Why Neptune is not a planet in the solar system. Why is Pluto no longer a planet? About the planet's atmosphere

Pluto is the most distant planet. From the central luminary, it is on average 39.5 times farther than our Earth. Figuratively speaking, the planet moves on the periphery of the Sun's domain - in the arms of eternal cold and darkness. That is why it was named after the god of the underworld, Pluto.

However, is it really so dark on Pluto?

It is known that light weakens in proportion to the square of the distance from the source of radiation. Consequently, in the firmament of Pluto, the Sun should shine about one and a half thousand times weaker than on Earth. And yet it is there almost 300 times brighter than our full moon. From Pluto, the Sun is seen as a very bright star.

Using Kepler's third law, it can be calculated that Pluto makes a revolution in its circumsolar orbit in almost 250 Earth years. Its orbit differs from the orbits of other large planets by its significant elongation: the eccentricity reaches 0.25. Due to this, the distance of Pluto from the Sun varies widely and periodically the planet "enters" inside the orbit of Neptune.

A similar phenomenon occurred from January 21, 1979 to March 15, 1999: the ninth planet became closer to the Sun (and to the Earth) than the eighth - Neptune. And in 1989, Pluto reached perihelion and was at a minimum distance from the Earth, equal to 4.3 billion km.

Further, it was noticed that Pluto experiences, although insignificant, but strictly rhythmic variations in brightness. The period of these variations researchers identify with the period of rotation of the planet around its axis. In terrestrial units of time, it is 6 days 9 hours and 17 minutes. It is easy to calculate that there are 14,220 such days in a Pluto year.

Pluto is noticeably different from all planets far from the Sun. Both in size and in many other parameters, it is more like an asteroid captured into the solar system (or a system of two asteroids).

Pluto is about 40 times farther from the Sun than the Earth, therefore, naturally, the flow of solar radiant energy on this planet is more than one and a half thousand times weaker than on Earth. However, this does not mean that Pluto is shrouded in eternal darkness: the Sun in its sky looks brighter than the Moon for the inhabitants of the Earth. But, of course, the temperature on the planet, to which the light from the Sun takes more than five hours, is low - its average value is about 43 K, so that only neon can remain in Pluto's atmosphere without experiencing liquefaction (lighter gases due to the low force gravity is removed from the atmosphere). Carbon dioxide, methane and ammonia solidify even at the maximum temperature for this planet. In the atmosphere of Pluto, there may be minor impurities of argon, and even smaller amounts of nitrogen. The pressure at the surface of Pluto, according to available theoretical estimates, is less than 0.1 atmospheres.

Data on Pluto's magnetic field are not yet available, but according to the theory of the baroelectric effect, its magnetic moment is an order of magnitude lower than that of the Earth. The tidal interactions of Pluto and Charon should also lead to the appearance of an electric field.

In recent years, thanks to the improvement of observational methods, our knowledge of Pluto has been significantly replenished with new interesting facts. In March 1977, American astronomers detected spectral lines of methane ice in Pluto's infrared radiation. But a surface covered with hoarfrost or ice should reflect sunlight much better than one covered with rocks. After that, we had to reconsider (and for the umpteenth time!) the size of the planet.

Pluto cannot be larger than the Moon - such was the new conclusion of specialists. But how to explain then the irregularities in the motion of Uranus and Neptune? Obviously, their movement is perturbed by some other celestial body, still unknown to us, and perhaps even several such bodies ...

The date of June 22, 1978 will go down forever in the history of the study of Pluto. You can even say that on this day the planet was rediscovered. And it began with the fact that the American astronomer James Christie was lucky to discover a natural satellite near Pluto, called Charon.

From refined ground-based observations, the radius of the satellite's orbit relative to the center of mass of the Pluto-Charon system is 19,460 km (according to the Hubble orbital astronomical station - 19,405 km), or 17 radii of Pluto itself. Now it has become possible to calculate the absolute dimensions of both celestial bodies: the diameter of Pluto was 2244 km, and the diameter of Charon was 1200 km. Pluto really turned out to be smaller than our Moon. The planet and the satellite rotate around their own axes synchronously with the orbital motion of Charon, as a result of which they face each other with the same hemispheres. This is the result of prolonged tidal braking.

