If we can stay on schedule, the new telescope will be operational before the Hubble Space Telescope stops operating. “The prospect of Hubble and Webb operating simultaneously is very exciting because their capabilities are complementary in many ways,” says John Gardner.
More than 7,000 astronomers who participated in the Hubble project over its more than two decades of operation are expected to use Webb. Hubble surveys in the ultraviolet, visible and near-infrared, while Webb will survey in the near and mid-infrared. Webb resolution of 0.1 arcsec [ arc second] will allow it to see objects the size of a football at a distance of 547 kilometers, which corresponds to the [diffraction] resolution of Hubble's 2.5-meter mirror [for visible wavelengths]. The difference is that Webb will operate in infrared at a resolution that will allow it to see objects 10 to 100 times fainter than Hubble can, thereby revealing the early days of the Universe.
Late last year, during Hubble's final servicing mission, the Atlantis shuttle crew installed the WFC 3 wide-angle camera, which significantly expanded the telescope's near-infrared capabilities. As a result, the telescope has surpassed 1 billion years after the Big Bang, which began the Universe 13.7 billion years ago, and is now observing objects 600-800 million years after it. Webb's greater infrared resolution and its ability to see past dust that obscures the universe's earliest days will give astronomers images of events that occurred 250 million years after the Big Bang.
Such a distant view will allow us to see how clusters of early objects in the Universe are formed, says John Mather. Marcia Rieke expects to see planets forming from the [protoplanetary] disk.
One of the main goals of Webb is to determine the physical and chemical parameters of planetary systems and the ability to support life. The telescope should be able to detect relatively small planets—several times larger than Earth—which Hubble cannot do. In addition, Webb will have higher sensitivity to the atmospheres of stars close to Earth. The telescope will be able to provide close-up images of the planets of the solar system, from Mars and beyond. The great brightness of Venus and Mercury lies beyond the telescope's optics.
The spacecraft will carry four scientific instruments. The mid-infrared instrument from a consortium of European countries, the European Space Agency [ESA] and NASA's Jet Propulsion Laboratory will use three photoarrays operating at 4 K, which will require an active cooling system, but will not use liquid helium as this would limit the service life of the device.
The telescope's other three instruments are a near-infrared spectrograph from ESA, a near-infrared camera from the University of Arizona, and a Lockheed Martin filter and precision targeting system from the Canadian Space Agency. All three instruments will be passively cooled to a temperature of 35-40 K.
The launch will be carried out on an Ariane 5 ECA heavy-duty launch vehicle from ESA's Kourou spaceport in French Guiana. The Webb flight will take three months to the solar-terrestrial Lagrange point L2 at a distance of 1.5 million kilometers from Earth. Being at point L2 will provide gravitational stability, coverage of open space without being blocked by the Earth, in addition, it will make it possible to get by with one shield to cover the telescope from radiation from the Sun, Earth and Moon, which is important for ensuring temperature conditions. The telescope will orbit the Sun, not the Earth.
Currently, the largest space observatory is the 3.5-meter infrared Herschel space telescope, launched jointly with the Planck spacecraft in May 2009 to the L2 point of the Ariane 5 launch vehicle with a head fairing of 4.57 meters. The Herschel operating range lies in far infrared radiation down to submillimeter waves.
Infrared telescopes require large mirrors and a set of instruments cooled to very low temperatures in order to detect the dim light of very distant objects. Since the first such device, the Infrared Orbiting Observatory, launched in January 1983, their instruments have been actively cooled with liquid helium. The disadvantage of this approach is that the helium boils away. The IRAS mission lasted only 10 months. ESA estimates that the Herschel mission will last a maximum of four years.
NASA explored various design options for the Webb Telescope in an effort to avoid lifespan limitations. To achieve this, the contracting team, led by Northrop Grumman Space Systems, and a multinational scientific team are developing more than a dozen technology innovations.
Topping the list is the breakthrough achieved in the field of detectors for the near and mid-infrared ranges. One of the most unusual innovations is microgates, 100x200 µm cells, for NIRSpec. Each cell is individually controlled to block light from nearby sources when NIRSpec detectors are focused on distant, dim objects.
But the main innovation of the Webb is its size. The main mirror of the telescope will consist of 18 beryllium elements, each 1.5 meters in diameter. Their position is controlled so precisely that they will act as a single mirror, a technology Webb borrowed from large ground-based observatories.
Obtaining clear images requires keeping instruments cool, pointing accurately, and keeping the telescope on target. This was achieved through breakthroughs in beryllium mirror grinding, carbon composite structure design, solar control coatings and “thermal switches”. Hundreds of actuators are certified to operate at cryogenic temperatures in order to precisely position the mirrors. Other drives are needed to deploy the sunshade, which is shaped like a kite the size of a tennis court. If the screen does not work, the mission will be lost.
The 6.5-meter Webba primary mirror and other components included in the optical telescope module are too large to fit under the fairing of the Ariane 5 launch vehicle in the operating position, so they will be folded [ approx. watch the two videos at the end of the article].
Northrop Grumman is building the "Webba" solar shield [almost 22 meters long] and the spacecraft platform that will integrate all of the telescope's modules, including the Science Instruments Module being built by Goddard Space Flight Center. In addition to the above companies, ITT Corporation, which provides ground support and system testing, and Alliant Techsystems, which is responsible for the 6-meter main mirror backplane made of graphite composite, are involved in the project.
The telescope mirror is being developed by Ball Aerospace, Brush Wellman, Axsys Technologies and Tinsley Laboratories, and they spent 7 years creating it to tolerances of one thousandth the width of a human hair. "No one has polished mirrors of this size and level designed to operate in cryogenic temperatures," stated Mark Bergeland.
The creation of durable components for the flight product has already begun, the heads of the groups will conduct an examination of the project in May 2011. Work on some elements of the flight product, which have passed their own examination, has been underway for about 2 years.
