Egzoplanetya

Nathalie Bataglia of NASA's Ames Research Center, one of the world's foremost planet hunters, recently said in an interview that exoplanet discoveries have changed the way we see the universe. “We look at the sky and see not only stars, but also solar systems, because now we know that at least one planet revolves around every star,” she admitted.

from recent years, it can be said that they perfectly illustrate human nature, in which satisfying curiosity gives joy and satisfaction only for a moment. Because soon there are new questions and problems that need to be overcome in order to get new answers. 3,5 thousand planets and the belief that such bodies are common in space? So what if we know this, if we don't know what these distant objects are made of? Do they have an atmosphere, and if so, can you breathe it? Are they habitable, and if so, is there life in them?

Seven planets with potentially liquid water

One of the news of the year is the discovery by NASA and the European Southern Observatory (ESO) of the TRAPPIST-1 star system, in which as many as seven terrestrial planets were counted. In addition, on a cosmic scale, the system is relatively close, only 40 light-years away.

The history of the discovery of planets around a star TRAPPIST-1 it dates back to the end of 2015. Then, thanks to observations with the Belgian TRAPPIST Robotic Telescope Three planets were discovered at the La Silla Observatory in Chile. This was announced in May 2016 and research has continued. A strong impetus for further searches was given by observations of a triple transit of planets (i.e., their passage against the background of the Sun) on December 11, 2015, made using telescope VLT at the Paranal Observatory. The search for other planets has been successful - it was recently announced that there are seven planets in the system similar in size to Earth, and some of them may contain oceans of liquid water (1).

1. Recording observations of the TRAPPIST-1 system through the Spitzer telescope

The star TRAPPIST-1 is much smaller than our Sun - only 8% of its mass and 11% of its diameter. All . Orbital periods, respectively: 1,51 days / 2,42 / 4,05 / 6,10 / 9,20 / 12,35 and approximately 14-25 days (2).

2. Seven exoplanets of the TRAPPIST-1 system

Calculations for hypothesized climate models show that the best conditions for existence are found on the planets. TRAPPIST-1 e, f Oraz g. The nearest planets appear to be too warm, and the outermost planets appear to be too cold. However, it cannot be ruled out that in the case of planets b, c, d, water occurs on small fragments of the surface, just as it could exist on planet h - if there were some additional heating mechanism.

It is likely that the TRAPPIST-1 planets will become the subject of intensive research in the coming years, when work begins, such as James Webb Space Telescope (successor Hubble Space Telescope) or being built by ESO E-ELT telescope nearly 40 m in diameter. Scientists will want to test whether these planets have an atmosphere around them and look for signs of water on them.

Although as many as three planets are located in the so-called environment around the star TRAPPIST-1, but the chances that they will be hospitable places are rather small. This very crowded place. The farthest planet in the system is six times closer to its star than Mercury is to the Sun. in terms of dimensions than a quartet (Mercury, Venus, Earth and Mars). However, it is more interesting in terms of density.

Planet f - the middle of the ecosphere - has a density of only 60% of that of the Earth, while planet c is as much as 16% denser than the Earth. All of them, most likely, stone planets. At the same time, these data should not be overly influenced in the context of life-friendliness. Looking at these criteria, one might think, for example, that Venus should be a better candidate for life and colonization than Mars. Meanwhile, Mars is much more promising for many reasons.

So how does everything we know affect the chances of life on TRAPPIST-1? Well, naysayers rate them as lame anyway.

Stars smaller than the Sun have longevity, which gives enough time for life to develop. Unfortunately, they are also more capricious - the solar wind is stronger in such systems, and potentially lethal flares tend to be more frequent and more intense.

Moreover, they are cooler stars, so their habitats are very, very close to them. Therefore, the likelihood that a planet located in such a place will be regularly depleted of life is very high. It will also be difficult for him to maintain the atmosphere. The earth maintains its delicate shell thanks to the magnetic field, a magnetic field is due to rotational motion (although some have different theories, see below). Unfortunately, the system around TRAPPIST-1 is so "packed" that it is likely that all the planets always face the same side of the star, just as we always see one side of the Moon. True, some of these planets originated somewhere further from their star, having formed their atmosphere in advance and then approached the star. Even then, they are likely to be devoid of atmosphere in a short time.