In 1978, a sensational message appeared: in a photograph taken by D. Christie with a 155-cm telescope, the image of Pluto looked elongated, that is, it had a small protrusion. This gave grounds to assert that Pluto has a satellite located quite close to it. This conclusion was later confirmed by images from spacecraft. The satellite, called Charon (according to Greek mythology, this was the name of the carrier of souls to the kingdom of Pluto Hades across the river Styx), has a significant mass (about 1/30 of the mass of the planet), is located at a distance of only about 20,000 km from the center of Pluto and revolves around it with a period of 6.4 Earth days, equal to the period of revolution of the planet itself. Thus, Pluto and Charon rotate as a whole, and therefore they are often considered as a single binary system, which allows us to refine the values of masses and densities.

So, in the solar system, Pluto turned out to be the second double planet, and more compact than the Earth-Moon double planet.

By measuring the time that Charon spends on a complete revolution around Pluto (6.387217 days), astronomers were able to "weigh" the Pluto system, that is, determine the total mass of the planet and its satellite. It turned out to be equal to 0.0023 Earth masses. Between Pluto and Charon, this mass is distributed as follows: 0.002 and 0.0003 Earth masses. The case when the mass of the satellite reaches 15% of the mass of the planet itself is unique in the solar system. Before the discovery of Charon, the largest ratio of masses (satellite to planet) was in the Earth-Moon system.

With these sizes and masses, the average density of the components of the Pluto system should be almost twice that of water. In a word, Pluto and its satellite, like many other bodies moving on the outskirts of the solar system (for example, satellites of giant planets and comet nuclei), should consist mainly of water ice mixed with rocks.

On June 9, 1988, a group of American astronomers observed Pluto's occultation of one of the stars and discovered Pluto's atmosphere in the process. It consists of two layers: a haze layer about 45 km thick and a "clean" atmosphere layer about 270 km thick. The researchers of Pluto believe that at a temperature of -230 ° C prevailing on the surface of the planet, only inert neon is still able to remain in a gaseous state. Therefore, the rarefied gaseous shell of Pluto may consist of pure neon. When the planet is at the farthest distance from the Sun, the temperature drops to -260 ° C and all gases must “freeze out” from the atmosphere completely. Pluto and its moon are the coldest bodies in the solar system.

As you can see, although Pluto is located in the area of domination of the giant planets, it has nothing in common with them. But with their "ice" satellites, he has a lot in common. So Pluto was once a moon? But what planet?

The following fact may serve as a clue to this question. For every three complete revolutions of Neptune around the Sun, there are two such revolutions of Pluto. And it is possible that in the distant past, Neptune, in addition to Triton, had another large satellite that managed to gain freedom.

But what force was able to throw Pluto out of the Neptune system? "Order" in the Neptune system could be disturbed by a massive celestial body flying by. However, events could also develop according to another "scenario" - without the involvement of a perturbing body. Celestial mechanical calculations showed that the approach of Pluto (then still a satellite of Neptune) with Triton could change its orbit so much that it moved away from Neptune's sphere of gravity and turned into an independent satellite of the Sun, that is, into an independent planet ...

In August 2006, at the General Assembly of the International Astronomical Union, a decision was made to exclude Pluto from the major planets of the solar system.

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.

The discovery of Pluto was largely complicated by its relatively small size and mass on a cosmic scale, 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, in terms of its characteristics, was able to meet all the requirements except the last one, and as a result, it and all space objects like it were reduced to a new category of dwarf planets.

Briefly about Pluto

The existence of Pluto was first discovered at the Lovell Observatory in Flagstaff, Arizona. Astronomers had long predicted the existence of a distant ninth planet in the solar system, which they called among themselves Planet X. The discovery of the planet Pluto Twenty-two-year-old Tombo was given the laborious task of comparing photographic plates.

The task was to compare two images of a section of outer space taken with a difference of two weeks. Any object moving in space, like an asteroid, comet or planet, would have to have a different location in the images. After a year of observations, Tombo finally managed to locate an object in the correct orbit and realized that he had discovered Planet X.

Since the celestial body was discovered by Lovell's team, the team was given the right to assign a name to it. It was decided to give the celestial body the name Pluto. The name was proposed by an eleven-year-old schoolgirl from Oxford (in honor of the Roman god - the guardian of the underworld). From that moment on, the solar system had 9 planets.