As with other spacecraft, NASA established an independent Permanent Review Board to review the mission's [element performance tests] results in detail to provide an outside perspective on the fundamentals of the testing and the tests themselves. The council expects to submit recommendations to NASA this fall. If additional tests or changes to the design of the vehicle are required, the JWST project will face schedule delays and increased costs.
After launch and its attendant vibrations, the mirror array must be deployed to what designers call a “pre-position.” This process involves releasing each of the 18 segments of the primary mirror from the launch grips. Each segment has a computer controlled position with six degrees of freedom, in addition, the computer controls the extension/retraction of the center point of each mirror to change the radius of curvature of the surface. Each mirror has its own drive system to carry out these movements. Once the mirrors are unlocked, the actuators must align their position with the wavefront to within 20 nanometers.
But the stunning alignment accuracy of the 18-mirror ensemble is not the main focusing challenge. This honor goes to the composite backplane, which holds the mirrors together, with a very low coefficient of thermal expansion, so changes in position will be no more than 40 - 50 nanometers. The telescope will be tested twice a month so that any changes to the backplane geometry will be eliminated by refocusing the mirrors.
Another challenge was the sunscreen. It uses five layers of DuPont Kapton-E to protect the telescope mirrors from sunlight and heat [as well as radiation from the Earth, Moon and instruments mounted under the screen] of the telescope instruments. Kapton membranes are coated with quartz and aluminum deposited onto the surface using vapor deposition.
An outer membrane with a thickness of 0.0508 millimeters will reflect 80% of the radiation incident on it; subsequent layers of the screen with a thickness of 0.0254 millimeters will continue to reduce the flux. Each membrane is curved in such a way as to remove heat from the central part of the screen, above which the telescope itself is located. The screen reflects and rejects heat so effectively that 100 kW of solar radiation incident on the first membrane will be reduced to 10 mW behind the last membrane [10 million times reduction].
In addition, the screen acts as a shield for micrometeorites. It is expected that after breaking through the first layer, they will break into dust on the second, exactly as in the case of micrometeorites hitting extremely hard beryllium mirrors. If the telescope is hit by a large meteorite, it will cause serious damage, but L2 is not considered as their main transport artery.
The number of exoplanets discovered in data collected by the Kepler space telescope, and confirmed by independent observations using other astronomical instruments, has exceeded a thousand after eight more exoplanets were discovered among 544 new planet candidates, located in zones favorable for the formation and existence on them life. Let us remind our readers that the Kepler space telescope collected the main body of information during its main mission, observing for almost four years the night sky in the region of the Lyra constellation, in which it monitored more than 150 thousand stars. Analyzing the massive amount of data collected over time, the Kepler mission science team discovered 4,175 potential planet candidates and confirmed the existence of 1,000 of that number. But the methods used by scientists to analyze data are constantly being improved, and this makes it possible to find traces of more and more planets in seemingly already studied data.
Until now, the Kepler telescope has been hunting for exoplanets using the transit method. The telescope's highly sensitive sensors caught the slightest changes in the brightness of the stars, which occurred at those moments when a planet of a distant system passed between the star and the Earth. By recording curves of changes in brightness and making other high-precision calculations, the telescope equipment allowed scientists to find out whether the planet was really causing the decrease in brightness, and if the first question was answered positively, to calculate the characteristics of the planet, such as the range and period of the orbit, mass, size, presence of an atmosphere and etc.
The last eight planets discovered in Kepler data are truly the crown jewels of the collection. The sizes of all the planets do not exceed the size of the Earth by more than twice, and their orbits pass in favorable zones where the temperature on the surface allows the existence of liquid water. In addition, six of the eight planets orbit Sun-like stars, and two of them are rocky planets, similar to the planets in the inner solar system.
The first of the two planets mentioned above, Kepler-438b, located 475 light-years away and 12 percent larger than Earth, orbits its star with a period of 35.2 days. The second planet, Kepler-442b, located 1,100 light-years away, is 33 percent larger than Earth and has an orbital “year” of 112 days. Such short orbital periods indicate that these planets are much closer to their stars than the Earth is to the Sun, however, they are still in favorable zones due to the fact that their stars are smaller and cooler than the Sun.
"The Kepler telescope collected data for four years. That's quite a long time and in the huge amount of data collected, we can still find planets the size of Earth rotating around their stars in orbits no greater than the distance from the Earth to the Sun for a very long time," says Fergal Mullally Fergal Mullally, a scientist at NASA Ames Research Center and a member of the Kepler mission science team, said: "And new methods for analyzing the collected data, which are improving every time, bring us even closer to discovering planets."
By the flickering of a star's light, one can determine the period of revolution of a planet around it, its approximate size and some other characteristics. However, additional observations using other telescopes are needed to confirm the planetary status of each object.
First results
Scientists received the first results of the telescope six months after its launch. Then Kepler found five potential exoplanets: Kepler 4b, 5b, 6b, 7b and 8b - “hot Jupiters” on which life cannot exist.
In August 2010, scientists confirmed the discovery of the first planet in a system with more than one, or rather three, planets orbiting a star: Kepler-9.
Kepler Space Telescope. Illustration: NASA
In January 2011, NASA announced Kepler's discovery of the first rocky planet, Kepler-10b, about 1.4 times the size of Earth. However, this planet turned out to be too close to its star for life to exist on it - 20 times closer than Mercury is to the Sun. When discussing the possibility of the existence of life, astronomers use the expression “life zone” or “habitable zone.” This is the distance from a star at which it is neither too hot nor too cold for liquid water to exist on the surface.
