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.

The ninth planet in the solar system is Pluto. It bears the name of one of the main deities of Ancient Greece, who ruled in the underworld of the dead. Pluto is so far from the Sun that it cannot be seen with the naked eye and even through binoculars.

Discovery history

Since the beginning of the twentieth century, scientists have reported that behind Uranus there is necessarily another, the 9th planet of the solar system, since the ellipse of Uranus's orbit deviated from the norm. The reason for this could only be the cosmic body influencing it. According to Wikipedia, the American astronomer Tombo became the discoverer of the ninth planet. Having traced its trajectory, the researcher calculated and compiled a mathematical model of the orbit of this still unknown cosmic body. The scientist just had to direct the telescope to the calculated sector of space in order to discover Pluto in 1930, a new planet in the solar system. For this, hard work has been done. We had to compare the mass of photographs of the starry sky, taken with a two-week interval, in order to identify a celestial object by changing its position in the photographs.

The new planet was found from the Lowell Observatory in the US state of Arizona. According to the tradition that existed in those years, the staff of this institution received the right to name a new astronomical object. After much debate and gossip, they accepted the proposal of a schoolgirl from English Oxford, and named the found cosmic body by the name of the ancient Greek god of the underworld and death.

Features of an open planet

At first, the size of the found object was estimated as equal to the Earth, however, with the growth of the possibilities of astronomy, changes were periodically made to these data. Such errors are not surprising, because an open celestial body is located from the Sun at a distance equal to 39 distances from the Earth to the star, and scientists did not have computers at their disposal.

Upon discovery, and for a long time after that, astronomers were unable to calculate the weight of the newcomer to the planetary club. This was only possible in 1978, immediately after the discovery of Charon, a satellite of Pluto. Having calculated the weight of the ninth planet, which was equal to 0.0021 of the mass of our Earth, the calculations of its geometric parameters were corrected. It turned out that the diameter of the nine is about 2.4 thousand kilometers. On a cosmic scale, this is a modest size.

physical characteristics

Composition and structure

In terms of its geometric dimensions and physical characteristics, it is inferior even to a number of satellites, including the Moon. So Pluto is the least massive planet in the solar system, the size of the diameter of the dwarf is slightly more than half of the moon.

It is impossible to see Pluto even with a professional optical telescope. Even in the most powerful optics, it seems to be a dim star, of which there are millions in the sky. Observing through the Hubble electron telescope, launched into near-Earth orbit, scientists managed to create only brightness maps. And only in 2015, with the help of the New Horizons automatic interplanetary complex, it was possible to obtain more or less intelligible pictures that gave more information about the dwarf.

Pluto's surface is rather inhomogeneous. It is known that 50% of Pluto's interior is chemically water ice. Water in the same form is also on the surface, the rest is rock. Above this layer, scientists saw a cover of volatile ice, the lion's share of which is nitrogen.

With the help of a NASA ship flying near the plutonian orbit, chains of mountains, plains, and other characteristic landscape objects were discovered on the surface.

By the way, at the request of the International Astronomical Union of February 2017, the characteristic parts of the landscape of the nine are named only according to established topics:

• in honor of mythical deities associated with the underworld or death;
• names of the underworld in various literary sources;
• in honor of people who became famous in the study of the underworld;
• memory of engineers, researchers, astronomers who took an active part in the research of the planet and the Kuiper belt;
• in honor of interplanetary space stations;
• the memory of the pioneers who discovered something new and important.

Orbit and rotation

The orbit of the planet, which is located almost on the outskirts of our system, looks like an elongated ellipse. It passes at distances of 4.4 - 7.3 billion kilometers from the central star. That is, sometimes it even crosses the orbit of Neptune, flying closer to the Sun than this gas giant. The plane in which Pluto moves around the star is inclined to the plane of the ecliptic by 17.14 degrees. At the same time, its movement does not occur along a strict ellipse, but is constantly shifting with each revolution. In addition, Neptune has a very strong influence on the movement of the nine in orbit around the Sun. They are in an orbital resonance of 3 to 2. That is, when making three annual cycles of rotation around the giant star, two years pass on the dwarf. This entire process takes 495 Earth years.

The direction of rotation of the dwarf around its axis is opposite to the rotation of space objects in their orbit around the Sun. Venus and Uranus have similar directions of rotation. Pluto's day, that is, the period of revolution around itself, lasts a little more than 6 days on our planet. Due to the angle of the axis of rotation, the seasons here are more expressive than in the cradle of mankind.

