Mass and size of the pluto. Why Pluto is no longer a planet

Huge heart shaped region at front center. Several craters are visible, and much of the surface appears 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 began to be classified as a "dwarf planet" due to the discovery of other trans-Neptunian objects (TNOs) of comparable size. However, this does not change its importance 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, most of the research time has been 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 the massive amounts of data sent back, our understanding of this world grew by leaps and bounds.

Opening:

Pluto's existence was predicted before its discovery. In the 1840s, the French mathematician Urban before Le Verrier used Newtonian mechanics to (which had not yet been discovered) based on perturbations (perturbations of the orbit). In the 19th century, widespread observations of Neptune led astronomers to believe that some planet was causing disturbances in 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 went unnoticed.

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

After Lowell's death, the search was not resumed until 1929, after which Lowell Observatory Westo Director Melvin Slifer was assigned the task of finding Planet X with Clyde Tombaugh. 23-year-old astronomer Clyde Tombaugh from Kansas spent the next year photographing patches of the night sky and then analyzing the photos to determine whether 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 object's existence, 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 names for the new planet. , 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 recommended 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 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 introduced Mickey's bloodhound, Pluto, to the public. In 1941, Glenn T. Seaborg named the newly discovered element plutonium, after Pluto. This was in keeping with the tradition of naming elements after newly discovered planets - such as uranium, called , and neptunium, called .

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 directly orbiting 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 of the landscape. Credit: NASA/JHUAPL.

Pluto has a moderately eccentric, inclined orbit that wobbles. 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 full revolution around the Sun. Meanwhile, the period of rotation around its axis (one day) is 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 variations. At its solstices, one quarter of the surface is in constant daylight, while the other three quarters are in constant darkness.

Composition 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 admixtures of methane and carbon monoxide. The surface is very varied with large differences in brightness and color. A distinctive 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. The diameter of the core is believed to be approximately 1,700 km, 70% of Pluto's diameter. Due to the decay of radioactive elements, it is possible that the thickness of the core and mantle is 100-180 km.

Pluto has a thin atmosphere of nitrogen (N2), methane (CH4) and carbon monoxide (CO), which 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 temperature of the planet's surface 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 in Pluto's orbit is Charon. This moon was first identified in 1978 by astronomer James Christie using photographic plates from the United States Naval Observatory (USNO) in Washington, DC. with multiple orbits - Styx, Nix, Kerberos and Hydra, respectively.

Nikta and Hydra were discovered simultaneously in 2005 by a team searching for Pluto's companions using the Hubble telescope. The same team opened Kerber in 2011. The fifth and final moon, 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 the influence of their own gravity. Nyx and Hydra, however, have an elongated shape. The Pluto-Charon system is unusual in that it is one of the few systems in the world whose barycenter lies above the surface of the planet. In short, causing some scientists to claim that it is a "double dwarf system" instead of a dwarf planet and a satellite in its orbit.

In addition, it is also unusual in that each body has tidal locking (synchronous rotation) with each other. Charon and Pluto always face 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, Gemini Observatory observations 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. The moons of Pluto are believed to have been formed by a collision between Pluto and a similar-sized celestial body in the ancient history of the Solar System. The collision ejected material that later consolidated into moons around Pluto.

Classification:

Since 1992, many celestial bodies have been discovered orbiting in the same region as Pluto, demonstrating that Pluto is part of a population. This brought its official status as a planet into question, with many questioning whether Pluto should be considered separately from its surrounding populations, like Pallas, Juno, and Pluto, which lost their planetary status after .

On July 29, 2005, the discovery was announced, which was believed to be much larger than Pluto. Originally referring to the tenth planet in 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 debate came to a close on August 24, 2006, with a resolution by the International Astronomical Union (IAU) that created an official definition of the term "planet". According to the XXVI General Assembly of the IAU, 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 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 moon Dysnomia in the Minor Planet Catalog.

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

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

On August 14-16, 2008, researchers on both sides of the issue gathered for what became known as "The Great Planet Debate" at the Johns Hopkins University 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 henceforth be used to refer to Pluto and other similar objects.

(OPK). This led to the planning of the Pluto Kuiper Express mission, and NASA instructed the Jet Propulsion Laboratory to plan 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, called 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 captured its first photographs of Pluto while testing an instrument called LORRI. These images, taken from a distance of approximately 4.2 billion km or 28.07 AU, were released on November 28, 2006, confirming the spacecraft's ability to track distant targets.