Thousands of new planets
In February of that year, scientists released Kepler's 2009 results—a list of 1,235 exoplanet candidates. Of these, 68 are approximately Earth-sized (5 of them in the habitable zone), 288 are larger than Earth, 662 are Neptune-sized, 165 are Jupiter-sized, and 19 are larger than Jupiter. In addition, at the same time it was announced the discovery of a star (Kepler-11) with six planets larger than Earth orbiting it.
In September, scientists reported that Kepler had discovered a planet (Kepler-16b) that orbits a binary star, meaning it has two suns.
By December 2011, the number of exoplanet candidates discovered by Kepler had grown to 2,326, 207 approximately Earth-sized, 680 larger than Earth, 1,181 Neptune-sized, 203 Jupiter-sized, 55 larger than Jupiter. At the same time, NASA announced the discovery of the first planet in the habitable zone near a star similar to the Sun, Kepler-22b. It was 2.4 times the size of Earth. It became the first confirmed planet in the habitable zone.
A little later in December of the same year, scientists announced the discovery of Earth-sized exoplanets, Kepler-20e and Kepler-20f, orbiting a star similar to the Sun, although too close to it to fall into the habitable zone.
Artist's rendering of the planet Kepler-62f. Illustration: NASA Ames/JPL-Caltech/Tim Pyle
In January 2013, NASA announced that another 461 new planets had been added to the list of exoplanet candidates. Four of them were not twice the size of the Earth and at the same time were in the life zone of their stars. In April, scientists reported the discovery of two planetary systems in which three planets larger than Earth were in the habitable zone. In total, there were five planets in the Kepler-62 star system, and two in the Kepler-69 system.
The telescope breaks down...
In May 2013, the telescope’s second of four gyrodynes—devices it needed for orientation and stabilization—failed. Without the ability to hold the telescope in a stable position, it became impossible to continue the “hunt” for exoplanets. However, the list of exoplanets continued to grow as the data accumulated during the telescope’s operation was analyzed. Thus, in July 2013, the list of potential exoplanets already included 3,277 candidates.
In April 2014, scientists reported the discovery of an Earth-sized planet, Kepler-186f, in the star's habitable zone. It is located in the constellation Cygnus, 500 light years away. Along with three other planets, Kepler-186f orbits a red dwarf star half the size of our Sun.
...but continues to work
In May 2014, NASA announced the continued operation of the telescope. It was not possible to completely repair it, but scientists found a way to compensate for the breakdown using the pressure of the solar wind on the device. In December 2014, a telescope operating in the new mode was able to detect the first exoplanet.
At the beginning of 2015, the number of candidate planets in the Kepler list reached 4,175, and the number of confirmed exoplanets was a thousand. Among the newly confirmed planets were Kepler-438b and Kepler-442b. Kepler-438b is 475 light-years away and 12% larger than Earth, Kepler-442b is 1,100 light-years away and 33% larger than Earth. They orbit in the habitable zone of stars smaller and cooler than the Sun.
Planet Kepler-69c as imagined by an artist. Illustration: NASA Ames/JPL-Caltech/T. Pyle
At the same time, NASA announced the discovery by Kepler of the oldest known planetary system, 11 billion years old. In it, five planets smaller than Earth orbit the star Kepler-444. The star is a quarter smaller than our Sun and cooler, it is located 117 light years from Earth.
On July 23, 2015, scientists reported a new batch of candidate planets added to the Kepler catalog. Now their number is 4696, and the number of confirmed planets is 1030, among them 12 planets are not more than twice the size of the Earth and are in the habitable zone of their stars. One of them is Kepler 452b, which is 1,400 light-years from Earth and orbits a star that is similar to the Sun, only 4% more massive and 10% brighter.
A few months ago, scientists summed up the work of the “main exoplanet hunter” - the Kepler space telescope. Out of 4,700 candidates for “sisters of the Earth,” researchers selected only 20 planets that are most similar to our home world. At the request of the Life editors, astronomer and lecturer at the St. Petersburg Planetarium Maria Borukha told us what exoplanets are, how they are looked for and what they can look like.
A little about the solar system
The modern definition of the word “planet”, given by the International Astronomical Union (IAU), contains three points. A planet is a celestial body that:
- Orbits around the Sun.
- It has sufficient mass to come to a state of hydrostatic equilibrium under the influence of its own gravity.
- Clears the surroundings of its orbit from other objects.
In the solar system, eight objects fit this definition: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
Largest Solar System bodies to scale
The first four planets are small and rocky, followed by two huge gas giants, then two ice giants. Moreover, the orbits of all planets are practically circular and lie close to the same plane (Mercury stands out most strongly: the orbital inclination is 7 degrees, and eccentricity (this is what scientists call the difference between any conic section, for example ellipse, from a regular circle) is 0.2.
Orbits of Solar System bodies to scale
This arrangement of the planetary system is familiar to us. But this does not mean at all that all planetary systems in the Universe or at least in our Galaxy should be arranged in this way. Moreover, the further exploration of other planetary systems progresses, the clearer it becomes that the natural diversity of planets is much richer than one can imagine.
First discoveries
Thus, exoplanets (from ancient Greek ἔξω - “outside, outside”) are any planets orbiting other stars. Now they open almost every day. As of August 11, 2016, the total number of discovered exoplanets was 3,496 (with several thousand more candidates awaiting confirmation). And this is only the beginning of a long journey of research into extrasolar systems.
Growing number of discovered exoplanets
TO It is difficult to say when and by whom the first exoplanet was discovered: the fact is that many statements about the discovery of exoplanets have not been confirmed. At the same time, in 1988, a work appeared in which researchers pointed to the possibility of the existence of a third stellar component in the double star Gamma Cephei. But, as it turned out 15 years later, Campbell and his co-authors discovered not a star at all, but an exoplanet. According to modern estimates, the mass of this planet lies in the range from 4 to 18 masses of Jupiter and it orbits the star Gamma Cephei A (the Alrai star) in 903 days (the orbital period of Jupiter in the Solar System is almost five times longer). In 2003, the new planet received the name Gamma Cephei A b - in accordance with the rules for naming exoplanets (a letter of the Latin alphabet is assigned to the name of the star, starting with b). The star Gamma Cephei has a magnitude of 3.2 m and visible in the sky earthlings even with the naked eye.
