What type of celestial body is pluto. Pluto is the ninth planet in the solar system

Why is Pluto no longer a planet? The sensational decision was made on August 25, 2006 by 2.5 thousand participants of the Congress of the International Astronomical Union. Millions of astronomy students‚ thousands of star charts‚ hundreds of scientific papers will be rewritten. From now on, Pluto will be removed from the list of planets in the solar system. In ten days of debate, the International Astronomical Union has stripped the most mysterious object of the solar system of the status that it had for only 76 years. However, over the past few decades, new powerful ground-based and space-based observatories have completely changed previous ideas about the outer regions of the solar system. Rather than being the only planet in its region, like all the other planets in the solar system, Pluto and its moons are now known to be an example of a large number of objects united under the name Kuiper belt. This region extends from the orbit of Neptune to a distance of 55 astronomical units (the boundary of the belt is 55 times farther from the Sun than the Earth). According to the new rules for identifying planets, the fact that Pluto's orbit is inhabited by such objects is the main reason why Pluto is not a planet. Pluto is just one of many Kuiper belt objects. And his orbit is not a circle, but an ellipse, and he himself is very small, so he cannot be on the same list with such as the Earth and with such giants as the planet Jupiter. "It has a different density, and the dimensions are small. It cannot be attributed either to the terrestrial planets, or to the giant planets, and it is not a satellite of the planets," explains Vladislav Shevchenko, professor at Moscow State University named after M.V. Lomonosov. The conference in Prague left only eight planets on the star maps instead of the usual nine. Since 1930, when Pluto was discovered, astronomers have found at least three more objects in space comparable to it in size and mass - Charon, Ceres and Xena. Pluto is six times smaller than the earth, Charon, its satellite, is ten times smaller. And Xena is bigger than Pluto. Could it be that these are all the planets? Yes, and the Moon was then undeservedly named "satellite". None of the contenders for planetary status could compare with its dimensions. "If we say that Pluto is a planet, then we should attribute to this class not one, but already at first several planets. And then the solar system should not consist of nine planets, but of 12, and a little later - 20 -30 and even hundreds of planets. Therefore, the decision is correct. Both culturally correct‚ and physically correct," says Andrey Finkelstein, director of the Institute of Applied Astronomy of the Russian Academy of Sciences. In the end, astronomers voted for a rather controversial decision by the standards of that time and attributed Pluto (and other similar objects) to a new class of objects - to the "dwarf planets". What is a planet according to the new definition? Is Pluto a planet? Does it pass the classification? For an object in the Solar System to be considered a planet, it must meet four requirements defined by the IAU: 1. The object must orbit the Sun - AND Pluto passes. 2. It must be massive enough to form a spherical shape with its gravitational force - And here everything seems to be in order with Pluto. 3. It must not be a satellite of another object. Pluto itself has 5 moons. 4. He must be able to clear the space around his orbit from other objects - Aha! This rule breaks Pluto, it is the main reason why Pluto is not a planet. What does it mean to "clear the space around your orbit from other objects"? At a time when the planet is just being formed, it becomes the dominant gravitational body in a given orbit. When it interacts with other, smaller objects, it either absorbs them or pushes them away with its gravity. Pluto is only 0.07 of the mass of all objects in its orbit. Compare with the Earth - its mass is 1.7 million times the mass of all other objects in its orbit combined. Any object that does not meet the fourth criterion is considered a dwarf planet. Therefore, Pluto is a dwarf planet. In the solar system, there are a lot of objects with similar sizes and masses that move in approximately the same orbit. And until Pluto collides with them and takes their mass to its hands, it will remain a dwarf planet. The same is true of Eris. But astrophysicists protest. If we classify objects by size and type of orbit, then any shapeless, but very large cosmic body that revolves around the Sun, is also a contender for the name of the planet. Planets‚ say opponents of astronomers‚ is a sphere‚ created by gravity. "Just the size does not mean anything. If the body is loose, then even a small one can be supported only by gravity and will have round shapes. That is, a small body can be a planet," explains Vladimir Lipunov, astrophysicist, professor of Moscow State University named after M.V. Lomonosov. The results of this conference put an end to the long-term dispute of astronomers and answered the question why Pluto is not a planet in the solar system. Pluto has always been the least explored planet. The only one where the atmosphere appears only for a while, when the cosmic body approaches the Sun - the ice melts from the heat. But they again tighten Pluto as soon as it moves away from the star. Now the American scientists are in frustration. Not only does the US own the discovery of 1930, but the status of the greatest expedition of the already sent New Horizons probe is in jeopardy. In nine years, the Earth was supposed to see pictures of the planet farthest from us, and would receive only a photo of the asteroid. So, by the will of the earth, the most mysterious planet of the solar system has been crossed out from the lists. Pluto is beautiful, it is a very regular ball, reflecting sunlight several hundred times brighter than the moon. In motion, he is sedateness itself: one year on Pluto is 248 of ours. Finally, Pluto is so far from the Sun that the celestial body from its orbit is just a point. Hence the cold - minus 223 degrees Celsius. Enough reasons to be mysterious! Not even a hundred years have passed since the discovery of the planet. (Consequently, Pluto was not taken into account in ancient astrological forecasts.) Yes, and having opened it, they did not immediately figure out what it was. At first it was believed that it was much larger than it is now proven, and in textbooks it is called the ninth planet, although it moves in its orbit in such a way that sometimes it turns out to be the eighth planet from the sun! And for a long time it was considered a double planet, until it was found out that Charon, its satellite, has no atmosphere. But the controversy over Pluto led to the adoption (this is 400 years after Galileo pointed the first telescope at the stars) the following definition: only celestial bodies that revolve around the Sun, have sufficient gravity to have a shape close to a sphere and occupy its orbit alone. Although Pluto is now considered a dwarf planet, it is still a fascinating object to explore. And so NASA sent the New Horizons spacecraft to visit Pluto. New Horizons will reach Pluto in July 2015 and will take a close-up photo of Pluto for the first time in human history. Of course, it is worth noting that Nature, in general, does not care how a tiny civilization in one of the billions of star systems classifies the objects of this system. Earth, Mars, Pluto are just clumps of matter revolving around a much more massive body, and Pluto will always be just Pluto, no matter what category of objects we have invented, we refer to it. But there is no cause for concern, since nothing has changed. Pluto, at least, remains in its original place.