But what about these red dwarfs?

Before we were crazy about the "seven sisters" of TRAPPIST-1, we were crazy about an Earth-like planet in the immediate vicinity of the solar system. Accurate radial velocity measurements made it possible to detect in 2016 an Earth-like planet called Proxima Centauri b (3), orbiting Proxima Centauri in the ecosphere.

3. Fantasy on the surface of the planet Proxima Centauri b

Observations using more precise measurement devices, such as the planned James Webb Space Telescope, are likely to characterize the planet. However, since Proxima Centauri is a red dwarf and a fiery star, the possibility of life on a planet orbiting it remains debatable (regardless of its proximity to Earth, it has even been proposed as a target for interstellar flight). Concern about flares naturally leads to the question of whether the planet has a magnetic field, like Earth, that protects it. For many years, many scientists believed that the creation of such magnetic fields was impossible on planets like Proxima b, since synchronous rotation would prevent this. It was believed that the magnetic field was created by an electric current in the core of the planet, and the movement of charged particles needed to create this current was due to the rotation of the planet. A slowly rotating planet may not be able to transport charged particles fast enough to create a magnetic field that can deflect flares and make them able to maintain an atmosphere.

but More recent research suggests that planetary magnetic fields are actually held together by convection, a process in which hot material inside the core rises, cools, and then sinks back down.

Hopes for an atmosphere on planets like Proxima Centauri b are tied to the latest discovery about the planet. Gliese 1132revolves around a red dwarf. There is almost certainly no life there. This is hell, frying at a temperature not lower than 260 ° C. However, it's hell with the atmosphere! Analyzing the transit of the planet at seven different wavelengths of light, scientists found that it has different sizes. This means that in addition to the shape of the object itself, the star's light is obscured by the atmosphere, which only allows some of its lengths to pass through. And this, in turn, means that Gliese 1132 b has an atmosphere, although it seems to be not according to the rules.

This is good news because red dwarfs make up over 90% of the stellar population (yellow stars only about 4%). We now have a solid foundation on which to count on at least some of them to enjoy the atmosphere. Although we do not know the mechanism that would allow it to be maintained, its discovery itself is a good predictor for both the TRAPPIST-1 system and our neighbor Proxima Centauri b.

First discoveries

Scientific reports of the discovery of extrasolar planets appeared as early as the XNUMXth century. One of the first was William Jacob from the Madras Observatory in 1855, who discovered that the binary star system 70 Ophiuchus in the constellation Ophiuchus had anomalies suggesting the very likely existence of a "planetary body" there. The report was backed up by observations Thomas J. J. See from the University of Chicago, who around 1890 decided that the anomalies proved the existence of a dark body orbiting one of the stars, with an orbital period of 36 years. However, later it was noticed that a three-body system with such parameters would be unstable.

In turn, in the 50-60s. In the XNUMXth century, an American astronomer Peter van de Kamp astrometry proved that the planets revolve around the nearest star Barnard (about 5,94 light years from us).

All of these early reports are now considered incorrect.

The first successful detection of an extrasolar planet was made in 1988. The planet Gamma Cephei b was discovered using Doppler methods. (i.e. red/purple shift) – and this was done by Canadian astronomers B. Campbell, G. Walker and S. Young. However, their discovery was finally confirmed only in 2002. The planet has an orbital period of about 903,3 Earth days, or about 2,5 Earth years, and its mass is estimated at about 1,8 Jupiter masses. It orbits the gamma-ray giant Cepheus, also known as Errai (visible to the naked eye in the constellation Cepheus), at a distance of about 310 million kilometers.

Soon after, such bodies were discovered in a very unusual place. They revolved around a pulsar (a neutron star formed after a supernova explosion). April 21, 1992, Polish radio astronomer - Alexander Volshan, and the American Dale Fryl, published an article reporting the discovery of three extrasolar planets in the planetary system of the pulsar PSR 1257+12.

The first extrasolar planet orbiting an ordinary main sequence star was discovered in 1995. This was done by scientists from the University of Geneva - Michelle Mayor i Didier Keloz, thanks to observations of the spectrum of the star 51 Pegasi, which lies in the constellation Pegasus. The exterior layout was very different from. The planet 51 Pegasi b (4) turned out to be a gaseous object with a mass of 0,47 Jupiter masses, which orbits very close to its star, only 0,05 AU. from it (about 3 million km).