Moons and rings of the planet Pluto

A lot of small bodies rotate in circum-Pluto orbits, which include satellites of the dwarf and small space objects nailed from the asteroid belt, circling around it since ancient times.

Pluto's moons

The dwarf planet of the solar system Pluto is the owner of 5 own satellites. The first was Charon, discovered in 1978 by astronomer James Christie. Decades later, in 2005, with the direct participation of the Hubble orbital telescope, Hydra and Nix were discovered. 2011 - the year of the discovery of Kerberos, 2012 - the year of Styx.

Satellites are in almost circular orbits and move along them in the direction of the planet's rotation. With the help of New Horizons, their exact number and size were confirmed, which turned out to be rather small by space standards.

The presence of tiny satellites prompted scientists to put forward a hypothesis about the existence of a ring system around the dwarf planet. The hypothesis was taken so seriously that the flight path of New Horizons was adjusted to avoid passing through the region of the rings. They, according to scientists, consist of small stone particles and pieces of ice that can damage the apparatus. However, in the pictures sent to Earth, the rings were not found.

Exploration of the dwarf planet Pluto

Due to the fact that the solar system has a large extent, it is problematic to conduct full-fledged research activities with distant Pluto. After trying to see anything in detail from Earth, the Hubble Space Orbital Telescope took over. However, scientists were not satisfied with his pictures either. The researchers had the idea to turn to Pluto, the next automatic complex "Voyager 1" in that direction. However, for a number of reasons, it was redirected to other space objects.

After that, in the research programs for Pluto, which was already considered a planetary dwarf at that time, there was a break until 2003. By this time, a company began to prepare for the launch of the unmanned spacecraft "New Horizons". The device was built, and in 2006 launched to the ninth planet of our star system. In July 2015, an unmanned aerial vehicle passed the orbit of the nine, transmitting images of its surface to the ground.

Why is Pluto excluded from the list of planets in the solar system?

August 24, 2006 was fatal for the ninth planet - the International Astronomical Union (IAU) transferred it to the group of dwarf planets. This was due to Pluto's inconsistency with some of the characteristics that are required for bodies called "planets".

It is worth considering what kind of celestial body, according to the charter of the International Astronomical Union, is a planet. To do this, it must meet four conditions:

• obligatory rotation around the Sun - Pluto corresponds;
• obligatory massiveness, which allows under the influence of gravity to take the form of a ball - and here the nine is suitable;
• you can’t be someone’s satellite - Pluto is the owner of five similar celestial bodies;
• a cosmic body claiming a planetary role must free its own orbit from foreign bodies, which the nine failed to accomplish.

By agreement of all representatives of the International Astronomical Union, it was established that the celestial body did not fulfill the fourth condition. And now it, even with three completed, is ranked among the class of planets - dwarfs. So, earlier this requirement was ignored, and the number of planets in the solar system was 9.

Surface map

A flyby of the New Horizons spacecraft has produced the most accurate black-and-white map of Pluto yet. When deciphering the images, scientists discovered many interesting points that have yet to be studied. Unfortunately, no signs of life have yet been found on the dwarf.

Photos of the dwarf planet Pluto

Due to the huge distance from the Earth, amateur astronomers, and professionals, will not be able to take pictures of it. An interplanetary station launched into space coped with this task. So, approaching this planet, a number of high-quality images of the ice dwarf were taken. For several years now, scientists have been processing these photos of the planet that was removed from the solar system.

In August 2006, incredible news thundered: the solar system lost one of the planets! Here you will really be on your guard: today one planet has disappeared, tomorrow another, and there, you see, the turn will reach the Earth!

However, there was no reason to panic then, nor now. It was only about the decision of the International Astronomical Union, which, after long disputes, deprived Pluto of the status of a full-fledged planet. And, contrary to misconceptions, on that day the solar system did not shrink, but, on the contrary, expanded unimaginably.

Briefly:
Pluto is too small for the planet. There are celestial bodies that were previously considered asteroids, although they are the same size, or even larger, than Pluto. Now both they and Pluto are called dwarf planets.

Search for wanderers

The discovery of Pluto, which has long been considered the ninth planet of the solar system, has a prehistory.

Before the advent of telescopes, mankind knew five celestial bodies called planets (translated from Greek - “wanderers”): Mercury, Venus, Mars, Jupiter, Saturn. For four centuries, two more large planets were discovered: Uranus and Neptune.