Constellation Cepheus. The star Gamma Cephei is highlighted with a blue arrow.
What did researchers see in this area of the sky? How could they confuse a star and a planet? The fact is that most exoplanets are discovered using indirect methods: out of almost three and a half thousand discovered exoplanets, astronomers have seen the light of only a few dozen. Finding such objects and estimating their parameters without seeing them directly is possible only by measuring the influence of the exoplanet on the star around which it orbits. Campbell and his co-authors discovered the exoplanet Gamma Cephei A b using one of the indirect methods - the radial velocity method.
What is the radial velocity method?
Imagine that you are looking at a car that is driving away from you. The distance between you is increasing all the time, which means that its radial velocity relative to you is positive. If a car is moving towards you and the distance between you decreases, the radial velocity is negative. If the car circles around you, neither approaching nor moving away, its radial velocity is zero. A more formal definition of radial (radial) velocity is possible.
Now listen to what happens to the car's horn as it approaches and moves away from you:
Doppler effect when a car is moving
First, when the car's speed is low, we hear the "real" sound of a horn. As the vehicle speed increases, the sound of the signal gradually increases. At the same time, as soon as the car begins to move away from us, we hear a decrease in the frequency of the beep. This effect of the signal frequency changing as a function of radial velocity is called the Doppler effect. 
Yes, yes, this is the same “striped” effect, because it is applicable to any waves, not only to sound, but also to visible light. For example, if a yellow flashlight is flying quickly towards you, it will appear green; if it is coming from you, it will appear red. 
How does the Doppler effect apply to exoplanetary systems? Let's consider two bodies - a star and a planet. At first glance, it may seem that the planet is revolving around a star, but the star is standing still. But in fact, the star also rotates, with the same period as the planet, while describing a small circle around the center of mass of the system. And if at the same time the system is located in relation to you in such a way that the radial velocity of the star for you at some moments of time is different from zero, you may notice the Doppler effect in such a system and suspect that a massive body is orbiting the star. For example, the radial velocity of the star Gamma Cephei A ranges from -27.5 m/s to +27.5 m/s due to the exoplanet orbiting it.
Thus, when researchers announce the discovery of a star using the radial velocity method, they do not “see” the exoplanet, as they say, with their own eyes, but measure its influence on the star. Moreover, the magnitude of the radial velocity of the star will be greater than:
- more massive planet;
- lighter star;
- the distance between the star and the planet is smaller;
- the inclination of the system's orbital plane to our line of sight is less.
A similar situation arises when planets are discovered by the most effective method today - transit.
Open a planet by transit
The transit method (passages across the disk) involves measuring changes in the flux of radiation (in other words, luminosity) coming from the star. Even with the naked eye you can observe the transit, albeit within the Solar System. The passage of bodies such as the Moon, Venus or Mercury across the solar disk is a classic example of such a phenomenon.
Transit of Venus across the solar disk, observed decrease in brightness
To detect a planet using the transit method, it is necessary that:
- the system's orbit lay in the plane of the observer's line of sight;
- the system had a period shorter than the observation time.
Moreover, the smaller the difference in the sizes of the planet and the star, the easier it is to detect a transit in such a system. 
Most of the planets discovered by the transit method are objects photographed by the Kepler space telescope. At the moment, about four thousand exoplanet candidates discovered by this telescope are awaiting their final confirmation. And all these planets are located only in a small area of the sky into which this telescope is directed.
Field of view of the Kepler telescope
The first planet whose transit was observed in 2005 was discovered back in 1999 using the radial velocity method. She received the name HD 209458 b, but due to her particular popularity among scientists she was also given her own name - Osiris. This planet orbits its solar-type star in just 3.5 days and has a radius 1.4 times that of Jupiter in the solar system. The mass of the planet (0.7 the mass of Jupiter) was determined by the radial velocity method - Osiris causes fluctuations in the radial velocity of its star from -84 m/s to +84 m/s.
Planets such as Osiris are classified as “hot Jupiters.” They are close in mass to Jupiter, but they orbit very close to their stars and, therefore, are very hot. And although there are no planets of this type in the Solar System, several hundred “hot Jupiters” have already been found in our Galaxy. It was precisely such planets that were discovered first - by the transit method and the radial velocity method, the presence of large planets close to the star is easier to establish. Some "hot Jupiters" (including Osiris) have had their chemical composition partially studied and their atmospheres have been modeled, but, unfortunately, seeing the light of such objects is a very difficult task.
Number of exoplanets discovered by various methods
Exoplanet images
At the moment, there are only a few dozen images of exoplanets. To highlight light from a planet, it is necessary to “block” the light from the star around which the planet orbits (either before the light hits the radiation receiver, or after - using software methods). Accordingly, it is easier to photograph a large planet located at a considerable distance from its star. Moreover, in the infrared region of the spectrum, it turns out to be easier to isolate the light of an exoplanet near a star.
The first planet discovered by imaging in 2004 was an object named 2M1207 b.
Infrared photograph of the 2M1207 system. On the left is a planet, on the right is a brown dwarf
The image of 2M1207 b, a gas giant orbiting the brown dwarf 2M1207 (at a distance 55 times greater than the distance between the Sun and Earth), was obtained using one of the VLT telescopes. The same area of the sky in the constellation Centaurus was observed by the Hubble telescope in order to confirm the joint motion of the components. The flux from the planet, which may continue to shrink, in this system is only a hundred times less than the flux from the dwarf 2M1207 (for comparison, when observing the Solar System from the side, the brightest planets will have a brightness about a billion times fainter than the Sun) . At the end of 2015, a work appeared in which, using precise photometric observations, the rotation period of the planet 2M1207 b was established, which is approximately 10 hours.
