of the habitable zone. This is possible because Proxima Centauri is a red dwarf whose luminosity is 60 times less than the Sun. Therefore, all planets with a year lasting from 4 to 15 Earth days are potentially habitable there.

Proxima is a red dwarf with a surface temperature of 3,000 Kelvin (half that of the Sun), so the planets in its habitable zone are very close to it. Proxima Centauri b lies just 7 million kilometers from the star. Because of this, the gravity of the star has long ago achieved tidal locking - a state in which the rotation of the planet and star is synchronized by gravitational interaction (as in the Moon-Earth pair).

This means that the planet always faces the same side towards the sun, where eternal day reigns. In the other hemisphere, accordingly, there is eternal night. At the border of the illuminated and unlit zones of the planet, an equally eternal sunrise and sunset dominates. Previously, a number of researchers expressed doubts about the possibility of the existence of complex life in conditions that are unusual by our standards.

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Using telescopes from the European Southern Observatory (ESO), astronomers managed to make another amazing discovery. This time they discovered definitive evidence of the existence of an exoplanet orbiting the star closest to Earth, Proxima Centauri. The world, named Proxima Centauri b, has long been sought by scientists all over the Earth. Now, thanks to its discovery, it has been established that the period of its orbit around its native star (a year) is 11 Earth days, and the surface temperature of this exoplanet is suitable for the possibility of finding liquid water. This stone world itself is slightly larger than the Earth and, like the star, has become the closest to us of all such space objects. In addition, this is not just the closest exoplanet to Earth, it is also the closest world suitable for the existence of life.

Proxima Centauri is a red dwarf, and it is located at a distance of 4.25 light years from us. The star got its name for a reason - this is another confirmation of its proximity to Earth, since proxima is translated from Latin as “closest”. This star is located in the constellation Centauri, and its luminosity is so weak that it is completely impossible to notice with the naked eye, and besides, it is quite close to the much brighter pair of stars α Centauri AB.

During the first half of 2016, Proxima Centauri was regularly studied using the HARPS spectrograph mounted on the 3.6-meter telescope in Chile, as well as simultaneously with other telescopes from around the world. The star was studied as part of the Pale Red Dot campaign, during which scientists from the University of London studied the vibrations of the star caused by the presence of an unidentified exoplanet in its orbit. The name of this program is a direct reference to the famous image of the Earth from the distant reaches of the Solar System. Then Carl Sagan called this picture (blue speck). Since Proxima Centauri is a red dwarf, the name of the program was adjusted.

As this exoplanet search topic generated widespread public interest, the scientists' progress in this work was continuously published publicly from mid-January to April 2016 on the program's own website and through social media. These reports were accompanied by numerous articles written by experts from around the world.

“We received the first hints of the possibility of the existence of an exoplanet here, but our data then turned out to be inconclusive. Since then we have worked hard to improve our observations with the help of the European Observatory and other organizations. For example, the planning of this campaign took approximately two years,” Guilhem Anglada-Escudé, head of the research team.

Data from the Pale Red Dot campaign, combined with earlier observations from ESO and other observatories, showed a clear signal of the presence of an exoplanet. It has been very precisely established that from time to time Proxima Centauri approaches the Earth at a speed of 5 kilometers per hour, which is equal to normal human speed, and then moves away at the same speed. This regular cycle of changes in radial velocities repeats with a period of 11.2 days. Careful analysis of the resulting Doppler shifts indicated the presence of a planet with a mass at least 1.3 times that of Earth at a distance of 7 million kilometers from Proxima Centauri, just 5 percent of the distance from Earth to the Sun. In general, such detection has become technically possible only in the last 10 years. But, in fact, signals with even smaller amplitudes have been detected before. However, stars are not smooth balls of gas, and Proxima Centauri is a very active star. Therefore, accurately detecting Proxima Centauri b was only possible after obtaining a detailed description of how the star changes on time scales ranging from minutes to decades, and monitoring its luminosity with light-measuring telescopes.

“We continued to check the data to ensure that the signal we received did not contradict what we had discovered. This was done every day for another 60 days. After the first ten days we had confidence, after 20 days we realized that our signal was as expected, and after 30 days all the data categorically claimed the discovery of the exoplanet Proxima Centauri b, so we began to prepare articles on this event.”

