The mass and size of the pluton. Why Pluto is no longer a planet

Huge heart-shaped region in the front center. Several craters are visible, and much of the surface looks recycled rather than ancient. Pluto. Credit: NASA.

After its discovery by Clyde Tombaugh in 1930, Pluto was considered for almost a century. In 2006, it was classified as a "dwarf planet" due to the discovery of other trans-Neptunian objects (TNOs) of comparable size. However, this does not change its significance in our system. In addition to large TNOs, it is the largest and second most massive dwarf planet in the Solar System.

As a result, much of the exploration time was devoted to this former planet. And with the successful flyby of it by the New Horizons mission in July 2016, we finally have a clear idea of ​​what Pluto looks like. As scientists became bogged down in massive amounts of data being sent back, our understanding of the world grew by leaps and bounds.

Opening:

The existence of Pluto was predicted before its discovery. In the 1840s, the French mathematician Urban do Le Verrier used Newtonian mechanics for (which had not yet been discovered), based on perturbations (perturbations of the orbit). In the 19th century, inhabitant observations of Neptune led astronomers to believe that some planet was perturbing its orbit.

In 1906, Percival Lowell, an American mathematician and astronomer who founded the Lowell Observatory in Flagstaff, Arizona in 1894, initiated a project to search for "Planet X", a possible ninth planet. Unfortunately, Lowell died in 1916 before the discovery was confirmed. But unbeknownst to him, his surveys of the sky recorded two faint images of Pluto (March 19 and April 7, 1915) that simply were not noticed.

The first photographs of Pluto, dated January 23 and 29, 1930. Credit: Archives Department of the Lowell Observatory.

After Lowell's death, the search was not resumed until 1929, at which time the director of the Lowell Vesto Observatory, Melvin Slifer, was assigned the task of finding Planet X with Clyde Tombaugh. A 23-year-old Kansas astronomer, Clyde Tombaugh, spent the next year photographing patches of the night sky and then analyzing the photographs to determine if any objects had moved out of place.

On February 18, 1930, Tombaugh discovered a possible moving object on photographic plates taken in January of that year. After the observatory received additional photographs to confirm the existence of the object, news of the discovery was telegraphed to the Harvard College Observatory on March 13, 1930. The mysterious Planet X has finally been discovered.

Naming:

After the discovery, it was announced that the Lowell Observatory was inundated with proposals for the names of the new planet. , named after the Roman god of the underworld, was suggested by Venetia Burney (1918-2009), then an 11-year-old schoolgirl in Oxford, England. She suggested it in a conversation with her grandfather, who suggested the name to astronomy professor Herbert Hall Turner, who informed his colleagues in the United States.

The surface of Pluto as seen by the Hubble Space Telescope in several images in 2002 and 2003. Credit: NASA/Hubble.

The object was given an official name on March 24, 1930, and it came down to a vote between three options - Minerva, Kronos and. Every member of the Lowell Observatory voted for Pluto and it was announced on May 1, 1930. The choice was based on the fact that the first two letters in the word Pluto - P and L - correspond to the initials.

This name quickly caught on among the general public. In 1930, Walt Disney was apparently inspired by this event when he presented to the public a bloodhound for Mickey named Pluto. In 1941, Glenn T. Seaborg named the newly discovered element plutonium after Pluto. This followed the tradition of naming elements after recently discovered planets - such as uranium, named , and neptunium, named .

Size, mass and orbit:

With a mass of 1.305±0.007 x 102² kg - which is the equivalent of and - Pluto is the second-largest dwarf planet and the tenth-largest known object in direct orbit around the Sun. It has a surface area of ​​1.765 x 10 7 km and a volume of 6.97 x 10 9 km.

A map of Pluto's surface with informal names for several of the larger features in the landscape. Credit: NASA/JHUAPL.

Pluto has a moderately eccentric inclined orbit that oscillates. This means that Pluto periodically gets closer to the Sun than Neptune, but a stable orbital resonance with Neptune prevents them from colliding.

Pluto has an orbital period of 247.68 Earth years, meaning it takes almost 250 years to complete one complete orbit around the sun. Meanwhile, the period of rotation around its axis (one day) is equal to 6.39 Earth days. Like Uranus, Pluto rotates on its side with an axial tilt of 120° relative to the orbital plane, resulting in extreme seasonal changes. At its solstice, one quarter of the surface is in permanent daylight, while the other three quarters are in permanent darkness.

Ingredients and Atmosphere:

With an average density of 1.87 g/cm³, Pluto's composition is differentiated between an icy mantle and a rocky core. The surface consists of more than 98% nitrogen ice with impurities of methane and carbon monoxide. The surface is very variable with great differences in brightness and color. The distinguishing feature is .

The theoretical internal structure of Pluto, consisting of 1) frozen nitrogen, 2) water ice, 3) rock. Credit: NASA/Pat Rawlings.

