Planets outside the solar system. Why Pluto is no longer a planet. Why Pluto is no longer a planet

Planets of the solar system

According to the official position of the International Astronomical Union (IAU), an organization that assigns names to astronomical objects, there are only 8 planets.

Pluto was removed from the category of planets in 2006. because in the Kuiper belt are objects that are larger / or equal in size to Pluto. Therefore, even if it is taken as a full-fledged celestial body, then it is necessary to add Eris to this category, which has almost the same size with Pluto.

As defined by MAC, there are 8 known planets: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

All planets are divided into two categories depending on their physical characteristics: terrestrial and gas giants.

Schematic representation of the location of the planets

terrestrial planets

Mercury

The smallest planet in the solar system has a radius of only 2440 km. The period of revolution around the Sun, for ease of understanding, equated to the earth's year, is 88 days, while Mercury has time to complete a revolution around its own axis only one and a half times. Thus, its day lasts approximately 59 Earth days. For a long time it was believed that this planet was always turned to the Sun by the same side, since the periods of its visibility from the Earth were repeated with a frequency approximately equal to four Mercury days. This misconception was dispelled with the advent of the possibility of using radar research and conducting continuous observations using space stations. The orbit of Mercury is one of the most unstable; not only the speed of movement and its distance from the Sun change, but also the position itself. Anyone interested can observe this effect.

Mercury in color, as seen by the MESSENGER spacecraft

Mercury's proximity to the Sun has caused it to experience the largest temperature fluctuations of any of the planets in our system. The average daytime temperature is about 350 degrees Celsius, and the nighttime temperature is -170 °C. Sodium, oxygen, helium, potassium, hydrogen and argon have been identified in the atmosphere. There is a theory that it was previously a satellite of Venus, but so far this remains unproven. It has no satellites of its own.

Venus

The second planet from the Sun, the atmosphere of which is almost entirely composed of carbon dioxide. It is often called the Morning Star and the Evening Star, because it is the first of the stars to become visible after sunset, just as before dawn it continues to be visible even when all other stars have disappeared from view. The percentage of carbon dioxide in the atmosphere is 96%, there is relatively little nitrogen in it - almost 4%, and water vapor and oxygen are present in very small amounts.

Venus in the UV spectrum

Such an atmosphere creates a greenhouse effect, the temperature on the surface because of this is even higher than that of Mercury and reaches 475 ° C. Considered the slowest, the Venusian day lasts 243 Earth days, which is almost equal to a year on Venus - 225 Earth days. Many call it the sister of the Earth because of the mass and radius, the values ​​​​of which are very close to the earth's indicators. The radius of Venus is 6052 km (0.85% of the earth). There are no satellites, like Mercury.

The third planet from the Sun and the only one in our system where there is liquid water on the surface, without which life on the planet could not develop. At least life as we know it. The radius of the Earth is 6371 km and, unlike the rest of the celestial bodies in our system, more than 70% of its surface is covered with water. The rest of the space is occupied by the continents. Another feature of the Earth is the tectonic plates hidden under the planet's mantle. At the same time, they are able to move, albeit at a very low speed, which over time causes a change in the landscape. The speed of the planet moving along it is 29-30 km / s.

Our planet from space

One rotation around its axis takes almost 24 hours, and a complete orbit lasts 365 days, which is much longer in comparison with the nearest neighboring planets. The Earth day and year are also taken as a standard, but this is done only for the convenience of perceiving time intervals on other planets. The Earth has one natural satellite, the Moon.

Mars

The fourth planet from the Sun, known for its rarefied atmosphere. Since 1960, Mars has been actively explored by scientists from several countries, including the USSR and the USA. Not all research programs have been successful, but water found in some areas suggests that primitive life exists on Mars, or existed in the past.

The brightness of this planet allows you to see it from Earth without any instruments. And once every 15-17 years, during the Opposition, it becomes the brightest object in the sky, eclipsing even Jupiter and Venus.

The radius is almost half that of the earth and is 3390 km, but the year is much longer - 687 days. He has 2 satellites - Phobos and Deimos .