Red dwarfs like Proxima Centauri are active stars and have many tricks up their sleeve to be able to mimic the presence of an exoplanet in their orbits. To eliminate this error, the researchers monitored changes in the star's brightness using the ASH2 telescope at the San Pedro de Atacami Observatory in Chile and the Las Cumbres Observatory telescope network. Information on radial velocities as the star's luminosity increased was excluded from the final analysis.

Despite the fact that Proxima Centauri b orbits much closer to its star than Mercury around the Sun, Proxima Centauri itself is much fainter than our star. As a result, the discovered exoplanet is located exactly in the region around the star suitable for the existence of life as we know it, and the estimated temperature of its surface allows the presence of liquid water. Despite this moderate orbit, conditions on its surface can be greatly influenced by ultraviolet radiation and X-ray flares from the star, which are much more intense than the effects that the Sun has on Earth.

The actual ability of this kind of planet to support liquid water and have Earth-like life is a matter of intense but mostly theoretical debate. The main arguments against the presence of life are related to the proximity of Proxima Centauri. For example, conditions can be created on Proxima Centauri b in which one side is always facing the star, causing eternal night on one half and eternal day on the other. The planet's atmosphere could also slowly evaporate or have a more complex chemistry than Earth's due to strong ultraviolet and X-ray radiation, especially during the first billion years of the star's life. However, so far not a single argument has been conclusively proven, and it is unlikely that they will be eliminated without direct observational evidence and obtaining accurate characteristics of the planet’s atmosphere.

Two separate papers were devoted to the habitability of Proxima Centauri b and its climate. It has been established that today the existence of liquid water on the planet cannot be ruled out, and in this case it can be present on the surface of the planet only in the sunniest regions, or in the region of the planet’s hemisphere, always facing the star (synchronous rotation), or in the tropical zone (3: 2 resonant rotation). Proxima Centauri b's rapid motion around the star, Proxima Centauri's intense radiation, and the history of the planet's formation have made its climate completely different from Earth's, and it is unlikely that Proxima Centauri b has seasons at all.

Either way, this discovery will be the beginning of large-scale further observations, both with current instruments and with the next generation of giant telescopes, such as the European Extremely Large Telescope (E-ELT). In subsequent years, Proxima Centauri b will become the main target for the search for life elsewhere in the Universe. This is quite symbolic, since the Alpha Centauri system was also chosen as the target of humanity's first attempt to move to another star system. The Breakthrough Starshot project is a research and engineering project within the Breakthrough Initiatives program to develop a concept for a fleet of light sail spacecraft called the StarChip. This type of spacecraft would be able to travel to the Alpha Centauri star system, 4.37 light-years from Earth, at between 20 and 15 percent of the speed of light, taking 20 to 30 years respectively, and about 4 more years to notify Earth of successful arrival.

In conclusion, I would like to note that many accurate methods for searching for exoplanets are based on the analysis of its passage across the disk of a star and starlight through its atmosphere. There is currently no evidence that Proxima Centauri b is passing across the disk of its parent star, and opportunities to see the event are currently negligible. However, scientists hope that the efficiency of observational instruments will increase in the future.

The closest exoplanet to our solar system, orbiting the star Proxima Centauri just 4.2 light-years from the Sun, is found to be habitable, according to extensive computer modeling. Such conclusions were made possible by the latest model calculations made on the basis of data already known about the planet Proxima b.

Artist's representation of the planet Proxima b with its star Proxima Centauri and its companion stars Alpha Centauri A and B in the background. Copyright: ESO/M. Kornmesser

A team of researchers led by Anthony Del Genio of NASA's Goddard Institute for Space Studies wrote in a new issue of the journal Astrobiology, based on estimates from computer models used to simulate climate change on Earth, but with data known about Proxima Centauri b.

Modeling results show that Proxima b, even under various scenarios, may have large volumes of liquid water on its surface, which is why the likelihood of life on this planet increases significantly. “The key result of our comprehensive modeling is that the probability of the planet being suitable for life is indeed extremely high,” says Del Genio.