Until the discovery in 1978 of Pluto's largest moon, Sharon, astronomers could not accurately determine the mass of the planet. Knowing its mass (0.0021 Earth), scientists were able to more accurately determine the size of the object. At the moment, the most accurate calculations indicate that Pluto is 2,400 km in diameter. This is a very small value, for example: Mercury has a diameter of 4.880 km. Although Pluto is tiny, it is considered the largest celestial body beyond the orbit of Neptune.

Why was Pluto excluded?

In the past few decades, new ground-based and space-based observatories have begun to change previous ideas about the outer solar system. In contrast to the old assumption that Pluto was a planet like the others in the solar system, it was now believed that Pluto and its moons were a case of a large cluster of objects known as the Kuiper Belt.

This location extends from the orbit of Neptune by about 55 astronomical units (55 distances from the earth to the Sun). Authoritative astronomers estimate that there are at least 70,000 icy objects in the Kuiper Belt, with the same composition as Pluto, reaching a size of 100 kilometers or more.

According to the new terminology, Pluto was no longer a planet, but simply one of many Kuiper Belt objects.

How did Pluto stop being a planet?

The problem was that astronomers were able to discover larger and larger objects in the Kuiper Belt. FY9, discovered by Caltech astronomer Brown Mike and his team, was only slightly smaller than Pluto. There were also several other objects in the Kuiper Belt with the same classification.

Astronomers realized that the discovery of an object in the Kuiper Belt, more massive than Pluto, was only a matter of time. Finally, in 2005, Brown Mike and his team caused the effect of a “bombshell”. They managed to discover a celestial body located beyond the orbit of Pluto, which has the same, and maybe a larger size. Named UB13 since 2003, it was later named Eris. Since its discovery, scientists have been able to calculate its size - 2,600 km. It also has a mass 25% greater than that of Pluto.

Since Eris was larger, had the same ice-stony composition and was more massive than Pluto, the assumption that there are 9 planets in the solar system began to completely fall apart. The astronomers decided that they would make the final decision on the status of the planet at the XXVIth General Assembly of the Congress of the International Astronomical Union, which was held from 14 to 25 August 2006 in Prague, the capital of the Czech Republic.

IAU General Assembly

What was Eris, a palnet or a Kuiper Belt object; for that matter, what was Pluto (or was Pluto a planet)?

Astronomers were given an opportunity to review and determine the status of the planets. One of the proposals under consideration was: increasing the number of planets to 12. At the same time, Pluto remained a planet, and Eris and Ceres, which had previously had the status of giant asteroids, were equated to the status of planets. An alternative proposal suggested: leave the number of planets at nine, without any scientific justification. The meaning of the third proposal was to reduce the number of planets to eight, with the release of Pluto from among the planets. What was decided? .. In the end, a controversial decision was put up for a vote, to downgrade Pluto (and Eris) to the status of a "dwarf planet", according to the newly created classification.

What was decided? Is Pluto a planet? Or is it an asteroid? For an asteroid to be considered a planet, it must meet these three requirements defined by the IAU:

- it must orbit around the Sun - YES, so Pluto can be a planet.
“It must have enough gravity to form a ball on its own,” Pluto agrees.
- It must have a "cleaned orbit" - what is it. Here's where Pluto doesn't follow the rules and isn't a planet.

What is Pluto anyway?

What does “cleaned orbit” mean, why is Pluto not a planet? When planets form, they become the predominant gravitational object in their orbit in the solar system. When interacting with other, smaller objects, they either absorb or tie them into orbit with their gravitational force. In Pluto, there are only 0.07 masses of all objects in the vicinity of its orbit. In turn, the Earth, 1.7 million times the mass of all objects in the vicinity of its orbit, respectively.

Any object that does not meet at least one condition is considered a dwarf planet. Therefore, Pluto is a dwarf planet. There are many objects of various masses and sizes in the immediate vicinity of its orbit. And until Pluto collides with many of them and takes their mass, it will retain its status as a dwarf planet. Eris has a similar problem.

It's not that hard to imagine a future in which astronomers can find an object large enough to qualify as a planet in the far reaches of the solar system. Then our solar system will again have nine planets.

Even though Pluto is no longer officially a planet, it is still of great interest for research. This is the reason NASA launched their New Horizons spacecraft to explore Pluto. New Horizons will reach the planet's orbit in July 2015 and take the first close-up pictures of the dwarf planet.

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:

R = √2σy/πGρ2

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, with the help of its own gravity, overcome the resistance of matter 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").