Scientists also suspect that Pluto's internal structure is differentiated, with rock settled in a dense core surrounded by a mantle of water ice. It is believed that the diameter of the core is approximately 1700 km, 70% of the diameter of Pluto. Due to the decay of radioactive elements, it is possible that the thickness of 100-180 km at the boundary of the core and mantle.

Pluto has a thin atmosphere composed of nitrogen (N 2 ), methane (CH 4 ) and carbon monoxide (CO ) that are in equilibrium with their surface ices. However, the planet is so cold that during part of its orbit, the atmosphere thickens and falls to the surface. The average surface temperature of the planet is from 33 K (-240°C) at aphelion to 55 K (-218°C) at perihelion.

Satellites:

Pluto has five known moons. The largest and closest to Pluto's orbit is Charon. This satellite was first identified in 1978 by astronomer James Christie using photographic plates from the United States Naval Observatory (USNO) in Washington, DC. with a multiple orbit - Styx (Styx), Nix (Nix), Kerberos (Kerberos) and Hydra (Hydra), respectively.

Nyx and Hydra were discovered simultaneously in 2005 by the Pluto companion team using the Hubble telescope. The same team discovered Cerberus in 2011. The fifth and final moon of Styx was discovered in 2012 while photographing Pluto and Charon.

An illustration comparing the scale and brightness of Pluto's moons. Credit: NASA/ESA/M.Showalter.

Charon, Styx, and Kerberos are massive enough to collapse into a spheroid shape under their own gravity. Nyx and Hydra, however, are elongated. The Pluto-Charon system is unusual in that it is one of the few systems in , whose barycenter lies above the surface of the planet. In short, causing some scientists to claim it is a "double dwarf system" instead of a dwarf planet and a moon in its orbit.

In addition, it is also unusual in that each body has a tidal lock (synchronous rotation) with each other. Charon and Pluto are always facing the same side to each other, and from any location on the surface of either, the other is always in the same position in the sky, or always hidden. This also means that the periods of rotation around the axis of each of them are equal to the time it takes for the entire system to turn around the common center of mass.

In 2007, observations by the Gemini Observatory of patches of ammonia hydrates and water crystals on Charon's surface suggested the presence of . This would seem to indicate that Pluto has a warm subsurface ocean and that the core is geologically active. Pluto's moons are thought to have been formed by a collision between Pluto and a similarly sized celestial body in the ancient history of the solar system. The collision ejected matter, which then consolidated into satellites around Pluto.

Classification:

Since 1992, a lot of celestial bodies have been discovered orbiting in the same region as Pluto, demonstrating that Pluto is part of a population. This put its official status as a planet in question, many asking if Pluto should be considered separate from its surrounding population, like Pallas, Juno and Juno, which lost their planet status after.

On July 29, 2005, the discovery was announced, which was believed to be much larger than Pluto. Initially referring to the tenth planet of the Solar System, there was no consensus on whether Eris is a planet. Moreover, others in the astronomical community consider its discovery a strong argument for reclassifying Pluto as a minor planet.

The discussion came to a close on August 24, 2006 with the resolution of the International Astronomical Union (IAU), which created the official definition of the term "planet". According to the XXVI IAU General Assembly, a planet must meet three criteria: it must be in orbit around the Sun, it must have sufficient gravity to compress itself into a spherical shape, and it must clear its orbit of other objects.

Pluto does not satisfy the third condition because its mass is only 0.07 of the mass of all objects in its orbit. The IAU has also ruled that bodies that do not meet the third criterion should be called dwarf planets. On September 13, 2006, the IAU included Pluto, Eris and its satellite Dysnomia in the Catalog of Minor Planets.

The decision of the IAU was met with mixed reactions, especially in the scientific community. For example, Alan Stern, the principal investigator for the New Horizons mission, and Mark Buie, an astronomer at the Lowell Observatory, have both been outspoken about the reclassification. Others, such as Mike Brown, the astronomer who discovered Eris, have voiced their support.

Our evolving understanding of Pluto, represented by Hubble images from 2002-2003 (left) and photographs taken by New Horizons in 2015 (right). Credit: theguardian.com

On August 14-16, 2008, researchers from both sides of the issue gathered for what came to be called "The Great Planet Debate" at Johns Hopkins University's Applied Physics Laboratory. Unfortunately, no scientific consensus was reached, but on June 11, 2008, the IAU announced in a press release that the term "plutoid" would be used to refer to Pluto and other similar objects in the future.

(OPK). This led to planning for the Pluto Kuiper Express mission, and NASA instructed the Jet Propulsion Laboratory to schedule a flyby of Pluto and the Kuiper Belt.

By 2000, the program was revised due to expressed budget problems. After pressure from the scientific community, a revised mission to Pluto, dubbed New Horizons, finally received funding from the US government in 2003. The New Horizons spacecraft successfully launched on January 19, 2006.

From September 21 to 24, 2006, the New Horizons spacecraft managed to capture its first photographs of Pluto while testing an instrument called LORRI. These images, taken from approximately 4.2 billion km or 28.07 AU, were released on November 28, 2006, confirming the spacecraft's ability to track distant targets.