Kepler telescope goes into orbit

There are currently over 3,5 known exoplanets of all sizes, from larger than Jupiter to smaller than Earth. A (5) brought a breakthrough. It was launched into orbit in March 2009. It has a mirror with a diameter of approximately 0,95 m and the largest CCD sensor that has been launched into space - 95 megapixels. The main goal of the mission is determining the frequency of occurrence of planetary systems in space and the diversity of their structures. The telescope monitors a huge number of stars and detects planets by the transit method. It was aimed at the constellation Cygnus.

5. The Kepler telescope observes an exoplanet in front of the disk of its star.

When the telescope was closed due to a malfunction in 2013, scientists loudly expressed their satisfaction with its achievements. It turned out, however, that at that time it only seemed to us that the planet-hunting adventure was over. Not only because Kepler is broadcasting again after a break, but also because of the many new ways to detect objects of interest.

The telescope's first reaction wheel stopped working in July 2012. However, three more remained - they allowed the probe to navigate in space. Kepler seemed to be able to continue his observations. Unfortunately, in May 2013, the second wheel refused to obey. Attempts were made to use the observatory for positioning corrective motorshowever, the fuel quickly ran out. In mid-October 2013, NASA announced that Kepler would no longer search for planets.

And yet, since May 2014, a new mission of an honored person has been taking place. exoplanet hunters, referred to by NASA as K2. This was made possible through the use of slightly less traditional techniques. Since the telescope would not be able to operate with two efficient reaction wheels (at least three), NASA scientists decided to use pressure solar radiation as a "virtual reaction wheel". This method proved successful in controlling the telescope. As part of the K2 mission, observations have already been made of tens of thousands of stars.

Kepler has been in service for much longer than planned (until 2016), but new missions of a similar nature have been planned for years.

The European Space Agency (ESA) is working on a satellite whose task will be to accurately determine and study the structure of already known exoplanets (CHEOPS). The launch of the mission was announced for 2017. NASA, in turn, wants to send the TESS satellite into space this year, which will be focused primarily on searching for terrestrial planets., about 500 stars closest to us. The plan is to discover at least three hundred "second Earth" planets.

Both of these missions are based on the transit method. That's not all. In February 2014, the European Space Agency approved PLATEAU mission. According to the current plan, it should take off in 2024 and use the telescope of the same name to search for rocky planets with water content. These observations could also make it possible to search for exomoons, similar to how Kepler's data were used to do this. The sensitivity of PLATO will be comparable to Kepler telescope.

At NASA, various teams are working on further research in this area. One of the lesser known and still at an early stage projects is star shadow. It was a question of obscuring the light of a star with something like an umbrella, so that the planets on its outskirts could be observed. Using wavelength analysis, the components of their atmosphere will be determined. NASA will evaluate the project this year or next and decide if it's worth pursuing. If the Starshade mission is launched, then in 2022 it will

Less traditional methods are also being used to search for extrasolar planets. In 2017, EVE Online players will be able to search for real exoplanets in the virtual world. – as part of a project to be implemented by game developers, the Massively Multiplayer Online Science (MMOS) platform, Reykjavik University and the University of Geneva.

The project participants will have to hunt for extrasolar planets through a mini-game called Opening a project. During space flights, which can last up to several minutes, depending on the distance between individual space stations, they will analyze the actual astronomical data. If enough players agree on the appropriate classification of the information, it will be sent back to the University of Geneva to help improve the study. Michelle Mayor, winner of the 2017 Wolf Prize in Physics and the aforementioned co-discoverer of an exoplanet in 1995, will present the project at this year's EVE Fanfest in Reykjavik, Iceland.

Learn more

Astronomers estimate that there are at least 17 billion Earth-sized planets in our galaxy. The number was announced a few years ago by scientists at the Harvard Astrophysical Center, based primarily on observations made with the Kepler telescope.

François Fressen of the Center emphasizes that these data, of course, should not be understood in the sense that each of the billions of planets has favorable conditions for life. Alone размер that's not all. It's also important distance from the stararound which the planet revolves. Keep in mind that although most of these Earth-like objects move in narrow orbits similar to those of Mercury, they revolve around others.

stars, some of which are clearly smaller than our Sun. Scientists also suggest that in order to live, at least as we know it, it is necessary liquid water.