Proxima Centauri itself is a cool red dwarf star located 4.2 light-years from the Sun. And although it is located so close to our solar system, astronomers still know too little about the system surrounding this red dwarf. And even the first, and so far the only known planet of this star (Proxima Centauri b), was discovered only in 2016. Proxima b is 1.3 times the size of Earth, and it completes one revolution around its star in just 11 days.

“We assume that the planet has an atmosphere and oceans on the surface, while it orbits its star within its habitable zone,” the researchers say. “This allows the planet to receive enough light to keep surface temperatures above the freezing point of water.” But since the planet revolves around its star at a fairly close distance, it cannot be ruled out that between them there is the same connection as the Earth and the Moon, that is, the planet remains constantly turned to the star with only one side.

While earlier models suggested that only the star-facing side of the planet heats up, while the oceans freeze on the other side, Del Genio also did not rule out the possibility of such a thawed eyeball-shaped hemisphere facing the star, suitable for life - the so-called “eyeball planet”.

This is how the artist sees the “eyeball planet.” Copyright: NASA/JPL-Caltech

The complexity of the new simulations surpassed all previous model calculations, and they also included data on the dynamics of ocean and atmospheric circulation, through which global heat is distributed.

Given this state of affairs, it is quite possible to assume that although the side turned away from the luminary never sees the “sun’s rays,” a strip of liquid water stretches along the equator around the entire planet. Something similar is observed on our Earth, where, thanks to the Gulf Stream, the East Coast of the United States is always much warmer than it would have been without this warm current from the tropics.

In total, Del Genio's team carefully tested 18 potential planetary scenarios that included the effects of large continents, thin atmospheres, different atmospheric compositions, and even the effects of different salt concentrations in the proposed ocean.

And almost all of these options showed that at least parts of this planet must remain warm enough for liquid water and oceans to persist on the surface. “The larger the surface of potentially liquid water, the greater the likelihood that with the help of telescopes of future generations we will be able to discern life there,” Del Genio finally dreamed.

Perhaps we have found a second Earth?

A planet, possibly suitable for life, has been discovered near the star closest to the Sun; the imagination already pictures a dense atmosphere and oceans on it.

The discovered planet, named Proxima b, has an almost circular orbit, separated from the star by approximately 7.6 million kilometers (0.05 astronomical units, that is, the average distance of the Earth from the Sun). A year in this world lasts only 11 days, the mass of the planet is 1.3 times greater than that of Earth, and the average surface temperature is close to zero degrees Celsius - this is only ten degrees lower than that of Earth and several tens of degrees higher than that of Mars .

By cosmic standards, Proxima Centauri is very close - only 4.24 light years away.

The parent star Proxima Centauri itself, which is characterized by strong ultraviolet and X-ray flares, can prevent the emergence of this paradise. This is described in a study published in the journal Nature.

Computer modeling has long told astronomers that our neighbor has at least one planet, and exoplanets are mostly found around red dwarfs.

Opening Proxima b was accomplished by observing the Doppler shift of the star's spectrum due to the gravitational influence of the planet. The work was performed on two scientific instruments of the European Southern Observatory - HARPS (High Accuracy Radial velocity Planet Searcher) and UVES (Ultraviolet and Visual Echelle Spectrograph).

Despite the seemingly catastrophic proximity to the star, this world can be very good from the point of view of supporting life, because they are cold stars.

Proxima Centauri's surface temperature is more than twice (almost three thousand kelvins), its mass is ten times, and its luminosity is four orders of magnitude less than that of the Sun.

And in order for the water on the surface of the planet not to freeze, it must be much closer to its star than the Earth is to the Sun.

In the Solar System, Venus, Earth and Mars are located in a similar zone, and the distance range for the Proxima Centauri system is from 0.04 to 0.08 astronomical units. It would seem that everything speaks in favor of the emergence of life, but there is one unpleasant moment that can cancel out all the advantages.