Visual model of the solar system

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• The sun

  The sun is a star, which is a hot ball of hot gases at the center of our solar system. Its influence extends far beyond the orbits of Neptune and Pluto. Without the Sun and its intense energy and heat, there would be no life on Earth. There are billions of stars, like our Sun, scattered throughout the Milky Way galaxy.

• Mercury

  Sun-scorched Mercury is only slightly larger than Earth's moon. Like the Moon, Mercury is practically devoid of an atmosphere and cannot smooth out the traces of impact from the fall of meteorites, therefore, like the Moon, it is covered with craters. The day side of Mercury is very hot on the Sun, and on the night side the temperature drops hundreds of degrees below zero. In the craters of Mercury, which are located at the poles, there is ice. Mercury makes one revolution around the Sun in 88 days.

• Venus

  Venus is a world of monstrous heat (even more than on Mercury) and volcanic activity. Similar in structure and size to Earth, Venus is covered in a thick and toxic atmosphere that creates a strong greenhouse effect. This scorched world is hot enough to melt lead. Radar images through the mighty atmosphere revealed volcanoes and deformed mountains. Venus rotates in the opposite direction from the rotation of most planets.

• Earth is an ocean planet. Our home, with its abundance of water and life, makes it unique in our solar system. Other planets, including several moons, also have ice deposits, atmospheres, seasons, and even weather, but only on Earth did all these components come together in such a way that life became possible.

• Mars

  Although details of the surface of Mars are difficult to see from Earth, telescope observations show that Mars has seasons and white spots at the poles. For decades, people have assumed that the bright and dark areas on Mars are patches of vegetation and that Mars might be a suitable place for life, and that water exists in the polar caps. When the Mariner 4 spacecraft flew by Mars in 1965, many of the scientists were shocked to see pictures of the bleak, cratered planet. Mars turned out to be a dead planet. More recent missions, however, have shown that Mars holds many mysteries that have yet to be solved.

• Jupiter

  Jupiter is the most massive planet in our solar system, has four large moons and many small moons. Jupiter forms a kind of miniature solar system. To turn into a full-fledged star, Jupiter had to become 80 times more massive.

• Saturn

  Saturn is the most distant of the five planets that were known before the invention of the telescope. Like Jupiter, Saturn is made up mostly of hydrogen and helium. Its volume is 755 times that of the Earth. Winds in its atmosphere reach speeds of 500 meters per second. These fast winds, combined with heat rising from the planet's interior, cause the yellow and golden streaks we see in the atmosphere.

• Uranus

  The first planet found with a telescope, Uranus was discovered in 1781 by astronomer William Herschel. The seventh planet is so far from the Sun that one revolution around the Sun takes 84 years.

• Neptune

  Nearly 4.5 billion kilometers from the Sun, distant Neptune rotates. It takes 165 years to complete one revolution around the Sun. It is invisible to the naked eye due to its vast distance from Earth. Interestingly, its unusual elliptical orbit intersects with the orbit of the dwarf planet Pluto, which is why Pluto is inside Neptune's orbit for about 20 out of 248 years during which it makes one revolution around the Sun.

• Pluto

  Tiny, cold and incredibly distant, Pluto was discovered in 1930 and has long been considered the ninth planet. But after the discovery of Pluto-like worlds even further away, Pluto was reclassified as a dwarf planet in 2006.

The planets are giants

There are four gas giants located beyond the orbit of Mars: Jupiter, Saturn, Uranus, Neptune. They are in the outer solar system. They differ in their massiveness and gas composition.

Planets of the solar system, not to scale

Jupiter

The fifth planet from the Sun and the largest planet in our system. Its radius is 69912 km, it is 19 times larger than the Earth and only 10 times smaller than the Sun. A year on Jupiter is not the longest in the solar system, lasting 4333 Earth days (incomplete 12 years). His own day has a duration of about 10 Earth hours. The exact composition of the planet's surface has not yet been determined, but it is known that krypton, argon and xenon are present on Jupiter in much larger quantities than on the Sun.

There is an opinion that one of the four gas giants is actually a failed star. This theory is also supported by the largest number of satellites, of which Jupiter has many - as many as 67. To imagine their behavior in the orbit of the planet, a fairly accurate and clear model of the solar system is needed. The largest of them are Callisto, Ganymede, Io and Europa. At the same time, Ganymede is the largest satellite of the planets in the entire solar system, its radius is 2634 km, which is 8% larger than the size of Mercury, the smallest planet in our system. Io has the distinction of being one of only three moons with an atmosphere.