Operations for a distant rendezvous with Pluto began on January 4, 2015. From January 25 to January 31, the incoming probe took several images of Pluto, published by NASA on February 12, 2015. These photographs, taken from a distance of more than 203 million km, showed Pluto and its largest moon Charon.

Pluto and Charon, recorded by the New Horizons spacecraft from January 25 to January 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 flight and the “health” of the spacecraft reached Earth at 00:52:37 UTC.

During its flyby, the probe captured the clearest images of Pluto to date, and a full analysis of the data obtained 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 data collected, there is still much to learn about this distant and mysterious world. With time and more missions, we will finally be able to uncover 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 as always, enjoy your exploration!

Title of the article you read "Dwarf Planet Pluto".

More recently, Pluto, named after one of the Roman gods, was the ninth planet of the solar system, but in 2006 it lost this title. Why have modern astronomers stopped considering Pluto a planet and what exactly is it today?

History of discovery

The dwarf planet Pluto was discovered in 1930 by the American Clyde William Tombaugh, who at that time worked as an astronomer at the Percival Lowell Observatory in Arizona. Discovering this dwarf planet was very difficult for him. The scientist had to compare photographic plates with images of the starry sky, taken two weeks apart for almost a whole year. Any moving object: planet, comet or asteroid must have changed its location over time.

The discovery of Pluto was greatly 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 this research, the scientist was still able to discover the ninth planet of the solar system.

Just a "dwarf"

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

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

Just a little short of 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 it of the title “Planet”. The association formulated four requirements that absolutely all planets in the solar system must meet:

1. The potential object must be in its orbit around the Sun.
2. The object must have enough mass to use its gravity to force itself into a spherical shape.
3. The object should not belong to the satellites of other planets and objects.
4. The object must clear the space around itself from other small objects.

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

Briefly about Pluto

For a long time after the discovery of Pluto in the celestial horizon, astronomers did not consider it a planet. But everything 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. Our review contains interesting facts about this distant planet.

1. Minus 225°C.

Pluto's surface is one of the coldest places in the solar system. On average, the temperature on its surface 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, a probe was launched in January 2006 and flew close to Pluto for the first time (in July 2015).

4. The diameter of the planet is 2352 km

When Pluto was first discovered, it was initially thought to be larger than Earth in size. Astronomers now know that its diameter is only 2352 km, and its surface area is less than the size of Russia.

5. A year is equal to 248 Earth years

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

6. Intersecting orbits

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

7. Liquid water

Scientists suggest that there may be liquid water on the surface of Pluto, despite the extremely low temperature. 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 Nyx, Hydra, Kerberos and Styx are relatively small, Charon is only half the size of Pluto. Because of Charon's size, some astronomers consider Pluto and Charon to be a double dwarf planet.

9. Less Moon

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

10. One day is equivalent to six

A day on Pluto is equivalent to 6 days and 9 hours on Earth, meaning it is the second slowest to spin on 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 left his orbit.

12. Away from the Sun

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

13. Center of mass

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

14. Unusual gravitational relationships

You might think that Charon orbits Pluto like any “normal” satellite. In reality, Pluto and Charon orbit 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 located inside the Earth. In the case of Pluto and Charon, the common point is somewhere above Pluto's surface.

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

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

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

Pluto is the most distant planet. From the central body 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 embrace of eternal cold and darkness. That is why it was named after the god of the underworld Pluto.

However, is it really that 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 sky of Pluto the Sun should shine about one and a half thousand times weaker than on Earth. And yet it is almost 300 times brighter there than our full Moon. From Pluto, the Sun is visible as a very bright star.

Using Kepler's third law, we can calculate that Pluto completes its orbit around the Sun in almost 250 Earth years. Its orbit differs from the orbits of other large planets in that it is significantly elongated: its eccentricity reaches 0.25. Due to this, Pluto’s distance from the Sun varies widely and the planet periodically “enters” 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 its minimum distance from Earth, equal to 4.3 billion km.

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

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

Pluto cannot be larger than the Moon - this was the new conclusion of experts. But how then can we explain the irregularities in the movements of Uranus and Neptune? Obviously, their movement is disturbed by some other celestial body still unknown to us, and maybe even several such bodies...

The date June 22, 1978 will forever go down in the history of the study of Pluto. You could even say that on this day the planet was rediscovered. It started with the fact that the American astronomer James Christie was lucky enough 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 equal to 19,460 km (according to the Hubble orbital astronomical station - 19,405 km), or 17 radii of Pluto itself. It has now become possible to calculate the absolute sizes of both celestial bodies: the diameter of Pluto was 2244 km, and the diameter of Charon was 1200 km. Pluto actually turned out to be smaller than our Moon. The planet and 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. The result of prolonged tidal braking is obvious.