A distinctive feature of red dwarfs is their high activity. X-ray flares that periodically occur on Proxima Centauri are about 400 times stronger than the most intense flare on the Sun. How such radiation will affect the emergence and maintenance of life is unknown. Perhaps such a superflare can generate a chain of chemical reactions with the formation of molecules of organic substances, but, on the other hand, it can “rip” the atmosphere from the planet. Possess planet Proxima b, like the Earth, by its own magnetic field, the harmful effects of radiation would be reduced, but its presence could not be detected remotely.

As a result of the most powerful solar flares, up to a trillion megatons of TNT are released into the surrounding space in a few minutes. This is about a fifth of the energy emitted by the Sun in one second, and all the energy that a person would produce in a million years (assuming it was produced at modern rates). Superflares occur, as a rule, on larger stars of spectral classes F8-G8 - massive analogues of the Sun (belonging to the G2 class). These luminaries usually do not rotate quickly around their axis and may be part of a close binary system. The power of superflares exceeds typical solar flares by tens of thousands of times, however, scientists do not exclude the possibility of such a cataclysm on the Sun.

Besides, planet Proxima b due to its proximity to the star, one side is always turned towards it, that is, it is in a state of tidal locking, like the Moon in relation to the Earth. This means that one half of the planet is constantly warm, and the other is always cold. Modeling has shown that this will not be an insurmountable obstacle to the existence of life, provided there is a dense atmosphere. Constant convective currents will ensure heat exchange between the halves of the planet and a comfortable temperature can be established in the “border zone”.

Most likely, such a large planet formed in remote areas of the system and, over time, moved to its current position. Looking at the solar system, we can say that this celestial body contains a large amount of water.

Proxima Centauri is likely part of a triple star system, which also includes the double star Alpha Centauri, the stars in it are separated by only 23 astronomical units. The red dwarf's orbital period around two Sun-like stars is more than 500 thousand years.

Flight to Alpha Centauri

Astrophysicist Philip Lubin (University of California at Santa Barbara) proposed sending a group of small automatic stations with . A system of lasers in Earth orbit will accelerate them to near light speed. A similar idea was proposed by Russian businessman Yuri Milner and British theoretical physicist Stephen Hawking.

The plans for both missions include only flying through the system, because it will be impossible to slow down.

Difficulties in implementing the project are related to its technical component and price. To implement Lyubin’s project, it will be necessary to deploy a constellation in Earth orbit that is a hundred times larger in mass than the ISS. It would take the miniature probe 15 years to reach Alpha Centauri and send back a few photos, but the cost would be tens of trillions of dollars.

A modern spacecraft could do this much cheaper, but it would take 70 thousand years.

Lubin's idea was supported by Congressman John Culberson, who called on NASA to begin work on an automatic mission to Alpha Centauri as early as 2017. According to the Republican's plans, the station should launch in 2069 - the centenary of the astronaut landing on the Moon. The Milner-Hawking team also did not stand aside. At an event dedicated to the discovery of Proxima b, it was stated that the Russian businessman planned to send probes to the mother star and planet as early as 2030. The devices should reach the goal in 20 years. The first images of the closest exoplanetary system on Earth will be seen in 2055.

The ideas of scientists and politicians were met with skepticism by most of their colleagues, and the remote study of Proxima b remains in the foreground. Problems with observation from Earth and from near space may arise due to the low luminosity and modest size of Proxima Centauri.

The open world's proximity to the Sun makes it a prime target for future exploration. In addition, there is likely a super-Earth in orbit around Proxima Centauri, located outside the zone suitable for life. The period of its revolution around the star ranges from 100 to 400 days.

After several years of studying Proxima Centauri, astronomers have finally found evidence that this star has a planet, and one very similar to Earth: only slightly larger in size. In addition, the planet’s orbit is located in the habitable zone of the star, that is, liquid water can exist on its surface.

The modern public is no longer surprised by reports of the discovery of exoplanets. Thanks to the advent of effective detection methods and devices such as the Kepler space telescope, the number of recorded escoplanets goes into the thousands. Of interest are the discoveries of terrestrial exoplanets and exoplanets in star systems located near the solar system. The current news, reported by the European Southern Observatory, satisfies both conditions at once. A new Earth-like planet is so close to Earth that it couldn’t be closer.