Saturn

The second largest planet and the sixth largest in the solar system. In comparison with other planets, the composition of chemical elements is most similar to the Sun. The surface radius is 57,350 km, the year is 10,759 days (almost 30 Earth years). A day here lasts a little longer than on Jupiter - 10.5 Earth hours. In terms of the number of satellites, it is not far behind its neighbor - 62 versus 67. The largest satellite of Saturn is Titan, just like Io, which is distinguished by the presence of an atmosphere. Slightly smaller than it, but no less famous for this - Enceladus, Rhea, Dione, Tethys, Iapetus and Mimas. It is these satellites that are the objects for the most frequent observation, and therefore we can say that they are the most studied in comparison with the rest.

For a long time, the rings on Saturn were considered a unique phenomenon, inherent only to him. Only recently it was found that all gas giants have rings, but the rest are not so clearly visible. Their origin has not yet been established, although there are several hypotheses about how they appeared. In addition, it was recently discovered that Rhea, one of the satellites of the sixth planet, also has some kind of rings.

Pluto is one of the least explored objects in the solar system. Due to its great distance from the Earth, it is difficult to observe with telescopes. Its appearance is more like a small star than a planet. But until 2006, it was he who was considered the ninth planet of the solar system known to us. Why was Pluto excluded from the list of planets, what led to this? Let's consider everything in order.

Unknown to science "Planet X"

At the end of the 19th century, astronomers suggested that there must be another planet in our solar system. The assumptions were based on scientific data. The fact is that, while observing Uranus, scientists discovered a strong influence of foreign bodies on its orbit. So, after some time, Neptune was discovered, but the influence was much stronger, and the search for another planet began. It was called "Planet X". The search continued until 1930 and was crowned with success - Pluto was discovered.

Pluto's movement was noticed on photographic plates taken over the course of two weeks. Observations and confirmation of the existence of an object beyond the known limits of the galaxy of another planet took more than a year. Clyde Tombaugh, a young astronomer at the Lowell Observatory that initiated the research, announced the discovery to the world in March 1930. So, the ninth planet appeared in our solar system for 76 years. Why was Pluto excluded from the solar system? What was wrong with this mysterious planet?

New discoveries

At one time, Pluto, classified as a planet, was considered the last of the objects in the solar system. According to preliminary data, its mass was considered equal to the mass of our Earth. But the development of astronomy constantly changed this indicator. Today, Pluto's mass is less than 0.24% and its diameter is less than 2,400 km. These indicators were one of the reasons why Pluto was excluded from the list of planets. It is more suitable for a dwarf than for a full-fledged planet in the solar system.

It also has many of its own features that are not inherent in ordinary planets of the solar system. The orbit, its small satellites and atmosphere are unique in themselves.

unusual orbit

Orbits habitual for eight planets of the solar system are almost round, having a slight inclination along the ecliptic. But Pluto's orbit is a highly elongated ellipse and has an inclination angle of more than 17 degrees. If you imagine that eight planets will rotate uniformly around the Sun, and Pluto will cross the orbit of Neptune because of its angle of inclination.

In view of such an orbit, it makes a revolution around the Sun in 248 Earth years. And the temperature on the planet does not rise above minus 240 degrees. Interestingly, Pluto rotates in the opposite direction from our Earth, like Venus and Uranus. This unusual orbit for the planet was another reason why Pluto was excluded from the list of planets.

satellites

Today five Charons, Nikta, Hydra, Cerberus and Styx are known. All of them, except for Charon, are very small, and their orbits are too close to the planet. This is another one of the differences from the officially recognized planets.

In addition, Charon, discovered in 1978, is half the size of Pluto itself. But for a satellite it is too big. Interestingly, the center of gravity is outside of Pluto, and therefore it seems to swing from side to side. For these reasons, some scientists consider this object a double planet. And this also serves as an answer to the question of why Pluto was excluded from the list of planets.

