What is an exoplanet? Exoplanet Examples
People have long dreamed that sooner or later, in space, in the near vicinity of us, life will be revealed, even if in a form that is not similar to ours. Numerous fantastic stories and stories, films about the meeting of representatives of the Earth and extraterrestrial civilizations excite the imagination and enjoy the same success.
Among the multitude of space objects, the special attention of scientists is attracted to the so-called exoplanets as potential objects for the origin and development of extraterrestrial life forms. What do they represent?
For the first time an astronomer at the Madras Observatory, Captain Jacob, reported on the possible existence of planetary systems in other stars in 1855. It was about the system of the double star 70 Ophiuchi. The hypothesis was refuted by later studies conducted in the 90s of the XIX century, however, a precedent was created, and the search for planetary systems outside the solar system was begun.
During the twentieth century, “discoveries” periodically took place, which were not confirmed later. And only in 1988, Canadian scientists discovered the extrasolar planet near the star Gamma Cepheus A (Alrai). However, the confirmation of this amazing discovery took years, and its existence was confirmed only in 2002. Therefore, the championship still belongs to the Swiss astronomers Didier Kelo and Michel Mayor, who in 1995 discovered the first extraterrestrial planet - at the star 51 Pegasus.
What is an exoplanet? This is a celestial body, like the Earth, revolving around its star - the star. Today, there are about three thousand. The vast majority of them are gas giants, similar to our Jupiter, Neptune and Saturn, but significantly exceeding them in mass. Life on such hot celestial bodies in the usual sense, that is, in protein form, most likely, is absent.
As of January 2018, the existence of 3,726 exoplanets was officially confirmed, and about a thousand of these celestial bodies are still awaiting official confirmation of their status with the help of terrestrial telescopes.
Giant gas giants are classified according to their temperature and the characteristics of the atmosphere, in appearance. In total, there are five classes:
- Ammonia clouds. These are exoplanets that are far from their stars, on the backs of their solar systems, at temperatures below - 120 degrees Celsius. Year on exoplanets of this type will be very long by earthly standards. Solar planets such as Jupiter and Saturn belong to this type. Possible exoplanets of this type - Mu Altar e, 47 Ursa Major c. The main discoveries are still ahead.It is also possible that the exoplanet is at a not so significant distance from its star, but rotates around a weak star, the red dwarf. Then she, too, falls into this class.
- Water clouds. The surface temperature is -20 degrees Celsius or lower. Well reflect light. In addition to water suspension, there is a lot of methane and hydrogen in the clouds of such celestial bodies, therefore it is difficult to attribute them to exoplanets suitable for life. These are gas giants, whose remoteness from their star is comparable to that of the earth. An example is the exoplanet 47 Ursa Major b.There are no such celestial bodies in the solar system.
- Cloudless exoplanets. These planets, as their name suggests, are devoid of clouds, and therefore have a weak reflectivity. For the observer, their surface is blue. Temperatures range from +80 degrees Celsius to +530. There are no such planets in the solar system. If they were, they would be located approximately in the orbit of Mercury. An example is 79 Kit b.
- Exoplanets with strong spectral lines of alkali metals. They have a surface temperature of over + 600 (possibly up to +1000) degrees Celsius, and therefore carbon dioxide and alkali metal vapor prevails from their atmosphere. Possess very low reflectivity. An example is the TrES-2 b exoplanet, whose reflectivity is lower than that of soot. They have a gray-pink color; in the Solar System they would have to be in an orbit that is closer to the Sun than the Mercury one.
- Silicon clouds. What are exoplanets with silicon clouds? These are gas celestial bodies, whose temperature is more than +1100 degrees Celsius. Their surface is covered with continuous clouds consisting of silicates and vapors of iron.Because of this, the reflectivity is quite high. Such exoplanets suitable for life are as difficult to call as those covered with ammonia clouds, on which terrible cold reigns. They have a gray-green color and are located in close proximity to their sun, so it is impossible to visually detect them, because their luminosity will not be visible. The most famous representative is 51 Pegasus b.
The above classification was proposed by David Sudarsky, an astrophysicist from the University of Arizona.
Much more likely to detect life on other planets of alien star systems - those that are similar to our Earth. What is a terrestrial exoplanet? This is a celestial body, consisting not of hot gases, but solid, smaller than gas giants. Because of their relatively small size, such exoplanets are more difficult to detect, so they are not as well known as the gas giants - a little over two hundred.
Approximately seven hundred more have the size of the so-called super-earth. This term refers to celestial bodies, the mass of which is up to 10 earthly.The difference between them and the gas giants is not clearly defined, it is about 10 Earth masses. As an example of a “borderline” exoplanet, Mu Arae c, or Mu of Altar C, is a giant planet that revolves around a yellow dwarf in the constellation of Altar, discovered in 2004. Its mass is about 0.33 mass of Jupiter. Superstar stars are usually red or yellow dwarfs.
Exoplanet Discovery Methods
Currently, there are several methods for finding potentially habitable planets in other star systems. The best results are achieved when they are combined, since some of them work only under certain specific conditions. The main ones are described below.