The first planetary system to be photographed was HR 8799 in the constellation Pegasus.
The planetary system of the star HR 8799. The planets are designated by the letters b, c, e, d. In the center are artifacts of subtracting star light from the image.
The planetary system consists of giants five (HR 8799 b) and seven times more massive than Jupiter (HR 8799 c, HR 8799 e, HR 8799 d), and the size of the planetary system is close to the size of the Solar System. Researchers announced the acquisition of images of this planetary system using telescopes at the Keck and Gemini observatories in 2008.
So what's next?
To date, among the discovered exoplanets there are those whose surface is an ocean. Gas giants have been found that are losing their atmospheres, and chthonic planets that have already lost their gas shell. Planets have been discovered in the sky of which several suns can be seen at once, and multiple planetary systems near pulsars. There are planets orbiting their stars in very high orbits, and those planets that practically touch the surface of their star. Among the orbits of exoplanets, there are both circular and highly elongated ones, and all this is so unlike our Solar System.
With the increasing capabilities of observational technology, the number of planets will grow steadily - there is no doubt about that. There is no doubt that new planets will continue to surprise researchers. 20 exoplanets have already been recognized as most similar to Earth, however, confirming this status is still a matter of the very distant future. However, all of humanity cherishes one common dream - to find another world that would be as cozy as our home planet. And, of course, visit it someday.
The main task of the French space station COROT, launched from the Baikonur Cosmodrome in mid-October this year, is to search for possible life on other planets. Using a space telescope with a diameter of 30 cm, it is planned to find several dozen Earth-like planets around distant stars. Then, a detailed study of the discovered objects will be continued by other, more powerful space telescopes, the launch of which is scheduled for the coming years.
The first reliable report of the observation of a planet located near another star came at the end of 1995. Just ten years later, this achievement was awarded the "Nobel Prize of the East" - the award of Sir Run Run Shaw. For the third year, the Hong Kong media mogul is giving away $1 million to scientists who have achieved special achievements in astronomy, mathematics and life sciences, including medicine. The 2005 laureates in astronomy were Michel Mayor from the University of Geneva (Switzerland) and Geoffrey Marcy from the University of California at Berkeley (USA), who received the prize at a ceremony in Hong Kong from the hands of its founder, 98-year-old Mr. Shaw. In the time since the discovery of the first exoplanet, research teams led by these scientists have discovered dozens of new distant planets, with American astronomers led by Marcy accounting for 70 of the first 100 discoveries. In this way, they took a kind of revenge from the Swiss group of Mayor, which in 1995 was two months ahead of the Americans with the report of the very first exoplanet.Identification technology
The first to see planets near other stars through a telescope was the Dutch mathematician and astronomer Christiaan Huygens back in the 17th century. However, he could not find anything, since these objects are not visible even with powerful modern telescopes. They are located incredibly far from the observer, their sizes are small compared to stars, and the reflected light is weak. And, finally, they are located close to their home star. That is why, when observed from Earth, only its bright light is noticeable, and the dim points of exoplanets simply “drown” in its radiance. Because of this, planets outside the solar system remained unrecognized for a long time.
In 1995, astronomers Michel Mayor and Didier Queloz from the University of Geneva, conducting observations at the Haute-Provence Observatory in France, reliably recorded an exoplanet for the first time. Using an ultra-precise spectrometer, they discovered that star 51 in the constellation Pegasus “sways” with a period of just over four Earth days. (The planet, orbiting the star, rocks it with its gravitational influence, as a result of which, due to the Doppler effect, a shift in the spectrum of the star can be observed.) This discovery was soon confirmed by American astronomers Geoffrey Marcy and Paul Butler. Subsequently, another 180 exoplanets were discovered using the same method of analyzing periodic changes in the spectra of stars. Several planets were found using the so-called photometric method - by periodically changing the brightness of a star when the planet is between the star and the observer. It is this method that is planned to be used to search for exoplanets on the French COROT satellite, which is scheduled to be launched in October this year, as well as on the American Kepler station. Its launch is scheduled for 2008.
Hot Neptunes and Jupiters
The first discovered exoplanet resembles Jupiter, but is located very close to the star, causing its surface temperature to reach almost +1,000 ° C. This type of exoplanet, whose mass is hundreds of times greater than that of the Earth, is what astronomers call “hot gas giants” or “hot Jupiters.” In 2004, using advanced spectrometers, it was possible to discover a completely new class of exoplanets, much smaller in size - the so-called “hot Neptunes”, whose mass is only 15-20 times greater than that of the Earth. Reports about this were published simultaneously by both European and American astronomers. And at the beginning of this year, a very small exoplanet was discovered with a mass only 6 times greater than that of the Earth. It is significantly removed from its star, located in the cold region of the planetary system, and therefore should be an “ice giant” similar to Uranus or Neptune. Interestingly, two gas giants had already been discovered near the same star.
The discovery in 1995 of a planet located near star 51 in the constellation Pegasus marked the beginning of an entirely new field of astronomy - the study of extrasolar, or exoplanets. Before this, planets were known only around one star - our Sun. In order to search for planets outside the solar system, astronomers have examined about 3,000 stars over the past decade and found planets near 155 of them. In total, more than 190 exoplanets are now known. Two, three and even four planets have been found near some stars.Exoplanets discovered to date are located extremely far from our Solar System. The closest star to us (besides our Sun) - Proxima Centauri - is 270 thousand times further than the Sun - at a distance of 40,000 billion kilometers (4.22 light years). The nearest planetary system is 10 light years away, and the most distant one discovered is 20,000. Most exoplanets are tens or a few hundred (up to 400) light years away from us. Every year, astronomers discover about 20 exoplanets. Among them, more and more new varieties are being identified. The “heaviest” is 11 times more massive than Jupiter, and the largest in size has a diameter 1.3 times greater than that of Jupiter.