The discovery of Uranus is remarkable in that it was made by an amateur music teacher William Herschel. On March 13, 1781, he was surveying the sky and suddenly noticed a small yellow-green disk in the constellation Gemini. At first, Herschel thought he had discovered a comet, but observations by other astronomers confirmed that a real planet had been discovered with a stable elliptical orbit.

Herschel wanted to name the planet Georgia after King George III. But the astronomical community has decided that the name of any new planet must match the others, that is, come from classical mythology. As a result, the planet was named Uranus in honor of the ancient Greek god of heaven.

Observations of Uranus revealed an anomaly: the planet stubbornly refused to follow the laws of celestial mechanics, deviating from the calculated orbit. Twice astronomers calculated models of the motion of Uranus, adjusted for the gravity of other planets, and twice he “deceived” them. Then there was an assumption that Uranus is influenced by another planet located beyond its orbit.

On June 1, 1846, an article by the mathematician Urbain Le Verrier appeared in the journal of the French Academy of Sciences, where he described the expected position of a hypothetical celestial body. On the night of September 24, 1846, at his prompting, the German astronomers Johann Galle and Heinrich d'Arre, without spending much time searching, discovered an unknown object, which turned out to be a large planet and was named Neptune.

Planet X

The discovery of the seventh and eighth planets in just half a century has tripled the boundaries of the solar system. Satellites were discovered near Uranus and Neptune, which made it possible to accurately calculate the masses of the planets and their mutual gravitational influence. Based on these data, Urbain Le Verrier built the most accurate model of orbits at that time. And again, reality diverged from the calculations! A new mystery has inspired astronomers to search for a trans-Neptunian object, which has become conventionally called "Planet X".

The glory of the discoverer went to the young astronomer Clyde Tombaugh, who abandoned mathematical models and began to study the sky with the help of a photographic refractor. On February 18, 1930, comparing photographic plates in January, Tombaugh discovered the displacement of a faint star-shaped object - it turned out to be Pluto.

Astronomers soon determined that Pluto was a very small planet, smaller than the Moon. And its mass is clearly not enough to influence the movement of the huge Neptune. Then Clyde Tombaugh launched a powerful search program for another "planet X", but, despite all efforts, it was not possible to find it.

We know a lot more about Pluto today than we did in the 1930s. Thanks to many years of observations and orbiting telescopes, it was possible to find out that it has a very elongated orbit, which is inclined to the plane of the ecliptic (Earth's orbit) at a significant angle - 17.1 °. Such an unusual property made it possible to speculate on whether Pluto is the home planet of the solar system or whether it is accidentally attracted by the gravity of the Sun (for example, Ivan Efremov considers this hypothesis in the novel The Andromeda Nebula).

Pluto has small satellites, and many of them have been discovered quite recently. There are five of them: Charon (discovered in 1978), Hydra (2005), Nikta (2005), P4 (2011) and P5 (2012). The presence of such a complex system of satellites suggested that Pluto has rarefied rings of debris - such are always formed when small bodies collide in orbits around planets.

Maps compiled using data from the Hubble orbiting telescope showed that Pluto's surface is not uniform. The part facing Charon contains mostly methane ice, while the opposite side has more nitrogen and carbon monoxide ice. At the end of 2011, complex hydrocarbons were discovered on Pluto - this allowed scientists to assume that the simplest forms of life exist there. In addition, the rarefied atmosphere of Pluto, consisting of methane and nitrogen, has noticeably “swollen” in recent years, which means that there are climate changes on the planet.

What was Pluto called?

Pluto was named on March 24, 1930. Astronomers voted on a shortlist containing three final options: Minerva, Kronos and Pluto.

The third option turned out to be the most suitable - the name of the ancient god of the kingdom of the dead, also known as Hades and Hades. It was proposed by Venetia Burney, an eleven-year-old schoolgirl from Oxford. She was interested not only in astronomy, but also in classical mythology, and decided that the name Pluto best suits the dark and cold world. The name came up in a conversation with her grandfather Falconer Meidan, who had read about the planet's discovery in a magazine. He conveyed Venice's proposal to Professor Herbert Turner, who, in turn, telegraphed his colleagues in the United States. For her contribution to the history of astronomy, Venetia Burney received a prize of five pounds sterling.