The transit method says little about the planet itself. You can use it to determine its size and distance from the star. Technics radial velocity measurement can help determine its mass. The combination of the two methods makes it possible to calculate the density. Is it possible to take a closer look at an exoplanet?

It turns out it is. NASA already knows how best to view planets like Kepler-7 pfor which it was designed with the Kepler and Spitzer telescopes map of clouds in the atmosphere. It turned out that this planet is too hot for life forms known to us - it is hotter from 816 to 982 ° C. However, the very fact of such a detailed description of it is a big step forward, given that we are talking about a world that is a hundred light years away from us. In turn, the existence of a dense cloud cover around exoplanets GJ 436b and GJ 1214b was derived from spectroscopic analysis of the light from the parent stars.

Both planets are included in the so-called super-Earth. GJ 436b (6) is 36 light years away in the constellation Leo. GJ 1214b is located in the constellation Ophiuchus, 40 light years from Earth. The first is similar in size to Neptune, but is much closer to its star than the "prototype" known from the solar system. The second is smaller than Neptune, but much larger than Earth.

6. Cloud layer around GJ 436b - visualization

It also comes with adaptive optics, used in astronomy to eliminate disturbances caused by vibrations in the atmosphere. Its use is to control the telescope with a computer in order to avoid local distortions of the mirror (on the order of a few micrometers), thereby correcting errors in the resulting image. This is how the Gemini Planet Imager (GPI) based in Chile works. The device was first put into operation in November 2013.

The use of GPI is so powerful that it can detect the light spectrum of dark and distant objects such as exoplanets. Thanks to this, it will be possible to learn more about their composition. The planet was chosen as one of the first observation targets. Beta Painter b. In this case, the GPI works like a solar coronagraph, that is, it covers the disk of a distant star to show the brightness of a nearby planet. 

The key to observing "signs of life" is the light from a star orbiting the planet. Light passing through an exoplanet's atmosphere leaves a specific trail that can be measured from Earth. using spectroscopic methods, i.e. analysis of radiation emitted, absorbed or scattered by a physical object. A similar approach can be used to study the surfaces of exoplanets. However, there is one condition. The surface of the planet must absorb or scatter light sufficiently. Evaporating planets, meaning planets whose outer layers float around in a large dust cloud, are good candidates. 

With the instruments we already have, without building or sending new observatories into space, we can detect water on a planet a few dozen light-years away. Scientists who, with the help of Very Large Telescope in Chile - they saw traces of water in the atmosphere of the planet 51 Pegasi b, they did not need the transit of the planet between the star and the Earth. It was enough to observe subtle changes in the interactions between the exoplanet and the star. According to scientists, measurements of changes in reflected light show that in the atmosphere of a distant planet there is 1/10 thousand of water, as well as traces carbon dioxide i methane. It is not yet possible to confirm these observations on the spot ... 

Another method of direct observation and study of exoplanets not from space, but from the Earth is proposed by scientists from Princeton University. They developed the CHARIS system, a kind of extremely cooled spectrographwhich is capable of detecting light reflected by large, larger than Jupiter, exoplanets. Thanks to this, you can find out their weight and temperature, and, consequently, their age. The device was installed at the Subaru Observatory in Hawaii.

In September 2016, the giant was put into operation. Chinese radio telescope FAST (), whose task will be to search for signs of life on other planets. Scientists all over the world have high hopes for it. This is an opportunity to observe faster and farther than ever before in the history of extraterrestrial exploration. Its field of view will be twice that of Arecibo telescope in Puerto Rico, which has been at the forefront for the past 53 years.

The FAST canopy has a diameter of 500 m. It consists of 4450 triangular aluminum panels. It occupies an area comparable to thirty football fields. For work, I need ... complete silence within a radius of 5 km, and therefore almost 10 thousand. people living there have been displaced. Radio telescope it is located in a natural pool among the beautiful scenery of green karst formations in the south of Guizhou Province.

More recently, it has also been possible to directly photograph an exoplanet at a distance of 1200 light-years. This was done jointly by astronomers from the South European Observatory (ESO) and Chile. Finding the planet marked CVSO 30c (7) has not yet been officially confirmed.