Where do planets come from?
There is still no reliable theory explaining how planetary systems of stars are formed. There are only scientific hypotheses on this matter. The most common of them suggests that the Sun and planets arose from a single cloud of gas and dust - a rotating cosmic nebula. From the Latin word nebula (“nebula”), this hypothesis was called “nebular.” Oddly enough, it is quite old - two and a half centuries. The beginning of modern ideas about the formation of planets was laid in 1755, when the book “General Natural History and Theory of the Heavens” was published in Königsberg. It belonged to the pen of an unknown 31-year-old graduate of the University of Koenigsberg, Immanuel Kant, who at that time was a home teacher for the children of landowners and taught at the university. It is very likely that Kant got the idea of the origin of planets from a dust cloud from a book published in 1749 by the Swedish mystical writer Emanuel Swedenborg (1688-1772), who hypothesized (according to him, told to him by angels) about the formation of stars as a result of vortex motion substances of the cosmic nebula. In any case, it is known that Swedenborg’s rather expensive book, in which this hypothesis was presented, was bought by only three private individuals, one of whom was Kant. Kant would later become famous as the founder of German classical philosophy. But the book about heaven remained little known, since its publisher soon went bankrupt and almost the entire circulation remained unsold. Nevertheless, Kant's hypothesis about the emergence of planets from a dust cloud - the original Chaos - turned out to be very tenacious and in subsequent times served as the basis for many theoretical arguments. In 1796, the French mathematician and astronomer Pierre-Simon Laplace, apparently unfamiliar with Kant's work, put forward a similar hypothesis of the formation of the planets of the solar system from a gas cloud and gave its mathematical justification. Since then, the Kant-Laplace hypothesis has become the leading cosmogonic hypothesis, explaining how our Sun and planets originated. Ideas about the gas-dust origin of the Sun and planets were subsequently refined and supplemented in accordance with new information about the properties and structure of matter.
Today it is assumed that the formation of the Sun and planets began about 10 billion years ago. The initial cloud consisted of 3/4 hydrogen and 1/4 helium, and the proportion of all other chemical elements was negligible. The rotating cloud gradually compressed under the influence of gravity. The bulk of the matter was concentrated in its center, which gradually became denser to such a state that a thermonuclear reaction began with the release of a large amount of heat and light, that is, a star flared up - our Sun. The remnants of the gas and dust cloud, rotating around it, gradually acquired the shape of a flat disk. Clots of denser matter began to appear in it, which over billions of years “blended” into planets. Moreover, the planets first appeared near the Sun. These were relatively small formations with high density - iron-stone and stone spheres - terrestrial planets. After this, giant planets, consisting mainly of gases, formed in a region more distant from the Sun. Thus, the original dust disk ceased to exist, turning into a planetary system. Several years ago, a hypothesis appeared by geologist Academician A.A. Marakushev, according to which it is assumed that terrestrial planets in the past were also surrounded by extensive gaseous shells and looked like giant planets. Gradually, these gases were carried away to the outskirts of the solar system, and near the Sun only the solid cores of the former giant planets remained, which are now terrestrial planets. This hypothesis echoes the latest data on exoplanets, which are balls of gas located very close to their stars. Perhaps in the future, under the influence of heating and stellar wind flows (high-speed plasma particles emitted by the star), they will also lose powerful atmospheres and turn into twins of Earth, Venus and Mars.
Space panopticon
Exoplanets are very unusual. Some move along highly elongated orbits, which leads to significant changes in temperature, while others, due to their extremely close location to the star, are constantly heated to +1,200°C. There are exoplanets that make a full revolution around their star in just two Earth days, they move so quickly in their orbits. Over some, two or even three “suns” shine at once - these planets revolve around stars that are part of a system of two or three stars located close to each other. Such diverse properties of exoplanets initially stunned astronomers. We had to reconsider many established theoretical models of the formation of planetary systems, because modern ideas about the formation of planets from a protoplanetary cloud of matter are based on the structural features of the Solar system. It is believed that in the hottest region near the Sun, refractory materials remained - metals and rocks, from which terrestrial planets were formed. The gases escaped to a cooler, more distant region, where they condensed into giant planets. Some of the gases that ended up at the very edge, in the coldest region, turned into ice, forming many tiny planetoids. However, among exoplanets, a completely different picture is observed: gas giants are located almost close to their stars. Astronomers intend to discuss the theoretical explanation of these data and the first results of a new understanding of the formation and evolution of stars and planets in early 2007 at an international scientific conference at the University of Florida.
Most discovered exoplanets are giant balls of gas similar to Jupiter, with a typical mass of about 100 Earth masses. There are about 170 of them, that is, 90% of the total. Among them there are five varieties. The most common are “water giants,” so named because, judging by their distance from the star, their temperature should be the same as that of Earth. Therefore, it is natural to expect that they are shrouded in clouds of water vapor or ice crystals. Overall, these 54 cool “water giants” should look like bluish-white balls. The next most common are 42 “hot Jupiters.” They are very close to their stars (10 times closer than the Earth is from the Sun), and therefore their temperature is from +700 to +1,200°C. They are thought to have a brownish-purple atmosphere with dark streaks of clouds made of graphite dust. It is slightly cooler on 37 exoplanets with a bluish-lilac atmosphere, called “warm Jupiters,” whose temperatures range from +200 to +600 ° C. There are 19 “sulfuric acid giants” located in even cooler regions of planetary systems. It is assumed that they are shrouded in a cloud cover of sulfuric acid droplets - such as on Venus. Sulfur compounds can give these planets a yellowish-white color. The already mentioned “water giants” are located even further from the corresponding stars, and in the coldest regions there are 13 “Jupiter twins”, which are similar in temperature to the real Jupiter (from -100 to -200 ° C on the outer surface of the cloud layer) and, probably, look about the same - with bluish-white and beige stripes of clouds, interspersed with white and orange spots of large vortices.