Interestingly, Venice survived until the moment when Pluto lost its status as a planet. When asked about her attitude to this "demotion", she replied: "At my age, there is no such debate anymore, but I would like Pluto to remain a planet."

Edgeworth-Kuiper Belt

By all indications, Pluto is a normal planet, albeit a small one. Why did astronomers react so unfavorably to him?

The search for a hypothetical "Planet X" continued for decades, which led to many interesting discoveries. In 1992, a large cluster of small bodies, similar to asteroids and comet nuclei, was discovered beyond the orbit of Neptune. The existence of a belt of debris left over from the formation of the solar system was predicted long before by the Irish engineer Kenneth Edgeworth (in 1943) and the American astronomer Gerard Kuiper (in 1951).

The first trans-Neptunian Kuiper belt object was discovered by astronomers David Jewitt and Jane Lu while observing the sky with the latest technology. On August 30, 1992, they announced the discovery of the body 1992 QB1, which they named Smiley after the hero of the popular detective John Le Carré. However, this name is not officially used, since there is already an asteroid Smiley.

By 1995, seventeen more bodies had been discovered beyond the orbit of Neptune, eight of them beyond the orbit of Pluto. By 1999, the total number of registered objects of the Edgeworth-Kuiper belt exceeded one hundred, by now - over a thousand. Scientists believe that in the foreseeable future it will be possible to identify more than seventy thousand (!) Objects larger than 100 km. It is known that all these bodies move in elliptical orbits, like real planets, and a third of them have the same orbital period as Pluto (they are called “plutinos” - “plutons”). The objects of the belt are still very difficult to classify - it is only known that they have sizes from 100 to 1000 km, and their surface is dark with a reddish tint, which indicates an ancient composition and the presence of organic compounds.

By itself, the confirmation of the Edgeworth-Kuiper hypothesis could not cause a revolution in astronomy. Yes, now we know that Pluto is not a lonely wanderer, but the neighboring bodies are not able to compete with it in size, and besides, they have no atmosphere and satellites. The scientific world could continue to sleep peacefully. And then something terrible happened!

Dozens of Plutos

Mike Brown - "the man who killed Pluto"

Astronomer Mike Brown, in his memoirs, claims that even as a child, through observations, he independently discovered the planets, unaware of their existence. When he became a specialist, he dreamed of the greatest discovery - "Planet X". And he opened it. And not even one, but sixteen!

The first trans-Neptunian object, designated 2001 YH140, was discovered by Mike Brown with Chadwick Trujillo in December 2001. It was a standard celestial body of the Edgeworth-Kuiper belt with a diameter of about 300 km. Astronomers continued their vigorous search, and on June 4, 2002, the team discovered the much larger object 2002 LM60, 850 km in diameter (now estimated to be 1,170 km in diameter). That is, the size of 2002 LM60 is comparable to the size of Pluto (2302 km). Later, this body, which looks like a full-fledged planet, was called Quaoar - after the creator god worshiped by the Tongva Indians of Southern California.

Further more! On November 14, 2003, Brown's team discovers the trans-Neptunian object 2003 VB12, which is named Sedna, after the Eskimo goddess of the sea, who lives at the bottom of the Arctic Ocean. At first, the diameter of this celestial body was estimated at 1800 km; additional observations with the Spitzer Orbital Telescope reduced the estimate to 1,600 km; at the moment it is believed that the size of Sedna is 995 km. Spectroscopic analysis has shown that Sedna's surface is similar to some other trans-Neptunian objects. Sedna moves in a very elongated orbit - scientists believe that it was once influenced by a star that passed by the solar system.

On February 17, 2004, Mike discovers an object 2004 DW, named Orc (deity of the underworld in Etruscan and Roman mythology), with a diameter of 946 km. Spectral analysis of Ork showed that it is covered with water ice. Most of all, Orc is similar to Charon - a satellite of Pluto.

On December 28, 2004, Brown discovers object 2003 EL61, named Haumea (Hawaiian Goddess of Fertility), about 1300 km in diameter. Later it turned out that Haumea rotates very quickly, making one revolution around its axis in four hours. Hence, its shape must be strongly elongated. Modeling showed that in this case, the longitudinal size of Haumea should be close to the diameter of Pluto, and the transverse size - half as much. Perhaps Haumea appeared as a result of the collision of two celestial bodies. Upon impact, some of the light components evaporated and were ejected into space, subsequently forming two satellites: Hiiaka and Namaka.

goddess of discord

Mike Brown's finest hour struck on January 5, 2005, when his team discovered a trans-Neptunian object estimated to be 3000 km in diameter (later measurements gave a diameter of 2326 km). Thus, in the Edgeworth-Kuiper belt, a celestial body was found that is definitely larger than Pluto in size. Scientists made a noise: finally, the tenth planet is open!