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 was not 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:

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.
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.
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.
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.
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 dwarf planet Pluto is the dominant object in an unexplored and distant system of 6 small cosmic bodies located on the borders of the Sun's empire.

After the discovery, Pluto was perceived as the most distant, ninth planet in our system. It is located on the outskirts of the known world in the Kuiper Belt. Its planetary status after 76 years, by the decision of the International Astronomical Union. The assembly of this organization adopted an addition to the definition of "planet", it consists in the absence of other celestial bodies around its orbit, with the exception of its own satellites. Pluto does not correspond to this point, since there are various space objects near it. This marked the beginning of the emergence of a new category - small planets, their second name is plutoids.

Discovery history

As early as the end of the 19th century, scientists assumed the presence of an unknown planet that had an influence on. In 1906, an American professor of astronomy, the creator of a large private observatory, researcher Percival Lowell, took up an active search for the object.

He gave the name "Planet X" to the cosmic body, but he never managed to find it until the end of his days. In 1919, California scientists from Mount Wilson looked at photographs of the Pluto region, but due to a marriage, it was not seen in the pictures. For ten years, the search was suspended, and in 1929 they were continued by Clyde Tombaugh. Taking pictures of the approximate location of the mysterious planet at the coordinates calculated by Lowell, he worked 14 hours a day. Hundreds of asteroids and a comet were discovered, and in 1930 Pluto was discovered. The privilege of choosing the name of the planet went to associates of Professor Lowell, options were sent from everywhere. The name of the god of the dark realm of the dead was suggested by the young Englishwoman Venetia Burney. Most of the employees liked this option, and the planet became Pluto.

Surface and composition

The study of the planet is hampered by the huge distance, there is little information about it. In its structure, it has a stone core and a mantle of frozen nitrogen with an admixture of methane and carbon monoxide. The surface of Pluto has a different character, its color changes with the change of seasons. Darker regions consisting of methane ice are visible. The density of the planet - 2.03 g / cm3 - indicates the presence of 50% silicates in the composition of the internal structure. The study of Pluto is carried out on the basis of materials received from the Hubble, they noticed traces of complex hydrocarbons.