In addition to the giant gas planets, a dozen smaller exoplanets have been discovered in the last two years. They are comparable in mass to the “small giants” of the Solar System - Uranus and Neptune (from 6 to 20 Earth masses). Astronomers called this type "Neptunes." Among them there are four varieties. “Hot Neptunes” are the most common, with nine of them discovered. They are located very close to their stars and are therefore very hot. Two “cold Neptunes,” or “ice giants,” similar to Neptune from the solar system, have also been found. In addition, two “super-Earths” are also classified as this type - massive terrestrial-type planets that do not have such a dense and thick atmosphere as those of the giant planets. One of the “super-Earths” is considered “hot”, reminiscent in its characteristics of the planet Venus with very likely volcanic activity. On the other, “cold” one, the presence of a water ocean is assumed, for which it has already been unofficially dubbed the Oceanid. In general, exoplanets do not yet have their own names and are designated by a letter of the Latin alphabet added to the number of the star around which they revolve. The Cold Super-Earth is the smallest of the exoplanets. It was discovered in 2005 as a result of joint research by 73 astronomers from 12 countries. Observations were carried out at six observatories - in Chile, South Africa, Australia, New Zealand and the Hawaiian Islands. This planet is extremely far from us—20,000 light years.
America joins
In 2008, NASA plans to launch into space the first American apparatus designed to study exoplanets. This will be an automatic Kepler station. It is named after the German astronomer, who in the 17th century established the laws of planetary motion around the Sun. Using a space telescope with a diameter of 95 cm, capable of simultaneously monitoring the changes in the brightness of 100,000 stars, it is planned to find about 50 planets the size of Earth and up to 600 planets with a mass 2-3 times that of Earth. The search will be carried out by recording the periodic weakening of the star's light caused by the passage of a planet in its background. Unfortunately, this simple and visual technique has one drawback - it allows you to see only those planets that are on the same line between the Earth and the star, while many others circling in inclined planes go unnoticed. In 4 years, Kepler must study in detail two relatively small areas of the sky, each the size of the “bucket” of the constellation Ursa Major. The results of the work of this telescope will make it possible to construct a kind of “periodic table” of planetary systems - to classify them according to the characteristics of their orbits and other properties. This will give an idea of how typical or unique our own solar system is and what processes led to the formation of planets, including Earth.
Galactic ecosphere
Of course, the greatest interest is generated by those exoplanets on which life may exist. To purposefully start looking for “brothers in mind” in space, you must first find a planet with a solid surface on which they could hypothetically live. It is unlikely that aliens fly within the atmospheres of gas giants or swim in the depths of the oceans. In addition to a hard surface, you also need a comfortable temperature, as well as the absence of harmful radiation that is incompatible with life (at least with the forms of life known to us). Planets that have water are considered habitable. Therefore, the average temperature on their surface should be about 0°C (it can deviate significantly from this value, but not exceed +100°C). For example, the average temperature on the Earth’s surface is +15°C, and the range of fluctuations is from -90 to +60°C. Regions of space with conditions favorable for the development of life as we know it on Earth are called “habitable zones” by astronomers. Terrestrial planets and their satellites located in such zones are the most likely places for the manifestation of extraterrestrial life forms. The emergence of favorable conditions is possible in cases where the planet is located in two habitable zones at once - circumstellar and galactic.
The circumstellar habitable zone (sometimes also called the “ecosphere”) is an imaginary spherical shell around a star within which the temperature on the surface of the planets allows the presence of water. The hotter the star, the farther such a zone is from it. In our solar system, such conditions exist only on Earth. The planets closest to it, Venus and Mars, are located exactly on the boundaries of this layer - Venus is on the hot side, and Mars is on the cold side. So the location of the Earth is very favorable. If it were closer to the Sun, the oceans would evaporate and the surface would become a hot desert. Further from the Sun, global glaciation will occur and the Earth will turn into a frosty desert. The galactic habitable zone is that region of space that is safe for the manifestation of life. Such a region must be close enough to the center of the galaxy to contain many of the heavy chemical elements necessary for the formation of rocky planets. At the same time, this region must be at a certain distance from the center of the galaxy in order to avoid radiation bursts that occur during supernova explosions, as well as disastrous collisions with numerous comets and asteroids, which can be caused by the gravitational influence of wandering stars. Our Galaxy, the Milky Way, has a habitable zone approximately 25,000 light years from its center. Once again, we were lucky that the Solar System was in a suitable region of the Milky Way, which, according to astronomers, includes only about 5% of all the stars in our Galaxy.
Future searches for terrestrial planets near other stars, planned with the help of space stations, are aimed precisely at such areas favorable for life. This will significantly limit the search area and give hope for the discovery of life outside the Earth. A list of 5,000 of the most promising stars has already been compiled. The surroundings of 30 stars from this list, the location of which is considered the most favorable for the emergence of life, will be studied first.