Astronomers gave the new planet the unofficial name Xena in honor of the heroine. And when Xena found a companion, they immediately named him Gabriel - that was the name of Xena's companion. The International Astronomical Union could not accept such "frivolous" names, so Xena was renamed Eris (Greek goddess of discord), and Gabrielle - Dysnomia (Greek goddess of lawlessness).

Eris has indeed caused discord among astronomers. Logically, Xena-Eris should have been immediately recognized as the tenth planet, and the Michael Brown group should have been entered into the annals of history as its discoverers. But it was not there! Previous discoveries have indicated that perhaps dozens more objects comparable in size to Pluto are hiding in the Edgeworth-Kuiper Belt. What is easier - multiplying the number of planets, rewriting astronomy textbooks every couple of years, or throwing out Pluto from the list, and with it all the newly discovered celestial bodies?

The verdict was passed by Mike Brown himself, having discovered on March 31, 2005 the object 2005 FY9 with a diameter of 1500 km, named Makemake (the creator god of mankind in the mythology of the Rapanui people, the inhabitants of Easter Island). The patience of the colleagues ran out, and they gathered at the conference of the International Astronomical Union in Prague to determine once and for all what a planet is.

Previously, a planet could be considered a celestial body that revolves around the Sun, is not a satellite of another planet and has sufficient mass to acquire a spherical shape. As a result of the debate, astronomers added another requirement: that the body "clear" the surroundings of its orbit from bodies of comparable size. Pluto did not meet the last requirement and was deprived of the status of a planet.

He migrated to the list of "dwarf planets" (from the English "dwarf planet", literally - "dwarf planet") at number 134340.

This decision drew criticism and ridicule. Pluto scientist Alan Stern said that if this definition were applied to Earth, Mars, Jupiter and Neptune, in whose orbits asteroids were found, then they should also be stripped of the title of planets. In addition, according to him, less than 5% of astronomers voted for the decision, so their opinion cannot be considered universal.

However, Mike Brown himself accepted the definition of the International Astronomical Union, content that the discussion had finally ended to everyone's satisfaction. And indeed - the storm subsided, the astronomers went to their observatories.

Deprived of the status of a planet, Pluto has become an inexhaustible source for Internet creativity

Society reacted differently to the decision of the International Astronomical Union: someone did not attach importance, but someone was convinced that scientists were fooling around. The verb “to pluto” (“to pluto”) appeared in English, recognized as the word of 2006 by the American Dialectological Society. The word means "decrease in value or value."

The authorities of the states of New Mexico and Illinois, where Clyde Tombo lived and worked, decided by law to retain the status of a planet for Pluto and declared March 13 the annual Day of the planet Pluto. Ordinary citizens responded with both online petitions and street protests. It was difficult for people who had considered Pluto a planet all their lives to get used to the decision of astronomers. In addition, Pluto was the only planet discovered by an American.

Who benefits?

Pluto is the only one who lost in status. The rest of the dwarf planets were previously classified as asteroids. Among them is Ceres (named after the Roman goddess of fertility), discovered back in 1801 by the Italian astronomer Giuseppe Piazzi. For some time, Ceres was considered the very missing planet between Mars and Jupiter, but later it was attributed to asteroids (by the way, this term was specially introduced precisely after the discovery of Ceres and neighboring large objects). By the decision of the astronomical union in 2006, Ceres began to be considered a dwarf planet.

Ceres, whose diameter reaches 950 km, is located in the asteroid belt, which seriously complicates its observation. It is hypothesized to have an icy mantle or even oceans of liquid water below the surface. A qualitative step in the study of Ceres was the mission of the Dawn interplanetary apparatus, which reached the dwarf planet in the fall of 2015.

We won't be found!

The Pioneer 10 and Pioneer 11 interplanetary spacecraft, launched in the early 1970s, carried aluminum plates with a message to aliens. In addition to images of a man, a woman and an indication of where to look for us in the galaxy, there was a diagram of the solar system. And it consisted of nine planets, including Pluto.