Atmosphere

It is very difficult to study an object located at an almost inaccessible distance. It is assumed that Pluto consists of rocks and ice. The atmosphere on it was discovered in 1985. It consists mainly of nitrogen, methane and carbon monoxide. Its presence was able to determine when studying the planet, when it closed the star. Objects without an atmosphere cover the stars abruptly, while objects with an atmosphere close gradually.

Due to the very low temperature and elliptical orbit, the melting of ice produces an anti-greenhouse effect, which leads to an even greater decrease in temperature on the planet. After research conducted in 2015, scientists came to the conclusion that atmospheric pressure depends on the approach of the planet to the Sun.

Newest technologies

The creation of new powerful telescopes marked the beginning of further discoveries beyond the known planets. So, over time, those within the orbit of Pluto were discovered. In the middle of the last century, this ring was called the Kuiper belt. To date, hundreds of bodies are known with a diameter of at least 100 km and a composition similar to Pluto. The found belt turned out to be the main reason why Pluto was excluded from the planets.

The creation of the Hubble Space Telescope made it possible to study outer space in more detail, and especially distant galactic objects. As a result, an object called Eris was discovered, which turned out to be farther than Pluto, and over time, two more celestial bodies that were similar in diameter and mass to it.

The AMS New Horizons spacecraft, sent to explore Pluto in 2006, confirmed many of the scientific data. Scientists have a question about what to do with open objects. Are they classified as planets? And then in the solar system there will be not 9, but 12 planets, or the exclusion of Pluto from the list of planets will solve this issue.

Status review

When was Pluto removed from the list of planets? On August 25, 2006, the participants of the Congress of the International Astronomical Union, consisting of 2.5 thousand people, made a sensational decision - to exclude Pluto from the list of planets in the solar system. This meant that it was necessary to revise and rewrite many textbooks, as well as star charts and scientific works in this area.

Why was such a decision made? Scientists have had to rethink the criteria by which planets are classified. A long debate led to the conclusion that the planet must meet all the parameters.

First, the object must revolve around the Sun in its orbit. Pluto suits this parameter. Although its orbit is highly elongated, it revolves around the Sun.

Secondly, it should not be a satellite of another planet. This point also corresponds to Pluto. At one time it was believed that he was, but this assumption was discarded with the advent of new discoveries, and especially his own satellites.

The third point is to have enough mass to acquire a spherical shape. Pluto, although small in mass, is round, and this is confirmed by photographs.

And finally, the fourth requirement is to have a strong one to clear your orbit from others. For this one point, Pluto does not fit the role of a planet. It is located in the Kuiper belt and is not the largest object in it. Its mass is not enough to clear a path for itself in orbit.

Now it is clear why Pluto was excluded from the list of planets. But where do we list such objects? For such bodies, the definition of "dwarf planets" was introduced. They began to include all objects that do not correspond to the last paragraph. So Pluto is still a planet, albeit a dwarf one.

You have no idea how many people were upset when the decision was made to stop considering Pluto a planet in the solar system. Kids whose favorite cartoon dog, Pluto, is suddenly named after who knows what. Recall that in ancient Greek mythology, this is one of the names of the god of death. Chemists and nuclear physicists were saddened, who called this name plutonium - a radioactive element capable of destroying all of humanity. And what about astrologers? The unfortunate charlatans have fooled people for decades, describing how strong this degraded object has on their fate and character, and it’s good if indignant clients do not present material claims to them.

When did Pluto stop being considered a planet?

Be that as it may, Pluto ceased to be considered a planet in 2006. We must come to terms with this and live with the awareness of this fact. Does not work? Okay, then let's forget about feelings and try to look at the situation from the point of view of logic, which is what science always calls us to do.

The demolition of Pluto took place at the 26th General Assembly of the International Astronomical Society, held in Prague, and this decision caused a lot of controversy and objections. Some scientists wanted to keep it as a planet, but the only argument they could make to justify their desire was that "it would break tradition." The fact is that there is not, and never has been, any scientific reason to consider Pluto a planet. This is just one of the objects of the Kuiper belt - a huge cluster of heterogeneous celestial bodies located beyond the orbit of Neptune. There are about a trillion of them there, these objects. And all of them are blocks of stone and ice, like, in fact, Pluto. It's just the first one we've seen.