The discovered planet was named Proxima b. It orbits Proxima Centauri, a red dwarf star that is one of the three components of Alpha Centauri. The distance to Earth from Proxima Centauri is 4.25 light years; there are no stars that are even closer. The previous record for planets where life is possible was 11.7 light years. It belonged to the planet Wolf 1061c in the constellation Ophiuchus.

The discovery was first reported by journalists from the German weekly Der Spiegel in early August, citing an anonymous source. Astronomers were in no hurry to confirm this news. However, earlier this week the European Southern Observatory announced and on August 24 held a press conference at which scientists revealed details about Proxima b. The results of their work are also reflected in an article published in the journal Nature.

Scientists made observations of Proxima Centauri using the High Accuracy Radial velocity Planet Searcher (HARPS) installed at the La Silla Observatory in Chile on the instrument's 3.6-meter telescope. In 2012, with its help, they discovered a planet that orbits another component of the triple star, Alpha Centauri B, although the existence of this planet is now called into question.

To detect exoplanets, HARPS uses spectrometric measurements of the radial velocities of stars (“Doppler method”). It allows you to record signs of the movement of a star. Because if a star has a planet or several planets, they rotate around a common center of mass, then the movements of the star make it possible to calculate the planet invisible to us. Usually, for this effect to be noticeable, the star must have several planets or one, but very large planet (for example, the so-called “Super-Jupiter”). If we are talking about terrestrial planets, then their influence on the position of the star will be insignificant. The common center of mass of the star-planet system in this case will most likely be inside the star, so it will begin to make only small oscillations. But the proximity of Proxima Centauri to Earth made it possible to track them too.

Scientists observed signs of the planet Proxima b for 60 consecutive nights starting in January 2016. According to their calculations, the mass of this planet is only 1.3 times the mass of the Earth, and it orbits its star with a period of 11.2 days. Proxima b is located very close to the star, at a distance of only 5% of the distance from Earth to the Sun. But there is a chance that the surface of this planet still does not look like a hot desert. The fact is that Proxima Centauri is not a very bright star. According to calculations, Proxima b receives only 65% ​​of the energy that the Earth receives from the Sun. So liquid water can actually exist on its surface. “There is a reasonable suspicion that this planet may be capable of harboring life,” says co-author Guillem Anglada-Escudé of Queen Mary University of London.

But it’s still unlikely that conditions on Proxima b are particularly favorable for life. The force of gravity most likely oriented it so that one hemisphere always faces Proxima Centauri, and the other in the opposite direction, similar to how the Moon is rotated in relation to the Earth. As a result, it is constant day on one half of the planet and night on the other, and the temperature difference between them is enormous. So far, rough calculations show that the average temperature on Proxima b should be –40°C, but if it has an atmosphere, then this figure will be higher. By comparison, on Earth, without an atmosphere or oceans, the average surface temperature would be between –20°C and –30°C.

Due to its proximity to Proxima Centauri, the planet receives 100 times more high-energy radiation (in the ultraviolet and X-rays) than Earth. This factor is also not conducive to the presence of life. Complicating the situation is the fact that Prxima Centauri is a flare-up variable star, and during flares its luminosity can increase several times. A magnetic field can serve as protection against high-energy particles, but we do not know whether the planet Proxima b has one.

In addition to discussions about the possibility of water and life on Proxima b, which still seem somewhat premature, other mysteries are associated with the new planet. For example, the very formation of a rocky planet at such a short distance from a star seems unlikely. According to the assumption made by Guillem Anglada-Escudé, Proxima b could have formed in another place, further from the star, and then, for reasons that are still unclear, moved to a closer orbit. If this is true, then the presence of water on the planet becomes more likely.

Now astronomers began to try to record the passages of Proxima b against the background of the stellar disk of Proxima Centauri. Observing such passages will allow them to more accurately determine the size and mass of the planet, and therefore calculate its density, testing the hypothesis that it is a rocky planet and not a gas planet. Starlight passing through Proxima b's atmosphere will allow scientists to learn what gases are included in its composition. But the chances of observing such passages in the conditions of Proxima Centauri are slim. Therefore, the main hope is placed on the James Webb and TESS (Transiting Exoplanet Survey Satellite) space telescopes, which are still planning to be launched.