It turns out that if someday the "brothers in mind", guided by the "Pioneers" scheme, want to find us, they are very likely to pass by, confused in the number of planets. However, if they are evil alien invaders, you can always say that we deliberately confused them.

∗∗∗

Today it seems unlikely that the classification of Pluto, Eris, Sedna, Haumea and Quaoar will ever be revised. And only Mike Brown is not discouraged - he is sure that in the coming years, a celestial body the size of Mars will be discovered at the far edge of the Edgeworth-Kuiper belt. It's terrible to imagine what will happen then!

• Michael Brown "How I Killed Pluto and Why It Was Inevitable"
• David A. Weintraub “Is Pluto a planet? Journey through the Solar System (Is Pluto a Planet?: A Historical Journey through the Solar System)
• Elayne Scott When Is a Planet Not a Planet?: The Story of Pluto
• David Aguilar Thirteen Planets. A Modern View of the Solar System (13 Planets: The Latest View of the Solar System)

The most distant celestial body in the solar system is the dwarf planet Pluto. More recently, in school textbooks, it was written that Pluto is the ninth planet. However, the facts that were obtained in the process of studying this celestial body at the turn of the millennium made the scientific community doubt whether Pluto is a planet. Despite this and many other controversial points, a small and distant world continues to excite the minds of astronomers, astrophysicists and a huge army of amateurs.

History of the planet Pluto

Back in the 80s of the XIX century, many astronomers unsuccessfully tried to find a certain Planet-X, which, by its behavior, influenced the orbital characteristics of Uranus. Searches were conducted in the most separated regions of our space, approximately at a distance of 50-100 AU. from the center of the solar system. American Percival Lowell spent more than fourteen years unsuccessfully searching for a mysterious object that continued to excite the minds of scientists.

It will be half a century before the world receives proof of the existence of another planet in the solar system. The discovery of the planet was carried out by Clyde Tombaugh, an astronomer from the Flagstaff Observatory, which was founded by the same restless Lowell. In March 1930, Clyde Tombaugh, observing through a telescope for that part of space in which Lowell admitted the existence of a large celestial body, discovered a new rather large cosmic object.

Subsequently, it turned out that due to its small size and small mass, Pluto is not able to influence the larger Uranus. The oscillations and interaction of the orbits of Uranus and Neptune are of a different nature, associated with the special physical parameters of the two planets.

The discovered planet was named Pluto, thus continuing the tradition of naming the celestial bodies of the solar system in honor of the gods of the ancient Pantheon. There is another version in the history of the name of the new planet. It is believed that Pluto got its name in honor of Percival Lowell, because Tombo suggested choosing a name according to the initials of the troubled scientist.

Until the end of the 20th century, Pluto firmly occupied a place in the planetary row of the Solar family. Changes in the status of the planet occurred at the turn of the millennium. Scientists were able to identify a number of other massive objects in the Kuiper belt, which called into question the exceptional position of Pluto. This prompted the scientific world to reconsider the position of the ninth planet and answer the question why Pluto is not a planet. In accordance with the new formal definition of the term "planet", Pluto fell out of the general ensemble. The result of long debate and discussion was the decision of the International Astronomical Union in 2006 to transfer the object to the category of dwarf planets, putting Pluto on a par with Ceres and Eris. A little later, the status of the former ninth planet of the solar system was further lowered, including it in the category of minor planets with tail number 134,340.

What do we know about Pluto?

The former ninth planet is considered the most distant of all large celestial bodies known to this day. It is possible to observe such a distant object only with the help of powerful telescopes or from photographs. It is quite difficult to fix a dim small point in the sky, since the orbit of the planet has specific parameters. There are periods when Pluto has a maximum brightness and its luminosity is 14m. However, in general, the distant wanderer does not differ in bright behavior, and the rest of the time it is practically invisible, and only during the opposition period does the planet open itself for observation.

One of the best periods for the study and exploration of Pluto just fell on the 90s of the XX century. The most distant planet was at the minimum distance from the Sun, closer than its neighbor Neptune.

According to astronomical parameters, the object stands out among the celestial bodies of the solar system. The baby has the largest orbital eccentricity and inclination. Pluto completes its stellar journey around the main star in 250 Earth years. The average orbital speed is the smallest in the solar system, only 4.7 kilometers per second. At the same time, the period of rotation of a small planet around its own axis is 132 hours (6 days and 8 hours).