This involves measuring the radial velocities of stars using a spectrometer. With the help of the spectrometric method, it is possible to detect giant planets and exoplanets similar to the Earth, located near its star, whose mass is at least several times larger than that of the Earth. This is due to the fact that the rotation of these celestial bodies causes the Doppler shift of the spectrum of a star.According to statistics, more than 600 exoplanets have been discovered using this method.
It consists in the study of fluctuations in the glow of stars during the passage of hypothetical planets in front of their disk. With it, you can calculate the size of the planet, while its combination with the first method gives an idea of the density of a celestial body. This, in turn, suggests the presence of his atmosphere. Statistics show that due to the transit method about two hundred planets were discovered.
Gravity microlensing method
Like a transit route, for the use of which it is necessary that the observer and the exoplanet orbit are in the same plane, certain conditions are also needed for this method. It will be effective if there is another star between the earth observer and the star, which plays the role of a kind of lens. Allows detecting exoplanets in a star-lens, works for bodies with a small mass. But it is applied, due to the special requirements put forward to the arrangement of celestial bodies, limitedly. This way it was discovered about a dozen planets.
Based on changes in the movement of stars under the action of their own planets. Allows you to determine with sufficient accuracy the mass of exoplanets.
The above are not all known methods for detecting exoplanets, but those with the help of which more discoveries were made, which proved their effectiveness.
Designations of planetary type celestial bodies
Open exoplanets are usually given names derived from their star - the star around which they rotate. In this case, the letter of the Latin alphabet is added to the name of the star, starting with b, since a would indicate the star itself. Example: 51 Pegasi b. The next open planet in the star system is assigned the next letter of the alphabet. It turns out that the name of an exoplanet says nothing about its properties, nor about its distance from the star, but reports only on the order of its discovery in the star system. And only if they open two exoplanets simultaneously in the same system, they are assigned letters in the names, based on the distance from the star.
Prior to the discovery in 1995 of the Pegasus star system, exoplanets were given names consisting of complex combinations of Latin letters and numbers.In addition, some of them had their own names, often associated with mythology. In 2015, the voting of the International Astronomical Union, these names were formalized. In total, they received 31 exoplanets and 14 stars.
To date, exoplanets are found in about 10% of the stars around which searches were conducted.
Here is a short list of famous star systems with exoplanets:
- 51 Pegasus is the first sun-like star in which an exoplanet is found.
- Tau Ceti is theoretically the closest planetary system in us. but this discovery still requires confirmation.
- 55 Cancer - several exoplanets are already open in it.
- μ Altar - open in its system exoplanet has a small mass and, apparently, belongs to the terrestrial group.
- ε Eridanne is one of three stars that have an exoplanet and are visible without a telescope.
- Proxima Centauri - the star closest to the Sun (red dwarf), having an exoplanet.
- HD 209458 - a planet with its own name "Osiris" and amazing properties, nicknamed "evaporating", revolves around this star. Studies of its brightness showed the presence of vibrations, which from the point of view of science can only be explained by the gradual loss of its substance by the planet.Further observations have shown that not only the atmosphere, but also the solid constituents of the planetary substance evaporate. The reason for this probably lies in the strong warming up of the exoplanets, because it is located at a distance from its star, eight times smaller than Mercury from the Sun. The temperature on its surface can reach + 1000 degrees Celsius. Thanks to observations of the exoplanet Osiris, a new era has begun in the study of extraterrestrial planetary systems - the era of studying their chemical composition and the search for life-friendly conditions.
Of course, this list of exoplanetary systems is incomplete; today, much more is known.
Earth-like exoplanet with atmosphere
In April of last year, 2017, Western European astronomers first discovered traces of the atmosphere around an exoplanet of the earthly type. This is a celestial body GJ 1132b, which rotates around a star - a red dwarf Gliese 1132. The distance to it from the Earth is 39 light years (12 parsecs). The radius of the exoplanet GJ 1132b is 20% larger than our planet, and its mass is 1.6 Earth. It is understood that its composition is close to the composition of terrestrial rocks, and the surface is solid, rocky.This is the closest earth-like planet to us.
According to spectral analysis, the atmosphere of this exoplanet consists of a mixture of methane and water vapor. The temperature in its upper layers is approximately 260 degrees Celsius, but it is assumed that it is even higher near the surface, that is, the conditions on this exoplanet are even hotter than on Venus.
This is the nearest exoplanet to our solar system, which has the atmosphere. Scientists-astronomers called this discovery one of the most important in recent years.
Instead of conclusion
The article was about what exoplanets are, their types, rules of naming are considered. Summing up, we can say that the era of the mass discovery of exoplanets in the late twentieth - early twenty-first century is just beginning. To date, there are several effective methods for detecting these celestial bodies, but they all have some degree of error. The best result is the combination of several methods for detecting exoplanetary systems. Moreover, most of these discoveries require confirmation, which has to wait several years, or even decades.
The results of discoveries made by earthly observers make it possible to correct observations from space.For example, during the Gaia project, which was launched in 2013, a satellite carrying a space telescope was launched into Earth’s orbit. The main objective of the project was to refine the star charts and the masses of known exoplanets discovered before that time.