It is, of course, very large compared to most of its neighbors, but it is not the largest object in the Kuiper belt. Such is Eris, which, if inferior to Pluto in size, is quite a bit, so small that the debate about which of them is larger continues to this day. But it is a quarter heavier. This object is located twice as far from the Sun as Pluto. There are many other similar celestial bodies in the solar system. These are Haumea, and Makemane, and Ceres, which is located in the asteroid belt between Mars and Jupiter. According to scientists, in total we may have about a hundred such strong men. Waiting to be noticed.

There is no fantasy here. No animators, no chemists. Astrologers should have enough, but few serious people care about their interests. This is exactly the main reason why we stopped considering Pluto a planet. Because, together with him, we, in theory, should raise so many celestial bodies to this rank that the very word “planet” will lose its current meaning. In this regard, in the same 2006, astronomers defined clear criteria for objects claiming this status.

What are the criteria for a "planet"?

They must orbit the Sun, have enough gravity to bring themselves into a more or less spherical shape, and almost completely clear their orbit of other objects. Pluto cut off at the last point. Its mass is only 0.07% of the mass of everything that is on its circular trajectory. To give you an idea of ​​how insignificant this is, let's say that the mass of the Earth is 1,700,000 times the mass of other matter in its orbit.

Earth, Moon, Pluto for comparison

I must say that the International Astronomical Society turned out to be not entirely heartless. It came up with a new category for celestial bodies, satisfying only the first two criteria. Now they are dwarf planets. And in deference to the place that Pluto once occupied in our worldview and in our culture, it was decided to call the dwarf planets that are further than Neptune "plutoids." Which, of course, is pretty sweet.

And in the same year that astronomers decided that Pluto could no longer be called a planet, NASA launched the New Horizons spacecraft, whose mission is to visit this celestial body. As of this moment in time, this interplanetary station has completed its task by transmitting to Earth a lot of valuable data about Pluto, as well as picturesque photographs of this dwarf planet. Don't be lazy, find them online.
Let's hope that humanity's interest in Pluto does not end there. It is, after all, on our way to other stars and galaxies. We're not going to sit in our solar system forever.

Offended Pluto

- have small sizes and masses, the average density of these planets is several times greater than the density of water; they slowly rotate around their axes; they have few satellites (Mercury and Venus do not have them at all, Mars has two tiny ones, Earth has one).

The similarity of the terrestrial planets does not exclude a significant difference. For example, Venus, unlike other planets, rotates in the opposite direction to its movement around the Sun, and 243 times slower than the Earth (compare the length of the year and day on Venus). Mercury's period of revolution (i.e., the year of this planet) is only 1/3 more than the period of its rotation around the axis (in relation to the stars). The angles of inclination of the axes to the planes of their orbits for the Earth and Mars are approximately the same, but quite different for Mercury and Venus. And you know that this is one of the reasons that determines the nature of the change of seasons. The same as the Earth, the seasons are, therefore, on Mars (although each season is almost twice as long as on Earth).

It is possible that, according to a number of physical characteristics, distant Pluto, the smallest of the 9 planets, also belongs to the terrestrial planets. The average diameter of Pluto is about 2260 km. Only half the diameter of Pluto's moon Charon. Therefore, it is possible that the Pluto-Charon system, like the Earth-system, is a “double planet”.

atmospheres

Features of similarity and differences are also found in the study of the atmospheres of the planets of the terrestrial group. Unlike Mercury, which, like the Moon, is practically devoid of an atmosphere, Venus and Mars have it. Modern data on the atmospheres of Venus and Mars were obtained as a result of the flights of our (“Venus”, “Mars”) and American (“Pioner-Venus”, “Mariner”, “Viking”) AMS. Comparing the atmospheres of Venus and Mars with Earth's, we see that, in contrast to the nitrogen-oxygen atmospheres of the Earth, Venus and Mars have atmospheres mainly composed of carbon dioxide. The pressure near the surface of Venus is more than 90 times greater, and that of Mars is almost 150 times less than that of the surface of the Earth.