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

By measuring the time it takes Charon to complete a full 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 a satellite reaches 15% of the mass of the planet itself is unique in the Solar System. Before the discovery of Charon, the largest mass ratio (satellite to planet) was in the Earth-Moon system.

With such sizes and masses, the average density of the components of the Pluto system should be almost twice the density 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 with an admixture of rocks.

On June 9, 1988, a group of American astronomers observed Pluto's occultation of one of the stars and discovered Pluto's atmosphere. It consists of two layers: a layer of haze about 45 km thick and a layer of “clean” atmosphere about 270 km thick. Pluto researchers believe that at the temperature prevailing on the surface of the planet -230 ° C, only inert neon is still able to remain in a gaseous state. Therefore, Pluto's rarefied gas envelope may consist of pure neon. When the planet is at its 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 we see, although Pluto is located in the area of ​​dominance of the giant planets, it has nothing in common with them. But it has a lot in common with their “ice” companions. So, Pluto was once a satellite? But which planet?

The following fact can serve as a clue to this question. For every three full revolutions of Neptune around the Sun, there are two similar 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? The “order” in the Neptune system could be disrupted by a massive celestial body flying past. However, events could have developed according to a different “scenario” - without the involvement of a disturbing 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 list of major planets of the Solar System.

Pluto is one of the least studied objects in the solar system. Due to its great distance from Earth, it is difficult to observe with telescopes. Its appearance is more reminiscent of 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 look at 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, observing Uranus, scientists discovered a strong influence on its orbit of foreign bodies. 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 successful - Pluto was discovered.

Pluto's movement was noticed on photographic plates taken over a two-week period. Observations and confirmation of the existence of an object beyond the known boundaries of the galaxy of another planet took more than a year. Clyde Tombaugh, a young astronomer at the Lowell Observatory that initiated the research, reported the discovery to the world in March 1930. Thus, a 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 typical for ordinary planets in the solar system. The orbit, its small satellites and atmosphere are unique in themselves.

Unusual orbit

The orbits familiar to the eight planets of the Solar System are almost circular, with 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, eight planets will rotate evenly around the Sun, and Pluto will cross the orbit of Neptune due to its angle of inclination.

Due to this orbit, it completes 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 a planet was another reason why Pluto was excluded from the list of planets.

Satellites

Today there are five known: Charon, Nyx, Hydra, Kerberos and Styx. All of them, except Charon, are very small, and their orbits are too close to the planet. This is another difference from the officially recognized planets.

In addition, Charon, discovered in 1978, is half the size of Pluto itself. But it's too big for a satellite. Interestingly, the center of gravity is outside of Pluto, and therefore it seems to sway from side to side. For these reasons, some scientists consider this object to be 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. Pluto is believed to be composed of rock and ice. The atmosphere on it was discovered in 1985. It consists mainly of nitrogen, methane and carbon monoxide. Its presence was determined by studying the planet when it covered the star. Objects without an atmosphere cover the stars abruptly, while those with an atmosphere cover them gradually.

Due to the very low temperature and elliptical orbit, melting ice produces an anti-greenhouse effect, causing the planet's temperature to drop even further. After research conducted in 2015, scientists came to the conclusion that atmospheric pressure depends on the planet’s approach 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. Today, 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, and especially distant galactic objects, in more detail. As a result, an object was discovered, called Eris, which turned out to be further than Pluto, and over time, two more celestial bodies that were similar in diameter and mass to it.

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

Review of status

When was Pluto removed from the list of planets? On August 25, 2006, participants in 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 of the solar system. This meant that many textbooks had to be revised and rewritten, as well as star charts and scientific papers in the field.

Why was this decision made? Scientists have had to reconsider the criteria by which planets are classified. Long debates led to the conclusion that the planet must meet all parameters.

First, the object must be rotating around the Sun in its orbit. Pluto fits 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 appeared, but this assumption was discarded with the advent of new discoveries, and especially of 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 in order to clear your orbit from others. For this one point, Pluto is not suitable for 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 its way in orbit.

Now it’s clear why Pluto was excluded from the list of planets. But where should such objects be classified? For such bodies, the definition of “dwarf planets” was introduced. They began to include all objects that do not meet the last point. So Pluto is still a planet, albeit a dwarf one.