Characteristics

The initial assumptions of astronomers said that the weight of Pluto is commensurate with the earth. But studying the gravitational action of Charon, they found out that the mass of the planet reaches 1.305x10 in 22 kg - this is only a quarter of the weight of the Earth. It is inferior in size to the Moon and six other satellites in our system. Pluto has been recalculated several times, its value changed when new data was received. Now its diameter is considered to be equal to 2390 km.

The planet is surrounded by a thin layer of atmosphere, the state of which is related to the distance to the Sun. When approaching a star, the ice melts and evaporates, forming a rarefied gaseous shell, consisting mostly of nitrogen and partly of methane, and when removed, these substances freeze and fall to the surface. The temperature of the object is -223 degrees Celsius. The planet is characterized by slow rotation around its axis, it takes 6 days and 9 hours to change the day.

Orbit

The shape of Pluto's orbit is elongated, it is not like the others, and its deviation from the circle is 170. Because of this, the distance of the planet to the star changes cyclically. She, ahead of Neptune, approaches 4.4 billion km, and in the other part moves away by 7.4 billion km. The time of approach to the star lasts 20 years - then the most convenient moment comes to study the planet. Pluto and Neptune do not have points of contact, they are quite far from each other (17 AU). The planets have a 3:2 resonance, that is, while Pluto makes two revolutions, its neighbor manages to complete three. This stable relationship lasts for millions of years. The planet travels around the Sun in 248 years. The planet carries out its movement towards the Earth, like Uranus and Venus.

satellites

Pluto is surrounded by five small moons: Hydra, Charon, Nyx, Cerberus and Styx. They are very compact. The first was Charon, which has a diameter of 1205 km. Its mass is 8 times less than that of Pluto. Mutual eclipses of the planet and satellite were useful in calculating its diameter. The dimensions of all satellites are not calculated accurately, they have a difference of 10 km, in the case of Nikta (88-98 km), up to 86 km near Hydra (44-130 km). Pluto and Charon are recognized by some modern scientists as an exceptional form of connection between cosmic bodies - a double planet.

More recently, Pluto, which has the name of one of the Roman gods, was the ninth planet of the solar system, but in 2006 he lost this title. Why did modern experts in the field of astronomy cease to consider Pluto a planet and what is it in reality today?

Discovery history

The dwarf planet Pluto was discovered in 1930 by Clyde William Tombaugh, an American astronomer at the Percival Lowell Observatory in Arizona. Finding this dwarf planet was a very difficult task for him. The scientist had to compare photographic plates, with images of the starry sky, made with a difference of two weeks for almost a whole year. Any moving object: a planet, a comet or an asteroid had to change its location over time.

Finding Pluto has been largely hampered by its relatively small cosmic scale and mass, and its inability to clear its orbit of similar objects. But, having spent almost a whole year of his life on these studies, the scientist was still able to discover the ninth planet of the solar system.

Just a "dwarf"

Scientists for a very long time could not determine the size and mass of Pluto, until 1978, until a rather large satellite Charon was discovered, which made it possible to accurately determine that its mass is only 0.0021 Earth masses, and the radius is 1200 km. This planet is very small by space standards, but in those early years, scientists believed that this planet was the last in this system, and there was nothing further.

Over the past decades, ground-based and space-type technical devices have greatly changed mankind's understanding of space and helped to dot the i's in the question: why is Pluto not a planet? According to the latest data, there are about 70,000 Pluto-like objects in the Kuiper belt with the same size and composition. Scientists were finally able to understand that Pluto was just a small "dwarf" in 2005, when Mike Brown and his team discovered a cosmic body right beyond its orbit, later called Eris (2003 UB313), with a radius of 1300 km and a mass of 25% more Pluto.

Quite a bit lacked the ability to remain a planet

The twenty-sixth General Assembly of the International Astronomical Union, held in Prague from August 14 to 25, 2006, decided the final fate of Pluto, depriving him of the title - "Planet". The Association formulated four requirements that absolutely all planets of the solar system must meet:

A potential object must rotate in its orbit around the Sun.
An object must have enough mass to form a sphere using its gravity.
The object should not refer to satellites of other planets and objects.
The object must clear the space around itself from other small objects.

Pluto, according to its characteristics, was able to meet all the requirements except the last one, and as a result, it and all similar space objects were reduced to a new category of dwarf planets.

Briefly about Pluto

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.