At perihelion, the object is at a distance of 4 billion 425 million km from the Sun, and at aphelion it runs away by almost 7.5 billion km. (to be precise - 7375 million km.). At such huge distances, the Sun gives Pluto 1600 times less heat than we earthlings receive.

The axis deviation is 122.5⁰, the deviation of the orbital path of Pluto from the plane of the ecliptic has an angle of 17.15⁰. In simple terms, the planet lies on its side, rolling over as it orbits.

The physical parameters of a dwarf planet are as follows:

• equatorial diameter is 2930 km;
• the mass of Pluto is 1.3 × 10²²² kg, which is 0.002 of the Earth's mass;
• the density of the dwarf planet is 1.860 ± 0.013 g/cm³;
• free fall acceleration on Pluto is only 0.617 m/s².

With its size, the former ninth planet is 2/3 of the diameter of the moon. Of all the known dwarf planets, only Eris has a larger diameter. The mass of this celestial body is also small, which is six times less than the mass of our satellite.

Retinue of a dwarf planet

However, despite such a small size, Pluto bothered to get five natural satellites: Charon, Styx, Nyx, Kerberos and Hydra. All of them are listed in order of distance from the parent planet. The dimensions of Charon make it have the same pressure center as Pluto, around which both celestial bodies revolve. In this regard, scientists consider Pluto-Charon a double planetary system.

The satellites of this celestial body are of a different nature. If Charon has a spherical shape, then all the rest are huge and shapeless giant stones. Probably, these objects were captured by the gravitational field of Pluto from among the asteroids wandering in the Kuiper belt.

Charon is the largest moon of Pluto, which was discovered only in 1978. The distance between the two objects is 19640 km. At the same time, the diameter of the largest moon of the dwarf planet is 2 times smaller - 1205 km. The ratio of the masses of both celestial bodies is 1:8.

Other satellites of Pluto - Nikta and Hydra - are approximately the same in size, but they are much inferior in this parameter to Charon. Styx and Nix are generally barely noticeable objects with sizes of 100-150 km. Unlike Charon, the remaining four satellites of Pluto are located at a considerable distance from the mother planet.

When observing through the Hubble telescope, scientists were interested in the fact that Pluto and Charon have a significantly different color. Charon's surface appears darker than Pluto's. Presumably, the surface of the largest satellite of the dwarf planet is covered with a thick layer of cosmic ice, consisting of frozen ammonia, methane, ethane and water vapor.

Atmosphere and a brief description of the structure of a dwarf planet

In the presence of natural satellites, Pluto can be considered a planet, albeit a dwarf one. To a large extent, this is facilitated by the presence of Pluto's atmosphere. Of course, this is not an earthly paradise with a high content of nitrogen and oxygen, but Pluto still has an air cover. The density of the atmosphere of this celestial object varies depending on the distance from the Sun.

The atmosphere of Pluto was first discussed in 1988, when the planet was passing through the solar disk. Scientists admit the idea that the air-gas shell of a dwarf appears only during the period of maximum approach to the Sun. With a significant removal of Pluto from the center of the solar system, its atmosphere freezes out. Judging by the spectral images obtained from the Hubble Space Telescope, the composition of Pluto's atmosphere is approximately the following:

• nitrogen 90%;
• carbon monoxide 5%;
• methane 4%.

The remaining one percent is accounted for by organic compounds of nitrogen and carbon. The data on atmospheric pressure testify to the strong rarefaction of the air-gas shell of the planet. On Pluto it varies from 1-3 to 10-20 microbars.

The surface of the planet has a characteristic slightly reddish hue, which is caused by the presence of organic compounds in the atmosphere. After studying the obtained images, polar caps were discovered on Pluto. A version is allowed that we are dealing with frozen nitrogen. Where the planet is covered in dark patches, there are probably vast fields of frozen methane that darken under the influence of sunlight and cosmic radiation. The alternation of light and dark spots on the surface of the dwarf indicates the presence of seasons. Like Mercury, which also has a highly rarefied atmosphere, Pluto is covered in cosmic craters.

Temperatures in this distant and dark world are very low and incompatible with life. On the surface of Pluto there is eternal cosmic cold with a temperature of 230-260⁰С below zero. Due to the recumbent location of the planet, the poles of the planet are considered the warmest areas. Whereas the vast expanses of Pluto's surface is a zone of permafrost.

As for the internal structure of this distant celestial body, a typical picture is possible here, characteristic of the planets of the terrestrial group. Pluto has a rather large and massive core, consisting of silicates. Its diameter is estimated at 885 km, which explains the rather high density of the planet.