Remote rendezvous operations with Pluto began on January 4, 2015. From January 25 to 31, the approaching probe took several images of Pluto, published by NASA on February 12, 2015. These photographs, taken from over 203 million km away, showed Pluto and its largest moon, Charon.

Pluto and Charon recorded by the New Horizons spacecraft from January 25 to 31, 2015. Credit: NASA.

The New Horizons spacecraft made its close approach to Pluto at 11:49:57 UTC on July 14, 2015, followed by Charon at 12:03:50 UTC. Telemetry confirming the successful flyby and the "health" of the spacecraft reached Earth at 00:52:37 UTC.

During the flyby, the probe captured the clearest images of Pluto to date, and a full analysis of the data will take several years. The spacecraft is currently moving at 14.52 km/s relative to the Sun and 13.77 km/s relative to Pluto.

While the New Horizons mission has shown us a lot about Pluto and will continue to do so as scientists analyze the collected data, we still have a lot to learn about this distant and mysterious world. With time and more missions, we may finally be able to unravel some of its deepest secrets.

An illustration of the New Horizons spacecraft near Pluto, with Charon visible in the background. Credit: NASA/JPL.

In the meantime, we offer all the information that is currently known about Pluto. We hope you find what you're looking for in the links below and enjoy your exploration as always!

The title of the article you read "Dwarf Planet Pluto".

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 able to finally 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:

1. A potential object must rotate in its orbit around the Sun.
2. An object must have enough mass to form a sphere using its gravity.
3. The object should not refer to satellites of other planets and objects.
4. 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

For a long time after the discovery of Pluto in the sky, astronomers did not consider it a planet. But that all changed, however, when in 2006 the International Astronomical Union (IAU) reclassified Pluto as a "dwarf planet." This was a highly controversial decision, which was largely based on the discovery of numerous icy objects with elongated orbits similar to Pluto. In our review, curious facts about this distant planet.

1. Minus 225°C.

The surface of Pluto is one of the coldest places in the solar system. On average, its surface temperature is minus 225 degrees Celsius.

2 Dwarf Planet

Pluto is the only dwarf planet that was once considered an ordinary planet. Pluto became a dwarf planet only in 2006.

3. New Horizons probe

As part of NASA's New Horizons mission in January 2006, a probe was launched that flew near Pluto for the first time (in July 2015).

4. The diameter of the planet is 2352 km

When Pluto was first discovered, it was originally thought to be larger than Earth. Astronomers now know that it is only 2,352 km in diameter and has a surface area smaller than that of Russia.

5. A year is equal to 248 Earth years

To completely fly around the Sun in an orbit (i.e. 1 year), Pluto needs 248 Earth years. To further emphasize this fact, it is worth knowing that Pluto needs another 160 years to make a complete revolution around the Sun since it was first discovered.

6. Crossing orbits

Due to Pluto's strange orbit, its orbit intersects with Neptune's orbit periodically. This leads to the fact that Pluto at these moments is closer to the Earth than Neptune.

7. Liquid water

Scientists suggest that on the surface of Pluto, despite the extremely low temperature, there may be liquid water. It can be ejected to the surface by cryovolcanoes or geysers.

8. Five satellites

Pluto has five known moons: Charon, Nix, Hydra, and two recently discovered tiny moons, Kerberos and Styx. While Nikta, Hydra, Kerberus, and Styx are relatively small, Charon is only half the size of Pluto. Due to the size of Charon, some astronomers consider Pluto and Charon to be a double dwarf planet.

9. Smaller than the Moon

Pluto is the smallest dwarf planet in the solar system. It is smaller than Earth's moon, and 2 times smaller than Jupiter's moon, Ganymede.

10. One day is equivalent to six

A day on Pluto is equivalent to 6 days and 9 hours on Earth, meaning it has the second slowest rotation around its axis in the solar system. The first is Venus, where a day lasts 243 Earth days.

11. Escaped from Neptune

According to some astronomers, Pluto was once one of Neptune's moons. But then he went out of his orbit.

12. Away from the Sun

The sun will look like a bright star from Pluto, that's how far apart they are. If Pluto were to approach the Sun, then it would have a “tail” and become a comet.

13. Center of gravity

Charon and Pluto are gravitationally bound to each other. They always face each other, as they revolve around a common center of mass located somewhere between them.

14. Unusual gravitational relations

You might think that Charon revolves around Pluto, like any "normal" satellite. In reality, Pluto and Charon revolve around a common point in space. In the case of the Earth and the Moon, there is also such a common point, but this point is inside the Earth. In the case of Pluto and Charon, the common point is somewhere above the surface of Pluto.

15. The force of gravity is 1/12th on Earth

The force of gravity on Pluto is about 1/12th of that on Earth. This means that a person weighing 100 kg on Earth will weigh 8 kg on Pluto.

What can we say about distant planets, if people know very little about their own. So, there is at least .

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.

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.

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, it was decided to exclude Pluto from the major planets of the solar system.

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, melting 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.

The latest technology

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.