The temperature at the surface of Venus is very high (about 500°C) and remains almost the same. What is it connected with? At first glance, it seems with the fact that Venus is closer to the Sun than the Earth. But, as observations show, the reflectivity of Venus is greater than that of the Earth, and therefore heats both planets approximately equally. The high surface temperature of Venus is due to the greenhouse effect. It consists in the following: the atmosphere of Venus transmits the rays of the Sun, which heat the surface. The heated surface becomes a source of infrared radiation, which cannot leave the planet, as it is retained by the carbon dioxide and water vapor contained in the atmosphere of Venus, as well as the cloud cover of the planet. As a result of this, the balance between the influx of energy and its consumption in peaceful space is established at a higher temperature than that which would be on a planet that freely transmits infrared radiation.

We are accustomed to terrestrial clouds, consisting of small drops of water or ice crystals. The composition of the clouds of Venus is different: they contain droplets of sulfuric and, possibly, hydrochloric acid. The cloud layer greatly attenuates the sunlight, but, as the measurements performed on the Venera-11 and Venera-12 AMS showed, the illumination near the surface of Venus is approximately the same as near the Earth's surface on a cloudy day. Research carried out in 1982 by AMS Venera-13 and Venera-14 showed that the sky of Venus and its landscape are orange. This is explained by the peculiarity of light scattering in the atmosphere of this planet.

Gas in the atmospheres of the terrestrial planets is in continuous motion. Often, during dust storms that last for several months, a huge amount of dust rises into the atmosphere of Mars. Hurricane winds have been recorded in the atmosphere of Venus at heights where the cloud layer is located (from 50 to 70 km above the surface of the planet), but near the surface of this planet, the wind speed reaches only a few meters per second.

Thus, despite some similarities, in general, the atmospheres of the planets closest to the Earth differ sharply from the atmosphere of the Earth. This is an example of a discovery that could not have been predicted. Common sense dictated that planets with similar physical characteristics (for example, Earth and Venus are sometimes called “twin planets”) and about the same distance from the Sun should have very similar atmospheres. In fact, the reason for the observed difference is related to the peculiarities of the evolution of the atmospheres of each of the terrestrial planets.

The study of the atmospheres of the earth group plan not only allows a better understanding of the properties and history of the origin of the earth's atmosphere, but is also important for solving an environmental problem. For example, fogs - smogs, formed in the earth's atmosphere as a result of air pollution, are very similar in composition to Venusian clouds. These clouds, like dust storms on Mars, remind us that it is necessary to limit the release of dust and various kinds of industrial waste into the atmosphere of our planet if we want to maintain conditions on Earth suitable for the existence and development of life for a long time. Dust storms, during which dust clouds are held in the atmosphere of Mars for several months and spread over vast territories, make us think about some of the possible environmental consequences of a nuclear war.

surfaces

The terrestrial planets, like the Earth and the Moon, have solid surfaces. Ground-based optical observations allow us to obtain little information about them, since Mercury is difficult to see through a telescope even during elongations, the surface of Venus is hidden from us by clouds. On Mars, even during great oppositions (when the distance between Earth and Mars is minimal - about 55 million km), occurring once every 15 - 17 years, large telescopes can see details about 300 km in size. And yet, in recent decades, much has been learned about the surface of Mercury and Mars, as well as getting an idea of ​​the until recently completely mysterious surface of Venus. This became possible thanks to the successful flights of automatic interplanetary stations of the Venera, Mars, Viking, Mariner, Magellan types, which flew near the planets or landed on the surface of Venus and Mars, and thanks to ground-based radar observations.

The surface of Mercury, replete with craters, is very similar to the moon. There are fewer “seas” than on the Moon, and they are small. The diameter of the Mercury Sea of ​​Heat is 1300 km, like the Sea of ​​Rains on the Moon. Steep ledges stretch for tens and hundreds of kilometers, probably generated by the former tectonic activity of Mercury, when the surface layers of the planet were shifting and advancing. As on the Moon, most of the craters were formed as a result of meteorite impacts. Where there are few craters, we see relatively young areas of the surface. Old, destroyed craters are noticeably different from younger, well-preserved craters.