An infrared view of life
An important milestone in exoplanet research will begin with the launch of a fleet of space telescopes in 2015. This will require two entire Soyuz-Fregat rockets, launching from the Kourou spaceport in French Guiana (South America), located near the equator. The European Space Agency named this project Darwin in honor of the famous English naturalist Charles Darwin, whose work literally overturned the ideas about the evolution of living organisms on Earth that had existed by the mid-19th century. A century and a half later, his cosmic namesake may do something similar, but this time in relation to planets outside our solar system. To do this, three telescopes with mirrors with a diameter of 3.5 meters must be sent into orbit around the Sun, to a point located 1.5 million km from the Earth (4 times further than the Moon). They will observe terrestrial exoplanets in the infrared (thermal) range. These three automatic stations constitute a single system, the efficiency of which will correspond to a telescope with a much larger mirror. They will be placed along a circle with a diameter of 100 m, and their relative position will be corrected by a laser system. To do this, a navigation satellite will be launched along with the telescopes, coordinating their location and helping to orient the optical axes of all three telescopes strictly in a given direction. Using disk-shaped radiators, infrared photodetectors will be cooled to -240°C to provide high sensitivity - tens of times greater than that of the new James Webb Space Telescope. Unlike the previous stations COROT and Kepler, the search for signs of life will be carried out according to a pre-prepared list and only near stars located relatively close to us - no more than 8 light years. Analysis of the spectra of exoplanet atmospheres will reveal such traces of possible life activity as the presence of oxygen, carbon dioxide, and methane. The first images of exoplanets similar to Earth should also be obtained.
Planet Watch
The first specialized satellite to search for terrestrial planets outside the solar system will be COROT, which is scheduled to launch in mid-October this year. On board is a space telescope with a diameter of 30 cm, designed to observe periodic changes in the brightness of a star caused by the passage of a planet against its background. The data obtained will make it possible to determine the presence of a planet, establish its size and features of its orbit around the star. This project was developed by the French National Center for Space Research (CNES) with the participation of the European (ESA) and Brazilian (AEB) space agencies. Specialists from Austria, Spain, Germany and Belgium contributed to the preparation of the equipment. With the help of this satellite it is expected to find several dozen terrestrial planets only several times larger than the Earth, which is the largest of the “rocky” planets in our solar system. This is almost impossible to do from Earth, where atmospheric vibrations prevent such small objects from being detected - which is why all the exoplanets discovered so far are giant structures the size of Neptune, Jupiter and even larger. Earth-type rocky planets are several times smaller in diameter and tens and hundreds of times smaller in mass, but they are of interest in the search for extraterrestrial life.
The scientific equipment installed on the COROT satellite is distinguished not by size or quantity, but by quality - high sensitivity. The satellite contains a telescope consisting of two parabolic mirrors with a focal length of 1.1 m and a field of view of approximately 3x3°, a highly stable digital camera and an on-board computer. The satellite will fly around the Earth in a polar circular orbit at an altitude of 900 km. The first stage of observations will take five months, during which two areas of the sky will be studied. The total duration of the satellite's operation will be two and a half years. In the spring of 2006, COROT was delivered to the Baikonur Cosmodrome in Kazakhstan for pre-flight testing and installation on the launch vehicle. The launch is scheduled for October 15 this year using the Russian Soyuz-Fregat rocket. European automatic stations have already repeatedly launched into space on such rockets, heading to Mars and Venus. In addition to the main task of searching for exoplanets, the satellite will carry out observations of “starquakes” - vibrations of the surfaces of stars caused by processes in their interiors.
Four centuries ago, the Italian monk, doctor of theology and writer Giordano Bruno believed that life was present on all celestial bodies. He believed that “intelligent animals” of other worlds could be very different from people, but he had no opportunity to more definitely imagine what extraterrestrial life was like, since nothing was known about the nature of the planets at that time. He was not alone in his belief that there was life beyond the Earth. Nowadays, one of the discoverers of the double helix of the DNA molecule, the English scientist Francis Crick, noting that the genetic code is identical in all living objects, said that life on Earth could have originated thanks to microorganisms brought from outside. He even quite seriously believed that we might “still be under the surveillance of more intelligent beings from a planet located near some neighboring star.” What might extraterrestrial life be like? On the surface of small but massive planets, where gravity is strong, flat, crawling creatures would most likely live. And the inhabitants of the giant planets will have to float in their dense, humid atmosphere. It is easier to imagine life in the watery shells of planets—whether on the surface or under the ice—by analogy with Earth’s seas and oceans. There are no fundamental barriers to life on small planets far from their star - their inhabitants will simply be forced to hide from the cold in crevices and collect weak light with a reflector similar to a tulip flower.
Exo Object Hunters
Following the COROT satellite, other space stations should rush to search for exoplanets. Moreover, each subsequent flight will be carried out after analyzing the data received from previously launched vehicles. This will allow for a targeted search and reduce the time it takes to discover interesting objects. The nearest launch is scheduled for 2008: the American automatic station Kepler will take over the watch, with the help of which it is planned to find about 50 planets the size of the Earth. In another year, the second American station, SIM (Space Interferometry Mission), should begin its flight, the research of which will cover an even larger number of stars. It is expected to obtain information about several thousand exoplanets, including hundreds of terrestrial planets. At the end of 2011, the European apparatus Gaia (Global Astrometric Interferometer for Astrophysics) should be launched into space, with the help of which it is planned to find up to 10,000 exoplanets.
In 2013, under a joint project of the USA, Canada and Europe, it is planned to launch the large space telescope JWST (James Webb Space Telescope). This giant with a mirror with a diameter of 6 meters, bearing the name of the former director of NASA, is intended to replace the veteran of space astronomy - the Hubble telescope. Among its tasks will be the search for planets outside the solar system. In the same year, a complex of two automatic TPF (Terrestrial Planet Finder) stations will be launched, designed exclusively for observing the atmospheres of exoplanets similar to our Earth. With the help of this space observatory, it is planned to search for habitable planets, analyzing the spectra of their gas shells to detect water vapor, carbon dioxide and ozone - gases that indicate the possibility of life. Finally, in 2015, the European Space Agency will send a fleet of Darwin telescopes into space, designed to search for signs of life outside the solar system by analyzing the composition of the atmospheres of exoplanets.
If space exploration of exoplanets goes according to plans, then within ten years we can expect the first reliable news about planets favorable for life - data on the composition of the atmospheres around them and even information about the structure of their surfaces.