7. Star CVSO 30c - image from the VLT

Is there really extraterrestrial life?

Previously, it was almost unacceptable in science to hypothesize about intelligent life and alien civilizations. Bold ideas were tested by the so-called. It was this great physicist, Nobel laureate, who was the first to notice that there is a clear contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the absence of any observable traces of their existence. "Where are they?" the scientist had to ask, followed by many other skeptics, pointing to the age of the universe and the number of stars.. Now he could add to his paradox all the "Earth-like planets" discovered by the Kepler telescope. In fact, their multitude only increases the paradoxical nature of Fermi's thoughts, but the prevailing atmosphere of enthusiasm pushes these doubts into the shadows.

Exoplanet discoveries are an important addition to another theoretical framework that attempts to organize our efforts in the search for extraterrestrial civilizations - Drake Equations. Creator of the SETI program, Frank DrakeI learned that the number of civilizations with which mankind can communicate, that is, based on the assumption of technological civilizations, can be derived by multiplying the duration of the existence of these civilizations by their number. The latter can be known or estimated based on, among other things, the percentage of stars with planets, the average number of planets, and the percentage of planets in the habitable zone.. This is the data we just received, and we can at least partially fill equation (8) with numbers.

The Fermi Paradox poses a difficult question that we may only answer when we finally get in touch with some advanced civilization. For Drake, in turn, everything is correct, you just need to make a series of assumptions on the basis of which to make new assumptions. Meanwhile Amir Axel, prof. Bentley College statistics in their book "Probability = 1" calculated the possibility of extraterrestrial life at almost 100%.

How did he do it? He suggested that the percentage of stars with a planet is 50% (after the results of the Kepler telescope, it seems that more). He then assumed that at least one of the nine planets had suitable conditions for the emergence of life, and the probability of a DNA molecule is 1 in 1015. He suggested that the number of stars in the universe is 3 × 1022 (the result of multiplying the number of galaxies by the average number of stars in one galaxy). prof. Akzel lead to the conclusion that somewhere in the universe life must have arisen. However, it may be so far away from us that we do not know each other.

However, these numerical assumptions about the origin of life and advanced technological civilizations do not take into account other considerations. For example, a hypothetical alien civilization. she won't like it connect with us. They can also be civilizations. impossible to contact us, for technical or other reasons that we can't even imagine. Perhaps it we do not understand and do not even see signals and forms of communication that we receive from "aliens".

"Non-existent" planets

There are many traps in the unbridled hunt for planets, as evidenced by the coincidence Gliese 581 d. Internet sources write about this object: "The planet does not actually exist, the data in this section describe only the theoretical characteristics of this planet if it could exist in reality."

History is interesting as a warning to those who lose their scientific vigilance in planetary enthusiasm. Since its "discovery" in 2007, the illusory planet has been a staple of any compendium of "the closest exoplanets to Earth" over the past few years. It is enough to enter the keyword “Gliese 581 d” into a graphical Internet search engine to find the most beautiful visualizations of a world that differs from Earth only in the shape of the continents ...

The play of the imagination was brutally interrupted by new analyzes of the star system Gliese 581. They showed that the evidence of the existence of a planet in front of the stellar disk was taken rather as spots appearing on the surface of stars, as we well know from our sun. New facts have lit a warning lamp for astronomers in the scientific world.

Gliese 581 d is not the only possible fictional exoplanet. Hypothetical large gas planet Fomalhaut b (9), which was supposed to be in a cloud known as the "Eye of Sauron", is probably just a mass of gas, and is not far from us Alpha Centauri BB it can only be an error in the observational data.

9. Hypothetical exoplanet Fomalhaut b

Despite errors, misunderstandings and doubts, the massive discoveries of extrasolar planets are already a fact. This fact greatly undermines the once popular thesis about the uniqueness of the solar system and the planets as we know them, including the Earth. – everything points to the fact that we rotate in the same zone of life as millions of other stars (10). It also seems that claims about the uniqueness of life and beings such as humans may be equally unfounded. But—as was the case with exoplanets, for which we once only believed “they should be there”—scientific proof that life “is there” is still needed.

10. The zone of life in planetary systems depending on the temperature of the star