The stony desert and many separate stones are visible on the first photo-television panoramas transmitted from the surface of Venus by automatic stations of the Venus series. Ground-based radar observations have found many shallow craters on this planet, with diameters ranging from 30 to 700 km. In general, this planet turned out to be the smoothest of all the planets of the terrestrial group, although it also has large mountain ranges and lingering hills, twice the size of terrestrial Tibet. The extinct volcano Maxwell is grandiose, its height is 12 km (one and a half times more than Chomolungma), the diameter of the sole is 1000 km, the diameter of the crater at the top is 100 km. Very large, but smaller than Maxwell, are the volcanic cones Gauss and Hertz. Like rift gorges stretching along the bottom of the Earth's oceans, rift zones have also been discovered on Venus, indicating that active processes (for example, volcanic activity) once took place on this planet (and maybe they are happening now!)

In 1983 - 1984 From the stations "Venera - 15" and "Venera - 16" radar research was carried out, which made it possible to create a map and an atlas of the planet's surface (the dimensions of the surface details are 1 - 2 km). A new step in the study of the surface of Venus is associated with the use of a more advanced radar system installed on board the American AMS Magellan. This spacecraft reached the vicinity of Venus in August 1990 and entered an elongated elliptical orbit. Regular surveys have been carried out since September 1990. Clear images are transmitted to the Earth, some of them clearly distinguish details up to 120 m in size. By May 1993, almost 98% of the planet's surface was covered by the survey. It is planned to complete the experiment, which includes not only photographing Venus, but also conducting other studies (gravitational field, atmosphere, etc.) in 1995.

Replete with craters and the surface of Mars. Especially a lot of them in the southern hemisphere of the planet. The dark regions, which occupy a significant part of the planet's surface, are called the seas (Hellas, Argir, etc.). The diameters of some seas exceed 2000 km. Hills, reminiscent of terrestrial continents, which are light fields of orange-red color, are called continents (Tharsis, Elysium). Like Venus, there are huge volcanic cones. The height of the largest of them (Olympus) exceeds 25 km, the diameter of the crater is 90 km. The diameter of the base of this giant cone-shaped mountain is more than 500 km.

The fact that millions of years ago powerful volcanic eruptions occurred on Mars and the surface layers shifted is evidenced by the remains of lava flows, huge surface fractures (one of them - Mariner - stretches for 4000 km), numerous gorges and canyons. It is possible that it was some of these formations (for example, chains of craters or extended gorges) that explorers of Mars 100 years ago mistook for “channels”, the existence of which subsequently for a long time was tried to be explained by the activities of intelligent inhabitants of Mars.

The red color of Mars has ceased to be a mystery. It is explained by the fact that the soil of this planet contains many clays rich in iron.

Panoramas of the surface of the Red Planet were repeatedly photographed and transmitted from a close distance.

You know that almost 2/3 of the Earth's surface is occupied by oceans. There is no water on the surface of Venus and Mercury. There are no open bodies of water on the surface of Mars either. But, as scientists suggest, the water on Mars must be at least in the form of a layer of ice that forms the polar caps, or as a vast layer of permafrost. Perhaps you will witness the discovery of ice reserves on Mars, or even water under the ice. The fact that water was once on the surface of Mars is evidenced by the dried up channel-like winding hollows found there.

Against the backdrop of media hype caused by the American spacecraft "New Horizons", we invite you to recall the history of Pluto, as well as to understand the reasons why it was excluded from the list of planets.

History of Pluto

At the end of XIX - beginning of XX century. astronomers from all over the world hunted for the planet, which was conventionally called "Planet X". She, judging by the studies, was further than Neptune and had a significant impact on its orbit. In 1930, Clyde Tombaugh, an explorer at the Lowell Observatory in Arizona, claimed that he had finally found this planet. The discovery was made based on images of the night sky taken at intervals of two weeks, which made it possible to track changes in the location of objects. The right to name the new celestial body belonged to the Lowell Observatory, and the choice fell on the option proposed by an 11-year-old schoolgirl from England. Venice Burney, that was the name of the girl, suggested naming the planet " Pluto”, in honor of the Roman god of the underworld. In her opinion, such a name very well suited such a distant, dark and cold planet.

Pluto diameter, according to the latest data, is 2370 km, and the mass is 1022 kg. By cosmic standards, this is a tiny planet: pluto volume 3 times smaller than the volume of the moon, and weight and does 5 times inferior to the moon. Wherein pluto area is 16.647.940 km2, which is approximately equal to the area of ​​Russia (17.125.407 km2).