Interesting facts about the research of the former ninth planet

The vast distances that separate the Earth and Pluto make it difficult to study and study using technical means. It will take about ten Earth years for earthlings to wait until the spacecraft reaches Pluto. Launched in January 2006, the New Horizons space probe was able to reach this region of the solar system only in July 2015.

For five months, as the automatic station "New Horizons" approached Pluto, photometric studies of this region of space were actively carried out.

Flight of the probe "New Horizons"

This device was the first to fly in close proximity to a distant planet. The previously launched American probes "Voyagers", the first and second, focused on the study of larger objects - Jupiter, Saturn and its satellites.

The flight of the New Horizons probe made it possible to obtain detailed images of the surface of the dwarf planet numbered 134,340. The object was studied from a distance of 12,000 km. The Earth received not only detailed images of the surface of a distant planet, but also photographs of all five satellites of Pluto. Until now, NASA laboratories are working on detailing the information received from the spacecraft, as a result of which in the future we will get a clearer picture of that world remote from us.

Pluto is no longer a planet, and you are right about that. At the time of its discovery in 1930, there was still not enough knowledge to classify it. The correction of this error in 2006 and the "demotion" of Pluto still occupies human minds.

"Mein Vater erklärt mir jeden Sonntag unsere neun Planeten." (“My father tells me every Sunday about our nine planets.”) I learned this phrase in school. The first letters of the words in the sentence indicate the first letters of the names of the planets of our solar system: "Merkur, Venus, Erde, Mars, Jupiter, Saturn, Uranus, Neptun, Pluto" ("Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto). But in 2006, everything changed: At the General Assembly of the International Astronomical Union in Prague, a new definition of the word "planet" was given and Pluto did not meet its criteria. From that moment on, it was not a planet, but a "dwarf planet". This concept, in fact, means "large asteroid".

This decision was not without controversy among astronomers. But especially fierce discussions were among the public. If, for example, I report on the exploration of Pluto in reports or articles, I again, as before, receive comments from people who complain that this celestial body can no longer be called a "planet".

The American public is especially annoyed because of the “demotion”: after all, Pluto was the only planet discovered by an American (Clyde Tombaugh). Other American astronomers are also unhappy - they are trying again and again to propose such a definition of the planet so that Pluto gets its status back.

• Currently under discussion is Kirby Runyon's proposal from Johns Hopkins University: Any celestial body that does not undergo a nuclear fusion reaction and that is similar in shape to a sphere should be called a "planet." Then, of course, Pluto would become a planet again. Then it would be necessary to use the same term to designate a good hundred more celestial bodies in our solar system. The sphericity of a celestial body depends mainly on its size and the substances of which it is composed. This formula describes the physical processes that are responsible for the form:

Planet Formula

Next to the gravitational constant G and the number π is the density ρ of substances and the resistance to compression σ y , which determine the shape. It calculates "Kartoffelradius" ("potato radius"), the minimum radius of a dwarf planet R.

The smaller celestial body is not spherical, but has an irregular shape, like a potato. Only when a body is of sufficient size can its mass, by means of its own gravity, overcome the material's resistance to compression and form a spherical object.

Sphericity can also really tell something about the internal structure and thus can be used as an important parameter for research in planetary science. Despite this, the defining criterion used to define it as a "planet" is considered false. In addition, among other things, an important fact is ignored when it appears.

When planets like Earth and Jupiter appeared, they grew in size fast enough to either collect all the nearby matter with their gravitational force, or use centrifugal forces to launch matter into a distant orbit, not to mention such special cases as the Trojan asteroids. But at a great distance from the sun, objects would move much more slowly.

There would be fewer collisions, celestial bodies would increase more slowly and could not affect the environment in a similar way. In this connection, Pluto would not be a planet at all, but a large asteroid, which would still be among the mass of other asteroids.

You can give many definitions of the concept of the term "planet". But none will be truly satisfactory. Nature did not provide for unshakable boundaries for celestial bodies. Bodies change, smoothly and measuredly. But while people are still working on such definitions, it is wiser not to put Pluto and all other small asteroids on a par with Jupiter-sized gas giants.

Pluto is a fascinating object, just the way it is classified! And at school they now teach simply: “Mein Vater erklärt mir jeden Sonntag unseren Nachthimmel.” ("My father tells me every day about our night sky").