Kuiper belt

When scientists discovered Pluto, they believed that there was nothing else beyond the orbit of Neptune. However, a few decades later, the researchers completely changed their minds. Thanks to powerful new telescopes, scientists have discovered that unlike other planets in our solar system, Pluto is surrounded by many other objects along its entire orbit, each with a diameter of more than 100 km, and similar in composition to Pluto itself. The accumulation of these objects began to be called Kuiper Belt. This region extends from the orbit of Neptune to a distance of 55 AU. (astronomical units) from the Sun (1 AU is equal to the distance from the Earth to the Sun).

Why Pluto is not a planet in the solar system

The Kuiper belt wasn't a problem until scientists began to discover larger and larger objects in it that were comparable in size to Pluto itself.

2005 was rich in discoveries. In January 2005 scientists discovered Eridu. This planet not only had its own satellite, but until July 2015 was considered bigger than Pluto. In the same year, scientists discovered 2 more planets - Makemake and Haumea, whose dimensions are also comparable to Pluto.

Thus, with 3 new planets (one of which was considered larger than Pluto), scientists had to make a serious decision: either increase the number of planets in the solar system to 12, or revise the criteria for classifying planets. As a result, on August 24, 2006, the participants of the XXVI General Assembly of the International Astronomical Union decided to change definition of the term "planet". Now, for an object in the solar system to be officially called a planet, it must meet all of the following conditions:

Orbit around the sun;
not be a satellite of another planet;
have sufficient mass to take a shape close to a ball under the influence of their own gravitational forces (in other words, to be round);
the force of gravity to clear the neighborhood of its orbit from other objects.

Neither Pluto nor Eris meet the latter condition, and therefore are not considered planets. But what does it mean to "clear the orbit of other objects?".

Everything is very simple. Each of the 8 planets of the solar system is the dominant gravitational body in its orbit. This means that when interacting with other, smaller objects, the planet either absorbs them or pushes them away with its gravity.

If we consider the situation on the example of our planet, then the mass of the Earth is 1.7 million times larger than all other bodies in its orbit. For comparison, the mass of Pluto is only 0.07 of the mass of all objects in its orbit, and this is absolutely not enough to clear the planet's vicinity from asteroids and other bodies.

For planets that cannot clear an orbit, scientists have introduced a new definition - "dwarf planets". Pluto, Eris, Makemake and many other relatively large objects of our solar system fall under this classification.

Pluto exploration. Results from New Horizons.

Due to its remoteness and small mass, Pluto has long been one of the least explored planets in our solar system. In January 2006, NASA launched an automatic interplanetary vehicle into space. "New Horizons", whose main mission was to study Pluto and its moon Charon.

The surface of the "heart of Pluto"

In July 2015, after 9 and a half years "New Horizons" reached the orbit of Pluto and began to transmit the first data. Thanks to the clear images taken by the station, scientists were able to make several important discoveries:

1. Pluto is bigger than we thought. The diameter of Pluto is 2.370 km, which means that it is still larger than Eris, whose diameter is 2.325 km. Despite this, the mass of Eris is still considered to be 27% more than the mass of Pluto.
2. Pluto reddish brown. This color is due to the interaction of methane molecules in Pluto's atmosphere and a specific type of ultraviolet light emitted by both the Sun and distant galaxies.
3. Pluto has a heart and ice mountains. Flying over the planet, New Horizons photographed a huge bright area in the form of a heart. As the more detailed pictures show, "Heart of Pluto", later called the Tombo region, is an area covered with ice mountains that reach a height of 3,400 m.
4. Snow may fall on Pluto. According to research, the glaciers on the planet are composed of methane and nitrogen, changing greatly throughout the year. Pluto makes one revolution around the Sun in 248 Earth years, significantly changing its distance from the sun. During the summer periods, as scientists suggest, glaciers melt and evaporate into the atmosphere, falling back in the form of snow in winter.
5. Pluto has an atmosphere made entirely of nitrogen. Studies show that Pluto's nitrogen atmosphere is rapidly escaping into space. Interestingly, this process is in many ways similar to what happened on Earth billions of years ago. Ridding the earth's atmosphere of nitrogen eventually led to the appearance of hydrogen and carbon dioxide, thanks to which life was born on our planet.